M42 - Correcting "Fisheye" effect

[ionia23]

Hello,

I haven't set up a dropbox yet so I had to convert this to .jpg for posting. Since I've been stuck with cloudy skies every night since, well, June, I've taken the opportunity to learn my tools so I can be better prepared when the weather clears up out here. This means visiting old images from years gone by and seeing what can be done with them. By and large, I've been really stunned with how much data I actually captured back then and didn't even know it. Startools fan for life.

This is M42 imaged on 08/28/2012 from my front yard. This was captured with a 203mm Orion reflector scope on a really crappy Chinese-knockoff equatorial mount that had clock drives, but no encoders, no error correction nothing. As if that isn't entertaining enough. the images are caught through an Orion 15mm (possibly 20mm) Expanse eyepiece using Eyepiece Projection, not prime focus. Yes, yes, I know...

I think I'm looking at about 2m30s of captured data. Deep Sky Stacker did what it could with my existing frames and I'm actually pleasantly surprised with the results. This is with no dark/bias/flat processing either.

Most of the things "wrong" with this image I can repair, no problem. But the "fisheye" effect is rather annoying. This is normal behavior for the Expanse eyepieces. The have a 55 degree AFOV but I didn't have a field flattener back then. You can see the effect get more pronounced as you approach the edge of the image. All the stars appear to "stretch" out more and more in the direction of the nearest edge.

I don't suppose it's possible that the Lens tool in Startools might be useful in offsetting this? I'm not quite sure where the best place to begin would be, and where to put that type of repair into a typical workflow. Suggestions greatly appreciated.

[admin]

Correct! The Lens module will ameliorate this (diffraction patterns "spikes" will distort however).

The new SVDecon module will further help correct for the changing Point Spread Function.

It won't be perfect, but it will be better.