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Onag
Hi Brett,
Most stars are from class M (<3700K) , which in NIR have about 70% as much as energy than in visible. Since the ONAG allows the guider to access the all scope FVO, and associated F number, most of the time there is plenty of signal level for guiding in NIR.
I used the SBIG remote guiding head with an AO8 unit, which is based on the TC237 CCD ship as well.
The performance is a matter of scope FOV and F number. With my C11 @F/10 I can track with stars form 9 to 10mag. Since the ONAG addresses a very large FOV for guide star searching there is a very high probability to find a suitable one for the job.
I use the AO8 at 3 to 5 HZ because faster does not make much difference. Unless you are looking at very close double stars, fast AO correction rate is not a good idea.
The isoplanitc angle for which the guide star has still enough correlation with the target is quite small, few arc-second. Above this atmospheric turbulences can not be corrected with an AO. As a matter of fact doing so will decrease the over all performance by chasing the seeing from the guide star.
To make a long story short do not use AO faster then few HZ. AO units for amateur correct only the mount left over errors, and "fast" noise, not seeing.
At that rate the ONAG should do find for most target and set ups.
I hope this help to answer your questions.
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