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Esprit 120 color fringing

Equipment Refractors Comet
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Anderl avatar
Anderl avatar
Hey 👋 

Yesterday was the first night i had the chance to run my new astro rig. 
after a lot of setting up and configuration struggle i managed to get a few minutes of c/2017 k2 panstarrs. 

https://www.astrobin.com/mfdw1f/

i am happy that i managed to get a shot of this comet but i noticed that my stars have some form of fringing around them. 


I bought the apo used without any test certification and was aware that this china apo could have some flaws. 

is it possible to collimate an apo as an amateur? Will it be worth to spend around 200 bucks to get it collimated by a professional? Or could the fringing come from something else in my imaging train? 

I used the aberration inspector in nina and the frames i looked at were looking good. 

cs
andi
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andrea tasselli avatar
andrea tasselli avatar
Colour fringing has nothing to do with collimation and I can't see any issue with it in your image. To be sure it is actually due to the lens you'd have to shoot a bright white star around zenith at the edge of the four corners of sensor being careful not to saturate the star and then stretch it.  If you see separation between the RGB components you have LCA. If insted you end up with a violet halo you simply have a not well corrected APO.
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Anderl avatar
Anderl avatar
andrea tasselli:
Colour fringing has nothing to do with collimation and I can't see any issue with it in your image. To be sure it is actually due to the lens you'd have to shoot a bright white star around zenith at the edge of the four corners of sensor being careful not to saturate the star and then stretch it.  If you see separation between the RGB components you have LCA. If insted you end up with a violet halo you simply have a not well corrected APO.

I will do that, in fact i have one single exposure of the veil nebula from yesterday night. The single exposure i have is overexposed (seems f ratio isn’t really comparable between camera lenses and telescopes).
i will take a look at that picture and take a new one as soon is i have time.
Jeff Coldrey avatar
Jeff Coldrey avatar
At ISO6400, a good exposure for star color is more like 5 seconds. 

Good luck.
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