Celestron | CG-4 | Instruction manual | Celestron CG-4 Instruction manual

Celestron CG-4 Instruction manual
ENGLISH
Omni XLT Series Telescopes
INSTRUCTION MANUAL
● Omni XLT 102 ● Omni XLT 102ED ● Omni XLT 120
● Omni XLT127 ● Omni XLT 150
● Omni XLT 150R
Table of Contents
INTRODUCTION .......................................................................................................................................................... 4
Warning ...................................................................................................................................................... 4
ASSEMBLY .................................................................................................................................................................... 8
Setting up the Tripod .................................................................................................................................. 8
Attaching the Equatorial Mount ................................................................................................................. 9
Attaching the Center Leg Brace ............................................................................................................... 10
Installing the Counterweight Bar.............................................................................................................. 10
Installing the Counterweights................................................................................................................... 11
Attaching the Slow Motion Control Knobs (Cables)................................................................................ 11
Attaching the Telescope Tube to the Mount............................................................................................. 12
Installing the Finderscope......................................................................................................................... 13
Installing the Visual Back......................................................................................................................... 13
Installing the Star Diagonal ...................................................................................................................... 14
Installing the Eyepieces ............................................................................................................................ 14
Moving the Telescope Manually .............................................................................................................. 15
Balancing the Mount in R.A..................................................................................................................... 15
Balancing the Mount in DEC ................................................................................................................... 16
Adjusting the Mount................................................................................................................................. 16
Adjusting the Mount in Altitude............................................................................................................... 17
Adjusting the Mount in Azimuth.............................................................................................................. 17
TELESCOPE BASICS ................................................................................................................................................. 18
Image Orientation..................................................................................................................................... 20
Focusing ................................................................................................................................................... 20
Aligning the Finderscope ......................................................................................................................... 21
Calculating Magnification ........................................................................................................................ 21
Determining Field of View....................................................................................................................... 22
General Observing Hints .......................................................................................................................... 22
ASTRONOMY BASICS............................................................................................................................................... 23
The Celestial Coordinate System ............................................................................................................. 23
Motion of the Stars ................................................................................................................................... 24
Latitude Scale ........................................................................................................................................... 25
Pointing at Polaris .................................................................................................................................... 25
Finding the North Celestial Pole .............................................................................................................. 26
Polar Alignment in the Southern Hemisphere .......................................................................................... 27
Pointing at Sigma Octantis ....................................................................................................................... 28
Finding the South Celestial Pole (SCP).................................................................................................... 28
Declination Drift Method of Polar Alignment.......................................................................................... 29
Aligning the R.A. Setting Circle .............................................................................................................. 30
Using the R.A. Vernier Scale ................................................................................................................... 31
CELESTIAL OBSERVING......................................................................................................................................... 32
Observing the Moon ................................................................................................................................. 32
Lunar Observing Hints ............................................................................................................................. 32
Observing the Planets ............................................................................................................................... 32
Observing the Sun .................................................................................................................................... 33
Solar Observing Hints .............................................................................................................................. 33
Observing Deep Sky Objects.................................................................................................................... 33
Seeing Conditions..................................................................................................................................... 33
2
Transparency ............................................................................................................................................ 33
Sky Illumination ....................................................................................................................................... 33
Seeing ....................................................................................................................................................... 34
Using the Lens Cap Aperture Stop with Refractor Telescopes ................................................................ 34
ASTROPHOTOGRAPHY ........................................................................................................................................... 35
Piggyback Photography............................................................................................................................ 35
Short Exposure Prime Focus Photography for Refractors & Newtonians................................................ 36
Short Exposure Prime Focus Photography for Schmidt-Cassegrains....................................................... 36
Eyepiece Projection for a Schmidt-Cassegrain......................................................................................... 37
Long Exposure Prime Focus Photography ............................................................................................... 38
Planetary and Lunar Photography with Special Imagers.......................................................................... 39
CCD Imaging for Deep Sky Objects ........................................................................................................ 40
Terrestrial Photography ............................................................................................................................ 40
Metering ................................................................................................................................................... 40
Reducing Vibration .................................................................................................................................. 40
TELESCOPE MAINTENANCE ................................................................................................................................. 41
Care and Cleaning of the Optics............................................................................................................... 41
Collimation of Refractors ......................................................................................................................... 41
Collimation of a Schmidt-Cassegrain....................................................................................................... 42
Collimation of a Newtonian ..................................................................................................................... 44
OPTIONAL ACCESSORIES ...................................................................................................................................... 48
APPENDIX A - TECHNICAL SPECIFICATIONS ...................................................................................................51
APPENDIX B - GLOSSARY OF TERMS.................................................................................................................. 52
SKY MAPS.................................................................................................................................................................... 55
CELESTRON TWO YEAR WARRANTY ................................................................................................................ 61
3
Congratulations on your purchase of an Omni XLT Series telescope. The Omni XLT Series of telescopes come in
several different models: 102mm refractor, 102mm ED refractor, 120mm refractor, 150mm refractor, 150mm
Newtonian, 127mm Schmidt-Cassegrain. The Omni Series is made of the highest quality materials to ensure
stability and durability. All this adds up to a telescope that gives you a lifetime of pleasure with a minimal amount
of maintenance. Furthermore, your Celestron telescope is versatile — it will grow as your interest grows. This
instruction manual covers all the different models of the Omni XLT telescopes.
No matter at what level you are starting out, the Omni XLT Series telescopes will unfold for you and your friends
all the wonders of the Universe.
Some of the many standard features of the Omni XLT include:
•
Hand selected optical glass and hand figured optics resulting in superior images.
•
Premium Celestron Starbright XLT optical coatings that provide maximum contrast and image sharpness.
•
Heavy-duty equatorial mount with a rugged and very stable stainless steel tripod.
•
Ball bearings in both axes of the mount ensure smooth performance.
•
CD-ROM “The Sky” --- astronomy software which provides education about the sky and printable sky maps.
Many other high performance features!
The Omni XLT deluxe features combined with Celestron’s legendary optical systems give amateur astronomers the
most sophisticated and easy to use telescopes available on the market today.
Take time to read through this manual before embarking on your journey through the Universe. It may take a few
observing sessions to become familiar with your telescope, so you should keep this manual handy until you have
fully mastered your telescope’s operation. The manual gives detailed information regarding each step as well as
needed reference material and helpful hints guaranteed to make your observing experience as simple and pleasurable
as possible.
Your telescope is designed to give you years of fun and rewarding observations. However, there are a few things to
consider before using your telescope that will ensure your safety and protect your equipment.
Warning
‰
‰
‰
Never look directly at the sun with the naked eye or with a telescope (unless you have the
proper solar filter). Permanent and irreversible eye damage may result.
Never use your telescope to project an image of the sun onto any surface. Internal heat build-up
can damage the telescope and any accessories attached to it.
Never use an eyepiece solar filter or a Herschel wedge. Internal heat build-up inside the telescope
can cause these devices to crack or break, allowing unfiltered sunlight to pass through to the eye.
Never leave the telescope unsupervised, either when children are present or adults who may not be
familiar with the correct operating procedures of your telescope.
-4-
1
12
2
3
11
4
5
10
6
9
7
8
Figure 1-1 Omni XLT 102 Refractor
(Omni XLT 102ED, Omni XLT 120 and Omni XLT 150R refractors are similar)
1.
2.
3.
4.
5.
6.
Optical Tube
Tube Rings
Finderscope
Eyepiece
Equatorial Mount
Latitude Adjustment Screw
7.
8.
9.
10.
11.
12.
-5-
1.75" Steel Tripod
Accessory Tray/ Leg Brace
Counterweights
Counterweight Bar
Dovetail Slide Bar
Objective Lens Shade
1
2
3
4
12
5
11
6
10
7
9
8
Figure 1-2 Omni XLT 150 Newtonian
1.
2.
3.
4.
5.
6.
Finderscope
Finderscope Bracket
Focuser
Eyepiece
Tube Rings
Equatorial Mount
7.
8.
9.
10.
11.
12.
-6-
1.75" Steel Tripod
Accessory Tray/ Leg Brace
Counterweights
Counterweight Bar
Dovetail Slide Bar
Optical Tube
1
12
2
11
3
10
4
9
5
8
6
7
Figure 1-3 Omni XLT 127 Schmidt-Cassegrain
1.
2.
3.
4.
5.
6.
Optical Tube
Finderscope
Finderscope Bracket
Equatorial Mount
Latitude Scale
Accessory Tray/ Leg Brace
7.
8.
9.
10.
11.
12.
-7-
1.75" Steel Tripod
Counterweights
Counterweight Bar
Declination Setting Circle
Dovetail Slide Bar
Schmidt Corrector Lens
This section covers the assembly instructions for your Celestron Omni XLT telescope. The equatorial mount is
exactly the same for all the Omni telescope models and the optical tubes have some differences which will be noted.
Your Omni telescope should be set up indoor the first time so that it is easy to identify the various parts and
familiarize you with the correct assembly procedure before attempting it outdoor.
Each Omni telescope comes in two boxes. One box contains the tripod, tripod accessory tray/brace, equatorial
mount, counterweight bar, two counterweights, R.A. knob, Dec knob, polar axis polar cap, and a Phillips head
screwdriver. The second box contains the telescope optical tube assembly, finderscope and bracket, eyepiece, and
other standard accessory items per the specific model that you have.
Setting up the Tripod
Remove the tripod from the box that it is in (Figure 2-1). The Omni tripod comes with an all metal center leg
brace/accessory tray to give rock solid support to the mount. The tripod comes fully assembled with a metal plate,
called the tripod head that holds the legs together at the top. In addition, there is a central rod that extends down
from the tripod head that attaches the equatorial mount to the tripod. To set up the tripod:
1.
Stand the tripod upright and pull the tripod legs apart until each leg is fully extended. The tripod will now stand
by itself (Figure 2-2). Once the tripod is set up, you can adjust the height at which it stands.
2.
Loosen the lever (turn counterclockwise) on the leg clamp so that the tripod leg can be adjusted (Figure 2-3).
3.
Slide the center portion of the tripod leg away from the tripod head until it is at the desired height.
4.
Tighten the levers (turn clockwise) on each leg clamp to hold the legs in place.
5.
The standard height of the tripod is 33” and it can be extended at any height up to a maximum of 47”.
Remember that the tripod will be the most rigid and stable at the lowest height.
Figure 2-1
Figure 2-2
-8-
Figure 2-3
Attaching the Equatorial Mount
The equatorial mount allows you to tilt the telescope’s axis of rotation so that you can track the stars as they move
across the sky. The Omni mount is a German equatorial mount that attaches to the tripod head. On one side of the
tripod head there is a metal alignment peg for aligning the mount. This side of the tripod will face north when
setting up for an astronomical observing session. To attach the equatorial head:
1.
Locate the azimuth adjustment screws on the equatorial mount (see Figure 2-4).
2.
Retract the screws so they no longer extend into the azimuth housing on the mount. DO NOT remove the
screws since they are needed later for polar alignment.
3.
Hold the equatorial mount over the tripod head so that the azimuth housing is above the metal peg.
4.
Place the equatorial mount on the tripod head so that the two are flush. You can rotate the mount slightly to the
center position (where the front latitude adjustment screw is directly over the “N” on the tripod). Then tighten
the azimuth adjustment screws.
5.
Tighten the mounting knob (attached to the central rod) on the underside of the tripod head to hold the
equatorial mount firmly in place.
Tripod
Head
Alignment
Peg
Equatorial
Mount
Mounting
Knob
Figure 2-5
Azimuth Adjustment
Screws
Figure 2-4
-9-
Attaching the Center Leg Brace
Tripod
Mounting Knob
Central Rod
Accessory Tray
Accessory Tray Knob
Figure 2-6
1.
Remove the accessory tray knob and washer from the central rod.
2.
Slide the accessory tray over the central rod so that each arm of the tray is pushing against the inside of the
tripod legs.
3.
Thread the accessory tray knob onto the central rod and tighten.
Installing the Counterweight Bar
To properly balance the telescope, the mount comes with a counterweight bar and two counterweights. To install
the counterweight bar:
1.
Remove the counterweight safety screw from the counterweight bar (opposite of the threaded end).
2.
Thread the counterweight bar through the counterweight bar locking nut.
3.
Locate the opening in the equatorial mount on the DEC axis.
4.
Thread the counterweight bar into the opening until tight.
5.
Tighten the counterweight bar lock nut fully for added support (see fig 2-7).
Once the bar is securely in place you are ready to attach the counterweights.
Counterweight Bar
Locking Nut
Counterweights
Counterweight Locking
Screw
Counterweight
Bar
Safety Screw
Figure 2-7
- 10 -
Since the fully assembled telescope can be quite heavy, position the mount so that the polar axis is pointing
towards north before the tube assembly and counterweights are attached. This will make the polar
alignment procedure much easier.
Installing the Counterweights
Each Omni mount comes with two counterweights (One weighs 7 lbs./3.2kg and the other weighs 4 lbs./1.8kg). To
install the counterweights:
1.
Orient the mount so that the counterweight bar points toward the ground.
2.
Loosen the locking screw on the side of the counterweights (it doesn’t matter which counterweight you attach
first) so that the threads do not protrude through the center hole of the counterweight.
3.
Slide the counterweight onto the shaft (see Figure 2-7).
4.
Tighten the locking screw on the side of the weight to hold the counterweight in place.
5.
Slide the second counterweight onto the shaft and tighten as in # 4.
6.
Replace the counterweight safety screw.
Attaching the Slow Motion Control Knobs (Cables)
The Omni mount comes with two slow motion control knobs (cables) that allows you to make fine pointing
adjustments to the telescope in both R.A. and Declination. To install the knobs:
1.
Locate the two knobs (one is longer than the other
and is for the R.A. axis). Make sure the screw on
each knob does not protrude through the knob shaft
opening.
Use the supplied Phillips head
screwdriver.
2.
Line up the flat area on the inner portion of the
R.A. slow motion knob with the flat area on the
R.A. shaft.
3.
Slide the R.A. slow motion knob onto the R.A.
Declination Shaft
R.A. Shaft
shaft. There are two R.A. shafts, one on either side
of the mount. It makes no difference which shaft
you use since both work the same.
Use
whichever one you find more convenient. If
after a few observing sessions you find the R.A.
slow motion knob is more accessible from the
Declination Knob
other side, reinstall it on the opposite side.
4.
Figure 2-8a
Tighten the screw on the R.A. knob to hold it
securely in place.
R.A. Knob
Figure 2-8b
- 11 -
5.
The DEC slow motion knob attaches in the same manner as the R.A. knob. The shaft that the DEC slow
motion knob fits over is toward the top of the mount, just below the telescope mounting platform. Once again,
you have two shafts to choose from. Use the shaft that is pointing toward the ground. This makes it easy to
reach while looking through the telescope, something which is quite important when you are observing but
again if it is more convenient for you to use, then reinstall the knob position that suits your needs.
6.
Put the polar axis cap over the polar axis. It is held into place by a tension fit.
