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Old 12-05-2017, 10:41 AM
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sil (Steve)
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sil is offline
Join Date: Jun 2012
Location: Canberra
Posts: 1,402
Originally Posted by bojan View Post
I was doing cropping, however I am reluctant to stop down, because of relatively large central obstruction I will loose too much light for very moderate (if any) improvement...
This lens is very light and handy to carry around, that is why I would like to somehow improve coma without exposure time and/or FOV.
Still I would try some test shots and just see, you might get an improvement for 1/3EV loss only,. I know its not nothing but any hardware fix will cause some loss. Another possibility that will cost you time, maybe a little money if you dont have it already. Is software to correct lens distortion/ chromatic aberations, maybe something you can profile your lens/camera combination yourself then turn all your RAWs into 16bit TIFFs then use those for your AP workflow.

Otherwise do what I do, rely on reframing and registration/integration to even out all the stars around my target. maybe if you can shoot tracking half subs with camera upside down or tilted 90 degrees? I find corner distortions often asymmetrical so turning the camera they all get more rounded after stacking.

Something I'd forgotten is some camera bodies allow front/back focus adjustments per lens. Maybe a tiny adjustment each way and take test shots. Hell I'd be making sure everything fits tight and firm in case tiny flex in the system is causing excess distortion. Anything I can think og and just take test shots, figure out the best of the bad. The coma is there in the optics but just in case another factor is causing a bit more than it should you might get a tiny improvement at no cost. Always worth testing rather than just assuming it wont make any difference.
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