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SBIG
ASTRONOMICAL
INSTRUMENTS
Operating Manual
CCD Camera Models
ST-7XE, ST-8XE, ST-9XE,
ST-10XE, ST-10XME and ST-2000XM
With High Speed USB Interface
Santa Barbara Instrument Group
147A Castilian Drive
Santa Barbara, CA 93117
Phone (805) 571-7244 • Fax (805) 571-1147
Web:<www.sbig.com> • Email:<[email protected]>
Note: This equipment has been tested and found to comply with the limits for a Class B
digital device pursuant to Part 15 of the FCC Rules. These limits are designed to provide
reasonable protection against harmful interference in a residential installation. This
equipment generates, uses, and can radiate radio frequency energy and if not installed and
used in accordance with the instructions, may cause harmful interference to radio
communications. However, there is no guarantee that interference will not occur in a
particular installation. If this equipment does cause harmful interference to radio or
television reception, which can be determined by turning the equipment off and on, the user
is encouraged to try to correct the interference by one or more of the following measures:
• Reorient or relocate the receiving antenna.
• Increase the separation between the receiver and the equipment.
• Connect the equipment into an outlet on a circuit different from that to which the
receiver is connected.
• Consult the dealer or an experienced radio/TV technician for help.
Shielded I/O cables must be used when operating this equipment.
You are also warned, that any changes to this certified device will void your legal right to
operate it.
OPERATION Manual for ST-XE/ST-8XE/ST-9XE/ST-10XE/ST-10XME/ST-2000XM
Revision 1.3
April 2002
Section 1 - Introduction
1.
1.1.
1.2.1.
1.2.2.
1.2.3.
1.2.4.
1.2.5.
1.2.6.
1.2.7.
2.
2.1.
2.2.
2.3.
2.4.
2.5.
2.6.
Introduction ............................................................................................................3
Getting Started. ......................................................................................................4
1.2.
Installing the USB Drivers for the First Time.......................................5
Installing CCDOPS ...............................................................................................5
Installing USB drivers for Window 95/98/Me Users .........................................7
Installing USB drivers for Windows 2000 Users ...............................................10
Installing USB drivers for Windows XP Users...................................................13
Getting Started with CCDOPS...........................................................................17
To try some functions with sample images:.......................................................17
Capturing Images with the CCD Camera.........................................................18
Introduction to CCD Cameras............................................................................19
Cameras in General...............................................................................................19
How CCD Detectors Work...................................................................................19
2.2.1. Full Frame and Frame Transfer / Interline CCDs.............................20
Camera Hardware Architecture ..........................................................................21
CCD Special Requirements...................................................................................23
2.4.1. Cooling.................................................................................................23
2.4.2. Double Correlated Sampling Readout ...............................................24
2.4.3. Dark Frames ........................................................................................24
2.4.4. Flat Field Images..................................................................................25
2.4.5. Pixels vs. Film Grains ..........................................................................25
2.4.6. Guiding................................................................................................27
Electronic Imaging ................................................................................................27
Black and White vs. Color ....................................................................................28
3.
3.1.
3.2.
3.3.
3.4.
3.5.
3.6.
3.7.
3.8.
3.9.
At the Telescope with a CCD Camera ..............................................................31
Step by Step with a CCD Camera........................................................................31
Attaching the Camera to the Telescope...............................................................31
Establishing a Communications Link...................................................................32
Focusing the CCD Camera...................................................................................33
Finding and Centering the Object........................................................................34
Taking an Image....................................................................................................34
Displaying the Image ............................................................................................35
Processing the Image.............................................................................................35
Advanced Capabilities..........................................................................................35
3.9.1. Crosshairs Mode (Photometry and Astrometry) ...............................35
3.9.2. Sub-Frame Readout in Focus..............................................................36
3.9.3. Track and Accumulate .......................................................................36
3.9.4. Autoguiding and Self Guiding ...........................................................37
3.9.5. Auto Grab............................................................................................38
3.9.6. Color Imaging......................................................................................38
4.
Camera Hardware ...............................................................................................39
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Section 1 - Introduction
4.1.
4.2.
4.3.
4.4.
4.5.
4.6.
4.7.
System Components..............................................................................................39
Connecting the Power ..........................................................................................39
Connecting to the Computer................................................................................39
Connecting the Relay Port to the Telescope ........................................................39
4.4.1 Using Mechanical Relays.......................................................................40
Modular Family of CCD Cameras .......................................................................43
Connecting accessories to the Camera.................................................................48
Battery Operation..................................................................................................48
5.
5.1.
5.2.
5.3.
5.4.
5.5.
5.6.
5.7.
5.8.
Advanced Imaging Techniques..........................................................................49
Lunar and Planetary Imaging..............................................................................49
Deep Sky Imaging.................................................................................................49
Terrestrial Imaging................................................................................................49
Taking a Good Flat Field.......................................................................................50
Building a Library of Dark Frames.......................................................................50
Changing the Camera Resolution ........................................................................50
Flat Fielding Track and Accumulate Images .......................................................51
Tracking Functions................................................................................................53
6.
6.1.
6.2.
6.3.
6.4.
6.5.
6.6.
6.7.
6.8.
Accessories for your CCD Camera ....................................................................55
Water Cooling .......................................................................................................55
Tri-color Imaging...................................................................................................56
Camera Lens Adapters and Eyepiece Projection ................................................56
Focal Reducers.......................................................................................................56
AO-7 and Lucy-Richardson Software .................................................................56
SGS - Self-Guided Spectrograph...........................................................................57
Third Party Products and Services.......................................................................57
6.7.1. Windows Software..............................................................................57
6.7.2. Image Processing Software.................................................................57
6.7.3. Getting Hardcopy................................................................................57
SBIG Technical Support........................................................................................58
7.
Common Problems ...............................................................................................59
8.
Glossary................................................................................................................61
A.
A.1.
A.2.
A.3.
A.4.
Appendix A - Connector and Cables.................................................................67
Connector Pinouts for the AO7/CFW8/SCOPE port: .......................................67
Connector Pinouts for the power jack: ................................................................67
Connector Pinouts for the I2C AUX port: ...........................................................67
SBIG Tracking Interface Cable (TIC-78) ..............................................................68
B.
B.1.
B.2.
Appendix B - Maintenance.................................................................................69
Cleaning the CCD and the Window....................................................................69
Regenerating the Desiccant ..................................................................................69
Page 2
Section 1 - Introduction
C.
C.1.
Appendix C - Capturing a Good Flat Field .......................................................70
Technique ..............................................................................................................70
D.
Appendix D - Use and Maintenance of the Cooling Booster .........................71
E.
Appendix E – Third Party Vendors Supporting SBIG Products.....................74
1.
Introduction
Congratulations and thank you for buying one of Santa Barbara Instrument Group's CCD
cameras. The model ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM are SBIG's
fifth generation CCD cameras and represent the state of the art in CCD camera systems with
their low noise and advanced capabilities, including Kodak's new Blue Enhanced E series of
CCDs and high speed USB interface. We feel that these cameras will expand your astronomy
experience by being able to easily take images like the ones you've seen in books and magazines,
of structure never seen through the eyepiece. SBIG CCD cameras offer convenience, high
sensitivity, and advanced image processing techniques that film just can't match. While CCDs
will probably never replace film in its large format, CCDs allow a wide range of scientific
measurements and have established a whole new field of amateur astronomy that is growing by
leaps and bounds.
The ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM cameras include
several exciting new features: improved self-guiding (US Patent 5,525,793), high speed USB
interface, improved cooling design and more. These cameras have two CCDs inside, one for
guiding and a large one for imaging. The low noise of the read out electronics virtually
guarantees that a usable guide star will be within the field of the guiding CCD for telescopes
with F/numbers F/6.3 or faster. The new cooling design is capable of performance similar to
that which used to require an optional second stage cooling booster. The relay output plugs
directly into most recent commercial telescope drives and is easily modifiable to virtually any
drive system. As a result, you can take hour long guided exposures with ease, with no
differential deflection of guide scope relative to main telescope, and no radial guider setup
hassles, all from the computer keyboard. This capability, coupled with the phenomenal
sensitivity of the CCD, will allow the user to acquire observatory class images of deep sky images
with modest apertures! The technology also makes image stabilization possible through our AO7, or self-guided spectroscopy with our SGS.
The new ST-X series of cameras (ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST2000XM) incorporate the following design improvements over their parallel based predecessors:
Ø
Ø
Ø
Ø
Ø
Uses High Speed USB vs. Parallel Port for 10X to 15X faster downloads.
Adds a new I2C bi-directional AUX port for future use.
LEDs on the Digital Board show Relay Activations (helpful for troubleshooting).
New Heat Exchanger with Water Circulation Capability built-in.
No firmware ROM to update, software uploads to camera at boot-up.
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Section 1 - Introduction
Ø New capabilities can be added to the camera by replacing the loader driver.
Ø New Boot sequence, LED flashes and fan comes on when firmware upload is
complete.
Ø LED flashes when initializing shutter.
Ø Mechanical/electronic design work to reduce shutter errors and stray light.
Ø TC237 autoguider CCD added to the ST-8XE, ST-9XE, ST-10XE and ST-10XME.
Ø Premier software, CCDSoftV5 and TheSky included with each camera.
Ø CCDOPS version 5 camera control software included with major improvements
o Support for USB cameras
o Support for Ethernet (Ethernet to Parallel) for parallel cameras
o Read FITS files
o Save in several formats (including ASCII format that imports to Excel).
o Multiple images open at once
o New universal drivers
o Works with all 32-bit Windows OS (95/98/Me/NT/2000/XP).
o Version 5 (Gold Icon) can co-exist with Version 4 (Black Icon).
o Focus Mode Dialog has big numbers for peak brightness to aid focusing.
o Added 1xN, 2xN and 3N readout modes to ST-7/8/9/10/1001
o Magnified preview in crosshairs window
o Sharpen preview in contrast dialog.
o Dockable Icon bar.
1.1. Getting Started.
This manual describes the ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM CCD
Camera Systems from Santa Barbara Instrument Group. The first section contains USB driver
installation instructions. The USB driver installation process must be completed by anyone
installing an SBIG USB camera for the first time on a particular computer. If you wish to run
your SBIG USB camera from more than one computer, you must go through the USB driver
installation process for each computer you intend to use.
For users new to the field of CCD Astronomy, Sections 2, 3 and 4 offer introductory
material about CCD Cameras and their applications in Astronomy. Users who are familiar with
CCD cameras may wish to skip section 2 and browse through sections 3 and 4, reading any new
material.
Thoroughly experienced SBIG customers may wish to jump right to the separate Software
Manual, which gives detailed and specific information about the SBIG software. Sections 5 and 6
offer hints and information about advanced imaging techniques and accessories for CCD
imaging that you may wish to read after your initial telescope use of the CCD camera. Finally,
section 7 may be helpful if you experience problems with your camera, and the Appendices
provide a wealth of technical information about these systems.
Page 4
Section 1 - Introduction
1.2.
Installing the USB Drivers for the First Time
If you are installing an SBIG USB camera for the first time use this section to walk you through
the driver installation process. To operate the camera you must first install camera control
software onto your computer or laptop. Your camera comes with two programs: CCDOPS from
SBIG and CCDSoftV5 which was jointly written by Software Bisque and SBIG. CCDSoftV5 is a
very comprehensive program that incorporates many of the camera control functions of
CCDOPS. However, because we use CCDOPS solely to develop and test our cameras we are
able to post more frequent updates for CCDOPS at our web site for free download. You can use
either program to control the camera but we suggest starting with CCDOPS to install the USB
drivers and to make sure everything is working properly and then move to CCDSoftV5 when
you are more familiar with the operations of the camera. Follow the instructions below to install
and run the CCDOPS software and display and process sample images found at our web site.
Please follow these directions IN SEQUENCE. Do not connect the camera to the PC or turn it
on until instructed to do so below. USB drivers can be difficult to install if you don’t follow
the instructions.
With USB devices you don’t pre-install the drivers like you did in the past. With USB the
first time you connect to a new USB device the system walks you through the driver installation
procedure. It’s a bit complicated, and it’s easy to make a mistake so please follow these
instructions for your OS to the letter for best results.
The SBIG USB Cameras actually use two USB drivers. The cameras contain no
permanent memory for firmware and thus need to be booted up by the PC. When they are first
plugged into the computer they present themselves as an “SBIG Loader” device and the
SBIGULDR.SYS driver downloads the camera control code to the camera. At this point the LED
and FAN on the camera come on, indicating the camera is fully booted. Once that is complete
the cameras remove themselves from the USB and then, through a process call “renumeration”,
present themselves as a “SBIG USB Camera”. At this point the SBIGUDRV.SYS driver takes over
and allows CCDOPS and other third party software packages to control the camera. .
1.2.1. Installing CCDOPS
The first thing you should do in all cases is install CCDOPS Version 5. This is relatively simple:
1. Make sure the camera is not connected to the computer. You will do this later.
2. Run the Installer
Page 5
Section 1 - Introduction
3. Towards the end of the installation the installer will run the SBIGDriverChecker.exe
program. This utility checks to make sure you have the latest version of the SBIG camera
drivers installed on your system. When the SBIGDriverChecker utility is run you see a
dialog like:
If you have previously installed CCDOPS you’ll see some entries in the table. Most likely
one or more drivers is not installed or is not up to date.
Page 6
Section 1 - Introduction
4. Click on the Update button. This will copy the current drivers to your system and make
sure they are properly installed. After you click the Update button you should see something
like:
You may be asked to reboot your system as well. If so, click Done and do so. Otherwise
simply click Done.
1.2.2. Installing USB drivers for Window 95/98/Me Users
1. With the power off, plug the camera into the computer with the supplied USB cable.
2. Plug in or turn on the power supply. The computer will then present you with the Add
New Hardware Wizard shown below:
Click the Next button.
Page 7
Section 1 - Introduction
3. Click “Search for the best driver..” then click the Next button as shown below:
4. Uncheck al the options other than “Specify a location” as shown below then click the
Browse button
Page 8
Section 1 - Introduction
5. Navigate through the Browser window to the “Program Files\CCDOPS5\SBIG Drivers”
directory as shown below
then click the OK button
6. You’ll see the dialog below. Click the Next button.
Page 9
Section 1 - Introduction
7. Windows will spin for a while, then present you with the dialog below. Click the Finish
button and you’re done. The SBIG cameras actually use two drivers and after you click
Finish the system will automatically install the second driver.
1.2.3. Installing USB drivers for Windows 2000 Users
1. With the power off, plug the camera into the computer with the supplied USB cable.
2. Plug in or turn on the power supply. The computer will then present you with the Found
New Hardware Wizard shown below. Click the Next button.
Page 10
Section 1 - Introduction
3. Click the “Search for suitable driver…” radio button as shown below:
then click the Next button.
4. Uncheck all the options other than “Specify a location” as shown below:
then click the Next button.
Page 11
Section 1 - Introduction
5. As shown below click the Browse button then navigate to the
“Program Files\SBIG\CCDOPS5\SBIG Drivers” directory. Click OK in the Find File
dialog then click OK back at the New Hardware Wizard.
6. Windows will find the driver and present you with the dialog below:
Click the Next button.
Page 12
Section 1 - Introduction
7. Windows will spin for a while, then present you with the dialog below. Click the Finish
button and you’re done. The SBIG cameras actually use two drivers and after you click
Finish the system will automatically install the second driver.
1.2.4. Installing USB drivers for Windows XP Users
1. With the power off, plug the camera into the computer with the supplied USB cable.
2. Plug in or turn on the power supply. The computer will then present you with the Found
New Hardware Wizard. Click the “Install from a list…” radio button then click the Next
button.
Page 13
Section 1 - Introduction
3. As shown below, click the “Search for the best driver…” radio button then check the
“Include this location…” checkbox then click the Browse button.
4. Navigate through the directory structure of you hard drive to the
Program Files\SBIG\CCDOPS5\SBIG Drivers directory and click the OK button. You’ll
then be back in the Found New Hardware Wizard as shown below. Click the Next
button.
Page 14
Section 1 - Introduction
5. Windows will show the dialog below while it is copying the driver:
6. You may be presented with the dialog below warning you the SBIG USB Loader driver
has not passed the Windows Logo testing procedure. At this point click the Continue
Anyway button.
Page 15
Section 1 - Introduction
7. Windows will continue installing the driver as shown in the dialog below:
8. Windows will finish installing the SBIG USB Loader driver as shown in the dialog below
Hit the Finish button to move onto the SBIG USB Camera driver.
Page 16
Section 1 - Introduction
9. Again you will be presented with the Found New Hardware wizard for the SBIG USB
Camera driver as shown in the dialog below. Repeat steps 3 through 8 for this driver just
like you did for the SBIG USB Loader driver.
1.2.5. Getting Started with CCDOPS
•
Use Camera->Establish Com Link. After a few seconds should see “Link:[ST-10]USB” in
lower-right corner of CCDOPS main window where ST-10 is the camera model. You
are now talking to the camera.
•
From this point you should follow the software instructions / help menus to Set Up the
camera’s cooling, Focus, Grab images, etc.
1.2.6. To try some functions with sample images:
•
Double-click on the CCDOPS icon to launch the program.
• Use the Open command in the File menu to load one of the sample images. A window
showing the exposure time, etc. will appear. Click in it to make it disappear. The image will
show up in its own window.
•
Try using the crosshairs. Use the Crosshairs command in the Display menu.