Attaching the Telescope Tube to the Mount
The telescope optical tube attaches to the mount via a dovetail slide bar mounting bracket. For the refractors and the
Newtonian, the mounting bracket is the long bracket which is attached to the tube rings. For the SchmidtCassegrain the mounting bracket is attached along the bottom of the telescope tube. Before you attach the optical
tube, make sure that the declination and right ascension clutch knobs (clamps) are tight. This will ensure that
the mount does not move suddenly while attaching the telescope optical tube. To mount the telescope tube:
1.
2.
3.
Remove the protective paper covering the optical
tube. You will have to remove the tube rings on the
refractors and Newtonian before removing the paper.
Loosen the mounting knob and the mounting safety
screw on the side of the mount platform so they do
not protrude into the mounting platform
Tube Rings
Mounting Bracket
Slide the dovetail mounting bracket into the recess on
the top of the mounting platform (see figure 2-9).
Mounting
Platform
4.
Tighten the mounting knob on the Omni mounting
platform to hold the telescope in place.
Telescope
Mounting
Screw
5.
Hand tighten the mounting platform safety screw
until the tip touches the side of the mounting bracket.
Figure 2-9
Refractor Optical Tube is shown. The Newtonian and
Schmidt-Cassegrain attach similarly.
NOTE: Never loosen any of the knobs on the telescope tube or mount other than the R.A. and DEC knobs.
- 12 -
Installing the Finderscope
To install the finderscope onto the telescope you must first mount the finderscope through the finder bracket and
then attach it to the telescope. Toward the rear of the telescope tube (on refractors and Schmidt-Cassegrain) and
front of the telescope tube (Newtonian), there is a small bracket with a set screw in it. This is where the finderscope
bracket will be mounted. To install the finderscope:
1.
2.
3.
Loosen the finderscope adjustment screws so
they don’t protrude into the bracket. Then
slide the rubber O-ring over the eyepiece end
of the finderscope (smallest diameter side) and
roll it 2/3 of the way up into the slot (groove)
in the finderscope.
Insert the eyepiece end of the finderscope
through the narrow part of the bracket until the
O-ring presses tightly between the finder and
the inside of the bracket. Once it stops, then
pull outward on the spring loaded adjustment
screw and continue inserting the finderscope
until it is approximately centered in the
bracket.
Finderscope
Mounting
Bracket
Finder
Bracket
Tighten the two adjustment screws until they
make contact with the finderscope body.
Set
Screw
Figure 2-10
4.
Locate the mounting bracket near the front (open) end of the telescope.
5.
Loosen the set screw on the mounting bracket on the telescope so it
does not protrude into the bracket.
6.
Slide the finder bracket (attached to the finderscope) into the mounting bracket on the telescope.
7.
The finderscope bracket will slide in from the back. The finderscope should be oriented so that the
objective lens is toward the front (open) end of the telescope.
8.
Tighten the set screw on the mounting bracket to hold the finderscope in place.
For information on aligning your finderscope, see the Telescope Basics section of this manual.
Installing the Visual Back
Only applicable to the Schmidt-Cassegrain, the Visual Back is the accessory that allows you to attach all visual
accessories to the telescope. The Omni Schmidt-Cassegrain normally comes with the Visual Back installed. If in
case it is not installed, follow these instructions for attaching it:
1.
Remove the cover on the rear cell and then place the knurled slip ring on the Visual Back over the threads
on the rear cell (Fig 2-11).
2.
Hold the Visual Back with the set screw in a convenient position and rotate the knurled slip ring clockwise
until tight. Once this is done, you are ready to attach other accessories, such as diagonals (for refractors
and the Schmidt-Cassegrain), eyepieces, etc. If you want to remove the Visual Back, rotate the slip ring
counterclockwise until it is free of the rear cell.
- 13 -
Installing the Star Diagonal
The Star Diagonal is a prism that diverts the light at a right angle to the light path of refractors and SchmidtCassegrain telescopes. This allows you to observe in positions that are
physically more comfortable than if you looked straight through. To
Eyepiece
attach the Star Diagonal onto the optical tube of a Schmidt-Cassegrain:
1.
Turn the set screw on the visual back until its tip no longer extends
into (i.e., obstructs) the inner diameter of the visual back.
2.
Slide the chrome portion of the Star Diagonal into the visual back.
3.
Tighten the set screw on the visual back to hold the Star Diagonal
in place.
If you wish to change the orientation of the Star Diagonal, loosen the
set screw on the visual back until the Star Diagonal rotates freely.
Rotate the diagonal to the desired position and tighten the set screw.
Star
Diagonal
Visual Back
Figure 2-11
Refractors – To use the Star Diagonal with refractor telescopes, insert it into the 1 ¼” eyepiece adapter.
Installing the Eyepieces
The eyepiece, or ocular as it is also called, is an optical element that magnifies the image focused by the telescope.
Without the eyepiece it would be impossible to use the telescope visually. The eyepiece fits directly into the focuser
of refractors and the Newtonian or into the visual back on the Schmidt-Cassegrain. To attach an ocular:
1.
Loosen the set screw on the eyepiece
adapter so that it does not obstruct the
inner diameter of the barrel.
2.
Slide the chrome portion of the eyepiece
into the focuser.
3.
Tighten the set screw to hold the eyepiece
in place.
To remove the eyepiece, loosen the set screw
on the focuser and slide the eyepiece out. You
can replace it with another ocular.
Focuser Tension
Screw
1 ¼" Eyepiece
Adapter
T-Adapter
Thread
2" Focuser
Barrel
Focuser Knob
Figure 2-12
Many times it will be more comfortable to use a star diagonal on the refractors and Schmidt-Cassegrain for most
areas of the sky. To install an eyepiece into the star diagonal:
A.
B.
C.
D.
Loosen the set screw on the star diagonal until the tip no longer extends into the inner diameter of
the eyepiece end of the diagonal.
Slide the chrome portion of the eyepiece into the star diagonal.
Tighten the set screw on the star diagonal to hold the eyepiece in place.
To remove the eyepiece, loosen the set screw on the star diagonal and slide the eyepiece out. You
can replace it with other optional eyepieces.
- 14 -
The refracting telescopes can use eyepieces and diagonals of a 2” barrel diameter. To use a 2” barrel eyepiece, the
1¼” eyepiece adapter must first be removed. To do this, simply loosen the two chrome thumbscrews located around
the focuser barrel (see figure 2-12) and remove the 1 ¼” adapter. Once removed, a 2” eyepiece or accessory can be
inserted directly into the focuser barrel and secured with the two thumb screws.
Eyepieces are commonly referred to by focal length and barrel diameter. The focal length of each eyepiece is
printed on the eyepiece barrel. The longer the focal length (i.e., the larger the number) the lower the eyepiece
magnification (i.e., power) and the shorter the focal length (i.e., the smaller the number) the higher the
magnification. Generally, you will use low-to-moderate power when viewing. For more information on how to
determine power, see the section on “Calculating Magnification.”
Moving the Telescope Manually
In order to properly balance your telescope, you will need to move your telescope manually at various portions of
the sky to observe different objects. To make rough adjustments, loosen the R.A. and DEC clutch knobs slightly
and move the telescope in the desired direction.
Both the R.A. and DEC axis have lock levers to clutch down each axis of the telescope. To loosen the clutches on
the telescope, rotate the lock levers counterclockwise.
Balancing the Mount in R.A.
To eliminate undue stress on the mount, the telescope should be properly balanced around the polar axis in R.A. In
addition, proper balancing is crucial for accurate tracking if using an optional motor drive. To balance the mount:
1.
Release the R.A. Clamp (see figure 2-13) and position the telescope off to one side of the mount (make sure
that the mounting bracket screw is tight). The counterweight bar will extend horizontally on the opposite side
of the mount (see figure 2-14).
2.
Release the telescope — GRADUALLY — to see which way the telescope “rolls.”
3.
Loosen the counterweight locking screw on the counterweight.
4.
Move the counterweights to a point where they balance the telescope (i.e., it remains stationary when the R.A.
clamp is released).
5.
Tighten the locking screw to hold the counterweights in place.
These are general balance instructions and will reduce undue stress on the mount. When taking
astrophotographs, this balance process should be done for the specific area at which the telescope is
pointing.
DEC Clamp
R.A. Clamp
Figure 2-13
- 15 -
Balancing the Mount in DEC
The telescope should also be balanced on the declination axis to prevent any sudden motions when the DEC clamp
(Fig 2-13) is released. To balance the telescope in DEC (all telescopes except the SCT):
1.
Release the R.A. clamp and rotate the telescope so that it is on one side of the mount (i.e., as described in the
previous section on balancing the telescope in R.A.).
2.
Lock the R.A. clamp to hold the telescope in place.
3.
Release the DEC clamp and rotate the telescope until the tube is parallel to the ground (see figure 2-15).
4.
Release the tube — GRADUALLY — to see which way it rotates around the declination axis. DO NOT LET
GO OF THE TELESCOPE TUBE COMPLETELY!
5.
Loosen the screws that hold the telescope tube inside the mounting rings and slide the telescope either forwards
or backwards until it remains stationary when the DEC clamp is released.
6.
Tighten the tube ring screws firmly to hold the telescope in place.
Note:
The Omni XLT150R is the most difficult to balance depending on the latitude, the accessories used, and
which part of the sky the telescope is pointing to. Balance this telescope as best you can.
Figure 2-14
Figure 2-15
Like the R.A. balance, these are general balance instructions and will reduce undue stress on the mount. When
taking astrophotographs, this balance process should be done for the specific area at which the telescope is pointing.
Adjusting the Mount
In order for a motor drive to track accurately, the telescope’s axis of rotation must be parallel to the Earth’s axis of
rotation, a process known as polar alignment. Polar alignment is achieved NOT by moving the telescope in R.A. or
DEC but by adjusting the mount vertically, which is called altitude, and horizontally, which is called azimuth. This
section simply covers the correct movement of the telescope during the polar alignment process. The actual process
of polar alignment is making the telescope’s axis of rotation parallel to the Earth’s, is described later in this manual
in the section on “Polar Alignment.”
- 16 -
Adjusting the Mount in Altitude
•
To increase the latitude of the polar axis, tighten the rear latitude adjustment screw and loosen the front screw
(if necessary).
•
To decrease the latitude of the polar axis, tighten the front (under the counterweight bar) latitude adjustment
screw and loosen the rear screw (if necessary).
The latitude adjustment on the Omni mount has a range from approximately 20° to 60°.
It is best to always make final adjustments in altitude by moving the mount against gravity (i.e. using the rear
latitude adjustment screw to raise the mount). To do this you should loosen both latitude adjustment screws and
manually push the front of the mount down as far as it will go. Then tighten the rear adjustment screw to raise the
mount to the desired latitude.
Front Latitude
Adjustment Screw
Rear Latitude Adjustment
Screw
Azimuth
Adjustment Screw
Figure 2-16
Adjusting the Mount in Azimuth
For rough adjustments in azimuth, simply pick up the telescope and tripod and move it. For fine adjustments in
azimuth:
•
Turn the azimuth adjustment knobs located on either side of the azimuth housing (see Fig 2-16). While
standing behind the telescope, the knobs are on the front of the mount.
•
Turning the right adjustment knob clockwise moves the mount toward the right.
•
Turning the left adjustment knob clockwise moves the mount to the left.
Both screws push off of the peg on the tripod head, which means you may have to loosen one screw while
tightening the other. The screw that holds the equatorial mount to the tripod may have to be loosened slightly.
Keep in mind that adjusting the mount is done during the polar alignment process only. Once polar aligned, the
mount must NOT be moved. Pointing the telescope is done by moving the mount in right ascension and
declination, as described earlier in this manual.
- 17 -
A telescope is an instrument that collects and focuses light. The nature of the optical design determines how the
light is focused. Some telescopes (known as refractors) use lenses and other telescopes, known as reflectors
(Newtonians), use mirrors. Then, the Schmidt-Cassegrain telescope uses both mirrors and lenses. Each optical
design is briefly discussed below:
Developed in the early 1600s, the refractor is the oldest telescope design. It derives its name from the method it
uses to focus incoming light rays. The refractor uses a lens to bend or refract incoming light rays, hence the name
(see Figure 3-1). Early designs used single element lenses. However, the single lens acts like a prism and breaks
light down into the colors of the rainbow, a phenomenon known as chromatic aberration. To get around this
problem, a two-element lens, known as an achromat, was introduced. Each element has a different index of
refraction allowing two different wavelengths of light to be focused at the same point. Most two-element lenses,
usually made of crown and flint glasses, are corrected for red and green light. Blue light may still be focused at a
slightly different point.
Figure 3-1
A cutaway view of the light path of the Refractor optical design
A Newtonian reflector uses a single concave mirror as its primary mirror. Light enters the tube traveling to the
mirror at the back end. There light is bent forward in the tube to a single point, its focal point. Since putting your
head in front of the telescope to look at the image with an eyepiece would keep the reflector from working, a flat
mirror called a diagonal intercepts the light and points it out the side of the tube at right angles to the tube. The
eyepiece is placed there for easy viewing.
Newtonian Reflector telescopes replace heavy lenses with mirrors to collect and focus the light, providing much
more light-gathering power for the dollar. Because the light path is intercepted and reflected out to the side, you can
have focal lengths up to 1000mm and still enjoy a telescope that is relatively compact and portable. A Newtonian
Reflector telescope offers such impressive light-gathering characteristics you can take a serious interest in deep
space astronomy even on a modest budget. Newtonian Reflector telescopes do require more care and maintenance
because the primary mirror is exposed to air and dust. However, this small drawback does not hamper this type of
telescope’s popularity with those who want an economical telescope that can still resolve faint, distant objects.
- 18 -
Figure 3-2
A cutaway view of the light path of the Newtonian optical design
The Schmidt-Cassegrain optical system (Schmidt-Cass or SCT for short) uses a combination of mirrors and lenses
and s referred to as a compound or catadioptric telescope. This unique design offers large-diameter optics while
maintaining very short tube lengths, making them extremely portable. The Schmidt-Cassegrain system consists of a
zero power corrector plate, a spherical primary mirror, and a secondary mirror. Once light rays enter the optical
system, they travel the length of the optical tube three times.
Inside the optical tube, a black tube extends out from the center hole in the primary mirror. This is the primary
baffle tube and it prevents stray light from passing through to the eyepiece or camera.
Figure 3-3
A cutaway view of the light path of the Schmidt-Cassegrain optical design
- 19 -
Image Orientation
The image orientation changes depending on how the eyepiece is inserted into the telescope. When using the star
diagonal with refractors and Schmidt-Cassegrains, the image is right-side-up, but reversed from left-to-right (i.e.,
mirror image). If inserting the eyepiece directly into the focuser of a refractor or the visual back of the SchmidtCassegrain (i.e., without the star diagonal), the image is upside-down and reversed from left-to-right (i.e., inverted).
Newtonian reflectors produce a right-side-up image but the image will appear rotated based on the location of the
eyepiece holder in relation to the ground. Newtonian reflectors are best for astronomical use where right-side-up
does not matter.
