Galaxies for Fun Astronomical CCD photos on peculiar galaxies and other astronomical stuff.
www.galaxies.se - by Ivar Hamberg
Adaptive Optics with the SBIG AOL.
By using the adaptive optics unit to the STL-camera, one can minimize the influence of the atmospheric turbulence as well as correct some of the imperfections of the drive.
Here are a few simple tests using the 12" Meade Schmidt Cassegrain at f/10 (3000mm f.l.). I used a 60 sec short exposure of M15 as test vehicle. M15 has a very strong guide star to the east (left of M15), SAO 107195, at magnitude 6.11. The guide star was about 15 mm off the center of the optical axis. Below are 5 different tests, with different settings. (Aggresivity was 5, out of max 10)
A: No AO. Mechanical drive only.
B. AO 5 sec between adjustments.
C. AO 1 sec exposure. Hence about ~1 sec between adjustments.
D. AO 0.1 sec.
E. AO 0.01 sec.
There are also other setting parameters that could be studied and optimized, but that will be left for some other occasion.
The tests were done at Nov 6, 2020, at moderate seeing conditions, with M15 pretty low in altitude. Not so optimal, but interesting anyway.
Results:
A: No AO. 3-4" resolution No Good
B. AO 5 sec. 3-4" resolution No Good
C. AO 1 sec. 2-3" resolution Rather OK, it works
D. AO 0.1 sec. 1-2" resolution Very Good
E. AO 0.01 sec. 1-2" resolution Very Good
So, to obtain good sharpness in this test of 60 sec exposures, it is advisable to go down to about 0.1 sec of exposure, if possible. This is almost 10 adjustments per second. (Some millisec of processing and download time..)
The Adaptive Optics unit is good for compensating small errors in the mechanical drive, imperfections of the programmed PEC, and most important, some of the atmospheric turbulence. It works best (i.e. has an effect) for longer focal lengths, where the used pixel size is below 1 arc second, and the main optics used is good for sub arc second resolution.
Adaptive Optics: Guide star Live image.