HH with weird stars?

TheAstroGuy (Shane Ross) · #1 05-12-2010, 07:28 PM

Hi Guys,

Here's a wide shot on the Horsey with an 80mm scope.

I stopped working on it when i realised the Coma on the edges was so bad, but this coma is weird its almost a perfect cross, normally coma would flare in one direction so if someone could please tell me what this is and how to fix it i'd be super happy. Is it a field flattener position from ccd focal plane issue perhaps?.

Here's the image : www.theastroguy.com.au/hh.jpg
Here's the strange coma magnified : www.theastroguy.com.au/d.jpg

Thanks

Shane

multiweb (Marc) · #2 05-12-2010, 07:53 PM

Not coma. Looks like astigmatism.

allan gould · #3 05-12-2010, 07:56 PM

Bet its a WO field flattener! I agree with Marc - its astigmatism induced by you FF.

Terry B · #4 05-12-2010, 08:45 PM

I had a similar result when I took an image with a wide open zoom lens. It was using a pentax645 80-160 zoom lens.
I posted the result here at the time.
I expect some astigmatism with a photographic lens but yours shouldn't have any. I agree that the field flattener needs to be adjusted.

TheAstroGuy (Shane Ross) · #5 05-12-2010, 09:01 PM

Thanks guys i thought it may have been as such, is adjusting the FF distance a waste of time or can this be fixed ?

Im thinking i might go back to using my MPCC on the 80mm, it actually used to do a very good job even though it's designed for a Newtonian.

Thanks gentlemen

Shane