Actual image orientation as seen
with the unaided eye
Reversed from left to right, as
viewed using a Star Diagonal on a
refractor or Schmidt-Cassegrain
Inverted image, normal with
Newtonians and as viewed with
eyepiece directly in other scopes
Figure 3-4
Focusing
To focus your refractor or Newtonian telescope, simply turn the focus knob located directly below the eyepiece
holder. Turning the knob clockwise allows you to focus on an object that is farther than the one you are currently
observing. Turning the knob counterclockwise from you allows you to focus on an object closer than the one you
are currently observing.
The Schmidt-Cassegrain focusing mechanism controls the primary mirror which is
mounted on a ring that slides back and forth on the primary baffle tube. The
focusing knob, which moves the primary mirror, is on the rear cell of the telescope
just below the star diagonal and eyepiece. Turn the focusing knob until the image
is sharp. If the knob will not turn, it has reached the end of its travel on the
focusing mechanism. Turn the knob in the opposite direction until the image is
sharp. Once an image is in focus, turn the knob clockwise to focus on a closer
object and counterclockwise for a more distant object. A single turn of the
focusing knob moves the primary mirror only slightly. Therefore, it will take many
turns (about 30) to go from close (near) focus to infinity.
For astronomical viewing, out of focus star images are very diffuse, making them
difficult to see. If you turn the focus knob too quickly, you can go right through
focus without seeing the image. To avoid this problem, your first astronomical
target should be a bright object (like the Moon or a planet) so that the image is
visible even when out of focus. Critical focusing is best accomplished when the
focusing knob is turned in such a manner that the mirror moves against the pull of
gravity. In doing so, any mirror shift is minimized. For astronomical observing,
both visually and photographically, this is done by turning the focus knob
counterclockwise.
Figure 3-5
The emblem on the end of the
focus knob shows the correct
rotational direction for
focusing your telescope.
Note: If you wear corrective lenses (specifically glasses), you may want to remove them when observing with an
eyepiece attached to the telescope. However, when using a camera you should always wear corrective lenses to
ensure the sharpest possible focus. If you have astigmatism, corrective lenses must be worn at all times.
- 20 -
Aligning the Finderscope
Accurate alignment of the finder makes it easy to find objects with the telescope, especially celestial objects. To
make aligning the finder as easy as possible, this procedure should be done in the daytime when it is easy to find
and identify objects. The finderscope has a spring-loaded adjustment screw that puts pressure on the finderscope
while the remaining screws are used to adjust the finder horizontally and vertically. To align the finder:
1
Choose a target that is in excess of one mile away. This eliminates any possible parallax effect between the
telescope and finder.
2
Release the R.A. and DEC clamps and point the telescope at your target.
3
Center your target in the main optics of the telescope. You may have to move the telescope slightly to center it.
4
Adjust the screw on the finder bracket that is on the right (when looking through the finder) until the cross hairs
are centered horizontally on the target seen through the telescope.
5
Adjust the screw on the top of the finder bracket until the cross hairs are centered vertically on the target seen
through the telescope.
Image orientation through the finder is inverted (i.e., upside down and backwards left-to-right). This is normal for
most astronomical finderscopes. Because of this, it may take a few minutes to familiarize yourself with the
directional change each screw makes on the finder.
Calculating Magnification
You can change the power of your telescope just by changing the eyepiece (ocular). To determine the
magnification of your telescope, simply divide the focal length of the telescope by the focal length of the eyepiece
used. In equation format, the formula looks like this:
Magnification =
Focal Length of Telescope (mm)
⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯
Focal Length of Eyepiece (mm)
Let’s say, for example, you are using the 25mm eyepiece that came with your telescope. To determine the
magnification you simply divide the focal length of your telescope (the Omni XLT 102 for this example has a focal
length of 1000mm) by the focal length of the eyepiece, 25mm. Dividing 1000 by 25 yields a magnification of 40
power.
Although the power is variable, each instrument under average skies has a limit to the highest useful magnification.
The general rule is that 60 power can be used for every inch of aperture. For example, the Omni XLT 102 is 4
inches in diameter. Multiplying 4 by 60 gives a maximum useful magnification of 240 power. Although this is the
maximum useful magnification, most observing is done in the range of 20 to 35 power for every inch of aperture
which is 80 to 140 times for the Omni XLT 102 telescope. You can determine the magnification for your telescope
the same way.
- 21 -
Determining Field of View
Determining the field of view is important if you want to get an idea of the angular size of the object you are
observing. To calculate the actual field of view, divide the apparent field of the eyepiece (supplied by the eyepiece
manufacturer) by the magnification. In equation format, the formula looks like this:
True (Actual) Field of View =
Apparent Field of Eyepiece
⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯
Magnification
As you can see, before determining the field of view, you must calculate the magnification. Using the example in
the previous section, we can determine the field of view using the same 25mm eyepiece that is supplied standard
with all Omni XLT telescopes. The 25mm eyepiece has an apparent field of view of 50°. Divide the 50° by the
magnification, which is 40 power. This yields an actual field of 1.25°.
To convert degrees to feet at 1,000 yards (which is more useful for terrestrial observing) simply multiply by 52.5.
Continuing with our example, multiply the angular field of 1.25° by 52.5 and this produces a linear field width of
65.6 feet at a distance of one thousand yards. The apparent field of each eyepiece that Celestron manufactures is
found in the Celestron Accessory Catalog (# 93685).
General Observing Hints
When working with any optical instrument, there are a few things to remember to ensure you get the best possible
image.
•
Never look through window glass. Glass found in household windows is optically imperfect, and as a result,
may vary in thickness from one part of a window to the next. This inconsistency can and will affect the ability
to focus your telescope. In most cases you will not be able to achieve a truly sharp image, while in some cases,
you may actually see a double image.
•
Never look across or over objects that are producing heat waves. This includes asphalt parking lots on hot
summer days or building rooftops.
•
Hazy skies, fog, and mist can also make it difficult to focus when viewing terrestrially. The amount of detail
seen under these conditions is greatly reduced. Also, when photographing under these conditions, the
processed film may come out a little grainier than normal with lower contrast and underexposed.
•
If you wear corrective lenses (specifically glasses), you may want to remove them when observing with an
eyepiece attached to the telescope. When using a camera, however, you should always wear corrective lenses
to ensure the sharpest possible focus. If you have astigmatism, corrective lenses must be worn at all times.
- 22 -
Up to this point, this manual covered the assembly and basic operation of your telescope. However, to
understand your telescope more thoroughly, you need to know a little about the night sky. This section deals
with observational astronomy in general and includes information on the night sky and polar alignment.
The Celestial Coordinate System
To help find objects in the sky, astronomers use a celestial coordinate system that is similar to our
geographical co-ordinate system here on Earth. The celestial coordinate system has poles, lines of longitude
and latitude, and an equator. For the most part, these remain fixed against the background stars.
The celestial equator runs 360 degrees around the Earth and separates the northern celestial hemisphere from
the southern. Like the Earth's equator, it bears a reading of zero degrees. On Earth this would be latitude.
However, in the sky this is referred to as declination, or DEC for short. Lines of declination are named for
their angular distance above and below the celestial equator. The lines are broken down into degrees, minutes
of arc, and seconds of arc. Declination readings south of the equator carry a minus sign (-) in front of the
coordinate and those north of the celestial equator are either blank (i.e., no designation) or preceded by a plus
sign (+).
The celestial equivalent of longitude is called Right Ascension (or R.A. for short). Like the Earth's lines of
longitude, they run from pole to pole and are evenly spaced 15 degrees apart. Although the longitude lines
are separated by an angular distance, they are also a measure of time. Each line of longitude is one hour apart
from the next. Since the Earth rotates once every 24 hours, there are 24 lines total. As a result, the R.A.
coordinates are marked off in units of time. It begins with an arbitrary point in the constellation of Pisces
designated as 0 hours, 0 minutes, 0 seconds. All other points are designated by how far (i.e., how long) they
lag behind this coordinate after it passes overhead moving toward the west.
Figure 4-1
The celestial sphere seen from the outside showing R.A. and DEC
23
Motion of the Stars
The daily motion of the Sun across the sky is familiar to even the most casual observer. This daily trek is not
the Sun moving as early astronomers thought, but the result of the Earth's rotation. The Earth's rotation also
causes the stars to do the same, scribing out a large circle as the Earth completes one rotation. The size of the
circular path a star follows depends on where it is in the sky. Stars near the celestial equator form the largest
circles rising in the east and setting in the west. Moving toward the north celestial pole, the point around
which the stars in the northern hemisphere appear to rotate, these circles become smaller. Stars in the midcelestial latitudes rise in the northeast and set in the northwest. Stars at high celestial latitudes are always
above the horizon, and are said to be circumpolar because they never rise and never set. You will never see
the stars complete one circle because the sunlight during the day washes out the starlight. However, part of
this circular motion of stars in this region of the sky can be seen by setting up a camera on a tripod and
opening the shutter for a couple hours. The image will reveal semicircles that revolve around the pole. (This
description of stellar motions also applies to the southern hemisphere except all stars south of the celestial
equator move around the south celestial pole.)
Starts seen near the north celestial
pole
Starts seen near the celestial
equator
Starts seen looking in the opposite
direction of the north celestial pole
Figure 4-2
All stars appear to rotate around the celestial poles. However, the appearance of
this motion varies depending on where you are looking in the sky. Near the north
celestial pole the stars scribe out recognizable circles centered on the pole (1).
Stars near the celestial equator also follow circular paths around the pole. But, the
complete path is interrupted by the horizon. These appear to rise in the east and
set in the west (2). Looking toward the opposite pole, stars curve or arc in the
opposite direction scribing a circle around the opposite pole (3).
24
Latitude Scale
The easiest way to polar align a telescope is with a latitude scale. Unlike other methods that require you to find the
celestial pole by identifying certain stars near it, this method works off of a known constant to determine how high the
polar axis should be pointed. The Omni CG-4 mount can be adjusted from about 20 to 60 degrees (see figure 4-3).
The constant, mentioned above, is a relationship between your latitude
and the angular distance the celestial pole is above the northern (or
southern) horizon. The angular distance from the northern horizon to the
north celestial pole is always equal to your latitude. To illustrate this,
imagine that you are standing on the North Pole, latitude +90°. The
north celestial pole, which has a declination of +90°, would be directly
overhead (i.e., 90 above the horizon). Now, let’s say that you move one
degree south — your latitude is now +89° and the celestial pole is no
longer directly overhead. It has moved one degree closer toward the
northern horizon. This means the pole is now 89° above the northern
horizon. If you move one degree further south, the same thing happens
again. You would have to travel 70 miles north or south to change your
latitude by one degree. As you can see from this example, the distance
from the northern horizon to the celestial pole is always equal to your
latitude.
Figure 4-3
If you are observing from Los Angeles, which is at latitude 34°, then the celestial pole is 34° above the northern
horizon. All a latitude scale does then is to point the polar axis of the telescope at the right elevation above the
northern (or southern) horizon. To align your telescope:
1.
Make sure the polar axis of the mount is pointing due north. Use a landmark that you know faces north.
2.
Level the tripod. There is a bubble level built into the mount for this purpose.
NOTE: Leveling the tripod is only necessary if using this method of polar alignment. Perfect polar alignment is still
possible using other methods described later in this manual without leveling the tripod.
3.
Adjust the mount in altitude until the latitude indicator points to your latitude. Moving the mount affects the angle
the polar axis is pointing. For specific information on adjusting the equatorial mount, please see the section
“Adjusting the Mount.”
This method can be done in daylight, thus eliminating the need to fumble around in the dark. Although this method
does NOT put you directly on the pole, it will limit the number of corrections you will make when tracking an object.
It will also be accurate enough for short exposure prime focus planetary photography (a couple of seconds) and short
exposure piggyback astrophotography (a couple of minutes).
Pointing at Polaris
This method utilizes Polaris as a guidepost to the celestial pole. Since Polaris is less than a degree from the celestial
pole, you can simply point the polar axis of your telescope at Polaris (see Figure 4-4). Although this is by no means
perfect alignment, it does get you within one degree. Unlike the previous method, this must be done in the dark when
Polaris is visible.
1.
Set the telescope up so that the polar axis is pointing north.
2.
Loosen the DEC clutch knob and move the telescope so that the tube is parallel to the polar axis. When this is
done, the declination setting circle will read +90°. If the declination setting circle is not aligned, move the
telescope so that the tube is parallel to the polar axis.
3.
Adjust the mount in altitude and/or azimuth until Polaris is in the field of view of the finder.
4.
Center Polaris in the field of the telescope using the fine adjustment controls on the mount.
25
Figure 4-4
Remember, while Polar aligning, DO NOT move the telescope in R.A. or DEC. You do not want to
move the telescope itself, but the polar axis. The telescope is used simply to see where the polar axis is
pointing.
Like the previous method, this gets you close to the pole but not directly on it. The following methods help
improve your accuracy for more serious observations and photography.
Finding the North Celestial Pole
In each hemisphere, there is a point in the sky around which all the other stars appear to rotate. These points
are called the celestial poles and are named for the hemisphere in which they reside. For example, in the
northern hemisphere all stars move around the north celestial pole. When the telescope's polar axis is pointed
at the celestial pole, it is parallel to the Earth's rotational axis.
Many methods of polar alignment require that you know how to find the
celestial pole by identifying stars in the area. For those in the northern
hemisphere, finding the celestial pole is not too difficult. Fortunately, we
have a naked eye star less than a degree away. This star, Polaris, is the
end star in the handle of the Little Dipper. Since the Little Dipper
(technically called Ursa Minor) is not one of the brightest constellations in
the sky, it may be difficult to locate from urban areas. If this is the case,
use the two end stars in the bowl of the Big Dipper (the pointer stars).
Draw an imaginary line through them toward the Little Dipper. They
point to Polaris (see Figure 4-6). The position of the Big Dipper (Ursa
Major) changes during the year and throughout the course of the night (see
Figure 4-5). When the Big Dipper is low in the sky (i.e., near the
horizon), it may be difficult to locate. During these times, look for
Cassiopeia (see Figure 4-6). Observers in the southern hemisphere are not
as fortunate as those in the northern hemisphere. The stars around the
south celestial pole are not nearly as bright as those around the north. The
closest star that is relatively bright is Sigma Octantis. This star is just
within naked eye limit (magnitude 5.5) and lies about 59 arc minutes from
the pole.
Spring
Polaris
(North Star)
Winter
Summer
Fall
Figure 4-5
The position of the Big
Dipper changes throughout
the year and the night.
Definition
The north celestial pole is the point in the northern hemisphere around which all stars appear to rotate. The
counterpart in the southern hemisphere is referred to as the south celestial pole.
26
Big Dipper
Litle Dipper
Cassiopela
N.C.P.
Polaris
(North Star)
Pointer Stars
Figure 4-6
The two stars in the front of the bowl of the Big Dipper point to Polaris which
is less than one degree from the true (north) celestial pole. Cassiopeia, the
“W” shaped constellation, is on the opposite side of the pole from the Big
Dipper. The North Celestial Pole (N.C.P.) is marked by the “+” sign.