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Section 1 - Introduction
•
Use the mouse to move the crosshair around in the image and see the pixel values.
• Close the crosshairs and try inverting the image. Click the Invert item in the Contrast
window.
• Try the photo display mode. Use the Photo Mode command in the Display menu. Click
the mouse to return to the menus.
• Load up the other sample images and display them using the photo display mode. You
have to close any existing image first.
• If you find that the display is too dark or bright, try setting Auto Contrast in the Contrast
window or adjust the background and range parameters to achieve the best display. You
may have to hit the Apply button in the Contrast window to see changes in the Background
and Range
1.2.7. Capturing Images with the CCD Camera
Unfortunately there really aren't many shortcuts you can take when using the CCD camera to
capture images. The instructions below refer you to various sections of the manual.
•
Find some relatively bright object like M51, the Ring Nebula (M57) or the Dumbbell
Nebula (M27) (refer to section 3.5).
•
Take a 1 minute exposure using the Grab command with the Dark frame option set to
Also (refer to Section 3.6).
•
Display the image (refer to Section 3.7).
•
Process the image (refer to Section 3.8).
If you happen to have purchased a camera lens adapter for your CCD Camera you can use that
to take images in the daytime. Additionally you could make a small pinhole aperture out of a
piece of aluminum foil after wrapping it around the camera's nosepiece.
• Shut down the F stop all the way to F/16 or F/22.
• Set the focus based upon the object and the markings on the lens.
• Take a short (<1 second) exposure with the Grab command.
• Display the image.
• Process the image .
Page 18
Section 2 - Introduction to CCD Cameras
2.
Introduction to CCD Cameras
This section introduces new users to CCD (Charge Coupled Device) cameras and their
capabilities and to the field of CCD Astronomy and Electronic Imaging.
2.1.
Cameras in General
The CCD is very good at the most difficult astronomical imaging problem: imaging small,
faint objects. For such scenes long film exposures are typically required. The CCD based
system has several advantages over film: greater speed, quantitative accuracy, ability to
increase contrast and subtract sky background with a few keystrokes, the ability to co-add
multiple images without tedious dark room operations, wider spectral range, and instant
examination of the images at the telescope for quality. Film has the advantages of a much
larger format, color, and independence of the wall plug (the SBIG family of cameras can be
battery operated in conjunction with a laptop computer, though, using a power inverter).
After some use you will find that film is best for producing sensational large area color
pictures, and the CCD is best for planets, faint objects, and general scientific work such as
variable star monitoring and position determination.
2.2.
How CCD Detectors Work
The basic function of the CCD detector is to convert an incoming photon of light to an
electron which is stored in the detector until it is read out, thus producing data which your
computer can display as an image. It doesn't have to be displayed as an image. It could just
as well be displayed as a spreadsheet with groups of numbers in each cell representing the
number of electrons produced at each pixel. These numbers are displayed by your computer
as shades of gray for each pixel site on your screen thus producing the image you see. How
this is accomplished is eloquently described in a paper by James Janesick and Tom Elliott of
the Jet Propulsion Laboratory:
"Imagine an array of buckets covering a field. After a rainstorm, the buckets
are sent by conveyor belts to a metering station where the amount of water in
each bucket is measured. Then a computer would take these data and display
a picture of how much rain fell on each part of the field. In a CCD the
"raindrops" are photons, the "buckets" the pixels, the "conveyor belts" the CCD
shift registers and the "metering system" an on-chip amplifier.
Technically speaking the CCD must perform four tasks in generating an image.
These functions are 1) charge generation, 2) charge collection, 3) charge
transfer, and 4) charge detection. The first operation relies on a physical
process known as the photoelectric effect - when photons or particles strikes
certain materials free electrons are liberated...In the second step the
photoelectrons are collected in the nearest discrete collecting sites or pixels.
The collection sites are defined by an array of electrodes, called gates, formed
Page 19
Section 2 - Introduction to CCD Cameras
on the CCD. The third operation, charge transfer, is accomplished by
manipulating the voltage on the gates in a systematic way so the signal
electrons move down the vertical registers from one pixel to the next in a
conveyor-belt like fashion. At the end of each column is a horizontal register of
pixels. This register collects a line at a time and then transports the charge
packets in a serial manner to an on-chip amplifier. The final operating step,
charge detection, is when individual charge packets are converted to an output
voltage. The voltage for each pixel can be amplified off-chip and digitally
encoded and stored in a computer to be reconstructed and displayed on a
television monitor."1
Readout Register
Output
Y=1
Amplifier
Y=N
X=1
X=M
Figure 2.1 - CCD Structure
2.2.1. Full Frame and Frame Transfer / Interline CCDs
In the ST-7XE, ST-8XE, ST-9XE, ST-10XE and ST-10XME, the CCD is read out electronically
by shifting each row of pixels into a readout register at the Y=0 position of the CCD (shown
in Figure 2.1), and then shifting the row out through an amplifier at the X=0 position. The
entire array shifts up one row when a row is shifted into the readout register, and a blank
row is inserted at the bottom. The electromechanical shutter built into the camera covers the
CCD during the readout to prevent streaking of the image. Without a shutter the image
would be streaked due to the fact that the pixels continue to collect light as they are being
shifted out towards the readout register. CCDs with a single active area are called Full Frame
CCDs.
For reference, the ST-5C, ST-237A, STV and guiding CCDs in the ST-X series of
cameras use a different type of CCD, which is known as a Frame Transfer CCD. In these
devices all active pixels are shifted very quickly into a pixel array screened from the light by a
metal layer, and then read out. This makes it possible to take virtually streak-free images
without a shutter. This feature is typically called an electronic shutter. The interline CCD
1
"History and Advancements of Large Area Array Scientific CCD Imagers", James Janesick, Tom Elliott.
Jet Propulsion Laboratory, California Institute of Technology, CCD Advanced Development Group.
Page 20
Section 2 - Introduction to CCD Cameras
used in the ST-2000XM is similar to a frame transfer except that the protected pixels are
interlaced with the active pixels.
2.3.
Camera Hardware Architecture
This section describes the ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM
CCD cameras from a systems standpoint. It describes the elements that comprise a CCD
camera and the functions they provide. Please refer to Figure 2.2 below as you read through
this section.
Figure 2.2 - CCD System Block Diagram
As you can see from Figure 2.2, the ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST2000XM are completely self-contained. Unlike our previous products, the ST-7XE, ST-8XE,
ST-9XE, ST-10XE, ST-10XME and ST-2000XM contain all the electronics in the optical head.
There is no external CPU like the ST-5C, ST-237, ST-6 and STV.
At the "front end" of any CCD camera is the CCD sensor itself. As we have already
learned, CCDs are a solid-state image sensor organized in a rectangular array of regularly
spaced rows and columns. The ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST2000XM use two CCDs, one for imaging (Kodak KAF series) and one for tracking (TI TC211
or TC237).
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Section 2 - Introduction to CCD Cameras
Table 2.1 below lists some interesting aspects of the CCDs used in the various SBIG
cameras.
Array
Number of
Camera
CCD
Dimensions
Pixels
TC211 Tracking CCD TC211
2.6 x 2.6 mm
192 x 164
TC237 Tracking CCD TC237
4.9 x 3.7 mm
657 x 495
ST-5C
TC255
3.2 x 2.4 mm
320 x 240
ST-237A
TC237
4.9 x 3.7 mm
640 x 480
STV/STV Deluxe
TC237
4.7 x 3.0 mm
320 x 200
ST-6B
TC241
8.6 x 6.5 mm
375 x 242
ST-7E/XE
KAF0401E
6.9 x 4.6 mm
765 x 510
ST-8E/XE
KAF1602E
13.8 x 9.2 mm
1530 x 1020
ST-9E/XE
KAF0261E
10.2 x 10.2 mm 512 x 512
ST-10E/XE/XME
KAF3200E
14.9 x 10.0 mm 2184 x 1472
ST-1001E
KAF1001E
24.6 x 24.6 mm 1024 x 1024
ST-2000XM
KAI2000M 11.8 x 8.9 mm
1600 x 1200
Table 2.1 - Camera CCD Configurations
Pixel Sizes
13.75 x 16 µ
7.4 x 7.4 µ
10 x 10 µ
7.4 x 7.4 µ
14.8 x 14.8 µ
23 x 27 µ
9x9µ
9x9µ
20 x 20 µ
6.8 x 6.8 µ
24 x 24 µ
7.4 x 7.4 µ
The CCD is cooled with a solid-state a thermoelectric (TE) cooler. The TE cooler pumps heat
out of the CCD and dissipates it into a heat sink, which forms part of the optical head's
mechanical housing. In the ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM
cameras this waste heat is dumped into the air using a new heat exchanger and a small fan.
The heat exchanger is also capable of water circulation for additional efficiency if needed in
hot climates. An inlet and outlet are provided at the back of the camera head for passing
water through the heat exchanger. Only a very small flow is required and an ordinary
aquarium pump is sufficient if it will pull the flow up the length of tubing you might require
at your installation. An optional 110VAC pump and tubing are also available from SBIG.
Since the CCD is cooled below 0°C, some provision must be made to prevent frost
from forming on the CCD. The ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-
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Section 2 - Introduction to CCD Cameras
2000XM have the CCD/TE Cooler mounted in a windowed hermetic chamber sealed with an
O-Ring. The hermetic chamber does not need to be evacuated, another "ease of use" feature
we employ in the design of our cameras. Using a rechargeable desiccant in the chamber
keeps the humidity low, forcing the dew point below the cold stage temperature.
Other elements in the self contained ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME
and ST-2000XM include the preamplifier and an electromechanical shutter. The shutter
makes taking dark frames a simple matter of pushing a button on the computer and provides
streak-free readout. Timing of exposures in ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME
and ST-2000XM cameras is controlled by this shutter.
The Clock Drivers and Analog to Digital Converter interface to the CCD. The Clock
Drivers convert the logic-level signals from the micro controller to the voltage levels and
sequences required by the CCD. Clocking the CCD transfers charge in the array and is used
to clear the array or read it out. The Analog to Digital Converter (A/D) digitizes the data in
the CCD for storage in the Host Computer.
The micro controller is used to regulate the CCD's temperature by varying the drive to
the TE cooler. The external Power Supply provides +5V and ±12V to the cameras. Finally,
the cameras contain a TTL level telescope interface port to control the telescope and the
optional CFW-6A motorized color filter wheel.
Although not part of the CCD Camera itself, the Host Computer and Software are an
integral part of the system. SBIG provides software for the ST-7XE, ST-8XE, ST-9XE, ST10XE, ST-10XME and ST-2000XM cameras for the IBM PC and Compatible computers
running Windows 95/98/2000/Me/NT/XP. The software allows image acquisition, image
processing, and auto guiding with ease of use and professional quality. Many man-years and
much customer feedback have gone into the SBIG software and it is unmatched in its
capabilities.
2.4.
CCD Special Requirements
This section describes the unique features of CCD cameras and the special requirements that
CCD systems impose.
2.4.1. Cooling
Random readout noise and noise due to dark current combine to place a lower limit on the
ability of the CCD to detect faint light sources. SBIG has optimized the ST-7XE, ST-8XE, ST9XE, ST-10XE, ST-10XME and ST-2000XM to achieve readout noises below 20 electrons rms
for two reads (light - dark). This will not limit most users. The noise due to the dark current
is equal to the square root of the number of electrons accumulated during the integration
time. For these cameras, the dark current is not significant until it accumulates to more than
280 electrons. Dark current is thermally generated in the device itself, and can be reduced by
cooling. All CCDs have dark current, which can cause each pixel to fill with electrons in only
a few seconds at room temperature even in the absence of light. By cooling the CCD, the
dark current and corresponding noise is reduced, and longer exposures are possible. In fact,
for roughly every 5 to 6° C of additional cooling, the dark current in the CCD is reduced to
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Section 2 - Introduction to CCD Cameras
half. The ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM have a single stage
TE cooler, efficient heat exchanger and water circulation capability. A temperature sensing
thermistor on the CCD mount monitors the temperature (Earlier parallel models offered a
cooling booster which used a second TE cooler but we feel that the new design provides
similar performance without the need for a second power supply). The micro controller
controls the temperature at a user-determined value for long periods. As a result, exposures
hours long are possible, and saturation of the CCD by the sky background typically limits the
exposure time. At 0 °C the dark current in the ST-7XE, ST-8XE and ST-10XE, high-resolution
mode, is only 60 electrons per minute! The ST-9XE, with bigger pixels, has roughly 8 times
this amount of dark current due largely to the larger pixel area but also due to the inherent
higher bulk dark current in the devices.
The sky background conditions also increase the noise in images, and in fact, as far as
the CCD is concerned, there is no difference between the noise caused by dark current and
that from sky background. If your sky conditions are causing photoelectrons to be generated
at the rate of 100 e-/pixel/sec, for example, increasing the cooling beyond the point where
the dark current is roughly half that amount will not improve the quality of the image. This
very reason is why deep sky filters are so popular with astrophotography. They reduce the
sky background level, increasing the contrast of dim objects. They will improve CCD images
from very light polluted sights.
2.4.2. Double Correlated Sampling Readout
During readout, the charge stored in a pixel is stored temporarily on a capacitor. This
capacitor converts the optically generated charge to a voltage level for the output amplifier to
sense. When the readout process for the previous pixel is completed, the capacitor is drained
and the next charge shifted, read, and so on. However, each time the capacitor is drained,
some residual charge remains.
This residual charge is actually the dominant noise source in CCD readout electronics.
This residual charge may be measured before the next charge is shifted in, and the actual
difference calculated. This is called double correlated sampling. It produces more accurate
data at the expense of slightly longer read out times (two measurements are made instead of
one). The ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM utilize double
correlated sampling to produce the lowest possible readout noise. At 10e- to 15e- rms per
read these cameras are unsurpassed in performance.
2.4.3. Dark Frames
No matter how much care is taken to reduce all sources of unwanted noise, some will remain.
Fortunately, however, due to the nature of electronic imaging and the use of computers for
storing and manipulating data, this remaining noise can be drastically reduced by the
subtraction of a dark frame from the raw light image. A dark frame is simply an image taken
at the same temperature and for the same duration as the light frame with the source of light
to the CCD blocked so that you get a "picture" of the dark. This dark frame will contain an
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Section 2 - Introduction to CCD Cameras
image of the noise caused by dark current (thermal noise) and other fixed pattern noise such
as read out noise. When the dark frame is subtracted from the light frame, this pattern noise
is removed from the resulting image. The improvement is dramatic for exposures of more
than a minute, eliminating the many "hot" pixels one often sees across the image, which are
simply pixels with higher dark current than average.
2.4.4. Flat Field Images
Another way to compensate for certain unwanted optical effects is to take a "flat field image"
and use it to correct for variations in pixel response uniformity across the area of your darksubtracted image. You take a flat field image of a spatially uniform source and use the
measured variations in the flat field image to correct for the same unwanted variations in
your images. The Flat Field command allows you to correct for the effects of vignetting and
nonuniform pixel responsivity across the CCD array.
The Flat Field command is very useful for removing the effects of vignetting that may
occur when using a field compression lens and the fixed pattern responsivity variations
present in all CCDs. It is often difficult to visually tell the difference between a corrected and
uncorrected image if there is little vignetting, so you must decide whether to take the time to
correct any or all of your dark-subtracted images. It is always recommended for images that
are intended for accurate photometric measurements.
Appendix D describes how to take a good flat field. It's not that easy, but we have
found a technique that works well for us.
2.4.5. Pixels vs. Film Grains
Resolution of detail is determined, to a certain degree, by the size of the pixel in the detector
used to gather the image, much like the grain size in film. The pixel size of the detector in the
ST-10XE is 6.8 x 6.8 microns (1 micron = 0.001mm, 0.04 thousandths of an inch). In the ST7XE and ST-8XE it is 9 x 9 microns, in the ST-9XE it's 20 x 20 microns and in the ST-2000XM
it is 7.4 x 7.4 microns. However, the effects of seeing are usually the limiting factor in any
good photograph or electronic image. On a perfect night with excellent optics an observer
might hope to achieve sub-arcsecond seeing in short exposures, where wind vibration and
tracking error are minimal. With the average night sky and good optics, you will be doing
well to achieve stellar images in a long exposure of 3 to 6 arcseconds halfwidth. This will still
result in an attractive image, though.
Using an ST-7XE or ST-8XE camera with their 9 micron pixels, an 8" f/10 telescope
will produce a single pixel angular subtense of 0.9 arcsecond. An 8" f/4 telescope will
produce images of 2.5 arcseconds per pixel. If seeing affects the image by limiting resolution
to 6 arcseconds, you would be hard pressed to see any resolution difference between the two
focal lengths as you are mostly limited by the sky conditions. However, the f/4 image would
have a larger field of view and more faint detail due to the faster optic. The ST-9XE, with its
20 micron pixels would have the same relationship at roughly twice the focal length or a 16
inch f/10 telescope. See table 4.4 for further information.
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Section 2 - Introduction to CCD Cameras
A related effect is that, at the same focal length, larger pixels collect more light from
nebular regions than small ones, reducing the noise at the expense of resolution. While many
people think that smaller pixels are a plus, you pay the price in sensitivity due to the fact that
smaller pixels capture less light. For example, the ST-9XE with its large 20 x 20 micron pixels
captures five times as much light as the ST-7XE and ST-8XE's 9 micron square pixels. For this
reason we provide 2x2 or 3x3 binning of pixels on most SBIG cameras. With the ST-7XE and
ST-8XE, for instance, the cameras may be configured for 18 or 27-micron square pixels.
