Dear Greg
My AO unit can sample up to about 8hz. It does this by only downloading a small box around the guide star- about 20 pixels square. The problem is getting a bright enough star to sample at that rate. I find that even 1/2sec exposures give very good results and this gives many more choices for guide stars
Quote:
Originally Posted by gregbradley
I asked about the increase in FWHM on the Starlight Xpress group and got a response that suggested that it was due to chasing poor seeing. That's certainly plausible, but I wanted to be correcting at a fast rate to deal with the wind. I will have to play with the parameters and learn how best to make use of the AO unit. It may require different strategies for different conditions. No surprise there!
Cheers,
Rick.
|
That doesn't make sense as the whole point of an AO unit is to overcome the effects of the seeing.
Perhaps it is more how many hertz you can get the thing running at.
For example I can get an ST402ME or a Lodestar or a Starfish autoguider running at .5 second exposure times. But by the time the download is done and the corrections are done it is more like 1 second or a tad more.
So the AO would have to beat that lag. I thought that was the whole theory of how they work. The mirror can shift faster than a correction in the mount motors can be executed.
So the whole game would be to try to achieve the highest hertz (number of times per second) you can and that would mean getting the brightest guide star.
Perhaps the ST402 might be better for it as it is more sensitive and cleaner and therefore able to produce brighter guide stars that can be guided off.
One thing I am not sure of - I assume the hertz means the guide camera takes that many exposures per second? Like 3 hertz means 3 camera exposures per second. That then would requite a fast guide camera and fast download time.
Perhaps an SBIG STi may be better as it is a CCD plus it has a reducer lens built in lowering the F ratio making brigher stars.
Greg.[/QUOTE]