Polar Alignment in the Southern Hemisphere
Polar alignment to the South Celestial Pole (SCP) is a little more challenging due to the fact that there is no very
bright star close to it like Polaris is in the NCP. There are various ways to polar align your telescope and for casual
observing the methods below are adequate and will get you reasonably close to the SCP.
Polar Alignment with the Latitude Scale
The easiest way to polar align a telescope is with a latitude scale (Figure 4-7).
Unlike other methods that require you to find the celestial pole by identifying
certain stars near it, this method works off of a known constant to determine how
high the polar axis should be pointed.
The constant, mentioned above, is a relationship between your latitude and the
angular distance the celestial pole is above the southern horizon. The angular
distance from the southern horizon to the south celestial pole is always equal to
your latitude. To illustrate this, imagine that you are standing on the South Pole,
latitude -90°. The south celestial pole (declination of -90°) would be directly
overhead (i.e., 90° above the horizon). Now, let’s say that you move one degree
Figure 4-7
north — your latitude is now -89° and the celestial pole is no longer directly
overhead. It has moved one degree closer toward the southern horizon. This means the pole is now 89° above the
southern horizon. If you move one degree further north, the same thing happens again. You would have to travel
70 miles north or south to change your latitude by one degree. As you can see from this example, the distance
from the southern horizon to the celestial pole is always equal to your latitude.
If you are observing from Sydney, which is at latitude -34°, then the celestial pole is 34° above the southern
horizon. All a latitude scale does then is to point the polar axis of the telescope at the right elevation above the
southern horizon. To align your telescope:
1.
2.
3.
Make sure the polar axis of the mount is pointing due south. Use a landmark that you know faces south.
Level the tripod. Leveling the tripod is only necessary if using this method of polar alignment.
Adjust the mount in altitude until the latitude indicator points to your latitude. Moving the mount affects the
angle the polar axis is pointing. For specific information on adjusting the equatorial mount, please see the
section “Adjusting the Mount” in your telescope manual.
4. If the above is done correctly, you should be able to observe near the pole through the finderscope and a low
power eyepiece.
This method can be done in daylight, thus eliminating the need to fumble around in the dark. Although this
method does NOT put you directly on the pole, it will limit the number of corrections you will make when
tracking an object.
27
Pointing at Sigma Octantis
This method utilizes Sigma Octantis as a guidepost to the celestial pole. Since Sigma Octantis is about 1° degree
from the south celestial pole, you can simply point the polar axis of your telescope at Sigma Octantis.. Although
this is by no means perfect alignment, it does get you within one degree. Unlike the previous method, this must
be done in the dark when Sigma Octantis is visible. Sigma Octantis has a magnitude of 5.5 and may be difficult to
see and a binocular may be helpful as well as the finderscope.
1.
2.
3.
4.
Set the telescope up so that the polar axis is pointing south.
Loosen the DEC clutch knob and move the telescope so that the tube is
parallel to the polar axis. When this is done, the declination setting circle
will read 90°. If the declination setting circle is not aligned, move the
telescope so that the tube is parallel to the polar axis.
Adjust the mount in altitude and/or azimuth until Sigma Octantis is in the
field of view of the finder.
If the above is done correctly, you should be able to observe near the
pole through the finderscope and a low power eyepiece.
Sigma Octantis
Southern Cross
SCP
Remember, while Polar aligning, do NOT move the telescope in R.A. or
DEC. You do not want to move the telescope itself, but the polar axis.
The telescope is used simply to see where the polar axis is pointing.
Figure 4-8
Like the previous method, this gets you close to the pole but not directly on it.
Finding the South Celestial Pole (SCP)
This method helps improve your polar alignment and gets you closer to the pole that the above methods. This will
improve your accuracy for more serious observations and photography.
In each hemisphere, there is a point in the sky around which all the other stars appear to rotate. These points are
called the celestial poles and are named for the hemisphere in which they reside. For example, in the southern
hemisphere all stars move around the south celestial pole. When the telescope's polar axis is pointed at the
celestial pole, it is parallel to the Earth's rotational axis.
Alpha Centauri
Many methods of polar alignment require that you
know how to find the celestial pole by identifying
stars in the area. Observers in the southern
hemisphere are not as fortunate as those in the
northern hemisphere. The stars around the south
celestial pole are not nearly as bright as those around
the north celestial pole. The closest star that is
relatively bright is Sigma Octantis. This star is just
within naked eye limit (magnitude 5.5) and lies about
1° from the south celestial pole but can be difficult to
locate.
Beta Centauri
Beta Crucis
Omega
Octanis
Alpha Crucis
SCP
Figure 4-9
Therefore, with this method, you will use star patterns to find the south celestial pole. Draw an imaginary line
toward the SCP through Alpha Crucis and Beta Crucis (which are in the Southern Cross). Draw another
imaginary line toward the SCP at a right angle to a line connecting Alpha Centauri and Beta Centauri. The
intersecting of these two imaginary lines will point you close to the south celestial pole.
28
Declination Drift Method of Polar Alignment
This method of polar alignment allows you to get the most accurate alignment on the celestial pole and is required
if you want to do long exposure deep-sky astrophotography through the telescope. The declination drift method
requires that you monitor the drift of selected stars. The drift of each star tells you how far away the polar axis is
pointing from the true celestial pole and in what direction. Although declination drift is simple and straightforward, it requires a great deal of time and patience to complete when first attempted. The declination drift
method should be done after any one of the previously mentioned methods has been completed.
To perform the declination drift method you need to choose two bright stars. One should be near the eastern
horizon and one due south near the meridian. Both stars should be near the celestial equator (i.e., 0° declination).
You will monitor the drift of each star one at a time and in declination only. While monitoring a star on the
meridian, any misalignment in the east-west direction is revealed. While monitoring a star near the east/west
horizon, any misalignment in the north-south direction is revealed. It is helpful to have an illuminated reticle
eyepiece to help you recognize any drift. For very close alignment, a Barlow lens is also recommended since it
increases the magnification and reveals any drift faster. When looking due south, insert the diagonal so the
eyepiece points straight up. Insert the cross hair eyepiece and align the cross hairs so that one is parallel to the
declination axis and the other is parallel to the right ascension axis. Move your telescope manually in R.A. and
DEC to check parallelism.
First, choose your star near where the celestial equator and the meridian meet. The star should be approximately
within 1/2 an hour of the meridian and within five degrees of the celestial equator. Center the star in the field of
your telescope and monitor the drift in declination.
•
If the star drifts south, the polar axis is too far east.
•
If the star drifts north, the polar axis is too far west.
Make the appropriate adjustments to the polar axis to eliminate any drift. Once you have eliminated all the drift,
move to the star near the eastern horizon. The star should be 20 degrees above the horizon and within five
degrees of the celestial equator.
•
If the star drifts south, the polar axis is too low.
•
If the star drifts north, the polar axis is too high.
Again, make the appropriate adjustments to the polar axis to eliminate any drift. Unfortunately, the latter
adjustments interact with the prior adjustments ever so slightly. So, repeat the process again to improve the
accuracy checking both axes for minimal drift. Once the drift has been eliminated, the telescope is very
accurately aligned. You can now do prime focus deep-sky astrophotography for long periods.
NOTE:
If the eastern horizon is blocked, you may choose a star near the western horizon, but you must reverse
the polar high/low error directions. Also, if using this method in the southern hemisphere, the
direction of drift is reversed for both R.A. and DEC.
29
Aligning the R.A. Setting Circle
Before you can use the setting circles to find objects in the sky you need to align the R.A. setting circle. The
declination setting circle is aligned during the process of polar alignment.
In order to align the R.A. setting circle, you will need to know the names of
a few of the brightest stars in the sky. If you don’t, they can be learned by
using the Celestron Sky Maps (#93722) or consulting a current astronomy
magazine.
Figure 4-10
To align the R.A. setting circle:
1.
Locate a bright star near the celestial equator. The farther you are from the celestial pole the better your
reading on the R.A. setting circle will be. The star you choose to align the setting circle with should be a
bright one whose coordinates are known and easy to look up.
2.
Center the star in the finderscope.
3.
Look through the main telescope and see if the star is in the field. If not, find it and center it.
4.
If you purchased an optional motor drive, start it now so that it will track the star.
5.
Look up the coordinates of the star.
6.
Rotate the circle until the proper co-ordinates line up with the R.A. indicator (the zero mark on the
vernier scale). The R.A. setting circle should rotate freely. If the circle does not move freely, loosen the
thumbscrew to the right of the scale.
NOTE:
Because the R.A. setting circle does NOT move as the telescope moves in R.A., the setting circle
must be aligned each time you want to use it to find an object. This holds true even if you are
using an optional motor drive. However, you do not need to use a star each time. Instead, you can
use the coordinates of the object you are currently observing.
Once the setting circles are aligned you can use them to find any objects with known coordinates. The
accuracy of your setting circles is directly related to the accuracy of your polar alignment.
1.
Select an object to observe. Use a seasonal star chart to make sure the object you chose is above the
horizon. As you become more familiar with the night sky, this will no longer be necessary.
2.
Look up the coordinates in a star atlas or reference book.
3.
Hold the telescope and release the DEC clamp.
4.
Move the telescope in declination until the indicator is pointing at the correct declination coordinate.
5.
Lock the declination clamp to prevent the telescope from moving.
6.
Hold the telescope and release the R.A. clamp.
7.
Move the telescope in R.A. until the indicator points to the correct coordinate.
30
8.
Lock the R.A. clamp to prevent the telescope from slipping in R.A. The telescope will track in R.A. as
long as the motor drive is operating.
9.
Look through the finderscope to see if you have located the object and center the object in the finder.
10. Look in the main optics and the object should be there. For some of the fainter objects, you may not be
able to see them in the finder. When this happens, it is a good idea to have a star chart of the area so that
you can “star hop” through the field to your target.
This process can be repeated for each object throughout any given night.
Using the R.A. Vernier Scale
To increase the accuracy of the R.A. setting circle, the mount comes with a vernier scale. This device allows
you to get more precise readings down to one minute of right ascension.
Before we go into the specifics on how to use the vernier, let’s take a look at the scale and learn how to read
it. First, the zero (0) mark on the vernier is the R.A. indicator and will hereafter be referred to as such. It is
on the extreme right end of the vernier scale with the other numbers increasing as you move toward the left.
If the R.A. indicator is right on one of the marks of the R.A. setting circle, then that is the coordinate the
telescope is pointing at. The problem arises when the R.A. indicator (zero mark) is in between two of the
marks on the R.A. setting circle. If this is the case you will notice that along the vernier scale, one of the
marks will line up with one of the marks on the setting circle. This mark indicates the number of minutes that
should be added to the R.A. reading of the indicator. Since the indicator is between two R.A. marks, add the
minutes to the lower value that the R.A. indicator falls between.
For example, let’s say the R.A. indicator (zero mark on the vernier) is just left of the 5h 40m mark. This
would place it between the 5h 40m mark and the 5h 50m mark. If you look down the vernier scale, you will
see that the “4” is the only mark to line up with any of the marks on the R.A. setting circle (see Figure 4-11).
This means that you are 4 minutes to the left of the 5h and 40m mark or more simply at 5h and 44m.
Figure 4-11 Vernier Scale
Here’s how to use the vernier:
1.
Look up the coordinates of the object you want to observe. For our example we will use the Ring Nebula
(M57) which is at 18h 53m right ascension.
2.
Release the R.A. clamp and rotate the telescope until the R.A. indicator is between the 18h 50m mark
and the 19h 00m mark on the R.A. setting circle.
3.
Lock the R.A. clamp to hold the telescope in place.
4.
Move the telescope in R.A. using the slow motion control handle until the three on the vernier scale lines
up with one of the marks on the R.A. setting circle. Remember, the R.A. indicator must stay between
the 18h 50m mark and the 19h 00m mark on the R.A. setting circle!
5.
Look through the telescope and the Ring Nebula should be within the field of view if you are using a low
power eyepiece (assuming you have already set the DEC).
31
With your telescope set up, you are ready to use it for observing. This section covers visual observing hints
for solar system and deep sky objects as well as general observing conditions which will affect your ability to
observe.
Observing the Moon
Often, it is tempting to look at the Moon when it is
full. At this time, the face we see is fully illuminated
and its light can be overpowering. In addition, little
or no contrast can be seen during this phase.
One of the best times to observe the Moon is during
its partial phases (around the time of first or third
quarter). Long shadows reveal a great amount of
detail on the lunar surface. At low power you will be
able to see most of the lunar disk at one time. For the
Schmidt-Cassegrain
telescope,
the
optional
Reducer/Corrector lens allows for breath-taking views
of the entire lunar disk when used with low power
eyepieces. Change to optional eyepieces for higher
power (magnification) to focus in on a smaller area.
Lunar Observing Hints
To increase contrast and bring out detail on the lunar surface, use optional eyepiece filters. A yellow filter
works well at improving contrast while a neutral density or polarizing filter will reduce overall surface
brightness and glare.
Observing the Planets
Other fascinating targets include the five naked eye planets. You
can see Venus go through its lunar-like phases. Mars can reveal a
host of surface detail and one, if not both, of its polar caps. You
will be able to see the cloud belts of Jupiter and the great Red Spot
(if it is visible at the time you are observing). In addition, you will
also be able to see the moons of Jupiter as they orbit the giant
planet. Saturn, with its beautiful rings, is easily visible at moderate
power.
Planetary Observing Hints
•
•
Remember that atmospheric conditions are usually the limiting factor on how much planetary detail will
be visible. So, avoid observing the planets when they are low on the horizon or when they are directly
over a source of radiating heat, such as a rooftop or chimney. See the "Seeing Conditions" section later
in this section.
To increase contrast and bring out detail on the planetary surface, try using Celestron eyepiece filters.
32
Observing the Sun
Although overlooked by many amateur astronomers, solar observation is both rewarding and fun. However,
because the Sun is so bright, special precautions must be taken when observing our star so as not to damage
your eyes or your telescope.
Never project an image of the Sun through the telescope. Because of the folded optical design (on the SCT),
tremendous heat build-up will result inside the optical tube. This can damage the telescope and/or any
accessories attached to the telescope.
For safe solar viewing, use a solar filter that reduces the intensity of the Sun's light, making it safe to view.
With a filter you can see sunspots as they move across the solar disk and faculae, which are bright patches seen
near the Sun's edge.
Solar Observing Hints
•
The best time to observe the Sun is in the early morning or late afternoon when the air is cooler.
•
To center the Sun without looking into the eyepiece, watch the shadow of the telescope tube until it forms a
circular shadow.
•
To ensure accurate tracking, be sure to select the solar tracking rate of the optional motor drive.
Observing Deep Sky Objects
Deep-sky objects are simply those objects outside the boundaries of our solar system. They include star
clusters, planetary nebulae, diffuse nebulae, double stars and other galaxies outside our own Milky Way. Most
deep-sky objects have a large angular size. Therefore, low-to-moderate power is all you need to see them.
