What causes these elongated stars?
Posted 20 October 2013 - 11:36 AM
Posted 20 October 2013 - 11:38 AM
Posted 20 October 2013 - 11:54 AM
Another alternative is you get flexure that is somewhat jumpy in nature.
Another alternative is wind gusts.
I have put these in order of what I consider most to least likely.
Posted 20 October 2013 - 01:04 PM
Posted 20 October 2013 - 01:45 PM
Posted 20 October 2013 - 02:02 PM
Put a star in the crosshairs on PHD guiding. Start an exposure on the main camera, and watch as PHD Guiding tracks the star. (Also, "Enable Graph" and watch thing bounce around.) Do the crosshairs in fact stay on the guide star? (Are the graph lines close to zero?) If they don't then something is wrong with the guiding.
If the crosshairs don't stay, is the motion up or down, back and forth, or what? Are the deviations from zero on the graph large or small? Is the motion in one direction and increasingly larger?
If the motion is increasingly larger, then maybe you need more aggressiveness, a longer max correction, or some other adjustment. If the motion is back and forth, then increase the exposure (although that is probably not the problem) on the guidestar to avoid chasing the seeing. Or decrease the aggressiveness.
If the crosshairs stay on the guide star BUT the stars are elongated, then you have either flexure or field rotation. If the elongation of the stars is in an arc, then it is field rotation. If the eongation is straight line, then you have flexure.
Apply fixes to flexure or polar align better. Then try it all again.
If it happens on one frame out of many, (and I suspect it happens more often than you think. I doubt the stars in the second post are as round as you think) then it is probably a periodic error. TO find these, you could use one of the fancy programs for this purpose ((There was a free one once called PEC Prep, I think--google it), of PemPro, or simply watch your PHD graph for a while. You will notice at some regular time, your mount goes off by itself. and then comes back where it should.
Give these things a try.
Posted 20 October 2013 - 02:54 PM
Posted 20 October 2013 - 03:38 PM
You need to show us your graph and your settings to get better advice.
Posted 20 October 2013 - 08:15 PM
Posted 21 October 2013 - 09:35 AM