Strategies for dealing with out-of-focus exposures

Mark Knecht

Hi,

   First post from a total newbie. I've only been playing with astrophotography for about 4-5 months and my setup is very, very simple - Canon T7, AZ-GTi mount, a couple of kit lenses and a Super Takumar 200mm lens which is the reason for this first post. I've been using PixInsight for a few months, have done the Fasttrack videos here, and am currently working my way through the Fundamentals coursework.

   QUESTION: What strategies might I explore to deal with exposures that I _KNOW_ are slightly out-of-focus?

   BACKGROUND: After looking at lots of YouTube videos I took a small plunge and bought a Pentax Super Takumar 200mm lens on Ebay as well as an M42 adapter to mate it with my DSLR. The lens is nice enough for daytime photography but sadly it doesn't focus correctly at infinity. It comes close but it just doesn't get there leaving stars slightly out-of-focus. I purchased a second M42 adapter but it didn't fix the problem.

   I've put a zipped file on my Google drive of the Beehive CLuster which includes one light frame, a master light generated from 205 30 second exposures and an additional image file that shows which stars are detected or problems when using running PhotometricColorCalibration.

https://drive.google.com/file/d/1Qnc0kBmadzYLBLmeUTVXHJKv_d6MNSly/view?usp=sharing

   If you look at the stars in the light frame the centers are bright-ish but all of them have a greenish halo around them caused by being unable to completely focus. I've attached a screenshot showing the color calibrated Master-light and the greenish individual light frame.

   I'm hoping someone can point toward how I might sharpen these stars. Is there a way to find these greenish halos, mask the stars in the center and generally replace the halo with what the background is in that area?

   Compute time is immaterial to me so if it can be scripted I'd be fine with fixing the 205 light frames, either the originals or maybe the registered versions.

   If I haven't provided necessary info please ask.

Thanks in advance,

Mark

BlockHead

You might be interested in the M51 example I have in the Workflows section. 

The data I was given had out of focus images in Red. 

 would be willing to put good money ZERO other people on YouTube or anywhere else demonstrate this. 

:)

Hopefully that is why you are here at ABS. 

You will need to wade through the example- but the quick answer is that Morphological Transformation on the green channel with erosion might help you a little. It can't fix everything.. but that is one technique.

-the Blockhead

Mark Knecht

I will investigate. Thanks very much!