Binning is selected using the Camera Setup Command. It is referred to as resolution (High =
9µ2 pixels, Medium = 18µ2 pixels, Low = 27µ2 pixels). When binning is selected the electronic
charge from groups of 2x2 or 3x3 pixels is electronically summed in the CCD before readout.
This process adds no noise and may be particularly useful on the ST-10XE with its very small
6.8 micron pixels. Binning should be used if you find that your stellar images have a
halfwidth of more than 3 pixels. If you do not bin, you are wasting sensitivity without
benefit. Binning also shortens the download time.
The halfwidth of a stellar image can be determined using the crosshairs mode. Find
the peak value of a relatively bright star image and then find the pixels on either side of the
peak where the value drops to 50% of the peak value (taking the background into account, if
the star is not too bright). The difference between these pixel values gives the stellar
halfwidth. Sometimes you need to interpolate if the halfwidth is not a discrete number of
pixels.
Another important consideration is the field of view of the camera. For comparison,
the diagonal measurement of a frame of 35mm film is approximately 43mm, whereas the
diagonal dimension of the ST-7XE chip is approximately 8 mm. The relative CCD sizes for all
of the SBIG cameras and their corresponding field of view in an 8" f/10 telescope are given
below:
Camera
TC211 Tracking CCD
TC237 Tracking CCD
ST-5C
ST-237A
STV
ST-7XE
ST-8XE
ST-9XE
ST-10XE (XME)
ST-1001E
ST-2000XM
35mm Film
Array Dimensions Diagonal
Field of View at 8" f/10
2.64 x 2.64 mm
3.73 mm
4.5 x 4.5 arcminutes
4.93 x 3.71 mm
6.17 mm
8.2 x 6.2 arcminutes
3.20 x 2.40 mm
4.00 mm
5.6 x 4.2 arcminutes
4.93 x 3.71 mm
6.17 mm
8.2 x 6.2 arcminutes
4.74 x 2.96 mm
5.58 mm
8.2 x 5.1 arcminutes
6.89 x 4.59 mm
8.28 mm
11.9 x 7.9 arcminutes
13.8 x 9.18 mm
16.6 mm
23.8 x 15.8 arcminutes
10.2 x 10.2 mm
14.4 mm
17.6 x 17.6 arcminutes
14.9 x 10.0 mm
17.9 mm
25.1 x 16.9 arcminutes
24.6 x 24.6 mm
34.8 mm
41.5 x 41.5 arcminutes
11.8 x 9.0 mm
14.8 mm
20.0 x 15.0 arcminutes
36 x 24 mm
43 mm
62 x 42 arcminutes
Table 2.2 - CCD Array Dimensions
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Section 2 - Introduction to CCD Cameras
2.4.6. Guiding
Any time you are taking exposures longer than several seconds, whether you are using a film
camera or a CCD camera, the telescope needs to be guided to prevent streaking. While
modern telescope drives are excellent with PEC or PPEC, they will not produce streak-free
images without adjustment every 30 to 60 seconds. The ST-7XE, ST-8XE, ST-9XE, ST-10XE,
ST-10XME and ST-2000XM allow simultaneous guiding and imaging, called self-guiding (US
Patent 5,525,793). This is possible because of the unique design employing 2 CCDs. One
CCD guides the telescope while the other takes the image. This resolves the conflicting
requirements of short exposures for guiding accuracy and long exposures for dim objects to
be met, something that is impossible with single CCD cameras. Up to now the user either
had to set up a separate guider or use Track and Accumulate to co-add several shorter
images. The dual CCD design allows the guiding CCD access to the large aperture of the
main telescope without the inconvenience of off-axis radial guiders. Not only are guide stars
easily found, but the problems of differential deflection between guide scope and main scope
eliminated.
Track and Accumulate is another SBIG patented process (US #5,365,269) whereby
short exposures are taken and added together with appropriate image shifts to align the
images. It is supported by the ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM
camera software, but will generally not produce as good as results as self guiding, where the
corrections are more frequent and the accumulated readout noise less. It is handy when no
connection to the telescope drive is possible and also works best on cameras with larger pixels
like the ST-9XE or for cameras with smaller pixels in binned mode. For cameras with smaller
pixels imaging in high resolution mode such as the ST-7XE, ST-8XE, ST-10XE, ST-10XME and
ST-2000XM, SBIG is proud to make self-guiding available to the amateur, making those long
exposures required by the small pixel geometry easy to achieve!
2.5.
Electronic Imaging
Electronic images resemble photographic images in many ways. Photographic images are
made up of many small particles or grains of photo sensitive compounds which change color
or become a darker shade of gray when exposed to light. Electronic images are made up of
many small pixels which are displayed on your computer screen to form an image. Each
pixel is displayed as a shade of gray, or in some cases a color, corresponding to a number
which is produced by the electronics and photo sensitive nature of the CCD camera.
However, electronic images differ from photographic images in several important aspects. In
their most basic form, electronic images are simply groups of numbers arranged in a
computer file in a particular format. This makes electronic images particularly well suited for
handling and manipulation in the same fashion as any other computer file.
An important aspect of electronic imaging is that the results are available immediately.
Once the data from the camera is received by the computer, the resulting image may be
displayed on the screen at once. While Polaroid cameras also produce immediate results,
serious astrophotography ordinarily requires hypersensitized or cooled film, a good quality
camera, and good darkroom work to produce satisfying results. The time lag between
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Section 2 - Introduction to CCD Cameras
exposure of the film and production of the print is usually measured in days. With electronic
imaging, the time between exposure of the chip and production of the image is usually
measured in seconds.
Another very important aspect of electronic imaging is that the resulting data are
uniquely suited to manipulation by a computer to bring out specific details of interest to the
observer. In addition to the software provided with the camera, there are a number of
commercial programs available which will process and enhance electronic images. Images
may be made to look sharper, smoother, darker, lighter, etc. Brightness, contrast, size, and
many other aspects of the image may be adjusted in real time while viewing the results on the
computer screen. Two images may be inverted and electronically "blinked" to compare for
differences, such as a new supernova, or a collection of images can be made into a large
mosaic. Advanced techniques such as maximum entropy processing will bring out otherwise
hidden detail.
Of course, once the image is stored on a computer disk, it may be transferred to
another computer just like any other data file. You can copy it or send it via modem to a
friend, upload it to your favorite bulletin board or online service, or store it away for
processing and analysis at some later date.
We have found that an easy way to obtain a hard copy of your electronic image is to
photograph it directly from the computer screen. You may also send your image on a floppy
disk to a photo lab which has digital photo processing equipment for a professional print of
your file. Make sure the lab can handle the file format you will send them. Printing the
image on a printer connected to your computer is also possible depending on your
software/printer configuration. There are a number of software programs available, which
will print from your screen. However, we have found that without specialized and expensive
equipment, printing images on a dot matrix or laser printer yields less than satisfactory detail.
However, if the purpose is simply to make a record or catalog the image file for easy
identification, a dot matrix or laser printer should be fine. Inkjet printers are getting very
good, though.
2.6.
Black and White vs. Color
The first and most obvious appearance of a CCD image is that it is produced in shades of
gray, rather than color. The CCD chip used in SBIG cameras itself does not discriminate
color and the pixel values that the electronics read out to a digital file are only numbers
proportional to the number of electrons produced when photons of any wavelength happen
to strike its sensitive layers.
Of course, there are color video cameras, and a number of novel techniques have been
developed to make the CCD chip "see" color. The most common way implemented on
commercial cameras is to partition the pixels into groups of three, one pixel in each triplet
"seeing" only red, green or blue light. The results can be displayed in color. The overall image
will suffer a reduction in resolution on account of the process. A newer and more
complicated approach in video cameras has been to place three CCD chips in the camera and
split the incoming light into three beams. The images from each of the three chips, in red,
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Section 2 - Introduction to CCD Cameras
green and blue light is combined to form a color image. Resolution is maintained. For normal
video modes, where there is usually plenty of light and individual exposures are measured in
small fractions of a second, these techniques work quite well. However, for astronomical
work, exposures are usually measured in seconds or minutes. Light is usually scarce.
Sensitivity and resolution are at a premium. The most efficient way of imaging under these
conditions is to utilize all of the pixels, collecting as many photons of any wavelength, as
much of the time as possible.
In order to produce color images in astronomy, the most common technique is to take
three images of the same object using a special set of filters and then recombine the images
electronically to produce a color composite or RGB color image. SBIG offers as an option an
integrated motorized color filter wheel. The CFW8A color filter wheel is attached to the front
of the camera in such a way that light entering the camera passes through the colored filter
before it strikes the CCD. An object is then exposed using a red filter. The wheel is
commanded to insert the green filter in place, and another image taken. Finally a blue image
is taken. When all three images have been saved, they may be merged into a single color
image using SBIG or third party color software.
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Section 3 - At the Telescope with a CCD Camera
3.
At the Telescope with a CCD Camera
This section describes what goes on the first time you take your CCD camera out to the
telescope. You should read this section throughout before working at the telescope. It will
help familiarize you with the overall procedure that is followed without drowning you in the
details. It is recommended you first try operating the camera in comfortable, well lit
surroundings to learn its operation.
3.1.
Step by Step with a CCD Camera
In the following sections we will go through the steps of setting up and using your CCD
camera. The first step is attaching the camera to the telescope. The next step is powering up
the camera and establishing a communication link to your computer. Then you will want to
focus the system, find an object and take an image. Once you have your light image with a
dark frame subtracted, you can display the image and process the results to your liking. Each
of these steps is discussed in more detail below.
3.2.
Attaching the Camera to the Telescope
ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM cameras are similar in
configuration. The CCD head attaches to the telescope by slipping it into the eyepiece holder
or attaching it via t-threads. A fifteen-foot cable runs from the head to the host computer's
USB port. The camera is powered by a desktop power supply. Operation from a car battery
is possible using the optional 12V power supply or with a 12V to 110V power inverter.
Connect the CCD head to the USB port of your computer using the supplied cable
and insert the CCD Camera's nosepiece into your telescope's eyepiece holder. Fully seat the
camera against the end of the draw tube so that once focus has been achieved you can swap
out and replace the camera without having to refocus. Orient the camera so that the CCD's
axes are aligned in Right Ascension and Declination. Use Figure 3.1 below showing the back
of the optical head as a guide for the preferred orientation. Any orientation will work, but it
is aggravating trying to center objects when the telescope axes don't line up fairly well with
the CCD axes.
Next, connect the power cable and plug in the desktop power supply. A few seconds
after you establish a link using CCDOPS software, the red LED on the rear of the camera
should glow and the fan should spin indicating that the firmware has been uploaded to the
camera and it is ready for operation. We recommend draping the cables over the
finderscope, saddle or mount to minimize cable perturbations of the telescope, and guard
against the camera falling out of the drawtube to the floor. In the alternative, there is a ¼-20
threaded hole on the side plate of the camera used for tripod mounting. This is also a
convenient place to attach a safety strap to prevent the camera from accidentally falling from
the telescope. We also recommend using the T-Ring attachments for connecting the camera
to the telescope, as the cameras are heavy.
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Section 3 - At the Telescope with a CCD Camera
Figure 3.1 Orientation of the Optical Head Viewed from Back.
(Pixel 1,1 is at the upper left in this view)
3.3.
Establishing a Communications Link
After setting up the software and the camera as described in the previous sections, using
CCDOPS software, establish a link to the camera by clicking on the “Establish Comm Link”
command from the Camera menu. If the software is successful the "Link" field in the Status
Window is updated to show the type of camera found. If the camera is not connected,
powered up, or the USB port has not yet been properly selected, a message will be displayed
indicating that the software failed to establish a link to the camera. If this happens, use the
Communications Setup command in the Misc menu to configure the CCDOPS software for
the USB. Then use the Establish COM Link command in the Camera Menu to establish
communications with the camera.
Note: It is not necessary to have a camera connected to your computer to run the software
and display images already saved onto disk. It is only necessary to have a camera
connected when you take new images.
Once the COM link has been established you may need to set the camera's setpoint
temperature in the Camera Setup command. The ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST10XME and ST-2000XM power up regulating to whatever temperature the CCD is at, which
in this case will be the ambient temperature. Use the Camera Setup command and choose a
setpoint temperature approximately 30°C below the ambient temperature. Type in the
setpoint, set the temperature control to active, and hit ENTER.
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Section 3 - At the Telescope with a CCD Camera
3.4.
Focusing the CCD Camera
Focusing a CCD camera can be a tedious operation, so a few hints should be followed.
Before using the software to focus the camera the first time you should place a diffuser (such
as scotch tape or ground glass) at the approximate location of the CCD's sensitive surface
behind the eyepiece tube and focus the telescope on the moon, a bright planet or a distant
street lamp. This preliminary step will save you much time in initially finding focus. The
approximate distance behind the eyepiece tube for each of our CCD cameras is listed in Table
3.1 below:
Camera
ST-7/8/9/10XE
ST-2000XM
Distance
~0.92 inch
~0.92 inch
Diffuser
Back Focus Distance
Table 3.1 - Camera Back Focus
from Table 3.1
To achieve fine focus, insert the CCD head into the eyepiece tube, taking care to seat
it, and then enter the CCDOPS FOCUS mode. The Focus command automatically displays
successive images on the screen as well as the peak brightness value of the brightest object in
the field of view. Point the telescope at a bright star. Center the star image in the CCD, and
adjust the focus until the star image is a small as can be discerned. Next, move the telescope
to a field of fainter stars that are dimmer so the CCD is not saturated. Further adjust the
focus to maximize the displayed star brightness in counts and minimize the star diameter.
This can be tedious. It helps considerably if a pointer or marker is affixed to the focus knob so
you can rapidly return to the best focus once you've gone through it.
An exposure of 1 to 3 seconds is recommended to smooth out some of the atmospheric
effects. While you can use the Full frame mode to focus, the frame rate or screen update rate
can be increased significantly by using Planet mode. In Planet mode the Focus command
takes a full image and then lets you position a variable sized rectangle around the star. On
subsequent images the Planet mode only digitizes, downloads, and displays the small area
you selected. The increase in frame rate is roughly proportional to the decrease in frame size,
assuming you are using a short exposure.
The telescope focus is best achieved by maximizing the peak value of the star image.
You should be careful to move to a dimmer star if the peak brightness causes saturation. The
saturation levels of the various resolution modes are shown in Table 3.2 below. Another point
you should also be aware of is that as you approach a good focus, the peak reading can vary
by 30% or so. This is due to the fact that as the star image gets small, where an appreciable
percentage of the light is confined to a single pixel, shifting the image a half a pixel reduces
the peak brightness as the star's image is split between the two pixels. The Kodak CCD pixels
are so small that this is not likely to be a problem.
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Section 3 - At the Telescope with a CCD Camera
Resolution
High Res
Saturation Counts
~20,000 for ST-7XE/8XE ABG Cameras,
~40,000 for ST-7XE/8XE Non ABG
cameras,
~50,000 for ST-10XE Camera
~65,000 for ST-9XE/2000XM Cameras
Med/Low Res
~65,000 for ST-7/8/9/10/2000
Table 3.2 - Saturation Values
Once the best focus is found, the focusing operation can be greatly shortened the second time
by removing the CCD head, being careful not to touch the focus knob. Insert a high power
eyepiece and slide it back and forth to find the best visual focus, and then scribe the outside of
the eyepiece barrel. The next time the CCD is used the eyepiece should be first inserted into
the tube to the scribe mark, and the telescope visually focused and centered on the object. At
f/6 the depth of focus is only 0.005 inch, so focus is critical. An adapter may be necessary to
allow the eyepiece to be held at the proper focus position. SBIG sells extenders for this
purpose.
3.5.
Finding and Centering the Object
Once best focus is achieved, we suggest using "Dim" mode to help center objects. This mode
gives a full field of view, but reduces resolution in order to increase the sensitivity, and
digitization and download rate. If you have difficulty finding an object after obtaining good
focus, check to be sure that the head is seated at best focus, then remove the head and insert a
medium or low power eyepiece. Being careful not to adjust the focus knob on the telescope,
slide the eyepiece in or out until the image appears in good focus. Then visually find and
center the object, if it is visible to the eye. If not, use your setting circles carefully. Then, reinsert the CCD head and use FOCUS mode with an exposure time of about ten seconds, if it
is dim. Center the object using the telescope hand controls.
Note: With a 10 second exposure, objects like M51 or the ring nebula are easily detected
with modest amateur telescopes. The cores of most galactic NGC objects can also be
seen.
3.6.
Taking an Image
Take a CCD image of the object by selecting the Grab command and setting the exposure
time. Start out with the Image size set to full and Auto Display and Auto contrast enabled.
The camera will expose the CCD for the correct time, and digitize and download the image.
One can also take a dark frame immediately before the light image using the Grab command.
Because the ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM have
regulated temperature control, you may prefer to take and save separate dark images,
building up a library at different temperatures and exposure times, and reusing them on
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Section 3 - At the Telescope with a CCD Camera
successive nights. At the start it's probably easiest to just take the dark frames when you are
taking the image. Later, as you get a feel for the types of exposures and setpoint
temperatures you use, you may wish to build this library of dark frames.
3.7.
Displaying the Image
The image can be displayed on the computer screen using the graphics capability of your PC.
Auto contrast can be selected and the software will pick background and range values which
are usually good for a broad range of images or the background and range values can be
optimized manually to bring out the features of interest.