Visually, they are too faint to reveal any of the color seen in long exposure photographs. Instead, they appear
black and white. And, because of their low surface brightness, they should be observed from a dark-sky
location. Light pollution around large urban areas washes out most nebulae making them difficult, if not
impossible, to observe. Light Pollution Reduction filters help reduce the background sky brightness, thus
increasing contrast.
Seeing Conditions
Viewing conditions affect what you can see through your telescope during an observing session. Conditions
include transparency, sky illumination, and seeing. Understanding viewing conditions and the effect they have
on observing will help you get the most out of your telescope.
Transparency
Transparency is the clarity of the atmosphere which is affected by clouds, moisture, and other airborne particles.
Thick cumulus clouds are completely opaque while cirrus can be thin, allowing the light from the brightest stars
through. Hazy skies absorb more light than clear skies making fainter objects harder to see and reducing
contrast on brighter objects. Aerosols ejected into the upper atmosphere from volcanic eruptions also affect
transparency. Ideal conditions are when the night sky is inky black.
Sky Illumination
General sky brightening caused by the Moon, aurorae, natural airglow, and light pollution greatly affects
transparency. While this is not a problem for the brighter stars and planets, bright skies reduce the contrast of
extended nebulae making them difficult, if not impossible, to see. To maximize observing, limit deep sky
viewing to moonless nights far from the light polluted skies found around major urban areas. LPR filters
enhance deep sky viewing from light polluted skies by blocking unwanted light while transmitting light from
certain deep sky objects. You can, on the other hand, observe planets and stars from light polluted areas or
when the Moon is out.
33
Seeing
Seeing conditions refers to the stability of the atmosphere and directly affects the amount of fine detail seen
in extended objects. The air in our atmosphere acts as a lens which bends and distorts incoming light rays.
The amount of bending depends on air density. Varying temperature layers have different densities and,
therefore, bend light differently. Light rays from the same object arrive slightly displaced creating an
imperfect or smeared image. These atmospheric disturbances vary from time-to-time and place-to-place.
The size of the air parcels compared to your aperture determines the "seeing" quality. Under good seeing
conditions, fine detail is visible on the brighter planets like Jupiter and Mars, and stars are pinpoint images.
Under poor seeing conditions, images are blurred and stars appear as blobs.
The conditions described here apply to both visual and photographic observations.
Figure 5-1
Seeing conditions directly affect image quality. These drawings represent a point
source (i.e., star) under bad seeing conditions (left) to excellent conditions (right).
Most often, seeing conditions produce images that lie some where between these two
extremes.
Using the Lens Cap Aperture Stop with Refractor Telescopes
As mentioned earlier, all refractive optics will exhibit some amount of chromatic aberration due to the
prism effect of lenses. Chromatic aberration will become more pronounced the farther the incoming light
rays are off-axis (i.e. passing through the edge of the objective lens) and virtually unnoticeable on-axis
(passing through the center of the objective lens). This type of aberration is only evident when observing
very bright sources of light, such as bright planets and very luminous stars (like Sirius). There are several
techniques that the observer can employ to suppress visible signs of chromatic aberration, these include;
reducing the aperture and using filters.
The objective lens cap covering the objective lens of the telescope has a built-in aperture stop in the center.
By leaving the lens cap on the telescope with the aperture stop removed, you will allow all the incoming
light to pass closer to the center of the optical axis. Since, most planets are extremely bright objects
(visible to the unaided eye) any loss of light from reducing the aperture will be unnoticeable.
The lens cap should always be completely removed when observing deep-sky objects such as galaxies and
nebulae, where aperture (light gathering power) is essential and chromatic aberration is not an issue.
Another useful technique for reducing aberrations and improving planetary detail is the use of colored
eyepiece filters. Filters are commonly used to bring out particular planetary detail, such as the polar caps
on Mars or the bands and zones around Jupiter. The use of Celestron's Minus Violet Refractor Filter
(#94121) reduces the effect of chromatic aberration as well as improves contrast and resolution.
34
After looking at the night sky for a while you may want to try photographing it. Several forms of photography are
possible with your telescope, including terrestrial and celestial photography. Both of these are discussed in
moderate detail with enough information to get you started. Topics include the accessories required and some
simple techniques. More information is available in various books on the subject matter.
Below is described the traditional photographic methods with traditional equipment. During the last several years,
digital cameras have become very popular and you can use this latest technology to take images through telescopes
and it is relatively simple. In addition, CCD cameras (specifically made for astrophotography as well as Lunar and
Planetary photography have become more economical for hobbyists to procure and have opened new avenues for
taking fantastic images.
In addition to the specific accessories required for each type of celestial photography, there is the need for a camera but not just any camera. The camera does not have to have many of the features offered on today's state-of-the-art
equipment. For example, you don't need auto focus capability or mirror lock up. Here are the mandatory features a
camera needs for celestial photography. First, a “B” setting which allows for time exposures and this excludes point
and shoot cameras and limits the selection to SLR cameras, the most common type of 35mm camera on the market
today.
Second, the “B” or manual setting should NOT run off the battery. Many new electronic cameras use the battery to
keep the shutter open during time exposures. Once the batteries are drained, usually after a few minutes, the shutter
closes, whether you were finished with the exposure or not. Look for a camera that has a manual shutter when
operating in the time exposure mode. Canon, Olympus, Nikon, Pentax, etc. have made such camera bodies.
The camera must have interchangeable lenses so you can attach it to the telescope and use a variety of lenses for
piggyback photography. If you can't find a new camera, you can purchase a used camera body that is not 100percent functional. The light meter, for example, does not have to be operational since you will be determining the
exposure length manually.
You also need a cable release with a locking function to hold the shutter open while you do other things.
Mechanical and air release models are available.
Piggyback Photography
The easiest way to enter the realm of deep-sky, long exposure astrophotography is via the piggyback method.
Piggyback photography is done with a camera and its normal lens riding on top of the telescope. Through
piggyback photography you can capture entire constellations and record large scale nebulae that are too big for
prime focus photography. Because you are photographing with a low power lens and guiding with a high power
telescope, the margin for error is very large. Small mistakes made while guiding the telescope will not show up on
film. To attach the camera to the refractor or Newtonian telescope, use the piggyback adapter screw located on the
top of the tube mounting ring. For the Schmidt-Cassegrain telescope there is an optional Piggyback Camera Mount
available. The cameras have a threaded hole at the bottom of the camera where the piggyback screw threads into.
As with any form of deep-sky photography, it should be done from a dark sky observing site. Light pollution
around major urban areas washes out the faint light of deep-sky objects. You can still practice from less ideal skies.
1.
Polar align the telescope (using one of the methods described earlier) and start the optional motor drive.
2.
Load your camera with slide film, ISO 100 or faster, or print film, ISO 400 or faster! 2a. When using
digital cameras, experiment with various settings and read the camera instructions as each is somewhat
different than film SLR cameras.
3.
Set the f/ratio of your camera lens so that it is a half stop to one full stop down from completely open.
35
4.
Set the shutter speed to the “B” setting and focus the lens to the infinity setting.
5.
Locate the area of the sky that you want to photograph and move the telescope so that it points in that
direction.
6.
Find a suitable guide star in the telescope eyepiece field of view. This is relatively easy since you can
search a wide area without affecting the area covered by your camera lens. If you do not have an
illuminated cross hair eyepiece for guiding, simply defocus your guide star until it fills most of the field of
view. This makes it easy to detect any drift.
7.
Release the shutter using a cable release.
8.
Monitor your guide star for the duration of the exposure making the necessary corrections needed to keep
the star centered.
Short Exposure Prime Focus Photography for Refractors &
Newtonians
Short exposure prime focus photography is the best way to begin recording celestial objects. It is done with the
SLR camera attached to the telescope without an eyepiece or camera lens in place. To attach your SLR camera
you need the T-adapter and a T-Ring for your specific camera (i.e., Canon, Nikon, Pentax, etc.). The focuser
for the refractors and Newtonian has a built-in T-adapter and is ready to accept a 35mm camera body. The TRing replaces the 35mm SLR camera’s normal lens. Prime focus photography allows you to capture the entire
solar disk (if using the proper filter) as well as the entire lunar disk. To attach your camera to your telescope:
See note about digital cameras below.
1.
Remove the eyepiece from the 1¼” eyepiece holder.
2.
Unthread the 1¼” eyepiece holder from the focuser assembly. This will expose the male thread of the builtin T-adapter.
3.
Thread the T-ring onto the exposed T-adapter threads.
4.
Mount your camera body onto the T-Ring the same as you would any other lens.
Short Exposure Prime Focus Photography for Schmidt-Cassegrains
Use a T-Adapter (# 93633-A) which threads on to the back of the telescope. The T-Ring threads onto the TAdapter and then mount your camera body onto the T-Ring like you would any other lens.
Using Digital Cameras
To attach a digital camera to your telescope you will need the Universal Digital Camera Adapter (# 93626). The
adapter allows the camera to be mounted rigidly. You will follow your camera instructions for capturing
images as the information below relates to 35mm SLR cameras.
With your camera attached to the telescope, you are ready for prime focus photography. Start with an easy
object like the Moon. Here’s how to do it:
1.
Load your camera with film that has a moderate-to-fast speed (i.e., ISO rating). Faster films are more
desirable when the Moon is a crescent. When the Moon is near full, and at its brightest, slower films are
more desirable. Here are some film recommendations:
• T-Max 100
• T-Max 400
• Any 100 to 400 ISO color slide film
• Fuji Super HG 400
36
2.
Center the Moon in the field of your telescope.
3.
Focus the telescope by turning the focus knob until the image is sharp.
4.
Set the shutter speed to the appropriate setting (see table 6-1).
5.
Trip the shutter using a cable release.
6.
Advance the film and repeat the process.
Lunar Phase
Crescent
Quarter
Full
ISO 50
1/2
1/15
1/30
ISO 100
1/4
1/30
1/60
ISO 200
1/8
1/60
1/125
ISO 400
1/15
1/125
1/250
Table 6-1
Above is a listing of recommended exposure times when photographing the Moon
at the prime focus of your telescope.
The exposure times listed in table 7-1 should be used as a starting point. Always make exposures that are longer and
shorter than the recommended time. Also, take a few photos at each shutter speed. This will ensure that you will
get a good photo.
•
If using black and white film, try a yellow filter to reduce the light intensity and to increase contrast.
•
Keep accurate records of your exposures. This information is useful if you want to repeat your results or if
you want to submit some of your photos to various astronomy magazines for possible publication!
•
This technique is also used for photographing the Sun with the proper solar filter.
Eyepiece Projection for a Schmidt-Cassegrain
This form of celestial photography is designed for objects with small angular sizes, primarily the Moon and planets.
Planets, although physically quite large, appear small in angular size because of their great distances. Moderate to
high magnification is, therefore, required to make the image large enough to see any detail. Unfortunately, the
camera/telescope combination alone does not provide enough magnification to produce a usable image size on film.
In order to get the image large enough, you must attach your camera to the telescope with the eyepiece in place. To
do so, you need two additional accessories; a deluxe tele-extender (#93643), which attaches to the visual back, and a
T-ring for your particular camera make (i.e., Canon, Nikon, Pentax, etc.).
Because of the high magnifications during eyepiece projection, the field of view is quite small which makes it
difficult to find and center objects. To make the job a little easier, align the finder as accurately as possible. This
allows you to get the object in the telescope's field based on the finder's view alone.
Another problem introduced by the high magnification is vibration. Simply
tripping the shutter ⎯ even with a cable release ⎯ produces enough vibration to
smear the image. To get around this, use the camera's self-timer if the exposure
time is less than one second ⎯ a common occurrence when photographing the
Moon. For exposures over one second, use the "hat trick." This technique
incorporates a hand-held black card placed over the aperture of the telescope to act
as a shutter. The card prevents light from entering the telescope while the shutter
is released. Once the shutter has been released and the vibration has diminished (a
few seconds), move the black card out of the way to expose the film. After the
exposure is complete, place the card over the front of the telescope and close the
shutter. Advance the film and you're ready for your next shot. Keep in mind that
the card should be held a few inches in front of the telescope, and not touching it.
It is easier if you use two people for this process; one to release the camera shutter
and one to hold the card. Here's the process for making the exposure.
37
35mm SLR
T-Ring
Tele-Extender
Eyepiece
Visual Back
Figure 6-1
Accessories for Projection
Photography
1.
Find and center the desired target in the viewfinder of your camera.
2.
Turn the focus knob until the image is as sharp as possible.
3.
Place the black card over the front of the telescope.
4.
Release the shutter using a cable release.
5.
Wait for the vibration caused by releasing the shutter to diminish. Also, wait for a moment of good seeing.
6.
Remove the black card from in front of the telescope for the duration of the exposure (see accompanying table).
7.
Replace the black card over the front of the telescope.
8.
Close the camera's shutter.
Advance the film and you are ready for your next exposure. Don't forget to take photos of varying duration and
keep accurate records of what you have done. Record the date, telescope, exposure duration, eyepiece, f/ratio, film,
and some comments on the seeing conditions.
The following table lists exposures for eyepiece projection with a 10mm eyepiece. All exposure times are listed in
seconds or fractions of a second.
Planet
Moon
Mercury
Venus
Mars
Jupiter
Saturn
ISO 50
4
16
1/2
16
8
16
ISO 100
2
8
1/4
8
4
8
ISO 200
1
4
1/8
4
2
4
ISO 400
1/2
2
1/15
2
1
2
Table 6-2
Recommended exposure time for photographing planets.
The exposure times listed here should be used as a starting point. Always make exposures that are longer and
shorter than the recommended time. Also, take a few photos at each shutter speed. This will ensure that you get a
good photo. It is not uncommon to go through an entire roll of 36 exposures and have only one good shot.
NOTE: Don't expect to record more detail than you can see visually in the eyepiece at the time you are
photographing.
Once you have mastered the technique, experiment with different films, different focal length eyepieces, and even
different filters.
Long Exposure Prime Focus Photography
This is the last form of celestial photography to be attempted after others have been mastered. It is intended
primarily for deep-sky objects, objects outside our solar system which includes star clusters, nebulae, and galaxies.
While it may seem that high magnification is required for these objects, just the opposite is true. Most of these
objects cover large angular areas and fit nicely into the prime focus field of your telescope. The brightness of these
objects, however, requires long exposure times and, as a result, is rather difficult.
There are several techniques for this type of photography, and the one chosen will determine the standard
accessories needed. The best method for long exposure deep sky astrophotography is with an off-axis guider when
you are using a Schmidt-Cassegrain. This device allows you to photograph and guide through the telescope
simultaneously. Celestron offers a very special and advanced off-axis guider, called the Radial Guider (# 94176).
In addition, you will need a T-Ring to attach your camera to the Radial Guider. With refractor and Newtonian
telescopes you can skip the comments about the Radial Guider but all else applies.
