Quote:
Originally Posted by PRejto
OK, for what this is worth since I'm not nearly as experienced as you and Greg. First, I agree with Greg that the max move of .2 seems way too small for such long exposures. Consider that the longer the exposure the more the mount could have drifted off, thus I have observed that longer exposures either need a larger max move or higher aggression (or both) compared to shorter exposures. So, when you decrease the exposure you are obviously correcting more often and the smaller max move is now able to keep up with the drift. With the longer exposure it seems to be taking a whole lot of smaller moves to bring the mount back to proper tracking so you get that wavy sort of guiding. Anyway, That's my first reaction. I hope you get it sorted!
Peter
|
Hmmm, that makes sense. I am not sure if I have tried a larger max move with longer guide exposures. I think I have, but that was quite a few months ago. I have been trying to nut this problem out for some time with the RC and PMX. It's worth a try for using longer guide exposures. I just found this all to be an intriguing problem and something that I could not seem to sort easily with trial and error. I have spent a fair bit of time reading up and have tried CCDware's online calculator and nothing really worked well except for the really short exposures with small max and min numbers. It might be worth trying a stronger aggression too. Thanks Peter for the suggestions.
Quote:
Originally Posted by Shiraz
Possibly you are getting some feedthrough of PE, due simply to the fact that guiding tries to correct the average error that existed in the past, when the guide exposure was taken, not the error that exists when the mount moves. Why not continue to use 0.5 second exposures, or just ignore it if the stars are still round?
|
That makes sense Ray that it could be feed through of PE. In any event I will be using shorter exposures when I install the AOX. Or I will need to use the shorter exposures to use the AOX effectively. The only real problem is guide star selection on many galaxies can be a problem. If I cannot use the AOX on dimmer stars then I would need to be able to use longer exposures to guide on and here in lies the problem I suppose. 1 second is about the longest I can go before I start to see the oscillation take effect and that sometimes is just on the board line of star fade and guiding with a barely visible star. Anything over 1 second and the stars start to elongate in RA. Since the DEC is about as flat as you can get it, the elongation is quite obvious. Thanks for taking the time to respond.
Quote:
Originally Posted by gregbradley
Protrack is good tool to correct for longer exposure drift. On my PME I found a 00 point T-point model Protrack with tracking corrections activated made the difference to getting rounder stars with the CDK17.
But using it recently on the PMX results are not so clear.
Greg.
|
I have protack enabled on the PMX. I found it does help to manage the guiding and I did a 250 point model. With PEC the guiding with short exposures produces quite round stars and tight guiding. The good seeing allows short exposures but as I explained to Ray, having the option of being able to use shorter exposures would really help in areas with dim guide stars. I'll try the counter weight shift and see what effect that has.