The image can also be displayed as a negative image, or can be displayed with
smoothing to reduce the graininess. Once displayed, the image can be analyzed using
crosshairs, or can be cropped or zoomed to suit your tastes.
3.8.
Processing the Image
If not done already, images can be improved by subtracting off a dark frame of equal
exposure. You will typically do this as part of the Grab command although it can also be
done manually using the Dark Subtract command. By subtracting the dark frame, pixels
which have higher dark current than the average, i.e., "hot" pixels, are greatly suppressed
and the displayed image appears much smoother. Visibility of faint detail is greatly
improved.
The CCDOPS program also supports the use of flat field frames to correct for
vignetting and pixel to pixel variations, as well as a host of other image processing commands
in the Utility menu. You can smooth or sharpen the image, flip it to match the orientation of
published images for comparison, or remove hot or cold pixels.
3.9.
Advanced Capabilities
The following sections describe some of the advanced features of SBIG cameras. While you
may not use these features the first night, they are available and a brief description of them is
in order for your future reference.
3.9.1. Crosshairs Mode (Photometry and Astrometry)
Using the crosshair mode enables examination of images on a pixel by pixel basis for such
measurements as Stellar and Diffuse Magnitude, and measurement of stellar positions. The
16 bit accuracy of SBIG systems produces beautiful low-noise images and allows very
accurate brightness measurements to be made. With appropriate filters stellar temperature
can be measured.
In the crosshair mode, you move a small cross shaped crosshair around in the image
using the keyboard or the mouse. As you position the crosshair, the software displays the
pixel value beneath the crosshair and the X and Y coordinates of the crosshair. Also shown is
the average pixel value for a box of pixels centered on the crosshair. You can change the size
of the averaging box from 3x3 to 31x31 pixels to collect all the energy from a star.
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Section 3 - At the Telescope with a CCD Camera
3.9.2. Sub-Frame Readout in Focus
The Focus command offers several frame modes for flexibility and increased frame
throughput. As previously discussed, the Full frame mode shows the entire field of view of
the CCD with the highest resolution, digitizing and displaying all pixels.
The "Dim" mode offers the same field of view but offers higher frame rates by
reducing the image's resolution prior to downloading. The resolution is reduced by
combining a neighboring block of pixels into a "super pixel". This reduces the download and
display times proportionately, as well as improving sensitivity. It is great for finding and
centering objects.
The Planet mode is suggested if high spatial resolution is desired for small objects like
planets. The Planet mode allows you to select a small sub-area of the entire CCD for image
acquisition. The highest resolution is maintained but you don't have to waste time digitizing
and processing pixels that you don't need. Again, the image throughput increase is
proportional to the reduction in frame size. It can be entered from Auto mode.
Another aspect of the Focus command and its various modes is the Camera
Resolution2 setting in the Camera Setup command. Briefly, the Resolution setting allows
trading off image resolution (pixel size) and image capture time while field of view is
preserved. High resolution with smaller pixels takes longer to digitize and download than
Low resolution with larger pixels. The cameras support High, Medium, Low and Auto
resolution modes. The Auto mode is optimized for the Focus command. It automatically
switches between Low resolution for Full frame mode to provide fast image acquisition, and
High resolution for Planet mode to achieve critical focus. While Auto resolution is selected all
images acquired using the GRAB command will be high resolution.
3.9.3. Track and Accumulate
An automatic Track and Accumulate mode (SBIG patented) is available in CCDOPS which
simplifies image acquisition for the typical amateur with an accurate modern drive. These
drives, employing PEC or PPEC technology and accurate gears, only need adjustment every
30 to 120 seconds. With Track and Accumulate the software takes multiple exposures and
automatically co-registers and co-adds them. The individual exposures are short enough
such that drive errors are not objectionable and the accumulated image has enough
integrated exposure to yield a good signal to noise ratio.
Operationally the camera will take an exposure, determine the position of a
preselected star, co-register and co-add the image to the previous image, and then start the
cycle over again. The software even allows making telescope corrections between images to
keep the object positioned in the field of view. The resulting exposure is almost as good as a
single long exposure, depending on the exposure used and sky conditions. The great
sensitivity of the CCD virtually guarantees that there will be a usable guide star within the
2
The Resolution setting in the Camera Setup command combines pixels before they are digitized. This is
referred to as on-chip binning and offers increases in frame digitization rates.
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Section 3 - At the Telescope with a CCD Camera
imaging CCD's field of view. This feature provides dramatic performance for the amateur,
enabling long exposures with minimal setup!
3.9.4. Autoguiding and Self Guiding
The CCDOPS software allows the ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST2000XM cameras to be used as autoguiders and self-guiders through the commands in the
Track menu. While these systems are not stand-alone like the ST-4, but require a host
computer, they can accurately guide long duration astrophotographs and CCD images with
equal or superior accuracy. Their sensitivity is much greater than an ST-4, and the computer
display makes them easier to use.
When functioning as an autoguider, the CCD camera repeatedly takes images of a
guide star, measures the star's position to a fraction of a pixel accuracy, and corrects the
telescope's position through the hand controller. While autoguiding alleviates the user of the
tedious task of staring through an eyepiece for hours at a time, it is by no means a cure to
telescope drive performance. All the things that were important for good manually guided
exposures still exist, including a good polar alignment, rigid tubes that are free of flexure and
a fairly good stable mount and drive corrector. Remember that the function of an auto guider
is to correct for the small drive errors and long term drift, not to slew the telescope.
One of the reasons that SBIG autoguiders are often better than human guiders is that,
rather than just stabbing the hand controller to bump the guide star back to the reticule, it
gives a precise correction that is the duration necessary to move the guide star right back to
its intended position. It knows how much correction is necessary for a given guiding error
through the Calibrate Track command. The Calibrate Track command, which is used prior
to autoguiding, exercises the telescope's drive corrector in each of the four directions,
measuring the displacement of a calibration star after each move. Knowing the displacement
and the duration of each calibration move calibrates the drive's correction speed. Once that is
known, the CCD tracker gives the drive corrector precise inputs to correct for any guiding
error.
When self guiding is selected by invoking the Self Guiding command under the Track
Menu, the computer prompts the user for the exposure time for the tracking and imaging
CCDs. Once these are entered, the computer takes and displays an image with the tracking
CCD, and the user selects a guide star using the mouse. Guide stars that are bright, but not
saturating, and isolated from other stars are preferred. Once the star is selected, the
computer starts guiding the telescope. When the telescope corrections settle down (usually
once the backlash is all taken up in the declination drive) the user starts the exposure by
striking the space bar. The computer then integrates for the prescribed time while guiding
the telescope, and downloads the image for display.
A calibration star should be chosen that is relatively bright and isolated. The
calibration software can get confused if another star of comparable brightness moves onto the
tracking CCD during a move. The unit will self guide on much fainter stars. Tests at SBIG
indicate that the probability of finding a usable guide star on the tracking CCD is about 95%
at F/6.3, in regions of the sky away from the Milky Way. If a guide star is not found the
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Section 3 - At the Telescope with a CCD Camera
telescope position should be adjusted, or the camera head rotated by a multiple of 90 degrees
to find a guide star. We recommend that the user first try rotating the camera 180 degrees.
Rotating the camera will require recalibration of the tracking function. [Note: CCDSoftV5
software allows SBIG cameras to calibrate and track in any orientation, similar to the STV
video autoguider].
3.9.5. Auto Grab
The Auto Grab command allows you to take a series of images at a periodic interval and log
the images to disk. This can be invaluable for monitoring purposes such as asteroid searches
or stellar magnitude measurements. You can even take sub-frame images to save disk space if
you don't need the full field of view.
3.9.6. Color Imaging
The field of CCD color imaging is relatively new but expanding rapidly. Since all SBIG
cameras are equipped with monochromatic CCDs, discriminating only light intensity, not
color, some provision must be made in order to acquire color images. SBIG offers a color filter
wheel, the CFW-8, which provides this capability for the ST-7XE, ST-8XE, ST-9XE, ST-10XE,
ST-10XME and ST-2000XM.
The color filter wheel allows remotely placing interference filters in front of the CCD in order
to take multiple images in different color bands. These narrow band images are then
combined to form a color image. With the SBIG system, a Red, Green and Blue filter are used
to acquire three images of the object. The resulting images are combined to form a tri-color
image using CCDOPS, CCDSoftV5 or third party software.
Color imaging places some interesting requirements on the user that bear mentioning.
First, many color filters have strong leaks in the infrared (IR) region of the spectrum, a region
where CCDs have relatively good response. If the IR light is not filtered out then combining
the three images into a color image can give erroneous results. If your Blue filter has a strong
IR leak (quite common) then your color images will look Blue. For this reason, SBIG
incorporates an IR blocking filter stack with the three color band filters.
Second, since you have narrowed the CCD's wavelength response with the
interference filters, longer exposures are required to achieve a similar signal to noise
compared to what one would get in a monochrome image with wide spectral response. This
is added to the fact that tri-color images require a higher signal to noise overall to produce
pleasing images. With black and white images your eye is capable of pulling large area detail
out of random noise quite well, whereas with color images your eye seems to get distracted by
the color variations in the noisy areas of the image. The moral of the story is that while you
can achieve stunning results with CCD color images, it is quite a bit more work.
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Section 4 – Camera Hardware
4.
Camera Hardware
This section describes the modular components that make up the CCD Camera System and
how they fit into the observatory, with all their connections to power and other equipment.
4.1.
System Components
The ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM CCD cameras consist of
four major components: the CCD Sensors and Preamplifier, the Readout/Clocking
Electronics, the Microcontroller, and the power supply. All the electronics are packaged in
the optical head in these cameras with an external desktop power supply.
The CCDs, Preamplifier, and Readout Electronics are mounted in the front of the
optical head. The optical head interfaces to the telescope through a 1.25 inch (or larger)
draw tube, sliding into the telescope's focus mechanism. The placement of the preamplifier
and readout electronics close to the CCD is necessary to achieve good noise performance.
The Microcontroller is housed in the rear of the Optical Head along with the interface logic to
the PC and Telescope.
4.2.
Connecting the Power
The desktop power supply is designed to run off voltages found in most countries (90 to 240
VAC). In the field however, battery operation may be the most logical choice. In that case
you need to use the optional 12V power supply or a 12VDC to 110 VAC power inverter.
4.3.
Connecting to the Computer
The ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM CCD Cameras are
supplied with a 15 foot cable to connect the system to the host computer. The connection is
between the camera and the Host Computer's USB port. If it is necessary or desirable to
extend the distance between the camera and the computer, third party USB extenders such
as the “Ranger” made by Icron (http://www.icron.com) may be used for remote operation
up to 500 meters.
4.4.
Connecting the Relay Port to the Telescope
The ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM camera systems can be
used as autoguiders where the telescope's position is periodically corrected for minor
variations in the RA and DEC drives. The host software functions as an autoguider in three
modes: the Track mode, the SBIG patented Track and Accumulate mode, and the SBIG
patented Self Guided mode (except for the ST-1001E).
In the Track mode and Self Guided mode the host software corrects the telescope as
often as once every second to compensate for drift in the mount and drive system. The host
software and the CCD camera operate in tandem to repeatedly take exposures of the
designated guide star, calculate its position to a tenth of a pixel accuracy, and then
Page 39
Section 4 – Camera Hardware
automatically activate the telescope's controller to move the star right back to its intended
position. It does this tirelessly to guide long duration astrophotographs.
In the Track and Accumulate mode the software takes a series of images and
automatically co-registers and co-adds the images to remove the effects of telescope drift.
Typically you would take ten 1 minute "snapshots" to produce an image that is comparable to
a single 10 minute exposure except that no guiding is required. The reason no guiding is
required is that with most modern telescope mounts the drift over the relatively short 1
minute interval is small enough to preserve round star images, a feat that even the best
telescope mounts will not maintain over the longer ten minute interval. The Track and
Accumulate software does allow correction of the telescope position in the interval between
snapshots to keep the guide star grossly positioned within the field of view, but it is the
precise co-registration of images that accounts for the streakless images.
The host software and the CCD camera control the telescope through the 9-pin
Telescope port on the camera. This port provides active low open collector signals to the
outside world. By interfacing the camera to the telescope's controller the CPU is able to move
the telescope as you would: by effectively closing one of the four switches that slews the
telescope.
Note: You only need to interface the camera's Telescope port to your telescope if you are
planning on using the camera system as an autoguider or selfguider, or feel you need
to have the Track and Accumulate command make telescope corrections between
images because your drive has a large amount of long term drift.
Some recent model telescopes (like the Celestron Ultima and the Meade LX200) have
connectors on the drive controller that interface directly to the camera's TTL level Telescope
port. All that's required is a simple cable to attach the 9 pin Telescope port to the telescope's
telephone jack type CCD connector. SBIG includes its TIC-78 (Tracking Interface Cable
Adapter) for this express purpose although it is easy to modify a standard 6-pin telephone
cable for interface to the Telescope port (see Appendix A for specific pin outs, etc.). The TIC78 plugs into the 9-pin port on the ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST2000XM, and a standard phone cable, which we supply, connects the adapter to the
telescope drive. Note: phone cables come in a few variations. We use the six-pin cable, and
the pin order is reversed left to right relative to the connector from one end to the other. This
is identical to what is typically sold at Radio Shack stores as an extension cable.
4.4.1 Using Mechanical Relays
Older telescopes generally require modifying the hand controller to accept input from the
camera's Telescope port. The difficulty of this task varies with the drive corrector model and
may require adding external relays if your drive corrector will not accept TTL level signals.
We maintain a database of instructions for the more popular telescopes that we will gladly
share with you. For a minimal charge will also modify your hand controllers if you feel you
do not have the skills necessary to accomplish such a task. We sell a mechanical relay box
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Section 4 – Camera Hardware
that interfaces to the ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM, and will
interface to the older drives. Contact SBIG for more information.
In general, the camera has four signals that are used in tracking applications. There is
one output line for each of the four correction directions on the hand controller (North,
South, East and West). Our previous cameras had internal relays for the telescope interface,
but with the proliferation of TTL input telescopes the relays were removed (We do offer an
external relay adapter accessory). The following paragraphs describe the general-purpose
interface to the telescope which involves using external relays.
In our older camera models and in the optional relay adapter accessory, each of the
relays has a Common, a Normally Open, and a Normally Closed contact. For example, when
the relay is inactivated there is a connection between the Common and the Normally Closed
contact. When the relay is activated (trying to correct the telescope) the contact is between
the Common and the Normally Open contacts.
If your hand controller is from a relatively recent model telescope it probably has four
buttons that have a "push to make" configuration. By "push to make" we mean that the
switches have two contacts that are shorted together when the button is pressed. If that's the
case then it is a simple matter of soldering the Common and Normally Open leads of the
appropriate relay to the corresponding switch, without having to cut any traces, as shown in
Figure 4.1 below.
A: Unmodified Push to Make Switch
B: Modified Push to Make Switch
c
common
relay
switch
nc
switch
no
normally open
Figure 4.1 - Push to Make Switch Modification
Another less common type of switch configuration (although it seems to have been used more
often in older hand controllers) involve hand controller buttons that use both a push to make
contact in conjunction with a push to break contact. The modification required for these
switches involves cutting traces or wires in the hand controller. Essentially the relay's
Normally Open is wired in parallel with the switch (activating the relay or pushing the hand
controller button closes the Normally Open or Push to Make contact) while at the same time
the Normally Closed contact is wired in series with the switch (activating the relay or
pushing the hand controller button opens the Normally Closed or the Push to Break contact).
This type of switch modification is shown in Figure 4.2 below.
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Section 4 – Camera Hardware
A: Unmodified Push to Make/Break Switch
B: Modified Push to Make/Break Switch
common
c
common
c
c
relay
switch
nc
nc
no
nc
no
no
normally open
normally open
normally closed
normally closed
Figure 4.2- Push to Make/Break Modification
The last type of hand controller that is moderately common is the resistor joystick. In this
joystick each axis of the joystick is connected to a potentiometer or variable resistor. Moving
the joystick handle left or right rotates a potentiometer, varying the resistance between a
central "wiper" contact and the two ends of a fixed resistor. The relays can be interfaced to
the joystick as shown in Figure 4.3 below. Essentially the relays are used to connect the wire
that used to attach to the wiper to either end of the potentiometer when the opposing relays
are activated.
A
+ relay
- relay
c
A
c
wiper
B
nc
C
potentiometer
B
A: Unmodified Joystick
nc
no
no
C
B: Modified Joystick
Figure 4.3 - Joystick Modification
A slight variation on the joystick modification is to build a complete joystick eliminator as
shown in Figure 4.4 below. The only difference between this and the previous modification is
that two fixed resistors per axis are used to simulate the potentiometer at its mid position.
You do not need to make modifications to the joystick; you essentially build an unadjustable
version. This may be easier than modifying your hand controller if you can trace out the
wiring of your joystick to its connector.
Page 42
Section 4 – Camera Hardware
A
- relay
+ relay
c
c
A
no
wiper
B
nc
nc
no
C
B
R
potentiometer
C
R/2
A: Unmodified Joystick
R/2
B: Joystick Eliminator
Figure 4.4- Joystick Eliminator
4.5.
Modular Family of CCD Cameras
With the introduction of the ST-6 CCD Camera in 1992 SBIG started a line of high quality,
low noise, modular CCD cameras. The ST-7E, ST-8E and ST-9E were a second family of
modular CCD cameras. The ST-10E allowed for upgrades to a faster USB interface and
larger tracking CCD.