Other equipment needs include a guiding eyepiece. Unlike other forms of astrophotography which allows for fairly
loose guiding, prime focus requires meticulous guiding for long periods. To accomplish this you need a guiding
ocular with an illuminated reticle to monitor your guide star. For this purpose, Celestron offers the Micro Guide
Eyepiece (# 94171). Here is a brief summary of the technique:
38
Note: Digital Cameras – follow the camera instructions on focusing and shutter data.
1.
Polar align the telescope. For more information on polar aligning see the Polar Alignment section earlier in the
manual.
2.
Remove all visual accessories.
3.
Thread the Radial Guider onto your telescope.
4.
Thread the T-Ring onto the Radial Guider.
5.
Mount your camera body onto the T-Ring the same as you would any other lens.
6.
Set the shutter speed to the "B" setting.
7.
Focus the telescope on a star.
8.
Center your subject in the field of your camera.
9.
Find a suitable guide star in the telescope field. This can be the most time consuming process.
10. Open the shutter using a cable release.
11. Monitor your guide star for the duration of the exposure using the buttons on the hand controller to make the
needed corrections.
12. Close the camera's shutter.
When getting started, use fast films to record as much detail in the shortest possible time. Here are proven
recommendations:
•
•
•
•
•
•
•
Ektar 1000 (color print)
Konica 3200 (color print)
Fujichrome 1600D (color slide)
3M 1000 (color slide)
Scotchchrome 400
T-Max 3200 (black and white print)
T-Max 400 (black and white print)
As you perfect your technique, try specialized films, that is films that are designed or specially treated for celestial
photography. Here are some popular choices:
•
•
•
•
Ektar 125 (color print)
Fujichrome 100D (color slide)
Tech Pan, gas hypered (black and white print)
T-Max 400 (black and white print)
There is no exposure determination table to help you get started. The best way to determine exposure length is to
look at published photos and see what film exposure combinations were used. Or take unguided sample photos of
various parts of the sky while the drive is running. Always take exposures of various lengths to determine the best
exposure
Planetary and Lunar Photography with Special Imagers
During the last few years a new technology has evolved which makes taking superb images of the planets and moon
relatively easy and the results are truly amazing. Celestron offers the NexImage (# 93712) which is a special camera
and included is software for image processing. You can capture planetary mages your first night out which rivals
what professionals were doing with large telescopes just a few short years ago.
39
CCD Imaging for Deep Sky Objects
Special cameras have been developed for taking images of deep sky images. These have evolved over the last
several years to become much more economical and amateurs can take fantastic images. Several books have been
written on how to get the best images possible. The technology continues to evolve with better and easier to use
products on the market.
Terrestrial Photography
Your telescope makes an excellent telephoto lens for terrestrial (land) photography. Your telescope is in essence a
long focal length telephoto lens. 35mm SLR cameras are mounted directly to the telescope (using the built-in TAdapter on the refractors and Newtonian or using the # 93633-A T-Adapter for the Schmidt-Cassegrain). For using
a digital camera you will need the Universal Digital Camera Adapter (# 93626).
You can take images of various scenic views, wildlife, nature, and just about anything. You will have to experiment
with focusing, speeds, etc. to get the best image desired.
Metering
The Omni Series telescopes have fixed apertures and, as a result, fixed f/ratios. To properly expose your subjects
photographically, you need to set your shutter speed accordingly. Most 35mm SLR cameras offer through-the-lens
metering which lets you know if your picture is under or overexposed. Adjustments for proper exposures are made
by changing the shutter speed. Consult your camera manual for specific information on metering and changing
shutter speeds.
Reducing Vibration
Releasing the shutter manually can cause vibrations, producing blurred photos. To reduce vibration when tripping
the shutter, use a cable release. A cable release keeps your hands clear of the camera and lens, thus eliminating the
possibility of introducing vibration. Mechanical shutter releases can be used, though air-type releases are best.
Blurry pictures can also result from shutter speeds that are too slow. To prevent this, use films that produce shutter
speeds greater than 1/250 of a second when hand-holding the lens. If the lens is mounted on a tripod, the exposure
length is virtually unlimited.
Another way to reduce vibration is with the Vibration Suppression Pads (#93503). These pads rest between the
ground and tripod feet. They reduce the vibration amplitude and vibration time.
40
While your telescope requires little maintenance, there are a few things to remember that will ensure your telescope
performs at its best. Each optical design type has special collimation instructions described below.
Care and Cleaning of the Optics
Occasionally dust and/or moisture may build up on the objective lens, the corrector plate, or primary mirror
depending on which type of telescope you have. Special care should be taken when cleaning any instrument so as
not to damage the optics.
If dust has built up on the optics, remove it with a brush (made of camel’s hair) or a can of pressurized air (spray at
an angle to the glass surface for approximately two to four seconds). Then, use an optical cleaning solution and
white tissue paper to remove any remaining debris. Apply the solution to the tissue and then apply the tissue paper
to the optics. Low pressure strokes should go from the center of the lens (or mirror) to the outer portion. DO NOT
rub in circles!
You can use a commercially made lens cleaner or mix your own. A good cleaning solution is isopropyl alcohol
mixed with distilled water. The solution should be 60% isopropyl alcohol and 40% distilled water. Or, liquid dish
soap diluted with water (a couple of drops per one quart of water) can be used.
Occasionally, you may experience dew build-up on the optics of your telescope during an observing session. If you
want to continue observing, the dew must be removed, either with a hair dryer (on low setting) or by pointing the
telescope at the ground until the dew has evaporated.
If moisture condenses on the inside of the optics, remove the accessories from the telescope. Place the telescope in a
dust-free environment and point it down. This will remove the moisture from the telescope tube.
To minimize the need to clean your telescope, replace all lens covers once you have finished using it. Since the cells
are NOT sealed, the covers should be placed over the openings when not in use. This will prevent contaminants from
entering the optical tube.
Internal adjustments and cleaning should be done only by the Celestron repair department. If your telescope is in
need of internal cleaning, please call the factory for information.
Collimation of Refractors
Be sure to completely read carefully before attempting collimation.
Collimation is the process of aligning the optical axis of each optical
element with each other and with the mechanical axis of the
telescope tube. For a refractor telescope design this means aligning
the optical axis of the objective lens with the optical axis of the
eyepiece on the other end of the tube. Your Omni refractor was
properly aligned at the factory. However, extremely rough handling
while traveling may eventually alter the alignment of the lens. Your
Omni refractor telescope may come with an adjustable objective lens
housing to assist in the alignment of the optical axis. It is rare that
collimation would be necessary and if your telescope does not have
collimation adjustment screws, you may have to send it to the factory
for alignment.
To determine whether or not re-collimation is necessary the
telescope should be set up outside at night. It should be a still night
and one in which you have let the telescope sit outside for 15 to 30
minutes before attempting collimation. You should also wait for a
night with good seeing conditions and avoid looking over anything
that produces heat waves (i.e., roof tops, car hoods, etc.).
41
Collimation
Screws
(Allen head)
Mounting Screws
(Phillips head)
Figure 7-1
Objective lens housing (with lens shade removed)
show mounting and collimation screws.
Pick a bright star and center it in the field of the telescope. Study the image of the star while racking it in and out of focus using
an eyepiece that yields 30 to 60 power for every inch of aperture. If an unsymmetrical focus pattern is present, then collimation is
necessary. (If the telescope is properly collimated, the out of focus star image will appear as a concentric ring pattern similar to
that shown in Figure 7-2).
To collimate, the telescope should be on either a motor driven (i.e., tracking) equatorial mount that is approximately polar aligned
or pointed at a stationary star without the motor drive running. Polaris, the North Star, is the perfect collimation star for northern
hemisphere observers since it appears motionless against the background sky long enough to perform the collimation procedure.
Polaris is the last star in the handle of the Little Dipper (Ursa Minor) and its distance above the northern horizon is always equal
to your latitude angle.
Prior to collimating, locate the three (3) mounting screws on the objective lens housing on the front of the tube. (These screws
attach the objective lens housing to the main tube and should not be removed). It may be necessary to remove the lens shade from
the front of the tube to allow easy access to the collimation screws. Next to each mounting screw is a shorter Allen screw
(collimation screw) that pushes against the optical tube to pivot the objective lens housing (see Figure 7-1). In order to make an
adjustment, the mounting screw is loosened while the Allen screw is turned in or out. Then, the mounting screw is tightened.
Only one of the three (3) sets is adjusted at a time. Normally motions on the order of 1/8 turn will make a difference, with only
about 1/2 to 3/4 turn being the maximum required. DO NOT remove or back out the mounting screws more than one (1) to
two (2) turns!
With Polaris or another bright star centered in the field of view, focus with your highest power
eyepiece (i.e., one with the shortest focal length). This includes eyepieces in the 4mm to 6mm range.
The star should be well centered in the field of view of the eyepiece. It may be helpful for two people
working together, while one views and instructs the other which screws are correctly turned and by
how much. Start by loosening one Phillips head (mounting) screw about 1 turn and advancing the
Allen screw to see if the motion is correct. If not, undo what you did and try another set of screws.
After making the first adjustment, it is necessary to re-aim the telescope tube to center the star again in
the field of view. It can then be judged for symmetry by going just inside and outside of exact focus
and noting the star’s pattern. Improvement should be seen if the proper adjustments are made. Since
three (3) sets of screws are present, it may be necessary to move at least two (2) sets of screws to
achieve the necessary lens movement. DO NOT over tighten the outer mounting screws!
Once in collimation, your telescope should not need additional collimation unless the telescope has
been bumped or jarred severely.
Figure 7-2
A collimated telescope
should appear as a
symmetrical ring pattern
similar to the diffraction
disk seen here.
Refractor Collimating Eyepiece- Your refractor includes a collimating eyepiece that can help you to
roughly check the alignment of your telescope in the daytime. The collimating eyepiece has a pinhole site that helps you
determine if the optics are properly aligned with the tube. With the focuser racked in all the way and the diagonal removed, place
the collimating eyepiece inside the focuser tube. If the telescope is properly collimated, you should be able to see the entire edge
of the objective lens when looking through the pin hole. If the objective lens appears oval, then it may be necessary to collimate
the telescope as described above.
Collimation of a Schmidt-Cassegrain
The optical performance of your telescope is directly related to its collimation, the
alignment of its optical system. Your telescope was collimated at the factory after it
was completely assembled. However, if the telescope is dropped or jarred severely
during transport, it may have to be collimated. The only optical element that may need
to be adjusted, or is possible, is the tilt of the secondary mirror.
To check the collimation of your telescope you will need a light source. A bright star
near the zenith is ideal since there is a minimal amount of atmospheric distortion.
Make sure that tracking (with an optional motor drive) is on so that you won’t have to
manually track the star. Or, if you do not want to power up your telescope, you can
use Polaris. Its position relative to the celestial pole means that it moves very little
thus eliminating the need to manually track it.
Figure 7-3
The three collimation screws are
located on the front of the
secondary mirror housing.
42
Before you begin the collimation process, be sure that your telescope is in thermal equilibrium with the
surroundings. Allow 45 minutes for the telescope to reach equilibrium if you move between large temperature
extremes.
To verify collimation, view a star near the zenith. Use a medium to high power ocular — 12mm to 6mm focal
length. It is important to center a star in the center of the field to judge collimation. Slowly cross in and out of
focus and judge the symmetry of the star. If you see a systematic skewing of the star to one side, then re-collimation
is needed.
Figure 7-4
Even though the star pattern appears the same on both sides of focus, they are asymmetric. The
dark obstruction is skewed off to the left side of the diffraction pattern indicating poor
collimation.
To accomplish this, you need to tighten the secondary collimation screw(s) that move the star across the field toward
the direction of the skewed light. These screws are located in the secondary mirror holder (see figure 7-3). Make
only small 1/6 to 1/8 adjustments to the collimation screws and re-center the star by moving the scope before
making any improvements or before making further adjustments.
To make collimation a simple procedure, follow these easy steps:
1.
While looking through a medium to high power eyepiece, de-focus a bright star until a ring pattern with a dark
shadow appears (see figure 7-4). Center the de-focused star and notice in which direction the central shadow is
skewed.
2.
Place your finger along the edge of the front cell of the telescope (be careful not to touch the corrector plate),
pointing towards the collimation screws. The shadow of your finger should be visible when looking into the
eyepiece. Rotate your finger around the tube edge until its shadow is seen closest to the narrowest portion of
the rings (i.e. the same direction in which the central shadow is skewed).
3.
Locate the collimation screw closest to where your finger is positioned. This will be the collimation screw you
will need to adjust first. (If your finger is positioned exactly between two of the collimation screws, then you
will need to adjust the screw opposite where your finger is located).
4.
Use the hand control buttons to move the de-focused star image to the edge of the field of view, in the same
direction that the central obstruction of the star image is skewed.
Figure 7-5
A collimated telescope
should appear
symmetrical with the
central obstruction
centered in the star's
diffraction pattern.
5.
While looking through the eyepiece, use an Allen wrench to turn the collimation
screw you located in step 2 and 3. Usually a tenth of a turn is enough to notice a
change in collimation. If the star image moves out of the field of view in the
direction that the central shadow is skewed, than you are turning the collimation
screw the wrong way. Turn the screw in the opposite direction, so that the star
image is moving towards the center of the field of view.
6.
If while turning you notice that the screws get very loose, then simply tighten the
other two screws by the same amount. Conversely, if the collimation screw gets
too tight, then loosen the other two screws by the same amount.
7.
Once the star image is in the center of the field of view, check to see if the rings are
concentric. If the central obstruction is still skewed in the same direction, then
continue turning the screw(s) in the same direction. If you find that the ring pattern
is skewed in a different direction, than simply repeat steps 2 through 6 as above for
the new direction.
43
Perfect collimation will yield a star image very symmetrical just inside and outside of focus. In addition, perfect
collimation delivers the optimal optical performance specifications that your telescope is built to achieve.
If seeing (i.e., air steadiness) is turbulent, collimation is difficult to judge. Wait until a better night if it is turbulent
or aim to a steadier part of the sky. A steadier part of the sky is judged by steady versus twinkling stars.
Collimation of a Newtonian
The optical performance of most Newtonian reflecting telescopes can be optimized by re-collimating (aligning) the
telescope's optics, as needed. To collimate the telescope simply means to bring its optical elements into balance.
Poor collimation will result in optical aberrations and distortions.
Before collimating your telescope, take time to familiarize yourself with all its components. The primary mirror is
the large mirror at the back end of the telescope tube. This mirror is adjusted by loosening and tightening the three
screws, placed 120 degrees apart, at the end of the telescope tube. The secondary mirror (the small, elliptical mirror
under the focuser, in the front of the tube) also has three adjustment screws. To determine if your telescope needs
collimation first point your telescope toward a bright wall or blue sky outside.
Never look directly at the sun with the naked eye or with a telescope (unless you have the proper solar filter).
Permanent and irreversible eye damage may result.
Aligning the Secondary Mirror
The following describes the procedure for daytime collimation of your telescope using the optional Newtonian
Collimation Tool (#94183) offered by Celestron. To collimate the telescope without the Collimation Tool, read the
following section on night time star collimation. For very precise collimation, the optional Collimation Eyepiece
1 ¼” (# 94182) is offered.
