Quote:
Originally Posted by troypiggo
What exposure times are these images? I have same scope and for focusing I use 2s exposure. Your shots look like seeing is affecting them with wobble.
And are you using a coma corrector like MPCC or Parracor?
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Cheers & Thanx Troy, yes these are 2sec's. No MPCC, cam connected straight on to rule out all other possible interferences, eg, MPCC & Filters.
Re: seeing and wobble,, agree there is some wobble from seeing, but on looking closely there are two consistent bright spots in the rings which I am suspect about, I also took about 5 shots at each focus position and the 'seeing wobble' was evident with the ring, but the bright spots were consistent in location on/in the ring and as two points at closer to focus.
What mainly gets me is the four points at focus, also 5 x 2sec shots showed these 4 points - therefore most likely ruling out seeing, not 100% sure though ?
Thanx again
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Quote:
Originally Posted by multiweb
Seems there are a few things going on in there. First I think you're slightly out of focus in your cluster shot. That would make coma and other aberrations worse in your field. I think you have coma and also astigmatism. The latter could be confirmed by comparing in and out of focus shots. Maybe pinched optics as well.
Here's what I'd do to eliminate possible causes.
1_ check the primary and secondary glass are not stressed (primary retaining clips and secondary bonding)
2_ check your on axis stars in and out of focus. If you have astigmatism rotate your primary until "it's better".
3_ once your on axis stars are sorted check your secondary position/tilt and collimation without corrector.
4_ tweak your coma corrector spacing to get the flatest field you can.
See how that goes.
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Appreciated this 'Check list' Marc
1_ I did do a main mirror retaining clip adjustment many months ago but the problem then was sorting the MPCC spacings & collimation - But will check them again ,, - Havent considered the 2ndary bonding ?
2_ Considering the chips on both cameras are so small I'd suspect all stars in the field would be well in the on axis zone, anyway, all stars doing the same thing across the field.
Astigmatism, havent notice any with my Ronchi testing ep fitting & have a mark on mirror so goes back in same position since new, but again, I may experiment with this ?
3_ Secondary I have considered, so I will be inspecting & adjusting this next chance.
4_ No Coma corrector in place
Thanx Marc
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Quote:
Originally Posted by troypiggo
I was going to get to those next 
If the weird star shapes were astig/coma, wouldn't they radiate out the shapes from the centre? His cluster shot they all seem to be same direction/orientation. That's why I was trying to rule out seeing if he had really short exposures and it was wobble of the stars due to seeing. |
Cheers Troy, Astigmatism should present itself across the field, Coma affects the outfield more than the center, ,
The slight diagonal direction/orientation effect is most likely drift over that 5-10sec capture, wasnt guiding ?
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Quote:
Originally Posted by billdan
With my 14 inch I get weird star shapes when I first start using the scope, but 1.5 hours later after the mirror has cooled down everything is OK.
So I was wondering did you allow enough time for the primary mirror to stabilise?
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Cheers Bill, This was done around middnight, was cloud about and after sunset, cleared somewhat around 10pm, from then on I do usual routine - two hrs of struggling, bumbling, pulling hair out
Then give up
Hence my other RANT Thread