The benefits of a modular line of CCD Cameras are many fold. Users can buy as
much CCD Camera as they need or can afford, with the assurance that they can upgrade to
higher performance systems in the future. With a modular approach, camera control
software like CCDOPS can easily support all models. This last point assures a wide variety of
third party software. Software developers can produce one package for the many users
across the model line instead of different packages for each of the cameras.
While the SBIG cameras have many similarities, there are also important differences
between the products. Table 4.2 below highlights the differences from a system's standpoint:
Camera
ST-5C
ST-237A
STV
ST-6
ST-7/8/9/10/1001/2000
A/D
Temperatur Electromechanical
Resolution e Regulation Shutter/Shutter
Wheel/Vane
16 bits
Closed Loop Shutter Wheel
16 bits
Closed Loop Shutter Wheel
10+2 bits
Closed Loop Shutter Wheel
16 bits
Closed Loop Vane
16 bits
Closed Loop Shutter
Table 4.2 - System Features
Electronic
Shutter
0.01 second
0.01 second
0.001 second
0.01 second
None
How these features affect the average user are discussed in the paragraphs below:
A/D Resolution - This is a rough indication of the camera's dynamic range. Higher precision
A/D Converters are able to more finely resolve differences in light levels, or for
larger CCDs with greater full well capacities, they are able to handle larger
total charges with the same resolution.
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Section 4 – Camera Hardware
Temperature Regulation - In an open loop system like the original ST-4 the CCD cooling is
either turned on or turned off. While this provides for adequate cooling of the
CCD, the CCD's temperature is not regulated which makes it important to take
dark frames in close proximity to the associated light frame. Closed loop
systems regulate the CCD's temperature to an accuracy of ±0.1° C making dark
frames useful over longer periods.
Electromechanical Vane - Having the vane in the ST-6 means the host software can
effectively "cover the telescope" and take dark frames remotely, without the
user having to get up and physically cover the telescope.
Electromechanical Shutter - Having the shutter in the ST-7E/8E/9E/10E/1001E gives streakfree readout and allows taking dark frames without having to cover the
telescope. While the minimum exposure is 0.11 seconds, repeatability and area
uniformity are excellent with SBIG's unique unidirectional shutter.
Shutter Wheel - The Shutter Wheel, used in conjunction with the camera's Electronic shutter,
allows you to cover the CCD for taking dark frames and in the case of the
ST-5C/237/237A allows replacement with a mini internal color filter wheel.
Electronic Shutter - Having an electronic shutter involves having a CCD with a frame
transfer region. These CCDs actually have an array that has twice the number
of rows advertised, where the bottom half is open to the light (referred to as the
Image Area), and the top half is covered with a metalization layer (referred to
as the Storage Area). In frame transfer CCDs at the end of the exposure, the
pixel data from the Image Area is transferred into the Storage Area very
rapidly where it can be read out with a minimum of streaking.
In addition to the system level differences between the various cameras, Table 4.3 below
quantifies the differences between different CCDs used in the cameras:
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Section 4 – Camera Hardware
Camera
CCD Used
TC-211
Number of
Pixels
192 x 164
Pixel
Dimensions
13.75 x 16 µ
Array
Dimension
2.6 x 2.6 mm
Read
Noise
12e - rms
Full Well
Capacity
150Ke -
TC211 Tracking CCD
TC237 Tracking CCD
TC-237
657 x 495
7.4 x 7.4 µ
4.9 x 3.7 mm
ST-5C
TC-255
320 x 240
10 x 10 µ
3.2 x 2.4 mm
12e- rms
20e - rms
20Ke50Ke -
ST-237A
TC-237
657 x 495
7.4 x 7.4 µ
4.9x 3.7 mm
STV
TC-237
320 x 200
14.8 x 14.8 µ
4.7 x 3.0 mm
15e - rms
17e - rms
20Ke 20Ke-
ST-7XE
KAF0401E
765 x 510
9x9µ
6.9 x 4.6 mm
15e- rms
ST-8XE
KAF1602E
1530 x 1020
9x9µ
13.8 x 9.2 mm
15e- rms
50/100Ke -3
50/100Ke -4
ST-9XE
KAF0261E
512 x 512
20 x 20 µ
10.2 x 10.2 mm
13e- rms
180Ke-
ST-10XE, XME
KAF3200E
2184 x 1472
6.8 x 6.8 µ
14.9 x 10.0 mm
11e- rms
77Ke-
ST-1001E
KAF1001E
1024 x 1024
24 x 24 µ
24.6 x 24.6 mm
16e- rms
180Ke-
ST-2000XM
KAI2000M
1600 x 1200
7.4 x 7.4 µ
11.8 x 9.0 mm
15e- rms
45Ke-
Table 4.3- CCD Differences
How these various specifications affect the average user is described in the following
paragraphs:
Number of Pixels - The number of pixels in the CCD affects the resolution of the final images.
The highest resolution device is best but it does not come without cost. Larger
CCDs cost more money and drive the system costs up. They are harder to cool,
require more memory to store images, take longer to readout, etc. With typical
PC and Macintosh computer graphics resolutions, the CCDs used in the SBIG
cameras offer a good trade off between cost and resolution, matching the
computer's capabilities well.
Pixel Dimensions - The size of the individual pixels themselves really plays into the user's
selection of the system focal length. Smaller pixels and smaller CCDs require
shorter focal length telescopes to give the same field of view that larger CCDs
have with longer focal length telescopes. Smaller pixels can give images with
higher spatial resolution up to a point. When the pixel dimensions (in
arcseconds of field of view) get smaller than roughly half the seeing, decreasing
the pixel size is essentially throwing away resolution. Another aspect of small
pixels is that they have smaller full well capacities.
For your reference, if you want to determine the field of view for a pixel
or entire CCD sensor you can use the following formula:
Field of view (arcseconds) =
3
8.12x size (µm)
focal length (inches)
The Kodak CCDs (KAF0400 and KAF1600) are available with or without Antiblooming Protection.
Units with the Antiblooming Protection have one-half the full well capacity of the units without it.
Page 45
Section 4 – Camera Hardware
Field of view (arcseconds) =
20.6x size ( um )
focal length (cm )
where size is the pixel dimension or CCD dimension in millimeters and the
focal length is the focal length of the telescope or lens. Also remember that
1° = 3600 arcseconds.
Read Noise - The readout noise of a CCD camera affects the graininess of short exposure
images. For example, a CCD camera with a readout noise of 30 electrons will
give images of objects producing 100 photoelectrons (very dim!) with a Signal
to Noise (S/N) of approximately 3 whereas a perfect camera with no readout
noise would give a Signal to Noise of 10. Again, this is only important for short
exposures or extremely dim objects. As the exposure is increased you rapidly
get into a region where the signal to noise of the final image is due solely to the
exposure interval. In the previous example increasing the exposure to 1000
photoelectrons results in a S/N of roughly 20 on the camera with 30 electrons
readout noise and a S/N of 30 on the noiseless camera. It is also important to
note that with the SBIG CCD cameras the noise due to the sky background will
exceed the readout noise in 15 to 60 seconds on the typical amateur telescopes.
Even the $30,000 priced CCD cameras with 10 electrons of readout noise will
not produce a better image after a minute of exposure!
Full Well Capacity - The full well capacity of the CCD is the number of electrons each pixel
can hold before it starts to loose charge or bleed into adjacent pixels. Larger
pixels hold more electrons. This gives an indication of the dynamic range the
camera is capable of when compared to the readout noise, but for most
astronomers this figure of merit is not all that important. You will rarely takes
images that fill the pixels to the maximum level except for stars in the field of
view. Low level nebulosity will almost always be well below saturation. While
integrating longer would cause more build up of charge, the signal to noise of
images like these is proportional to the square-root of the total number of
electrons. To get twice the signal to noise you would have to increase the
exposure 4 times. An ST-5C with its relatively low full well capacity of
50,000e- could produce an image with a S/N in excess of 200!
Antiblooming - Most SBIG CCD cameras have antiblooming protection. The TI CCDs used in
the ST-5C, ST-237, ST-237A, TC-237 autoguider and TC-211 autoguider have
antiblooming built into the CCDs. The Kodak CCDs used in the ST-7XE and
ST-8XE have Antiblooming versions of the CCDs available and the CCD used
in the ST-2000XM only comes with antiblooming. Blooming is a phenomenon
that occurs when pixels fill up. As charge continues to be generated in a full
pixel, it has to go somewhere. In CCDs without antiblooming protection the
charge spills into neighboring pixels, causing bright streaks in the image. With
the CCDs used in the SBIG cameras the excess charge can be drained off
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Section 4 – Camera Hardware
saturated pixels by applying clocking to the CCD during integration. This
protection allows overexposures of 100-fold without blooming. The trade off is
sensitivity. Antiblooming CCDs are less sensitive than non-antiblooming
CCDs. In the case of the ST-7XE and ST-8XE, for example, the nonantiblooming versions are very roughly twice as sensitive.
The CCDs used in the ST-9XE, ST-10XE and ST-10XME and ST-1001E
detectors do not come in an antiblooming version.
From the telescope's point of view, the different models offer differing fields of view for a
given focal length, or turned around, to achieve the same field of view the different models
require differing focal lengths. Tables 4.4 and 4.5 below compare the fields of view for the
cameras at several focal lengths, and vice versa.
C8, 8" f/10
Camera
TC211 Tracking CCD
TC237 Tracking CCD
ST-5C
ST-237A
STV
ST-7XE
ST-8XE
ST-9XE
ST-10XE
ST-1001E
ST-2000XM
Field of View Pixel Size
(arcmins)
(arcsecs)
LX200, 10" f/34
Field of View Pixel Size
(arcmins)
(arcsecs)
Field of View
(arcmins)
Pixel Size
(arcsecs)
4.2x4.2
8.2x6.2
5.4x4.1
8.2x6.2
8.0x5.0
11.9x7.9
23.8x15.8
17.6x17.6
25.1x16.9
41.6x41.6
20.0x15.0
11.7x11.7
21.9x16.5
14.4x10.8
21.9x16.5
21.6x13.5
31.2x20.8
62.4x41.6
46.2x46.2
67.0x45.2
111x111
53.4x40.1
2.3x2.3
4.3x3.2
2.8x2.1
4.3x3.2
4.0x2.5
6.1x4.1
12.2x8.2
9.1x9.1
13.0x8.8
21.6x21.6
10.4x7.8
0.7x0.8
0.39x0.39
0.5x0.5
0.39x0.39
0.75x0.75
0.5x0.5
0.5x0.5
1.1x1.1
0.36x0.36
1.27x1.27
0.39x0.39
1.3x1.5
0.75x0.75
1.0x1.0
0.75x0.75
1.5x1.5
0.9x0.9
0.9x0.9
2.0x2.0
0.7x0.7
2.4x2.4
0.75x0.74
3.7x4.3
2.0x2.0
2.7x2.7
2.0x2.0
4.0x4.0
2.4x2.4
2.4x2.4
5.3x5.3
1.8x1.8
6.5x6.5
2.0x2.0
14" f/11
Table 4.4 - Field of View
Object
Size
Focal Length to fill 211
Tracking CCD
Focal Length
to fill ST-7XE
Moon
0.5°
275mm = 11 inches
760mm = 30 inches
Jupiter
40 arcseconds
13000mm = 510 inches
34000mm = 1350 inches
M51-Whirlpool Galaxy
8x5 arcminutes
1040mm = 41 inches
3700mm = 145 inches
M27-Dumbell Nebula
8.5 x 5.5 arcminutes
1040mm = 41 inches
3700mm = 145 inches
M57-Ring Nebula
1.3 x 1 arcminutes
6400mm = 250 inches
23000mm = 900 inches
Table 4.5 - Focal Length Required
From these numbers you can deduce that the popular C8, an 8" f/10 telescope will nicely
frame many popular objects with the ST-7XE whereas a much shorter system (f/3, perhaps
4
f/6.3 telescope with an f/6.3 focal reducer and star diagonal.
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Section 4 – Camera Hardware
achieved with a focal reducer) will frame the same objects for the tracking CCD. Another
point to bear in mind is that, except for planetary images, you'll rarely take images where the
pixel size in seconds of arc is down near the seeing limit. Most objects are relatively large,
where the field of view is more important than whether the individual pixels are less than
half the seeing.
4.6 Connecting accessories to the Camera
There are two 9 pin accessory ports on the ST-X series of cameras. The first is labeled “AO7 /
CFW8/ SCOPE.” This is the port that supports our AO-7 Adaptive optics device, CFW8A
color filter wheel and relay adapter box. It is also the relay output for direct connection to
many popular telescopes’ “CCD” autoguiding port. (Note: This is not the same thing as the
telescope’s RS232 port that is commonly used to point and slew the telescope). The second
accessory port on the camera is labeled I2C AUX (“I squared C”) and is for future accessories.
Be sure to keep the static safe cap over this port to insure that you do not accidentally plug in
an accessory that is intended for the AO7/CFW8/SCOPE port. Plugging in the wrong
accessory to the I2C port could cause damage.
More than one accessory can be connected to the accessory ports by using multiple plug
adapters provided with the accessory.
4.7 Battery Operation
The ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM can be operated
off of a 12 volt car or marine battery using a the optional 12V power supply or using a power
inverter. We have used the Radio Shack model 22-132A, 12 volt DC to 115 volt AC Portable
Power Inverter (140 watt) with good success. The camera draws 2.2 amps from the battery
with this inverter, which should enable an evening's operation from a single battery. If your
camera has the older two-stage cooling booster, it will, when connected, draw another 2
amps. We recommend a separate battery for the camera; using your vehicle's battery with
the engine running may add undesirable readout noise, and using your vehicle's battery
without the engine running may result in a long walk home in the dark!
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Section 5 – Advanced Imaging Techniques
5.
Advanced Imaging Techniques
With practice, you will certainly develop methods of your own to get the most from your
CCD camera. In this section we offer some suggestions to save you time getting started in
each of the different areas outlined below, but these suggestions are by no means exhaustive.
5.1.
Lunar and Planetary Imaging
When imaging the moon using most focal lengths available in astronomical telescopes, you
will note that the moon's image typically fills the CCD. The image is also very bright. The
best way to image the moon is to use neutral density filters to attenuate the light.
You may also try an aperture mask to reduce the incoming light. If you feel that an
aperture mask reduces resolution to an unacceptable degree, consider using a full aperture
solar filter. This will result in an optimum exposure of only a few seconds. Another way to
reduce the incoming light is to increase the effective focal length of your telescope by using a
barlow lens or eyepiece projection. This is very desirable for planetary imaging since it also
increases the image size.
5.2.
Deep Sky Imaging
Ordinarily, with telescopes of 8" aperture or larger, a ten second exposure in focus mode,
with a dark frame subtracted, will show most common deep sky objects except for the very
faintest. This is a good starting point for finding and centering deep sky objects. If you find
ten seconds to be insufficient, a one minute exposure will clearly show nearly any object you
wish to image, particularly if 2x2 or 3x3 binning is selected. Using the Grab command,
exposures of five minutes will generally give you a clear image with good detail. Of course,
longer exposures are possible and desirable, depending on your telescope's tracking ability or
your desire to guide. Once you have determined the longest exposure possible with your
particular drive error, try Track and Accumulate exposures of a duration less than your
measurable error. We have found that exposures of thirty seconds to two minutes are best
depending on the focal length of telescope one is using. With the self guiding feature of the
ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM, one can take long
integrations while the internal tracking CCD guides the telescope.
We highly recommend that you initially pursue deep sky imaging with a fast
telescope, or focal reducer to produce a final F number of F/6.3 or faster at the CCD. The
sensitivity advantage is considerable!
5.3.
Terrestrial Imaging
An optional accessory for the SBIG cameras is the camera lens adapter. These accessories are
made to accommodate most popular camera models. You may attach a camera lens in place
of your telescope and use the CCD camera for very wide angle images of the night sky or for
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Section 5 – Advanced Imaging Techniques
terrestrial views in daylight. Begin with a tenth second exposure at f/16 for scenes at normal
room light and adjust as necessary for your conditions.
5.4.
Taking a Good Flat Field
If you find that flat field corrections are necessary due to vignetting effects, CCD sensitivity
variations, or for more accurate measurements of star magnitudes, try either taking an image
of the twilight sky near the horizon or take an image of a blank wall or neutral grey card.
The Kodak CCDs may have a low contrast grid pattern visible in the sky background. A flat
field will eliminate this.
Finding areas of the sky devoid of stars is very difficult after twilight. Therefore, you
should take flat field images of the night sky after sunset, but long before you can see any
stars. If this is not possible, take an image of a featureless wall or card held in front of the
telescope. However, if using this second method, be sure that the wall or card is evenly
illuminated. Appendix D describes how to do this. You will know if the flat field is good if
the sky background in your images has little variation across the frame after flat fielding,
displayed using high contrast (a range of 256 counts is good for showing this).
If you plan on flat fielding Track and Accumulate images you should also refer to
section 6.8. Since the same flat field is added to itself a number of times, be sure that you do
not saturate the flat field image by starting with pixel values too high. Typically try to keep
the pixel values between 10% to 20% of saturation for this purpose. For single flat field
images, try to keep the values to approximately 50% of saturation.
5.5.
