PHD Guiding – a short tutorial

PHD Guiding – a short tutorial
PHD Guiding – a short tutorial
INSTALLATION
Yes, I even messed this up. PHD relies on the ASCOM platform and drivers to talk to
your mount. They’re not included in the PHD setup package and PHD won’t connect to
your mount without them. You can’t just install PHD and go.
PHD is a free download from Stark Labs, http://www.stark-labs.com/. Other software is
needed to make it work with your mount! You must also download and install the
following:
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ASCOM platform - http://ascom-standards.org/
o The ASCOM platform download button is on the right
o Install this first
ASCOM driver for your mount
o The driver downloads are below the platform download button
o Install this second
If the installation program directs you to install other software like .NET
framework, do it.
Then install and configure PHD guiding
ASCOM is a standard that allows programs to talk to astronomy equipment such as
mounts, cameras, and filter wheels.
CONFIGURING, SETTINGS, CONNECTING
Once you’ve started PHD, it’s time to configure a few things. I messed this up the first
time too.
PHD should find any camera connected to your PC. PHD will need a little help talking to
your mount. I usually connect the camera first. The camera needs to be connected to
the PC first, via USB or fire wire. Click on the camera icon in the lower left corner of the
screen. The dialog below will appear. Pick you camera. Choices for webcams, which
include many planetary imaging cameras are at the bottom of the list (not shown). The
software will find the port your camera’s connected to.
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NOTE: Most status information is conveyed in the bottom bar of the PHD screen below
the icons at the bottom of the screen. Not very eye catching and in my opinion, too
easy to miss. In the screen above, the status displays No cam, No scope, No cal which
means PHD isn’t connected or calibrated.
In the screen shot below, note the No cam status has changed to Camera and the
message “Simulator Connected”. When you are connecting to the camera and mount,
pay attention to the messages in this area, they will tell you if your attempt to connect
was successful.
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Next, connect to the mount by clicking on the telescope icon on the lower left.
Select your scope from the ASCOM Telescope Chooser dialog that appears (lower
right above). Then click Properties and the driver setup dialog for your scope will
appear (upper right above). Configure the mount type, serial port connection,
hemisphere, and check hand control if you want to move the scope around from
inside PHD. Correctly setting the COM port is essential to connecting to the
telescope. Verify the status bar confirms successful connection to the mount.
Before you start capturing pictures and guiding, click on the brain icon on the lower
right and view the available settings. The purpose of each setting is explained in the
help. Read it! It will come in handy later.
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SELECT A GUIDE STAR
Now that you’re connected, you can start guiding. Normally you’ll point your scope
at the target you want to image, get it roughly framed, and then start guiding before
you begin taking long exposure images.
Now that you’ve connected the camera and scope, how do you start capturing
images? It’s that looping arrow to the right of the telescope icon. Click that and the
guide camera images will start displaying on the page. You should have focused the
camera during daylight on a distant (more than 1000 yds) target, so you should be
able to see any bright stars in the field of view. Don’t expect to see more than one
or two. Even for targets in the Milky Way, I rarely see more than one or two stars on
the guide chip. If you don’t see any, increase the duration of the guide image using
the drop down selection to the right of the stop sign. Fine focus once you see some
stars.
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Mouse over one of the stars. As the cursor moves over the screen, it turns in to
cross hairs that help you center the cursor over star you want to guide one. Click on
the guide star. The status line at the bottom of the screen will show the signal to
noise ratio of the star. Less than five has significant risk of being lost later in the
guide session. Increasing the exposure duration will raise the SNR.
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CALIBRATION
I messed this up too! And this is the easiest guiding program available.
After clicking on the guide star, a dashed box appears around the star. Once PHD
gets a good lock on the star, the dashed line turns solid and green. To start
calibration, click the guide icon. That’s the target icon to the left of the stop sign.
Now PHD will send movement signals to the mount and learn how the star moves on
the chip in response to East, West, North and South direction commands.
Remember that status line on the bottom of the screen. PHD displays the signals
being sent to the mount. Until the status line message changes from Calibrating to
Guiding, you’re not ready to start imaging. Many users, including myself, didn’t pay
enough attention to the status line and were quite alarmed to watch the guide star
dance around the screen, certain that guiding had failed.
Calibration can take a few minutes.
Once calibration is completed, the mount will automatically start guiding. If you
need to move the mount to reframe the image or touch the mount for any reason,
click the stop icon! Even a small movement will move the guide star and PHD will try
to issue a correction. You will be working at cross purposes with PHD, likely messing
up your framing or guiding or both. Yep, I’m speaking from experience.
NOTE: The stop icon stops guiding AND image capture. You have to click capture to
get up to date images before resuming guiding. Yes, I’ve messed that up to.
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TOOLS
So how well is your guiding working? The guide graph will help you figure that out.
The guide graph will plot two horizontal lines showing the guide star drift in RA and
Dec from the position PHD is trying to hold the guide star at. A big Dec excursion is
shown above, usually caused by a problem in or at the mount. As PHD issues
corrections to the mount, hopefully you will see the horizontal lines return to the
solid line at the center of the graph. Each dotted horizontal line represents a one
pixel deviation of the star on the guide camera. Whether this is going to harm your
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image depends on the image scale (in arc-seconds per pixel) of the guider and the
imaging camera.
If the guide graph looks like a seismograph after an earthquake or your images have
squiggly or oval starts, you can enable the guide log and plot the errors and
correction signals in a spreadsheet. I’ve learned a lot from these graphs that helped
me improve guiding performance.
This is just a short tutorial to get you over some of the usability challenges I
encountered while learning to use this otherwise easy guiding program. I
recommend you examine all the menu options and read the help files in detail.
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