Sometimes it selects a guide star with other similar guide stars in the little guide box. This causes confusion. Sometimes, it realizes it and picks a new guide star; sometimes I have to abort the session and hope it does better next time. Sometimes it does; sometimes it doesn't.
Is there a way for me to avoid this unpleasant randomness? I already have the guide box as small as it will allow.
There is nothing at all random about the process, whether used with Maxim or CCDSoft. Both camera control programs themself determine the brightest point in the field as the target guide star. The guide star location on the chip is determined at the start of the target's imaging serssion and only again after a meridian flip, if one occurs. Other than that, the same coordinates are used throughout a target session, unless for some reason AGSR is triggered. AGSR causes a re-acquiring of the guide star and if you have a field with a lot of stars in it, the originally chosen guide star may be replaced with another one if a color filter is being used and a different star is a better match (brighter) for a given filter. The way to avoid this is of course to make your guide exposure long enough and your guide error restrictions loose enough so that the guide star is alway there after a filter change.
Please post a log file where this occurred.
John CCDAutoPilot author
Posts: 3457 | Location: Tucson, AZ | Registered: 14 February 2005
John, the problem cropped up again last night, when the chosen guide star was fairly near another star of similar brightness. I have attached a log showing the guider switching back and forth between which star it was glomming onto. I had to abort and start again to get it to behave.
The best way I know of to minimize that happening is to look at the guider FOVI in TheSky6 when setting up the target and if multiple stars of the similar magnitude are in there, reframe the target just enough to eliminate the duplication. If you don't have a rotator on that particular scope, make sure you check the guidestars 180 degrees away if you will be crossing the meridian. Sometimes it takes some pretty careful planning to avoid that issue.
Posts: 865 | Location: Rock Hill, SC | Registered: 15 February 2005
I certainly do plan carefully with TheSky beforehand, but not having a rotator really limits what I can do about it, given that the camera has a relatively small chip (which limits my wiggle room). I guess I'm just stuck with the problem.