Building a Library of Dark Frames
The ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST-2000XM have regulated
temperature control, and therefore it is possible to duplicate temperature and exposure
conditions on successive nights. You can set the camera TE cooler temperature to a value
comfortably within reach on your average night, and then take and save on disk a library of
dark frames for later use. This is a good project for a rainy night. We recommend you build
a file of 5, 10, 20 ,40, and 60 minute dark frames at zero degrees Centigrade for a start.
Otherwise you will find yourself wasting a clear night taking hour long dark frames!
Note: Dark frames taken the same night always seem to work better. The adaptive
dark subtract will help if the ambient temperature changes slightly.
5.6.
Changing the Camera Resolution
The Camera Setup command allows you to select the resolution mode you wish to use for
taking and displaying images. The ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST2000XM cameras have High, Medium, Low and Auto modes. The High Resolution mode is
the best for displaying the greatest detail since it utilizes the maximum number of pixels for
your particular camera. The Medium Resolution Mode operates by combining 2x2 pixels
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Section 5 – Advanced Imaging Techniques
giving the same field of view as High Resolution Mode, but with 1/4 the resolution. This
results in significantly faster digitization and download times. Also, in Medium Resolution
Mode, with larger pixels and comparable readout noise there is a better signal to noise ratio
for very dim diffuse objects. This improved signal to noise ratio combined with faster
digitization and download times makes Medium Resolution Mode ideal for finding and
centering dim objects, and for imaging most objects. Additionally, a Low resolution mode is
provided which bins the CCD 3x3 before readout. Low resolution mode is sensational for
displaying faint nebulosity with short exposure times. In Auto Resolution Mode, the camera
and software will always use High Resolution for all imaging and display functions except
when you are in Full Frame Focus Mode. It will then automatically switch to Low Resolution
Mode. If you further select Planet Mode for focusing, the camera will switch back to High
Resolution on the selected box area. The small pixel size, is best for critical focusing. Planet
mode will result in fast digitization and download times since only a small portion of the
frame is read out.
In general, you should pick a binning mode that yields stars with two to three pixels
full width at half maximum. This is easily measured by using the crosshairs to determine the
peak brightness of a relatively bright star, and determining the number of pixels between the
50% values on either side of the peak. More than 3 pixels per stellar halfwidth merely wastes
sensitivity without improved resolution.
5.7.
Flat Fielding Track and Accumulate Images
This section gives the step by step procedure for flat field correcting images taken using the
Track and Accumulate command.
Flat field correcting images allow the user to remove the effects of CCD response nonuniformity (typically less than a few percent) and optical vignetting which for some optical
systems can be as much as a 50% effect from center to edge. The CCDOPS software allows
flat field correcting images using the Flat Field command, but some preparation must be
made to use that command with Track and Accumulate images. Essentially you must
prepare a special flat field correction image for Track and Accumulate images. This special
preparation is necessary to have the same set of alignment and co-addition operations apply
to the flat field file that have occurred in acquiring the Track and Accumulate image. In
general, the following procedure should be followed when flat field correction of Track and
Accumulate images is desired:
1. Take a normal flat field image using the Grab command. You can use the dusk
sky or a neutral gray or white card held in front of the telescope. Try to adjust
the illumination and/or exposure so that the build up of light in the image
yields values that when co-added several times will not overflow 65,000
counts. The number of times the image will need to be co-added without
overflowing is set by how many snapshots you intend to use in Track and
Accumulate. A good goal is to try and attain a maximum level in the flat field
image of 1,000 to 2,000 counts which will allow co-addition 32 times without
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Section 5 – Advanced Imaging Techniques
overflow.
Note: You will have to take a new flat field image anytime you change the optical
configuration of your telescope such as removing and replacing the optical head in the
eyepiece holder.
2. Save the flat field image on your disk using the Save command. In the
following discussions this flat field file will be referred to as FLAT.
3. Take your Track and Accumulate image using the Track and Accumulate
command and save it on the disk using the Save command. In the following
discussions this Track and Accumulate image file will be referred to as IMAGE.
4. Immediately after saving the IMAGE use the Save Track List command on the
PC or activate the Track List window on the Mac and use the Save command
to save the Track and Accumulate track list. The track list is a file that
describes what alignment operations were done to the individual components
of IMAGE to achieve the end result. In the following discussions this track list
file will be referred to as TRACK.
5. Repeat steps 3 and 4 as many times as desired for all the objects you wish to
image, each time choosing a set of corresponding new names for the IMAGE
and TRACK files.
6. You will now create a combined flat field image for each Track and
Accumulate image you captured. Invoke the Add by Track List command.
The software will bring up a file directory dialog showing all the track list files.
Select the TRACK file corresponding to the image you wish to correct. The
software will load the TRACK file and present you with another file directory
dialog showing all the images. Select the appropriate FLAT image. The
software will align and co-add the FLAT image using the same operations it
performed on the Track and Accumulate image. Finally save the combined flat
field image using the Save command. In the following discussions this
combined flat field image will be referred to as COMBINED-FLAT. Repeat this
step for each of the TRACK files using a corresponding name for the
COMBINED-FLAT image.
7. You will now flat field correct the Track and Accumulate image with the
combined flat field image. Use the Open command to load the IMAGE file,
then use the Flat Field command. The software will present you with a file
directory dialog where you should select the corresponding COMBINED-FLAT
image. After the software has finished correcting the image you can view the
results and save the flat field corrected image with the Save command. This
image will be referred to as the CORRECTED-IMAGE file. Repeat this step for
each of the IMAGE files using the corresponding COMBINED-FLAT image.
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Section 5 – Advanced Imaging Techniques
At SBIG we have adopted the following naming convention for our various image and
related files. If it helps you organize your files please feel free to adopt it or any method you
feel helps sort out the process of naming files:
Image type
Uncorrected image (IMAGE)
Flat field file (FLAT)
Track list file (TRACK)
Combined flat field (COMBINED-FLAT)
Flat field corrected image (CORRECTED-IMAGE)
5.8.
Name
XXXXXXXX.
FLATXXXX.
XXXXXXXX.TRK
FLATXXXX.C
XXXXXXXX.F
(blank extension)
(blank extension)
Tracking Functions
The CCDOPS software allows your ST-7XE, ST-8XE, ST-9XE, ST-10XE, ST-10XME and ST2000XM to be used as an autoguider or self-guided imager. It does not function as a standalone autoguider like the ST-4, but instead requires using a PC to perform the function. These
cameras have considerably better sensitivity than the ST-4.
CCD autoguiders alleviate you from having to stare down the eyepiece for hours at a
time while guiding astrophotographs. They are not the end-all, cure-all approach to
telescope mechanical problems, though. You still need a good polar alignment and a rigid
mount between the guide scope and the main scope or you need to use an off-axis guider,
with all its inherent difficulties. A good declination drive, free of backlash, is desirable
although not absolutely necessary. Finally, modern drive correctors with periodic error
correction (PEC) or permanent periodic error correction (PPEC) will ease the difficulty of
achieving good results.
The moral of the story is don't count on the CCD autoguider to fix all your problems.
The better the drive, the better results you will obtain.
Using the CCD as an autoguider requires interfacing the CPU's relay port to your hand
controller (as discussed in section 4.4) and then training the CCD system on your telescope.
This is done with the Calibrate Track command. Focus your system and then find and center
on a moderately bright calibration star (1000 to 20,000 peak counts will do) without any
nearby neighboring stars of similar brightness. Then execute Calibration command. It takes
a sequence of five images. In the first image it determines the pixel position of the calibration
star. In the four subsequent images, the software, in sequence, activates each of the
telescope's four correction directions, measuring the displacement of the calibration star.
From this calibration information, the software is able to calculate a precise correction when
the guide star moves away from its intended position.
At the start, you should pick a calibration star with roughly the same declination as
the intended object since the telescope's correction speeds vary with declination. As you get
used to the tracking functions you can calibrate on a star near the celestial equator and have
the software adjust for different declinations for you.
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Section 5 – Advanced Imaging Techniques
The tracking functions in CCDOPS are accessed through the Track menu. The
Calibrate Track command, as described above, is used to calibrate your telescope's drive
corrector. Once that is done, the Track command, which you would use for autoguiding
astrophotographs, allows you to select a guide star in the field of view, and then repeatedly
takes images, measuring the guide star's position and hence guiding error, and corrects the
telescope.
The Track and Accumulate command, discussed in section 3.9.2, also has provisions
for making telescope corrections between images. This is necessary only if your drive has a
large amount of long term drift, which results in Track and Accumulate images that are
reduced in width.
Finally, the Tracking Parameters command allows you to fine tune the CCDOPS
tracking performance. You can deactivate the RA or DEC corrections or even deactivate
both, a feature that can be used to monitor the uncorrected tracking accuracy of your drive.
You can also fine tune the correction speeds if you find the telescope is consistently over or
under correcting.
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Section 6 – Accessories for your CCD Camera
6.
Accessories for your CCD Camera
This section briefly describes the different accessories available for your CCD camera.
6.1.
Water Cooling
Your camera is equipped with a new heat exchanger design that is ready to accept
water circulation for additional cooling efficiency, if needed in warm climates.
The camera can be used either with or without flowing water. Water-cooling is
probably not necessary for most users when the air temperature is below 10 degrees C (50
degrees F), since the dark current is fairly low already. Think of it as a summertime
accessory! We do not recommend use of water cooling below freezing temperatures, where
antifreeze must be added to the water. It is simply not necessary then.
There is no problem using the camera at any time without water circulation. Adding
water circulation simply improves the cooling performance. With water circulation the
improvement in cooling is about 10 degrees C better than with air only.
You may supply your own pump and tubing or use the optional pump and tubing
available from SBIG. To operate the camera with water circulation using the optional pump
available from SBIG, start with the camera at the same level as the water reservoir. Connect
all the hoses, and make sure the water return goes back into the reservoir. Push the ¼ inch
internal diameter (ID) hoses onto the nipples on the back of the camera so they seal. Attach
one hose to the nipple onto the reducing connector that adapts the ¼ inch ID hose to the ½
inch diameter hose from the pump.
Turn on the pump, and let the flow establish itself through the hoses. Next, mount the
camera to the telescope. If you always keep the return hose outlet near the reservoir level the
pump will have no problem raising the water 2 meters (6 feet) off the floor. The limited
pressure capacity of the pump is only a problem when you let the water fall back into the
reservoir from a significant height above it, such a 0.3 meter (12 inches). Lastly, check for
leaks!
Once you have established water circulation, turn on the TE cooler to 100% by giving
it a target temperature of –50 degrees. Wait for about 10 to 20 minutes for the system to
stabilize at the lowest temperature it can achieve. Examine the camera temperature, and
reset the set point to 3 degrees C above the current temperature. This 3 degree temperature
margin will enable the camera to regulate the temperature accurately.
When using water cooling, avoid the temptation to put ice in the water to get the
camera even colder. If colder water is used, the head may fog or frost up, depending on the
dew point. At the end of the evening, stop the pump, and raise the outlet hose above the
camera to let all the water drain out of the system. Blowing it out with gently pressure helps
clear the water. You can leave the hoses full of water, but if a leak occurs while you’re not
there you may have a problem.
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Section 6 – Accessories for your CCD Camera
When packing the camera for a long time, or at the end of summer, disconnect the
hoses and blow out the heat sink to allow the enclosed spaces to dry out and minimize long
term corrosion.
6.2.
Tri-color Imaging
You can make splendid color images with your CCD camera by using the optional CFW-8
color filter wheel. The CFW-8 attaches to the front of the CCD head and allows you to take
images in red, green and blue light of the same object. When these images are aligned and
processed a full color image results.
6.3.
Camera Lens Adapters and Eyepiece Projection
Camera Lens adapters are available for the ST-7XE, 8XE, 9XE, 10XE, ST-10XME and ST2000XM. The camera lens adapter allows you to mount your camera lens in place of the
telescope for very wide field views of the night sky or for daytime terrestrial imaging. The
adapters are available for a variety of the most common camera lenses in use.
The cameras themselves can be used for eyepiece projection assuming you already
have a T-thread eyepiece projection adapter for. Instead of attaching a 35mm camera to the
T-thread camera adapter you can attach the CCD camera by unscrewing the T-Thread
nosepiece fom the front of the camera.
6.4.
Focal Reducers
Several third party vendors, including Optec, Celestron and Meade, make focal reducers for
their telescopes that could be used with the ST-7XE, 8XE, 9XE, 10XE, ST-10XME and ST2000XM cameras. While most will work with the ST-7XT some may have slight amounts of
vignetting when used on the larger 8XE, 9XE, 10XE, ST-10XME and ST-2000XM.
Note: Many very fast (F/3.3) commercial units will not accommodate a filter wheel.
6.5.
AO-7 and Lucy-Richardson Software
The AO-7 is the world's only Adaptive Optics accessory for the amateur CCD market and it
works only with the self guided feature of the ST-7XE, 8XE, 9XE, 10XE, ST-10XME and ST2000XM. The AO-7 is essentially an electromechanical driven diagonal mirror that goes
between the camera and the telescope. Using the AO-7 allows corrections to be made at rates
up to 40 Hz. This yields perfect, backlash-free guiding and allows removal of some
atmospheric effects. When used in conjunction with the CCDSharp software stellar peak
brightness can double and stellar half-widths can shrink by 25%.
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Section 6 – Accessories for your CCD Camera
6.6.
SGS - Self-Guided Spectrograph
The SGS Self Guided Spectrograph takes the tedium out of spectroscopy by allowing you to
image and guide the source on the tracking CCD while acquiring its spectra on the imaging
CCD. No more hunting around to place the object on the slit! With the SGS you can
measure galactic redshifts, stellar classifications and determine nebular constituency. This is
another example of the value of a self-guided camera like the ST-7XE, 8XE, 9XE, 10XE, ST10XME and ST-2000XM.
6.7.
Third Party Products and Services
There are numerous third party products and services available directed to the CCD user.
Appendix E mentions a few vendors who have supported SBIG products just to give you an
idea of the ever increasing interest in this new technology.
6.7.1. Windows Software
Our CCDOPS version 5 software is compatible with Windows 95/98/2000/Me/NT/XP.
However, many users also want additional image processing or analytical features not found
in CCDOPS. Therefore, since January 2001, all SBIG cameras also include CCDSoftV5 which
is a joint software development of SBIG and Software Bisque. There are also several other
commercial Windows programs available which include a stellar database, telescope control
for computerized telescopes like the Meade LX200, and CCD camera functions in an
integrated package.
6.7.2. Image Processing Software
There are a host of image processing software packages capable of reading and processing
FITS and TIFF files and many packages will read and process native SBIG image formats as
well. In addition to commercial software, a number of web sites offer public domain and
shareware programs.
6.7.3. Getting Hardcopy
One older way of producing a hard copy of images taken with the CCD camera is to simply
take a photograph of the computer screen while the image is displayed. It is best to use a
long lens and step back from the monitor to reduce the appearance of the curvature of the
edges of the screen, and use an exposure longer than 1/30th of a second to avoid the video
refresh rate of your monitor. Darken the room, and use a brighter background than is
visually optimum.
For the best quality hard copy, save the files in TIFF format and send a copy of the file on a
disk to a photo lab which offers printing of digital images. The Windows version of CCDOPS
allows for printing of the images, and there are a number of third party software programs
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Section 6 – Accessories for your CCD Camera
for the PC such as Pizzaz Plus which will capture and print the display on your computer
screen. These programs, however, do not produce very detailed prints and are useful only to
a very limited degree. Recently, photo quality color desktop printers have become
commonplace. Many of these printers will do a reasonable job with commercial image
processing programs such as Adobe Photoshop.
6.8.
SBIG Technical Support
If you have any unanswered questions about the operation of your CCD camera system or
have suggestions on how to improve it please don't fail to contact us. We appreciate all your
comments and suggestions. Additionally if you are interested in writing software supporting
SBIG cameras, we offer technical support regarding our file formats found in Appendix B,
and Technical Notes regarding the camera command protocol which we will make available
upon request.
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Section 8 – Glossary
7.
Common Problems
This section discusses some of the more common problems others have encountered while
using our CCD cameras. You should check here if you experience difficulties, and if your
problem still persists please contact us to see if we can work it out together.
Achieving Good Focus - Achieving a good focus is one of the most difficult areas in working
with CCD cameras due to the lack of real time feedback when focusing. Focus can
take a good deal of time, and as with all forms of imaging, focus is critical to getting
the most out of your camera.
Once you have achieved a good focus with your system, it can be very useful
for future observing sessions to scribe an eyepiece or mark down or log positions of
each component so the next time you will at least be close to focus at the start.
If you know where the focal plane lies for your telescope, you can use Table 3.1
to calculate exactly where the CCD is with respect to your system. By placing the
CCD close to the focal plane initially, you can save a lot of time.
The best kind of object to focus on is a star. As you converge towards focus,
more light from the star will be concentrated onto one pixel. Thus, watching your
peak reading while focusing and focusing for a maximum reading is a good way to
get best focus. This is how we do it. It helps to have a dial or indicator on the focus
knob so you can rapidly return to the best point after going through focus.
Elongated Guided Images - When using Track and Accumulate or Self Guiding, if you notice
guiding errors resulting in elongated star images, you are probably using too long a
snapshot time. If the snapshot time is longer than the amount of time your drive can
track unguided with acceptable guiding errors, you will see elongated stars in your
final images. If your snapshot times are getting down to 30 seconds or less you should
improve your drive.
