If you’ve been reading my blogs you will know that I’ve been struggling with tracking. It’s been months now and last night the problem finally became clear. I’m just a very slow learner.
My ST 402, is a great little guide camera, hanging off my MOAG I never fail to find a star. The problem was that I was getting pixel movements during guiding of up to 1.8 pixels in X and Y. Obviously the resulting images where poor. I was reading again about sampling and came across the old 2 arcsec per pixel rule. I run my FLI Proline 16803 at 2x binning to get a ratio of about 1.7 arcsec per pixel (as reported by Maxim). The ST 402 has pixels of 6.9 by 4.3 so the ratio when hanging off the back of my MOAG is about 0.36 (an average of the two dimensions). I changed the binning to 3×3 giving a ratio of about 1.1, and surprisingly the tracking variation is now reduced to a max of 0.4 pixels in either direction, average deviation is less than 0.15. The pictures look heaps better as well.
Now I have to go back and fix my auto focus, FocusMax is causing me grief.
26/01/2013 – I’ve worked out FocusMax and what a wonderful solution it is. Perfect focus every time! The trick is choosing a dim enough star (in my case around 7 is perfect) and following the instructions. They one major factor in this was counting the circles on the profile where the line began to diverge from straight, to determine the Near Focus HDF. After I got this right it worked like a charm. See the pictures below.