My GSO RC10 (carbon fibre tube) has had some problems for a while now - I have a go at trying to fix it occasionally but with no luck. A long time ago, it was great, but Something Happened (maybe during our house move) and it hasn't been really usable since then.
Here's a cropped image from the middle of the image:
Jpeg compression has ruined things a bit, but I think it's still possible to see the bad star shapes.
Here's a near focus image of a star:
Out of focus star, inwards focus:
Out of focus star, outwards focus:
Bright star, uncropped image (just massively resized), 5 sec exposure for the donut. Am I right in assuming that the donut should be centered on the star and not offset?
I've tried a number of things now, with some making a bit of difference, but others I suspect may have made things worse. I need suggestions or ideas on where to proceed from here.
What I know or have been able to eliminate in the process:
* It's not a camera issue - I've tried 2 different cameras.
* It's not a focuser issue - I've had 2 different focusers that give the same result, plus I can use the tak collimating scope with or without the focuser and it gives the same result
* Fairly certain there's no other real tilt that can come into play. And if so, with all my adjustments taking things on/off, I doubt I could replicate things 100%.
* PA is good, certainly good enough for at least 30 sec unguided at this focal length.
* For all these images, there's no flatteners/reducers in the image train.
What I have done (for good or bad):
* It's been partially taken apart. I go desperate enough to do it to check if there were any issues with the primary, so I took it off the tube to look. Nothing obvious. The secondary has also been unscrewed and checked - nothing obvious there.
* I got in contact with GSO for the exact length required between primary and secondary. I think I am very close to that figure - maybe a few mms either way. (It's difficult, because of the stupid way the distance is measured.)
* I have used a tak collimating scope and it seems the secondary was "nicely" aligned.
* I have done adjustments using the stars as well (taking images - my eyesight sucks a bit for visual).
* There's a few other things that have been tried as well, but overall, no luck.
Any ideas? Maybe I need to get a "professional" to look at the scope and fix it?