If you have an eyepiece in the focuser, remove it. Rack the focuser tube in completely, using the focusing knobs,
until its silver tube is no longer visible. You will be looking through the focuser at a reflection of the secondary
mirror, projected from the primary mirror. During this step, ignore the silhouetted reflection from the primary
mirror. Insert the collimating cap into the focuser and look through it. With the focus pulled in all the way, you
should be able to see the entire primary mirror reflected in the secondary mirror. If the primary mirror is not
centered in the secondary mirror, adjust the secondary mirror screws by alternately tightening and loosening them
until the periphery of the primary mirror is centered in your view. DO NOT loosen or tighten the center screw in the
secondary mirror support, because it maintains proper mirror position.
Aligning the Primary Mirror
Now adjust the primary mirror screws to re-center the reflection of the small secondary mirror, so it’s silhouetted
against the view of the primary. As you look into the focuser, silhouettes of the mirrors should look concentric.
Repeat steps one and two until you have achieved this.
Remove the collimating cap and look into the focuser, where you should see the reflection of your eye in the
secondary mirror.
44
Newtonian collimation views as seen through the focuser using the collimation cap
Primary mirror needs
adjustment
Secondary mirror needs
adjustment
Secondary
Mirror
Primary
Mirror
Both mirrors aligned with the collimating
cap in the focuser.
Mirror Clip
Both mirrors aligned with your eye looking
into the focuser.
45
Night Time Star Collimating
After successfully completing daytime collimation, night time star collimation can be done by closely adjusting the
primary mirror while the telescope tube is on its mount and pointing at a bright star. The telescope should be set up
at night and a star's image should be studied at medium to high power (30-60 power per inch of aperture). If a nonsymmetrical focus pattern is present, then it may be possible to correct this by re-collimating only the primary
mirror.
Procedure -- Please read this section completely before beginning.
To star collimate in the Northern Hemisphere, point at a stationary star like the North Star (Polaris). It can be found
in the north sky, at a distance above the horizon equal to your latitude. It’s also the end star in the handle of the
Little Dipper. Polaris is not the brightest star in the sky and may even appear dim, depending upon your sky
conditions. If you are in the Southern Hemisphere, point at Sigma Octantis.
Figure 7-6
Primary mirror. Large thumbscrews
are for collimation and small
thumbscrews are for locking the
mirror in place.
Prior to re-collimating the primary mirror, locate the collimation screws on the rear of the telescope tube. The rear
cell (shown in Figure 7-6) has three large thumbscrews which are used for collimation and three small thumbscrews
which are used to lock the mirror in place. The collimation screws tilt the primary mirror. You will start by
loosening the small locking screws a few turns each. Normally, motions on the order of an 1/8 turn will make a
difference, with approximately a 1/2 to 3/4 turn being the maximum required for the large collimation screws. Turn
one collimation screw at a time and with a collimation tool or eyepiece see how the collimation is affected (see the
paragraph below). It will take some experimenting but you will eventually get the centering you desire.
It is best to use the optional collimation tool or collimating eyepiece. Look into the focuser and notice if the
secondary reflection has moved closer to the center of the primary mirror.
With Polaris or a bright star centered within the field of view, focus with either the standard ocular or your highest
power ocular, i.e. the shortest focal length in mm, such as a 6mm or 4mm. Another option is to use a longer focal
length ocular with a Barlow lens. When a star is in focus it should look like a sharp pinpoint of light. If, when
focusing on the star, it is irregular in shape or appears to have a flare of light at its edge, this means your mirrors
aren’t in alignment. If you notice the appearance of a flare of light from the star that remains stable in location, just
as you go in and out of exact focus, then re-collimation will help sharpen the image.
46
When satisfied with the collimation, tighten the small locking screws.
Figure 7-7
Even though the star pattern appears the same on both sides of focus, they are asymmetric. The
dark obstruction is skewed off to the left side of the diffraction pattern indicating poor
collimation.
Take note of the direction the light appears to flare. For example, if it appears to
flare toward the three o'clock position in the field of view, then you must move
whichever screw or combination of collimation screws necessary to move the
star’s image toward the direction of the flaring. In this example, you would want
to move the image of the star in your eyepiece, by adjusting the collimation
screws, toward the three o'clock position in the field of view. It may only be
necessary to adjust a screw enough to move the star’s image from the center of the
field of view to about halfway, or less, toward the field's edge (when using a high
power ocular).
Collimation adjustments are best made while viewing the star's position in the field
of view and turning the adjustment screws simultaneously. This way, you can see
exactly which way the movement occurs. It may be helpful to have two people
working together: one viewing and instructing which screws to turn and by how
much, and the other performing the adjustments.
IMPORTANT:
Figure 7-8
A collimated telescope
should appear as a
symmetrical ring pattern
similar to the diffraction
disk seen here.
After making the first, or each adjustment, it is necessary to re-aim the telescope tube
to re-center the star again in the center of the field of view. The star image can then be
judged for symmetry by going just inside and outside of exact focus and noting the
star's pattern. Improvement should be seen if the proper adjustments are made. Since
three screws are present, it may be necessary to move at least two of them to achieve
the necessary mirror movement.
47
You will find that additional accessories for your Omni telescope will enhance your viewing pleasure and
expand the usefulness of your telescope. This is just a short listing of various accessories. Visit the Celestron
website for complete and detailed accessories available.
Barlow Lens - A Barlow lens is a negative lens that increases the focal length of a telescope. Used with any
eyepiece, it doubles the magnification of that eyepiece. Celestron offers several Barlow lenses in the 1-1/4"
size. The 2x Ultima Barlow (# 93506) is a compact triplet design that is fully multicoated for maximum light
transmission. The Omni Barlow (# 93326) is a compact achromatic Barlow lens that is less than three inches
long and weighs only 4 oz. and it works very well with all Celestron eyepieces.
Collimation Eyepiece 1 ¼” – # 94182 -- The collimation eyepiece is ideal for precise collimation of Newtonian
telescopes and helpful for aligning Schmidt-Cassegrains. This special eyepiece fits into 1 ¼” focusers and
diagonals.
Eyepieces - Like telescopes, eyepieces come in a variety of designs. Each design has its own advantages and
disadvantages. Below are just some of the eyepieces available.
•
Omni Plössl - Plössl eyepieces have a 4-element lens designed for low-to-high power observing. The
Plössls offer razor sharp views across the entire field, even at the edges! In the 1-1/4" barrel diameter, they
are available in the following focal lengths: 4mm, 6mm, 9mm, 12.5mm, 15mm, 20mm, 25mm, 32mm and
40mm.
•
X-Cel - This 6 element design allows each X-Cel Eyepiece to have 20mm of
eye relief, 55° field of view and more than 25mm of lens aperture (even with
the 2.3mm). In order to maintain razor sharp, color corrected images across its
55° field of view, extra-low dispersion glass is used for the most highly curved
optical elements. The excellent refractive properties of these high grade optical
elements make the X-Cel line especially well suited for high magnification
planetary viewing where sharp, color-free views are most appreciated. X-Cel
eyepieces come in the following focal lengths in 1 ¼” barrels: 2.3mm, 5mm,
8mm, 10mm, 12.5mm, 18mm, 21mm, and 25mm.
Filters Sets, Eyepiece -- 1 ¼”- Celestron offers four convenient filter sets, which
contain four different filters per set. Not only are these highly useful filter
combinations, but they also are an economical way to add versatility to your filter
collection.
Series 1 – # 94119-10
Orange, Light Blue, ND13%T, Polarizing (#s 21, 80A, #15, Polarizing)
Series 2 – # 94119-20
Deep Yellow, Red, Light Green, ND25% T (#s 12, 25, 56, 96ND-25)
Series 3 – # 94119-30
Light Red, Blue, Green, ND50% T (#s 23A, 38A, 58, 96ND-50)
Series 4 – # 94119-40
Yellow, Deep Yellow, Violet, Pale Blue (#s 8, 47, 82A, 96ND-13)
48
Flashlight, Night Vision - (# 93588) - Celestron’s premium model for astronomy, using two red LED's to
preserve night vision better than red filters or other devices. Brightness is adjustable. It operates on a single 9
volt battery (included).
Diagonal 2" Mirror (# 93519) - Celestron offers a 2" 90° Mirror Diagonal to thread on Schmidt- Cassegrain
telescopes or slides into the barrel of a 2" refractor focuser. This diagonal includes an adapter to accept 1¼"
eyepieces. It has a multicoated mirror and smooth mechanics that are precision manufactured for reliability.
Digital Camera Adapter – Universal (# 93626) – A universal mounting platform that allows you to do afocal
photography (photography through the eyepiece of a telescope) using 1 ¼” or 2” eyepieces with your digital
camera.
Erect Image Diagonal (#94112-A) - This accessory is an Amici prism arrangement that allows you to look into
the telescope at a 45° angle with images that are oriented properly (upright and correct from left-to-right). It is
useful for daytime, terrestrial viewing with refractor and Schmidt-Cassegrain telescopes.
Micro Guide Eyepiece (# 94171) - This multipurpose 1 ¼” 12.5mm illuminated reticle can be used for guiding
deep-sky astrophotos, measuring position angles, angular separations, and more. The laser etched reticle
provides razor sharp lines and the variable brightness illuminator is completely cordless.
Moon Filter (# 94119-A) - Celestron’s Moon Filter is an economical eyepiece filter for reducing the brightness
of the moon and improving contrast, so greater detail can be observed on the lunar surface. The clear aperture
is 21mm and the transmission is about 18%.
Motor Drive, Dual Axis (# 93522) - This dual axis motor drive, with drive corrector capabilities, is designed
for Celestron's Omni CG-4 mount. It precisely controls the telescope's tracking speed during long, timed
exposures of celestial objects, producing the best possible image sharpness. Four speeds are available—1x
(sidereal), 2x for guiding, 4x, and 8x for centering. These precision, state-of-the-art DC motor drives operate
from 4 D-cell batteries (not included). The hand controller module is very compact and fits easily in the palm of
your hand. Motors for both axes are included, along with brackets, clutches and hardware. Motor drives are a
must for those with a serious interest in astrophotography or CCD imaging.
NexImage – Solar System Imager (# 93712) – NexImage is a complete CCD solar system imager capable of
producing high quality planetary images with greater light sensitivity and color fidelity than comparable CMOS
imagers. Combined with the NexImage software package, NexImage can bring out tremendous detail and
reveal a final image that will rival those taken with astronomical CCD cameras costing thousands of dollars
more. The 1 ¼” adapter barrel makes NexImage compatible with most any telescope. Very easy to understand
operating instructions included.
Polar Axis Finderscope – This useful accessory speeds accurate polar alignment by providing a means of
visually aligning your German equatorial mount with Polaris and true north. As a result, you can spend more
time observing and less time setting up. The finderscope has an easy to use cross hair reticle.
Radial Guider (# 94176) - The Celestron Radial Guider is specifically designed for use in prime focus, deep
sky astrophography with Schmidt-Cassegrain telescopes, and takes the place of the T-Adapter. This device
allows you to photograph and guide simultaneously through the optical tube assembly of your telescope. This
type of guiding produces the best results since what you see through the guiding eyepiece is exactly reproduced
on the processed film. The Radial Guider is a “T”-shaped assembly that attaches to the rear cell of the
telescope. As light from the telescope enters the guider, most passes straight through to the camera. A small
portion, however, is diverted by a prism at an adjustable angle up to the guiding eyepiece. This guider has two
features not found on other off-axis guiders; first, the prism and eyepiece housing rotate independently of the
camera orientation making the acquisition of a guide star quite easy. Second, the prism angle is tunable
allowing you to look at guide stars on-axis. This accessory works especially well with the Reducer/Corrector.
49
Reducer/Corrector (# 94175) - This lens reduces the focal length of the SCT telescope by 37%, making your
Omni XLT127 a 788mm f/6.3 instrument. In addition, this unique lens also
corrects inherent aberrations to produce crisp images all the way across the field
when used visually. When used photographically, there is some vignetting that
produces a 26mm circular image on the processed film. It also increases the field
of view significantly and is ideal for wide-field, deep-space viewing. It is also
perfect for beginning prime focus, long-exposure astrophotography when used
with the radial guider. It makes guiding easier and exposures much shorter.
Sky Maps (# 93722) - Celestron Sky Maps are the ideal teaching guide for learning the night sky. You
wouldn’t set off on a road trip without a road map, and you don’t need to try to navigate the night sky without a
map either. Even if you already know your way around the major constellations, these maps can help you
locate all kinds of fascinating objects.
T-Adapter (# 93633-A) - T-Adapter (with additional T-Ring) allows you to attach your SLR camera to the rear
cell of your Schmidt-Cassegrain telescope. This turns your telescope into a high power telephoto lens perfect
for terrestrial photography and short exposure lunar and filtered solar photography.
T-Ring - The T-Ring couples your 35mm SLR camera body to the T-Adapter, radial guider, or tele-extender.
This accessory is mandatory if you want to do photography through the telescope. Each camera make (i.e.,
Canon, Nikon, Pentax, etc.) has its own unique mount and therefore, its own T-Ring. Celestron has 8 different
models for 35mm cameras.
Tele-Extender, Deluxe (# 93643) - The tele-extender is a hollow tube that allows you to attach a camera to the
Schmidt-Cassegrain telescope when the eyepiece is installed. This accessory is used for eyepiece projection
photography which allows you to capture very high power views of the Sun, Moon, and planets on film. The
tele-extender fits over the eyepiece onto the visual back.
UHC/LPR Filter 1 ¼” (# 94123) - These filters are designed to enhance your views of deep sky astronomical
objects when viewed from urban areas. LPR Filters selectively reduce the transmission of certain wavelengths
of light, specifically those produced by artificial lights. This includes mercury and high and low pressure
sodium vapor lights. In addition, they also block unwanted natural light (sky glow) caused by neutral oxygen
emission in our atmosphere.
