ASTRO-PHYSICS German Equatorial 1200GTO, Manual, Page: 32 / 38

problem. PLEASE, please make sure that you have identified the proper axis. In the case of any kind of motion problem like
this, it would be really helpful if you removed your camera, inserted an eyepiece with crosshairs and actually looked to see
what was happening. You can then identify exactly which direction, RA or DEC, is moving after a slew. Sometimes because
of mix-ups in the CCD software (Maxim, for instance), the axes are identified backwards.
When you are trouble shooting, remember, RA is the only axis that must move at the sidereal rate and is the only axis that
can trail a star if it is not moving correctly at that rate. The DEC axis does not move after a slew and will not trail a star except
by a very slow long period drift due to polar misalignment, etc. It will not trail a star image EVEN if it has 10 degrees of
backlash, so that analysis is definitely suspect.
I’m having a frustrating guiding problem with my mount and need to figure out my next steps.
Your next step would be to remove the camera and place a high power eyepiece with crosshair reticle into the focuser. Then
sit down and watch what happens to the guide star. With the eyepiece and reticle, you can see whether or not the mount is
tracking smoothly and how the periodic error is manifesting itself. Yes, you will have periodic error, and any good CCD
camera will pick it up to give you oval stars - that is a given. What you need to find out is whether this periodic error is within
limits (+- 3.5 arc seconds for the 900GTO and +-2.5 arc seconds for the 1200GTO) and whether it is smoothly varying. You
can also do some hand guiding using the 4 buttons on the keypad. It will tell you how responsive the mount is to your guiding
inputs and may even show some hidden problems when you try to keep the star on the crosshairs.
Alternately, you can use PEMProAP (or the full version of PEMPro) to characterize your periodic error. It will tell you things
like the peak value and the smoothness of the error.
You can also characterize your mount tracking and guiding abilities using the “Characterizing the Dec Motions” test outlined
in the Technical Support section of our AP website and included in the back of this manual. Many times a problem guiding in
RA can be the result of a Dec axis mechanical problem. Not knowing this, you will be forever chasing down the problem on
the RA axis, and never reaching a solution. Characterizing your Dec Axis will at least show you that the mount reacts
properly to the 4 guide directions. If it shows a problem area, then at least we will know how to fix it.
Once you know that the mount is tracking in a normal fashion with normal periodic error profile, you can go from there to
begin setting up your guiding parameters. It is not a piece of cake to get a guider like the ST4 to work flawlessly. It is an art,
but once you know that the mount responds properly to the guide inputs, it should be possible to set it up to work accurately.
If any problems occur, please don't hesitate to contact Astro-Physics for assistance.
We may add additional troubleshooting tips to future versions of this manual or in a separate technical document, so we
encourage you to check the Technical Support section of our website. We also strongly recommend that you participate in
the ap-gto discussion group at yahoogroups.com. In addition to the huge knowledge base of the various members, the
technical support staff at Astro-Physics also participates to help solve problems and answer questions.
ASTRO-PHYSICS, INC
11250 Forest Hills Road
Machesney Park, IL 61115
Telephone: (815)-282-1513
Fax: (815)-282-9847
support@astro-physics.com
www.astro-physics.com
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