Jim's Unconventional Astrophotography
Autoguide Interface for Celestron Advance Series Mounts
September 20, 2003
Here are some tips I can provide from my experience using the Autoguide Interface with the AS mount in my Dual Scope set up.
1.Focal Length - I use a guiding camera with a CCD with 5.6 micron pixels. When I use the C8 for guiding, I use a straight Cassigrain focus so the focal length is 2030 mm and the resolution is about .6 arc sec per pixel. When I use the ST80 for guiding, I use a 3x barlow system giving an effective focal length of 1200mm and the resolution is about .9 arc sec per pixel. These resolutions allow an accuracy of at least +/- 1.5 arc sec in guiding - this seems to be good - at least for the seeing I typically get at my observing sites.
2. Camera Position - Of course, the camera must be consistently mounted so that the errors that are recorded can act in the proper direction for the mount. To aid parfocal set up with eyepiece to camera, I usually mount the camera with a diagonal. I orient the camera for the Celestial North to be at the top of the image in the Eastern Hemisphere. In this orientation, all the guiding directions are correct. In the Western Hemisphere, I leave the camera mounted the same as that of the Eastern Hemisphere - so now Celestial North is the bottom of the image. In this way, the DEC directions remain correct, but the RA directions are reversed. In order to make the RA directions correct, I used the Vesta control panel and select "mirror image" - now all the directions are correct.
3. Guiding Settings - On the AS mount hand control I set the autoguide rate to 50% sidereal rate. The K3CCDTools settings I use for guide pulse width are as follows:
All images and content remain the property of Jim Thommes - copyright 2003, 2004
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