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D. T. Durig (The University of the South)
I recently upgraded my SBIG ST-8 CCD camera with the AO-7 Adaptive Optics unit. This has solved many of the problems with tracking errors and the stability of my telescope mount and allowed me to obtain useful astrometric information on asteroids, comets and supernovae. It is no longer easy to take automated remote images but as long as I am at the observatory, good quality data can be obtained.
The AO-7 unit allows me to pick a guide star for the guiding CCD just slightly out of the field of view of the imaging CCD. I am able to guide at the rate of 5 corrections per second with a 13th magnitude guide star. The fastest I have been able to guide is 30 times per second, but there are not usually bright enough stars near the image field to use this rate. When I have to use a dimmer star to guide on, and my rate is as slow as once per two seconds, good results are possible as long as the winds are not too strong.
With a focal length of 1775 mm (f/5.75) and 2x2 binning on the CDD I am able to reach at least 18th magnitude objects in a 30 second exposure, but the guiding has to be very good to use these images for astrometry. For objects dimmer than 17th magnitude I normally go to a 2 minute exposure. With this equipment I was the first to observe that a recently discovered object (Comet LINEAR S4) was a comet and not an asteroid as originally reported (see IAUC 7267). I have performed additional astrometric observations on Comets LINEAR S3, S4, T2 and Ferris U1. I have also performed measurements on over a dozen asteroids from the MPC Critical List.