|
Hi Greg,
What I mean is that in a run of say 10 x 30 second images with 10 seconds between each 30 sec sub, without autoguiding, just sidereal tracking. Every third or so image is showing coma like (teardrop) stars (even in the centre of the field) as if the mount has gone over a funny shaped tooth or something like that in the drive (worm gear?). This is where the 90 seconds comes from. The difference is only slight BUT when you flick from one good image to another using a preview in explorer, you can see which subs are duds quite easily.
This was worse when the scope was say 30 deg towards the east. When it was at zenith on Sagittarius, it didnt happen as much. Perhaps Drift alignment would highlight if I was dead on the SCP or not and fix the issue? On the run of ten images I would get 1&2 good, 3,4 bad, 5&6&7 good, then 8&9 bad, then say 10 would be good. This is an example of what I would get on average.
I had the SCP pretty much dead on in the polar scope as the octans constellation was within all the 4 star circles in the asterism shown on the polar scope so the only things I can think of that could be causing this aberration could be the alignment of the tube to the mount on the dovetail bar (which the manual cryptically tells you to adjust) or perhaps the tube is not exactly balanced?
I don't know if I am expecting too much from an unguided pic of longer than 30 seconds or not? Would autoguiding eliminate this problem?
I may have tried to shortcut the best practices in my haste to get some results so if I need to slow down and set things right, then this is probably a good place to start.
Sorry for all the questions embedded in there. I am just trying to explain what I mean.
Cheers
Chris
|