A full description of all Celestron accessories can be found in the Celestron Accessory Catalog (# 93685-08)
50
Appendix A Technical Specifications
Omni XLT Series
Optical Design
Aperture
Focal Length
Focal Ratio
Optical Coatings
21088
21092
21090
21094
31057
11084
Omni XLT 102
Omni XLT 102ED
Omni XLT 120
Omni XLT 150R
Omni XLT 150
Omni XLT 127
Refractor
Refractor
Refractor
Refractor
Newtonian
Schmidt-Cassegrain
102mm (4.0")
102mm (4.0")
120mm (4.7")
150mm (6.0")
150mm (6.0")
127mm (5.0")
1000mm
900mm
1000mm
750mm
750mm
1250mm
f/10
f/9
f/8.3
f/5
f/5
f/10
Starbright XLT
Starbright XLT
Starbright XLT
Starbright XLT
Starbright XLT
Starbright XLT
Finderscope
6x30
6x30
6x30
6x30
6x30
6x30
Star Diagonal
1.25"
1.25"
1.25"
1.25"
n/a
1.25"
Eyepiece - std. 1.25" MC 50° FOV
25mm (40x)
25mm (36x)
25mm (40x)
25mm (30x)
25mm (30x)
25mm (50x)
Mount - Equatorial
Omni CG-4
Omni CG-4
Omni CG-4
Omni CG-4
Omni CG-4
Omni CG-4
1.75" Stainless
3.2kg (7#) &
1.8kg (4#)
1.75 Stainless
3.2kg (7#) &
1.8kg (4#)
1.75" Stainless
3.2kg (7#) &
1.8kg (4#)
1.75" Stainless
3.2kg (7#) &
1.8kg (4#)
1.75" Stainless
3.2kg (7#) &
1.8kg (4#)
1.75" Stainless
3.2kg (7#) &
1.8kg (4#)
Highest Useful Magnification
240x
240x
283x
360x
360x
300x
Lowest Useful Magnification
15x
15x
17x
21x
21x
18x
Limiting Stellar Magnitude
12.5
12.5
12.9
13.4
13.4
13.1
Resolution: Raleigh -arc seconds
1.36
1.36
1.19
0.92
0.92
1.1
Tripod Legs
Counterweights
Resolution: Dawes Limit " "
1.14
1.14
0.97
0.76
0.76
0.91
Light Gathering Power
212x
212x
294x
459x
459x
329x
Field of View - Angular w/25mm ep
1.25°
1.4°
1.25°
1.67°
1.67°
1.0°
Field of View - Linear w/25mm ep
66 ft. @1000yds
74 ft. @1000yds
66 ft. @1000yds
88 ft. @ 1000yds
88 ft. @1000yds
53 ft. @1000yds
Optical Tube Length
39.5" (1003mm)
37.0" (940mm)
40.0" (1016mm)
34.0" (864mm)
26.5" (673mm)
11.0" (279mm)
Optical Tube Weight
9.5 # ( 4.3kg)
8.0# (3.6kg)
12.5 # ( 5.7kg)
16.0 # (7.3kg)
12.0 # (5.4kg)
6.5 # ( 3.0kg)
Mount & Counterweights - Weight
21.0 # ( 9.5kg)
21.0 # ( 9.5kg)
21.0 # ( 9.5kg)
21.0# (9.5kg)
21.0 # ( 9.5kg)
21.0 # ( 9.5kg)
Tripod Weight
12.5 # ( 5.7kg)
12.5 # ( 5.7kg)
12.5 # (5.7kg)
12.5 # (5.7kg)
12.5 # ( 5.7kg)
12.5 # ( 5.7kg)
Total Weight
43.0 # ( 19.5kg)
41.5 # ( 18.8kg)
46.0 # ( 20.9kg)
49.5 # ( 22.5kg)
45.5 # (20.6kg)
40.0 # (18.1kg)
Note:
Specifications subject to change without notice or obligation
51
Appendix B - Glossary of Terms
AAbsolute Magnitude
Airy Disk
Alt-Azimuth Mounting
Altitude
Aperture
Apparent Magnitude
Arc minute
Arc second
Asterism
Asteroid
Astrology
Astronomical Unit (AU)
Aurora
Azimuth
BBinary Stars
The apparent magnitude that a star would have if it were observed from a standard distance of 10
parsecs, or 32.6 light-years. The absolute magnitude of the Sun is 4.8, at a distance of 10 parsecs, it
would just be visible on Earth on a clear moonless night away from surface light.
The apparent size of a star's disk produced even by a perfect optical system. Since the star can never
be focused perfectly, 84 per cent of the light will concentrate into a single disk, and 16 per cent into
a system of surrounding rings.
A telescope mounting using two independent rotation axis allowing movement of the instrument in
Altitude and Azimuth.
In astronomy, the altitude of a celestial object is its Angular Distance above or below the celestial
horizon.
The diameter of a telescope's primary lens or mirror; the larger the aperture, the greater the
telescope's light-gathering power.
A measure of the relative brightness of a star or other celestial object as perceived by an observer on
Earth.
A unit of angular size equal to 1/60 of a degree.
A unit of angular size equal to 1/3,600 of a degree (or 1/60 of an arc minute).
A small unofficial grouping of stars in the night sky.
A small, rocky body that orbits a star.
The pseudoscientific belief that the positions of stars and planets exert an influence on human
affairs; astrology has nothing in common with astronomy.
The distance between the Earth and the Sun. It is equal to 149,597,900 km., usually rounded off to
150,000,000 km.
The emission of light when charged particles from the solar wind slams into and excites atoms and
molecules in a planet's upper atmosphere.
The angular distance of an object eastwards along the horizon, measured from due north, between
the astronomical meridian (the vertical line passing through the center of the sky and the north and
south points on the horizon) and the vertical line containing the celestial body whose position is to
be measured.
Binary (Double) stars are pairs of stars that, because of their mutual gravitational attraction, orbit
around a common Center of Mass. If a group of three or more stars revolve around one another, it
is called a multiple system. It is believed that approximately 50 percent of all stars belong to binary
or multiple systems. Systems with individual components that can be seen separately by a telescope
are called visual binaries or visual multiples. The nearest "star" to our solar system, Alpha Centauri,
is actually our nearest example of a multiple star system, it consists of three stars, two very similar
to our Sun and one dim, small, red star orbiting around one another.
CCelestial Equator
Celestial Pole
Celestial Sphere
Collimation
DDeclination (DEC)
EEcliptic
Equatorial Mount
The projection of the Earth's equator on to the celestial sphere. It divides the sky into two equal
hemispheres.
The imaginary projection of Earth's rotational axis north or south pole onto the celestial sphere.
An imaginary sphere surrounding the Earth, concentric with the Earth's center.
The act of putting a telescope's optics into perfect alignment.
The angular distance of a celestial body north or south of the celestial equator. It may be said to
correspond to latitude on the surface of the Earth.
The projection of the Earth's orbit on to the celestial sphere. It may also be defined as "the apparent
yearly path of the Sun against the stars".
A telescope mounting in which the instrument is set upon an axis which is parallel to the axis of the
Earth; the angle of the axis must be equal to the observer's latitude.
52
FFocal Length
JJovian Planets
KKuiper Belt
The distance between a lens (or mirror) and the point at which the image of an object at infinity is
brought to focus. The focal length divided by the aperture of the mirror or lens is termed the focal
ratio.
Any of the four gas giant planets that are at a greater distance from the sun than the terrestrial
planets.
A region beyond the orbit of Neptune extending to about 1000 AU which is a source of many short
period comets.
LLight-Year (LY)
MMagnitude
Meridian
Messier
NNebula
North Celestial Pole
Nova
OOpen Cluster
PParallax
Parfocal
Parsec
Point Source
A light-year is the distance light traverses in a vacuum in one year at the speed of 299,792 km/ sec.
With 31,557,600 seconds in a year, the light-year equals a distance of 9.46 X 1 trillion km (5.87 X 1
trillion mi).
Magnitude is a measure of the brightness of a celestial body. The brightest stars are assigned
magnitude 1 and those increasingly fainter from 2 down to magnitude 5. The faintest star that can be
seen without a telescope is about magnitude 6. Each magnitude step corresponds to a ratio of 2.5 in
brightness. Thus a star of magnitude 1 is 2.5 times brighter than a star of magnitude 2, and 100 times
brighter than a magnitude 5 star. The brightest star, Sirius, has an apparent magnitude of -1.6, the
full moon is -12.7, and the Sun's brightness, expressed on a magnitude scale, is -26.78. The zero
point of the apparent magnitude scale is arbitrary.
A reference line in the sky that starts at the North celestial pole and ends at the South celestial pole
and passes through the zenith. If you are facing South, the meridian starts from your Southern
horizon and passes directly overhead to the North celestial pole.
A French astronomer in the late 1700’s who was primarily looking for comets. Comets are hazy
diffuse objects and so Messier cataloged objects that were not comets to help his search. This
catalog became the Messier Catalog, M1 through M110.
Interstellar cloud of gas and dust. Also refers to any celestial object that has a cloudy appearance.
The point in the Northern hemisphere around which all the stars appear to rotate. This is caused by
the fact that the Earth is rotating on an axis that passes through the North and South celestial poles.
The star Polaris lays less than a degree from this point and is therefore referred to as the "Pole Star".
Although Latin for "new" it denotes a star that suddenly becomes explosively bright at the end of its
life cycle.
One of the groupings of stars that is concentrated along the plane of the Milky Way. Most have an
asymmetrical appearance and are loosely assembled. They contain from a dozen to many hundreds
of stars.
Parallax is the difference in the apparent position of an object against a background when viewed by
an observer from two different locations. These positions and the actual position of the object form a
triangle from which the apex angle (the parallax) and the distance of the object can be determined if
the length of the baseline between the observing positions is known and the angular direction of the
object from each position at the ends of the baseline has been measured. The traditional method in
astronomy of determining the distance to a celestial object is to measure its parallax.
Refers to a group of eyepieces that all require the same distance from the focal plane of the
telescope to be in focus. This means when you focus one parfocal eyepiece all the other parfocal
eyepieces, in a particular line of eyepieces, will be in focus.
The distance at which a star would show parallax of one second of arc. It is equal to 3.26 light-years,
206,265 astronomical units, or 30,800,000,000,000 km. (Apart from the Sun, no star lies within one
parsec of us.)
An object which cannot be resolved into an image because it to too far away or too small is
considered a point source. A planet is far away but it can be resolved as a disk. Most stars cannot
be resolved as disks, they are too far away.
53
RReflector
Resolution
Right Ascension: (RA)
SSchmidt Telescope
Sidereal Rate
TTerminator
UUniverse
VVariable Star
WWaning Moon
Waxing Moon
ZZenith
Zodiac
A telescope in which the light is collected by means of a mirror.
The minimum detectable angle an optical system can detect. Because of diffraction, there is a limit
to the minimum angle, resolution. The larger the aperture, the better the resolution.
The angular distance of a celestial object measured in hours, minutes, and seconds along the
Celestial Equator eastward from the Vernal Equinox.
Rated the most important advance in optics in 200 years, the Schmidt telescope combines the best
features of the refractor and reflector for photographic purposes. It was invented in 1930 by
Bernhard Voldemar Schmidt (1879-1935).
This is the angular speed at which the Earth is rotating. Telescope tracking motors drive the
telescope at this rate. The rate is 15 arc seconds per second or 15 degrees per hour.
The boundary line between the light and dark portion of the moon or a planet.
The totality of astronomical things, events, relations and energies capable of being described
objectively.
A star whose brightness varies over time due to either inherent properties of the star or something
eclipsing or obscuring the brightness of the star.
The period of the moon's cycle between full and new, when its illuminated portion is decreasing.
The period of the moon's cycle between new and full, when its illuminated portion is increasing.
The point on the Celestial Sphere directly above the observer.
The zodiac is the portion of the Celestial Sphere that lies within 8 degrees on either side of the
Ecliptic. The apparent paths of the Sun, the Moon, and the planets, with the exception of some
portions of the path of Pluto, lie within this band. Twelve divisions, or signs, each 30 degrees in
width, comprise the zodiac. These signs coincided with the zodiacal constellations about 2,000 years
ago. Because of the Precession of the Earth's axis, the Vernal Equinox has moved westward by
about 30 degrees since that time; the signs have moved with it and thus no longer coincide with the
constellations.
54
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56
57
58
59
60
Celestron Two Year Warranty
A.
Celestron warrants this telescope to be free from defects in materials and workmanship for two years. Celestron will repair or
replace such product or part thereof which, upon inspection by Celestron, is found to be defective in materials or workmanship.
As a condition to the obligation of Celestron to repair or replace such product, the product must be returned to Celestron together
with proof-of-purchase satisfactory to Celestron.
B.
The Proper Return Authorization Number must be obtained from Celestron in advance of return. Call Celestron at (310) 3289560 to receive the number to be displayed on the outside of your shipping container.
All returns must be accompanied by a written statement setting forth the name, address, and daytime telephone number of the
owner, together with a brief description of any claimed defects. Parts or product for which replacement is made shall become
the property of Celestron.
The customer shall be responsible for all costs of transportation and insurance, both to and from the factory of
Celestron, and shall be required to prepay such costs.
Celestron shall use reasonable efforts to repair or replace any telescope covered by this warranty within thirty days of receipt. In
the event repair or replacement shall require more than thirty days, Celestron shall notify the customer accordingly. Celestron
reserves the right to replace any product which has been discontinued from its product line with a new product of comparable
value and function.
This warranty shall be void and of no force of effect in the event a covered product has been modified in design or
function, or subjected to abuse, misuse, mishandling or unauthorized repair. Further, product malfunction or
deterioration due to normal wear is not covered by this warranty.
CELESTRON DISCLAIMS ANY WARRANTIES, EXPRESS OR IMPLIED, WHETHER OF MERCHANTABILITY OF
FITNESS FOR A PARTICULAR USE, EXCEPT AS EXPRESSLY SET FORTH HEREIN.
THE SOLE OBLIGATION OF CELESTRON UNDER THIS LIMITED WARRANTY SHALL BE TO REPAIR OR
REPLACE THE COVERED PRODUCT, IN ACCORDANCE WITH THE TERMS SET FORTH HEREIN. CELESTRON
EXPRESSLY DISCLAIMS ANY LOST PROFITS, GENERAL, SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES
WHICH MAY RESULT FROM BREACH OF ANY WARRANTY, OR ARISING OUT OF THE USE OR INABILITY TO
USE ANY CELESTRON PRODUCT. ANY WARRANTIES WHICH ARE IMPLIED AND WHICH CANNOT BE
DISCLAIMED SHALL BE LIMITED IN DURATION TO A TERM OF TWO YEARS FROM THE DATE OF ORIGINAL
RETAIL PURCHASE.
Some states do not allow the exclusion or limitation of incidental or consequential damages or limitation on how long an implied
warranty lasts, so the above limitations and exclusions may not apply to you.
This warranty gives you specific legal rights, and you may also have other rights which vary from state to state.
Celestron reserves the right to modify or discontinue, without prior notice to you, any model or style telescope.
If warranty problems arise, or if you need assistance in using your telescope contact:
Celestron
Customer Service Department
2835 Columbia Street
Torrance, CA 90503 U.S.A.
Tel. (310) 328-9560
www.celestron.com
Monday-Friday 8AM-4PM PST
This warranty supersedes all other product warranties.
NOTE: This warranty is valid to U.S.A. and Canadian customers who have purchased this product from an Authorized
Celestron Dealer in the U.S.A. or Canada. Warranty outside the U.S.A. and Canada is valid only to customers who purchased
from a Celestron Distributor or Authorized Celestron Dealer in the specific country and please contact them for any
warranty service.
61
Celestron
2835 Columbia Street
Torrance, CA 90503 U.S.A.
Tel. (310) 328-9560
Fax. (310) 212-5835
Website www.celestron.com
Copyright 2008 Celestron
All rights reserved.
(Products or instructions may change without notice or obligation.)
Item # 21088-INST
Rev. 02
Printed in China
$10.00
08-08
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