If you are using your camera as an autoguider for film photography and are noticing
unacceptable guiding errors, please check the following before calling SBIG:
1. Can you move the telescope using the Move command? This is an
indicator as to whether or not you are properly connected to your
drive system via the relay cable from the CPU.
2. Be sure that your calibration time gives at least 10 to 50 pixels of
movement for each step of the Calibrate Track command.
3. Check for flexure between the CCD camera head and your system.
Check for flexure between the guide scope or off-axis guider and
your telescope system. This is a very common source of guiding
errors. A very small movement of the CCD head with respect to the
guide scope during an exposure can cause unacceptable streaking.
Page 59
Section 8 – Glossary
4. If your mount is stable, try longer exposure times while tracking to
average out the atmospheric effects.
Finding Objects - The size of the CCD used in the ST-7 (roughly 8mm diagonal) can make
finding objects a little difficult. If you experience this problem you might try the
following suggestions.
The easiest method of finding objects is to use a reticule eyepiece, if the object is
bright enough to see. Pull the CCD optical head from the eyepiece holder and insert a
12-20mm eyepiece, focusing the eyepiece by sliding it in and out of the eyepiece
holder, not by adjusting the telescope's focus mechanism. Center the object carefully
(to within 10% of the total field) and then replace the CCD optical head. Since the
head was fully seated against the eyepiece holder when you started, fully seating it
upon replacement will assure the same focus.
If the object is too dim to see visually you will have to rely on your setting
circles. Go to a nearby star or object that is easily visible and center that object in the
CCD image. Calibrate your RA setting circle on the known object's RA and note any
DEC errors. Reposition the telescope at the intended object, using the correct RA
setting and the same DEC offset noted with the calibration object. Try a ten second or
one minute exposure and hopefully you will have winged the object. If not you will
have to hunt around for the object. You can use the Focus mode in Low resolution
mode for this and hopefully you won't have to search too far. Check in DEC first, as
DEC setting circles are often smaller and less accurate.
Telescope Port doesn't Move Telescope - If you find the camera is not moving the telescope
for Tracking, Track and Accumulate or Self Guiding you should use the Move
Telescope command with a several second period to isolate the problem down to a
specific direction or directions. If you set the Camera Resolution to the Low mode in
the Camera Setup Command, you can move the telescope and Grab an image fairly
quickly to detect movement of the telescope pointed at a moderately bright star. Try
each of the four directions and see which ones move and which ones don't. At this
point the most likely culprit is the hand controller modification. Trace the signals from
the camera's telescope connector back through the hand controller, paying particular
attention to the offending wires.
Can't Reach Low Setpoint Temperatures - If you find that the camera isn't getting as cold as
expected the problem is probably increased ambient temperatures. While these
cameras have temperature regulation, they still can only cool a fixed amount below
the ambient temperature (30 to 40 °C). Lowering the ambient temperature allows the
cameras to achieve lower setpoint temperatures.
CCD Frosts - If your camera starts to frost after a year of use it's time to regenerate the
desiccant as described in Appendix C. This is a simple matter of unscrewing the
desiccant container and baking it (without the little O-ring) in an oven at 350°F for 4
hours.
Page 60
Section 8 – Glossary
No Image is Displayed - Try the Auto Contrast setting or use the crosshairs to examine the
image pixel values and pick appropriate values for the Background and Range
parameters.
Horizontal Faint Light Streaks in Image - some PCs apparently have the mouse generate
non-maskable interrupts when moved. These interrupts can slightly brighten the line
being read out. If this occurs, do not move the mouse during read out.
8.
Glossary
Antiblooming Gate - When a CCD pixel has reached its full well capacity, electrons can
effectively spill over into an adjoining pixel. This is referred to as blooming. Kodak
CCDs with the antiblooming option can be used to help stop or at least reduce
blooming when the brighter parts of the image saturate.
Astrometry - Astrometry is the study of stellar positions with respect to a given coordinate
system.
Autoguider - All SBIG CCD cameras have auto guiding or "Star Tracker" functions. This is
accomplished by using the telescope drive motors to force a guide star to stay precisely
centered on a single pixel of the CCD array. The camera has four relays to control the
drive corrector system of the telescope. The CCD camera head is installed at the guide
scope or off axis guider in place of a guiding eyepiece.
CCD - The CCD (Charged Coupled Device) is a flat, two dimensional array of very small
light detectors referred to as pixels. Each pixel acts like a bucket for electrons. The
electrons are created by photons (light) absorbed in the pixel. During an exposure,
each pixel fills up with electrons in proportion to the amount of light entering the
pixel. After the exposure is complete, the electron charge buildup in each pixel is
measured. When a pixel is displayed at the computer screen, its displayed brightness is
proportional to the number of electrons that had accumulated in the pixel during the
exposure.
Dark Frame - The user will need to routinely create image files called Dark Frames. A Dark
Frame is an image taken completely in the dark. The shutter covers the CCD. Dark
Frames are subtracted from normal exposures (light frames) to eliminate fixed pattern
and dark current noise from the image. Dark Frames must be of the same integration
time and temperature as the light frame being processed.
Dark Noise - Dark Noise or Dark Current is the result of thermally generated electrons
building up in the CCD pixels during an exposure. The number of electrons due to
Dark Noise is related to just two parameters; integration time and temperature of the
CCD. The longer the integration time, the greater the dark current buildup.
Conversely, the lower the operating temperature, the lower the dark current. This is
why the CCD is cooled for long integration times. Dark noise is a mostly repeatable
noise source, therefore it can be subtracted from the image by taking a "Dark Frame"
Page 61
Section 8 – Glossary
exposure and subtracting it from the light image. This can usually be done with very
little loss of dynamic range.
Double Correlated Sampling - Double Correlated Sampling (DCS) is employed to lower the
digitization errors due to residual charge in the readout capacitors. This results in
lower readout noise.
False Color - False Color images are images that have had colors assigned to different
intensities instead of gray levels.
FITS Image File Format - The FITS image file format (which stands for Flexible Image
Transport System) is a common format supported by professional astronomical image
processing programs such as IRAF and PC Vista. CCDOPS can save image files in this
format but can not read them..
Flat Field - A Flat Field is a image with a uniform distribution of light entering the telescope.
An image taken this way is called a flat field image and is used with CCDOPS to
correct images for vignetting.
Focal Reducer - A Focal Reducer reduces the effective focal length of an optical system. It
consists of a lens mounted in a cell and is usually placed in front of an eyepiece or
camera. With the relatively small size of CCDs compared to film, focal reducers are
often used in CCD imaging.
Frame Transfer CCDs - Frame Transfer CCDs are CCDs that have a metal mask over some
portion (usually half) of the pixel array. The unmasked portion is used to collect the
image. After the exposure is complete, the CCD can very quickly shift the image from
the unmasked portion of the CCD to the masked portion, thus protecting the image
from light which may still be impinging on the CCD. This acts as an electronic shutter.
Full Well Capacity - Full Well Capacity refers to the maximum number of electrons a CCD
pixel can hold. This number is usually directly proportional to the area of the pixel.
Histogram - The Histogram is a table of the number of pixels having a given intensity for
each of the possible pixel locations of the image file. Remember that, in the end, the
image file is nothing more than a list of pixel values, one for each CCD pixel. These
value numbers can be displayed in two formats; as a table or plotted as a graph.
Light Frame - The Light Frame is the image of an object before a Dark Frame has been
subtracted.
Photometry - Photometry is the study of stellar magnitudes at a given wavelength or
bandpass.
Page 62
Section 8 – Glossary
Pixel Size - The smallest resolution element of a CCD camera is the CCD pixel. The pixel
sizes for each of the SBIG cameras are as follows:
Camera
TC-211 Tracking CCD
TC-237 Tracking CCD
ST-5C
ST-237/237A
STV
ST-7XE/ST-8XE
ST-9XE
ST-10XE, ST-10XME
ST-1001E
ST-2000XM
Pixel Size (microns)
13.75 x 16
7.4 x 7.4
10 x 10
7.4 x 7.4
14.8 x 14.8
9x9
20 x 20
6.8 x 6.8
24 x 24
7.4 x 7.4
Planet Mode - Planet Mode is the most useful way to achieve focus. When you select Planet
mode, a full frame is exposed, downloaded, and displayed on the computer monitor.
A small window can be placed anywhere in the image area and the size of the
window can be changed. Subsequent downloads will be of the area inside the box
resulting in a much faster update rate.
Quantum Efficiency - Quantum Efficiency refers to the fractional number of electrons
formed in the CCD pixel for a given number of photons. Quantum Efficiency is
usually plotted as a function of wavelength.
Readout Noise - Readout noise is associated with errors generated by the actual
interrogation and readout of each of the CCD pixels at the end of an exposure. This is
the result of fixed pattern noise in the CCD, residual charge in the readout capacitors
and to a small extent the noise from the A/D converter and preamplifier.
Resolution Mode - The resolution of a CCD camera is determined by pixel size. Pixel size can
be increased by combining or binning more than one pixel and displaying it as one
pixel. Doing so decreases the effective resolution but speeds up the download time of
the image. Maximum resolution is determined by the size of the individual CCD pixel.
The ST-7XE, 8XE, 9XE, 10XE, ST-10XME and ST-2000XM can run in High, Medium,
Low and Auto resolution modes.
Response Factor - Response Factor is a multiplier used by CCDOPS to calibrate CCDOPS to
a given telescope for photometric calculations. The Response Factor multiplied by
6700 is the number of photoelectrons generated in the CCD for a 0th magnitude star
per second per square inch of aperture.
Saturation - Saturation refers to the full well capacity of a CCD pixel as well as the maximum
counts available in the A/D converter. The pixel is saturated when the number of
electrons accumulated in the pixel reaches its full well capacity. The A/D is saturated
when the input voltage exceeds the maximum. The saturation values for the various
cameras are shown in the table below.
Page 63
Section 8 – Glossary
Camera
Full Well
Capacity
Maximum
Electrons
A/D Counts per A/D
count5
ST-5C
50,000 e-
65,535
1.25
ST-237
20,000 e-
4,095
3.4
ST-237A
20,000 e-
65,535
0.7
ST-7XE/ST-8XE9 ABG High Res
50,000 e-
20,000
2.3
ST-7XE/ST-8XE Med/Low Res
100,000 e-
65,535
2.3
ST-9XE
180,000 e-
65,535
2.8
ST-10XE, ST-10XME
77,000 e-
65,535
1.5
ST-1001E
180,000e-
65,535
2.8
ST-2000XM
45,000e-
65,535
0.72/1.4
TC-211 Tracking CCD
150,000 e-
65,535
1.3
TC-237 Tracking CCD
20,000 e-
65,535
0.72
Sky Background - The sky background illumination or brightness is the number of counts in
the image in areas free of stars or nebulosity and is due to city lights and sky glow.
High levels of sky background can increase the noise in images just like dark current.
For some objects deep sky filters can be used to reduce the sky background level.
Seeing - Seeing refers to the steadiness and the clarity of the atmosphere during an observing
session.
TE Cooler - The TE Cooler is a Thermal Electric cooling device used to cool the CCD down to
operating temperature. The CCD is mounted to the TE Cooler which is mounted to a
heat sink, usually the camera head housing.
TIFF Image File Format - The TIFF image file format (which stands for Tagged Interchange
File Format) was developed jointly by Microsoft and Aldus Corporations to allow easy
interchange of graphics images between programs in areas such as presentation and
desktop publishing. CCDOPS can save image files in this format but it can not read
them.
Track and Accumulate - The Track and Accumulate function is a SBIG patented feature of
CCDOPS that allows the user to automatically co-register and co-add (including dark
frame subtraction) a series of images of an object. These exposures can be taken
unguided as long as the "Snapshot time" does not exceed the length of time before
tracking errors of your clock drive become apparent. This allows you to image and
track without guiding or the need to connect the CCD Relay port to your drive
motors.
5
9
The e-/Count shown are for the High Resolution readout mode. These numbers can be different for other
readout modes. Use the Parameters command in the Display menu to see the actual value for images acquired
in other readout modes.
The non-ABG versions of the ST-7E/8E have twice the full well capacity of the values shown. ABG version
may also vary from camera to camera with maximum counts being as high as ~30,000.
Page 64
Section 8 – Glossary
Track List - The Track List is an ASCII file generated by CCDOPS during a Track and
Accumulate session. The Track List logs all the corrections made by CCDOPS for each
of the images. Track lists are required when flat fielding Track and Accumulate
images.
Tri-Color - Tri-Color refers to color images created using three different colors mixed into a
balanced color image using red, green and blue filters. An object is imaged three times,
once with each color filter. The three images are then co-added and color balanced
with the appropriate software.
Vignetting - Vignetting is obstruction of the light paths by parts of the instrument. It results
in an uneven illumination of the image plane. The effects of vignetting can be
corrected using flat field images.
Page 65
Appendix A - Connector Pinouts
A.
Appendix A - Connector and Cables
A.1.
Connector Pinouts for the AO7/CFW8/SCOPE port:
Pin Number
1
2
3
4
5
6
7
8
AUX)
9
Shell
A.2.
Function
Chassis Ground
CFW-8 Pulse/AO-7 Data Out
Plus X (Active Low Open Drain) 6
Plus Y (Active Low Open Drain)
Signal Ground
Minus X (Active Low Open Drain)
Minus Y (Active LowOpen Drain)
+12 Volts Out (100mA max shared with I2C
+5 Volts Out (300 mA max shared with I2C AUX)
Chassis Ground
Table A1 Telescope Connector
Connector Pinouts for the power jack:
Pin Number
Function
6, Shell
Earth Ground
5
DC Ground
4
-12V DC, 100mA
3
No contact
2
+12V DC, 500mA
1
+5V DC, 2A
Table A2 Power Connector Power Jack
A.3.
Connector Pinouts for the I2C AUX port:
Pin Number
1
2
3
4
5
6
7
8
6
Function
+5V DC (300 mA max shared with AO7/CFW8)
No Contact
Serial Clock
Serial Data
Signal Ground
No Contact
No Contact
+12V DC (100mA max shared with AO7/CFW8)
The Open Drain outputs can sink 100 mA maximum
Page 67
Appendix A - Connector Pinouts
9
Shell
A.4.
+3.3V DC (500mA max)
Chassis Ground
Table A3 I2C Accessory Port
SBIG Tracking Interface Cable (TIC-78)
Many of the newer telescopes have a phone-jack connector on the drive corrector for
connecting directly to the ST-7XE, 8XE, 9XE, 10XE, ST-10XME and ST-2000XM Camera's
Telescope Port. These include the Celestron Ultima, Losmandy CG11 and Meade LX-200.
You can interface these telescopes to the Telescope port with our TIC-78 (Tracking Interface
Cable), or you can make your own cable. Figure A1 below shows the pinouts on some of
these telescopes.
Hand Controller
Modular Phone
Button
Wire Color
Telescope Port Pin
Special
White
None
Common
Black
5
Left
Red
6
Down
Green
7
Up
Yellow
4
Right
Blue
3
Figure A1 - CCD Connector for TIC Mating
Telescope electronic designs are changing rapidly. You should check with the
manufacturer of your telescope for the actual pinouts of your particular model. If this
TIC cable does not match your drive port, then you can use the information in Table A1 to
make a cable to work with your specific telescope/drive system.
Page 68
Appendix B - Maintenance
B.
Appendix B - Maintenance
This appendix describes the maintenance items you should know about with your CCD
camera system.
B.1.
Cleaning the CCD and the Window
The design of SBIG cameras allows for cleaning of the CCD. The optical heads are not
evacuated and are quite easy to open and clean. When opening the CCD chamber, one
should be very careful not to damage the structures contained inside.
To open the CCD Chamber, remove the six screws that hold the 5 inch front cover in
place. Remove the six screws and lift the front cover, exposing the structures inside. There is a
rubber O-Ring that sets in the groove on the top of the Chamber housing.
The CCD array is protected by a thin cover glass that can be cleaned with Q-Tips
and Isopropyl Alcohol. Do not get alcohol on the shutter. Dust on the CCD should be blown
off. Use alcohol only if necessary. The optical window of the chamber housing can be
cleaned the same way. When reinstalling the chamber housing, be very careful to make sure
the O-ring is in the groove when seated.
B.2.
Regenerating the Desiccant
This section describes the regeneration procedure for the desiccant used in the ST-7XE, 8XE,
9XE, 10XE, ST-10XME and ST-2000XM. The desiccant absorbs moisture in the CCD
chamber, lowering the dew point below the operating temperature of the cooled CCD, thus
preventing the formation of frost. The desiccant is contained in a small cylindrical plug that
screws into the chamber from the rear. In normal operation the useful life of the desiccant is
over a year. If the CCD chamber is opened often, the desiccant should be regenerated when
frosting is noticed. Follow the procedure below to regenerate the desiccant:
1. Unscrew the brass desiccant container from the rear of the camera and
remove the O-ring.
2. Plug the resulting hole by screwing in the supplied bolt or plug 2 or 3 turns.
Finger tight is adequate. Don't put a wrench on it.
3. Heat the desiccant container in an oven at 350°F (175 deg C) for 4 hours.
The solder used to seal the can melts at 460 degrees F, so be sure to stay at
least 50 degrees below this number. Preheating the oven to avoid hot spots
is advised.
4. Replace the desiccant container into the rear of the camera, being careful to
reinstall the O-ring and insure that it does not get pinched.
5. Expect the camera to take an hour or two to reach the frost free state. If it
does seem to frost and you need to capture images, reduce your cooling to
the zero degree C range - the CCD dark current will still be quite low.
