First of all, I'm newbie and own telescope only for a few months and had only several sessions taking pictures of DSO.
And long story short - I cant get round stars no matter what I tried.
Initially, I thought it might be guiding issue, bought guiding camera and now I'm guiding when taking pictures but still cant get round stars.
I also bought coma corrector (Baader MPCC III), that did not fix issues I'm having too.
And I spent a lot of time on collimating the scope and I believe it is well collimated right now (both laser collimator and cheshir showing that collimation is fine)
I think I already tried everything, so I decided to ask for help on this forum. Hopefully, you guys can point me in the right direction.
- 200mm f/5 Newtonian reflector (SkyWatcher)
- SkyWathcher HEQ5 GoTo mount
- Finder scope with guiding camera (QHY5L-II-M)
- Sony Alpha 99 as my main imaging camera (its full-frame camera), connected to the focuser through Baader MPPC III to correct coma issues
The problem is that I cant really get round stars. They are more or less round in the center of frames, but not on the edges of frames.
And I believe there is a pattern in the way how stars are "elongated". I'm hoping it will give experienced people a clue to the reason of the problem.
The best way I can describe the pattern is that the stars are following in "circle direction". It's like when you are making a photo of the sky pointing to Polaris without guiding, you then see how other stars around Polaris are running in circles. Hopefully, I'm explaining it clearly. Also, I must point that the severity of "elongation" does NOT seems to depend on the length of exposure, i.e., 5seconds long exposures and 60seconds long seems to show almost the same level of elongation. Usually, I'm taking light frames with 60 seconds long exposure.
Here you can download the selection of RAW files if you like to closely inspect them (some are 5 seconds, some 60 seconds, note that its 183mb 7zip archive) - https://www.sugarsyn...09685078_662175
Let me show you a few screenshots of the light frame with M31 with its core in the center of the frame. Its 5 seconds exposure frame at 8000 ISO.
The central part (with more or less rounded stars) - https://prnt.sc/p75w1r
Top Left corner - https://prnt.sc/p75wh8
Top Mid side - https://prnt.sc/p75wqj
Top Right corner - https://prnt.sc/p75wy4
Mid Right side - https://prnt.sc/p75x5d
Bottom Right corner - https://prnt.sc/p75xel
Bottom Mid side - https://prnt.sc/p75xm9
Bottom Left corner - https://prnt.sc/p75y38
Mid Left side - https://prnt.sc/p75ycl
and just for the comparison - the central part of 60sec long exposure - https://prnt.sc/p7605u - the stars become "longer" and have "tails" and look somewhat like triangle - this is another problem i'm fighting too (stars as triangles) and cant get rid of it.
Can you guys suggest what should I try to remove this elongation and get round stars?
Could it be guiding issue? Would it look like stars "running in circles" around the central object if the problems are in guiding?
I believe I have an issue with guiding in RA, but I'm not sure how this can lead to stars "running in circles", but maybe I dont understand something.
I believe I have more or less good DEC guiding but I'm aways hawing "saw-like" guiding in RA - see the screenshot of the guiding log - https://prnt.sc/p75yps
Also maybe someone can detect issues in calibration - this is a screenshot of calibration log https://prnt.sc/p75z4w
I'm going to attach PHD2 guiding log and calibration log as files too; maybe someone can find some wrong things within them.
Or maybe this is a collimation issue?
Or the polar alignment issue?
Maybe balancing issue?
Or something entirely different?
I'm out of ideas and its really disappointing when you are wasting those rare clear sky nights and don't end up with pictures with decent round stars. I want to get it fixed and hoping you can help me. Thanks in advance!
Edited by axlns, 17 September 2019 - 08:26 AM.