Posted 15 November 2012 - 12:38 AM
I've been doing a fair amount of comparing my results using AO vs. ordinary auto guiding, and so far the AO system has shown a small but consistent improvement in FWHM values versus the guider. The differences seem to be around 0.2" FWHM improvement on nights of average or better seeing when I have a guide star bright enough to allow 2 Hz corrections, and more like 0.1" FWHM when guiding at 1 Hz or slower.
I don't have anything really conclusive yet. Traditional guiding on the AP-900 is certainly enough to achieve stars that appear round, so you don't need an AO unit to get good results, but I do believe that the AO system gives a small but measurable advantage in resolution.
Before I can post more than preliminary results, though, I've still got some optimization to do. I'm in the process now of adjusting mirror spacing to introduce a small amount of over correction into the system since my Planewave has a small amount of under correction in the optics when spaced according to the Ronchi grating. Also, I haven't done a drift alignment on the mount yet, so even my AO images include the occasional "bump" from the autoguider when the AO gets near the limit of its travel--I suspect this may be "robbing" me of a little bit of resolution that would be there if I had better alignment.
The goal I have set for myself is to consistently produce (on nights of reasonably good seeing) five to ten minute subexposures with less than 2" FWHM across the field of view. I'm pretty sure e equipment is up to the task once I get everything dialed in, but that's getting pretty close to my typical seeing limited conditions (based on short subexposures of a couple or three seconds), so everything has to be working juuusssstt riiiiiggghhtt.