9 replies to this topic

[Starspawn]

Hello. I am using a reducer/flattener on a Sharpstar 76 and it was working nicely with reducer, I was getting nice, round stars on all parts of the picture. Then I ran into some trouble with focuser and I disassembled and reassembled the whole scope and after that I'm getting oval stars in corners of my photos (here is an example: https://ibb.co/PGzZ6Vg1).

 

I tried repeating the process, to make sure I screwed everything correctly, I think I did and it's the same. Any ideas on how to fix that?

[Celerondon]

The image that you linked is not visible.  Did you know that you can upload images to an Album in your Gallery on Cloudy Nights and avoid this issue altogether?  Once an image has been uploaded then you can display it in your post by clicking on the My Media button in the post editor toolbar. 
 

Don

 

 

 

Edited by Celerondon, 14 June 2025 - 12:35 PM.

[Starspawn]

Tnx, here it goes:

 

[Yomamma]

Check your backfocus from the reducer to the camera

[RetiredDave]

Did you measure the elongation? Looks like there is more elongation in the upper left corner. In addition to backspacing, check for tilt. Tilt may have been introduced by the disassembly/reassembly.

[Starspawn]

Check your backfocus from the reducer to the camera

It should be fine, 5,5cm, I wasn't changing anything here IIRC. I did try adding those tiny spacers, will test in 2 days when I get clear skies.

 

Did you measure the elongation? Looks like there is more elongation in the upper left corner. In addition to backspacing, check for tilt. Tilt may have been introduced by the disassembly/reassembly.

I don't know how to measure the elongation (I don't have PI). Yeah I already checked for tilt and I don't see it with naked eye. 

 

While googling on how to measure the elonagion I found out couple of other possible causes, one of them being ventilator from camera cooling, will try with cooler on off.

[Tapio]

You can test tilt with ASTAP, which is free software.

[Starspawn]

Ok this is the result, but I don't know how bad the numbers are and if this is what is causing the elongated stars

 

[Tapio]

The numbers are good, and as you can see at bottom 'Tilt (4% none).
But maybe you need to tweak back space distance.

[Starspawn]

Oh, I didn't notice that. Well that's good news then. So then it's the backfocus I guess. When I check for distorsions in Siril it's really bad. It's weird because I don't know what could have caused it. I just disassembled and reassembled the scope, everything is the same.