Page 69
Appendix C – Capturing a Good Flat Field
C.
Appendix C - Capturing a Good Flat Field
This appendix describes how to take a good flat field. A good flat field is essential for
displaying features little brighter than the sky background. The flat field corrects for
pixel non-uniformity, vignetting, dust spots (affectionately called dust doughnuts),
and stray light variations. If the flat field is not good it usually shows up as a
variation in sky brightness from on side of the frame to the other.
C.1.
Technique
The first consideration in capturing a flat field is to use the telescope-CCD
combination in exactly the configuration used to collect the image. This means you
probably have to capture the flat field at the telescope. Do not rotate the head
between image and flat field, since the vignetting is usually slightly off center. Do not
be tempted to build a little LED into the telescope or camera for doing flat fields; it
doesn't work at all. The dust debris shadows would be different!
Arrange a light source such as a flashlight, two white cards, the telescope and
CCD as shown in Figure D-1.
Figure D-1: Flat Field Geometry
Telescope
CCD
Flat White
Surface
Flashlight
Flat White
Surface
The key aspects of this geometry are that the reflection off two diffuse surfaces is used,
and the large flat surface is square to the illumination from the small flat surface.
When we do this, the first flat surface is typically a white T-shirt worn by the
operator! Take care that no apparent shadows are cast onto the larger flat white
surface. Use an exposure at the camera that yields an average light level equal to
about half of full scale.
Page 70
Appendix D – Use and Maintenance of the Cooling Booster
D.
Appendix D - Use and Maintenance of the Cooling Booster
The cooling booster was an option or included accessory for the parallel versions of
the ST-7E, ST-8E, ST-9E, ST-10E and ST-10XME. When a parallel camera with this accessory
is upgraded to the USB version, the cooling booster is left in place instead of changing to the
new cooling design. The cooling booster is a second TE cooling module that goes inside the
back compartment of the camera. It requires a second power supply. This memo is a stepby-step guide to using the booster for those upgraded cameras that kept the earlier design.
CAUTION! Please be sure that whenever the cooling booster is on (i.e., plugged into
12VDC), the camera is also powered up so that the fan is running. The fan is needed to
dissipate the heat generated by the cooling booster. If you power up the booster by plugging
it into 12VDC without the camera fan running it can overheat and damage the cooling
booster system. This won't happen immediately if you happen to accidentally power up the
booster before turning on the camera, but running it more than few minutes without the fan
could damage the unit.
For users with fixed sites, or small observatories, water circulation and the attendant
tubes and pump are easier to manage. For field use, however, you may wish to forgo water
circulation and use the cooling booster with 12VDC only to simplify the setup. When using
water circulation, the major problem one must deal with is routing the rather heavy water
tubes off the mount to minimize perturbations to the mount during tracking. In general, try
to route tubes (and wires) over the mount, rather than just let the tubes dangle from the end
of a long tube. Water cooling is probably not necessary for most users when the air
temperature is below 10 degrees C (50 degrees F), since the dark current is fairly low already.
Think of it as a summertime accessory! We do not recommend use of water cooling below
freezing temperatures, where antifreeze must be added to the water. It is simply not
necessary then. There is no problem with using the cooling booster with only air cooling in
the winter, though.
With the cooling booster installed on your camera, you have a choice of three levels of
cooling. First, you can ignore the booster and operate the camera with single stage cooling
only by simply not connecting 12VDC to the booster's power plug. Second, with the camera
power on and fan funning, you can also power up the cooling booster by plugging in 12VDC
to increase the cooling capability of the camera without using any water circulation. Third,
you can power up the cooling booster with 12VDC and use water circulation to further
increase the cooling capability of the camera.
Without flowing water the cooling improvement is about 6 degrees C. With it the
cooling improvement is about 15 degrees C. If you plan to use it without the water then you
should disconnect the hoses from the camera and shake out the water trapped in the heat
sink. Disconnecting the hoses will reduce the potential perturbation to your telescope mount.
Page 71
Appendix D – Use and Maintenance of the Cooling Booster
To operate the cooling booster without water cooling, mount the camera to the
telescope as before and simply plug the auxiliary 12 volt supply jack into the connection on
the camera back plate. Turn on the TE cooling to 100% by giving it a target temperature of –
50 degrees. After 10 minutes examine the camera temperature, and reset the set point to 3
degrees C above the current temperature. This 3 degree temperature margin will enable the
ST-7/8 to regulate the temperature accurately.
To operate the camera with water cooling, the procedure is the same except that the
water flow must be established before mounting the camera to the telescope, since the water
pumps have limited pressure capability. To do this, put the camera at the same level as the
water reservoir. Connect all the hoses, and make sure the water return goes back into the
reservoir. Push the ¼ inch internal diameter (ID) hoses onto the nipples on the back of the
camera so they seal. Attach one hose to the nipple onto the reducing connector which adapts
the ¼ inch ID hose to the ½ inch diameter hose from the pump.
Turn on the pump, and let the flow establish itself through the hoses. Next, mount the
camera to the telescope. If you always keep the return hose outlet near the reservoir level the
pump will have no problem raising the water 2 meters (6 feet) off the floor. The limited
pressure capacity of the pump is only a problem when you let the water fall back into the
reservoir from a significant height above it, such a 0.3 meter (12 inches). Lastly, check for
leaks!
When using water cooling, avoid the temptation to put ice in the water to get the
camera even colder. As the cooling booster is designed, the camera will not be cooled below
ambient temperature if ambient temperature water is used. If colder water is used, the head
may fog or frost up, depending on the dew point. . The exposed electronics inside the ST-7/8
will get wet, and corrode. The hoses will start dripping condensation, and you will have a
mess. Keep the ice for a cold drink!
At the end of the evening, stop the pump, and raise the outlet hose above the camera
to let all the water drain out of the system. Blowing it out with gently pressure helps clear the
water. You can leave the hoses full of water, but if a leak occurs while you’re not there you
may have a problem. When packing the camera for a long time, or at the end of summer,
disconnect the hoses and blow out the heat sink to allow the enclosed spaces to dry out and
minimize long term corrosion.
A 110VAC to 12VDC transformer is supplied with the cooling booster. The booster
requires approximately 2 amps at 12VDC. If you wish to connect direct to 12VDC, please
note polarity of the DC Power Jack on back plate of camera. The power jack is electrically
isolated from the camera body.
Page 72
Appendix D – Use and Maintenance of the Cooling Booster
+12VDC on outside
Ground in Center
Mating plug is 5.5mm
outside and 2.1mm inside
Figure A - DC Power Jack
Page 73
Appendix E – Third Party Vendors Supporting SBIG Products
E.
Appendix E – Third Party Vendors Supporting SBIG Products
Company / Author
Software Bisque
912 12th Street Golden, CO 80401-1114 USA
Sales: (800) 843-7599 International: (303) 278-4478
Facsimile: (303) 278-0045
E-mail Sales: [email protected]
E-mail Support: [email protected]
Web site: www.bisque.com
Product
CCDSoftV5,
TheSky,
Orchestrate,
T-point,
Paramount
Diffraction Ltd.
100 Craig Henry Drive,
Unit 106, Ottawa, ON, K2G 5W3, Canada
Telephone (613) 225-2732 FAX (613) 225-9688
E-mail Sales: [email protected]
E-mail Support: [email protected]
Web site: www.cyanogen.com
Axiom Research
1830 East Broadway Blvd, Suite 124-202
Tucson, AZ 85719
Voice 520-323-8600 Fax 520-822-1435
E-mail Sales [email protected]
E-mail Support [email protected]
Web http://www.axres.com
Axilone Multimedia
18, ch. des Ajoncs, 31470 Saint-Lys FRANCE
Phone: +33 5 34 47 20 52 Fax: +33 5 34 47 10 20
E-mail: [email protected]
M.S.B. di Fabio Cavicchio, Via Romea Vecchia 67,
Classe, 48100 Ravenna RA. P.IVA 01379350398,
TEL/FAX +39 0544 473589 Mobile +39 0339 2739548
E-Mail [email protected], [email protected]
Web site: http://www.msb-astroart.com
New Astronomy Press, Ron Wodaski
PO Box 1766, Duvall, WA 98019
E-mail: [email protected]
FAX: 425-844-1535
Web site: http://www.newastro.com
The Minor Planet Observer, Brian Warner
e-mail: [email protected]
Web site: http://www.minorplanetobserver.com
Maxim
DL.CCD
Page 74
Notes
Camera control, Image
Processing, Astrometry,
Minor Planet Searches,
Planetarium and Charting,
Scripting, Remote
operation and telescope
control. Robotic mounts.
Authorized SBIG Dealer
Image Processing,
Camera Control software
Authorized SBIG Dealer
Mira
software
Camera control, Image
processing, analysis,
spectroscopy
Prism 5
Image processing, camera
control
Astroart
Image processing
software and camera
control. FITS viewer
The New
Astronomy
Book: Basics of CCD
Imaging, background and
techniques.
Minor Planet
Observer
software
Astrometry, Minor planet
searches
Appendix E – Third Party Vendors Supporting SBIG Products
Bruce Johnston Computing
7124 Cook Rd.
Swartz Creek, MI 48473 U.S.A.
Phone: 810-635-9191 Fax: 1-810-750-1761
E-mail: [email protected]
Web site: http://members.aol.com/bjohns7764
Phase Space Technology
Phone: +61 3 9735 2270 Fax:: +61 3 9739 4996
Web site: http://www.phasespace.com.au
E-mail Support: [email protected]
E-mail General: [email protected]
E-mail Orders: [email protected]
Steve Mandel
Hidden Valley Observatory
1425 Hidden Valley Rd., Soquel, CA 95073
E-mail: [email protected]
Web: http://www.galaxyimages.com/ccdwidefield.html
Dr. Brady Johnson
E-mail: [email protected]
Web site:
http://members.rogers.com/bradydjohnson/widefield.htm
Astro-Physics, Inc.
11250 Forest Hills Road, Rockford, IL 61115, U.S.A.
Phone: 815-282-1513 Fax: 815-282-9847
E-mail: [email protected]
Web site: http://www.astro-physics.com
RC Optical Systems
Brad Ehrhorn
3507 Kiltie Loop, Flagstaff, AZ 86001
Tel: (928) 773-7584
E-mail: [email protected]
Web site:
http://www.rcopticalsystems.com/index.html
Astro Works Corporation
P.O. Box 699, Aguila, Arizona 85320
Tel: (928) 685-2422
Web site: http://www.astroworks.com
MexaFix
Software
Image processing
Astra Image
Image Processing
Software
Mandel Wide
Field Adapter
Nikon lens adapter for
SBIG color filter wheel
Johnson Wide Pentax, Olympus and
Field Adapter Minolta lens adapters for
SBIG color filter wheel
APO
Refractors
and mounts
4” to 6” APO refractors
and GOTO mounts.
Authorized SBIG OEM
RitcheyChretien
telescopes
RC Telescopes and
accessories for CCD
imaging. Authorized
SBIG OEM
Centurion 18
telescope
18” F/2.8 telescope made
specifically for CCD
imaging. Authorized SBIG
OEM
Disclaimer: Mention is made of third party vendors in this section as a courtesy only. These
vendors are independent companies and/or individuals. SBIG does not endorse or support any
particular company, product or service by virtue of mentioning them in this section. SBIG is
Page 75
Appendix E – Third Party Vendors Supporting SBIG Products
not responsible for the use of any product or service mentioned in this section that is not
manufactured or made by SBIG.
Page 76
Index
A/D converter, 20, 39
accessories, 53
adaptive optics, 52
antiblooming, 41, 59
Antiblooming Gate (def), 59
AO-7, 52
astrometric measurements, 59
Astrometry (def), 59
astrophotography, 25
atmospheric effects, 29
auto contrast, 30
Auto Grab Command, 33
autoguider, 21, 32, 35, 48, 59
Autoguider (def), 59
background parameter, 30
battery operation, 27, 35
binning, 23
Calibrate Track Command, 33, 49
calibration star, 49
camera lens adapter, 45, 52
Camera Setup Commands, 32
CCD, 20, 24
(def), 59
cameras, 17, 18, 21, 27, 35, 38, 39, 40
cleaning, 67, 68
detector, 17, 19, 35
orientation, 27
CCDCOLOR software, 34
CCDOPS software, 21
centering objects, 30
cleaning the CCD, 67, 68
clock drivers, 20
co-add images, 17, 32, 35
cold pixels, 31
color filter wheel, 33, 52
color images, 25, 33
color table, 59
commands
Auto Grab, 33
Calibrate Track, 33, 49
Dark Subtract, 31
Focus, 29, 31
Grab, 30, 31, 45
Track, 49
Track and Accumulate, 32, 45, 49
Tracking Parameters, 49
Commands
Establish COM Link, 28
PC Setup, 28
communications link, 28
connector
Telescope, 65
connector (CPU)
RELAYS, 35, 49
cooling, 21, 62
co-register images, 32, 35
crop, 30
crosshairs, 30
dark current, 21
dark frame, 20, 22, 27, 30, 31
Dark Frame (def), 59
Dark Noise (def), 59
Dark Subtract Command, 31
dark subtracted, 22, 27, 31
DCS, 22, 59
Declination, 27, 35, 49, 56
desiccant, 67
Diffuse Magnitude, 31
diffuser, 28
Dim mode, 31
displaying images, 30
double correlated sampling, 22
Double Correlated Sampling (def), 59
drive corrector, 32
electromechanical shutter, 39
electromechanical vane, 39
electronic images, 24
electronic shutter, 39
Establish COM Link Command, 28
eyepiece, 30
eyepiece holder, 27
eyepiece projection, 52
eyepiece tube, 29
False Color (def), 59
77
Index
field of view, 23, 40, 41, 42, 49
film, 17, 23
film grain, 23
filter wheel, 26
filters, 26, 31, 33, 52
finding objects, 30
fine focus, 29
FITS format (def), 59
flat field, 22, 31, 46, 47
Flat Field (def), 60
flip, 31
focal length, 42
focal reducer, 52
Focal Reducer (def), 60
focus
Dim mode, 30, 31
fine, 29
Full frame mode, 29
Full Frame mode, 31
peak, 29
Planet mode, 29, 31, 61
Focus Command, 29, 31
focus mode, 29, 31
Focusing, 28
Frame Transfer CCDs, 18
Frame Transfer CCDs (def), 60
frost, 20
Full Frame CCDs, 18
full well capacity, 41
Full Well Capacity (def), 60
Grab Command, 30, 31, 45
graphics, 30
guiding, 24
guiding error, 32, 49
hand controller, 30, 32, 35, 36
hermetic chamber, 20
Histogram (def), 60
host computer, 21, 27, 35
hot pixels, 31
IBM PC, 21
image processing, 21, 25, 31, 53
interference, ii
IR blocking filter, 34
joystick, 37
joystick modification, 38
library of dark frames, 30, 46
light frame, 22, 27, 30
light frame (def), 60
Link, 28
LPT port, 27, 28, 35
magnitude
diffuse, 31
stellar, 31
maintenance, 67, 68
microcontroller, 20
modifying hand controller, 36
moon, 29, 42, 45
negative image, 30
nosepiece, 27
observatory, 35
optical head, 27, 35
optical head orientation, 28
O-ring, 20
path (def), 60
path/filter (def), 60
PC, 21
PC Setup Command, 28
PEC drive correctors, 32, 49
photometric measurements, 60
Photometry (def), 60
pixel nonuniformity, 31
pixel size, 23, 40
Pixel Size (def), 60
pixel uniformity, 22
planet mode, 31
Planet mode (def), 61
planets, 17, 29, 42, 45
POWER connector, 27
power supply, 20, 27
power supplyr, 35
PPEC drive correctors, 32, 49
preamp, 20, 35
printing images, 25, 53
push to make switch modification, 37
push to make/break switch modification,
37
78
Index
Quantum Efficiency (def), 61
range parameter, 30
readout
electronics, 35
noise, 41
Noise (def), 61
register, 18
regenerating desiccant, 67
RELAYS connector, 35, 49
resolution, 23, 32, 46
Resolution (def), 61
Response factor (def), 61
Right Ascension, 27, 35, 49, 56
Saturation (def), 61
scribing the eyepiece, 30
seeing, 23, 29, 32, 43
Seeing (def), 62
self guiding, 35
separations, 31
setup, 27
SGS-Self Guided Spectrograph, 52
sharpen, 31
shutter, 20
signal to noise ratio, 34, 41
sky background, 17, 32
smoothing, 31
snapshot, 36
software, 39, 53
spectral range, 17
spectrograph, 52
Status Window, 28
Link field, 28
stellar magnitude, 31
stellar temperature, 31
super pixel, 31
taking images, 30
TE cooler, 20
TE Cooler, 20
TE Cooler (def), 62
Technical Support, 53
telescope, 23, 27, 30, 32
Telescope connector, 65
telescope hand controller, 30, 32, 35, 36
temperature regulation, 30, 39
thermistor, 21
TIC, 65
TIC-78, 36
TIFF format (def), 62
Track and Accumulate (def), 62
Track and Accumulate Command, 32, 45,
49
Track and Accumulate mode, 35, 47
Track Command, 49
track list, 48
Track List (def), 62
track mode, 35
tracking interface cable (TIC), 36, 65
Tracking Parameters Command, 49
Tri-Color (def), 63
tri-color images, 52
T-Thread, 52
vane, 39
vignetting, 22, 31
Vignetting (def), 63
zoom, 30
79
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