Repairing elongated stars in edge of field with software

[RyanParle]

Whilst I know that the only real way to ensure a flat field is to use a field flattener to produce raw images with round stars, at this point in time I cannot justify spending out on one, as my 80mm/550mm APO will soon become some what obsolete when I get my Officina Stellare Veloce 200 MK2 in a few months.

So I am wondering if there are any software alternatives to help make my images more appealing in the meantime?

[davew]

You could try this - https://www.youtube.com/watch?v=YuEX3KLrAUo

Or wait for the next scope

Dave

[RyanParle]

That looks fun! ?

I've been messing with Photoshop Lens Correction, which looks like it could have potential. at the moment most of my attempts seem to really stretch out the centre of the image, but i might just get it to work.

So far manual corrections seem ok.

Before:

After:

If apply more correction the stars in the middle seem to squish as if they were affected by coma so I think this is as far as you can go for manual correction. However I have just found the Adobe Lens Profiling Tool, which with requires a few shots of a printed calibration grid to perform an analysis of the optical distortions, hopefully this might get me even closer, I will probably have to set up my telescope in a big enough area so I can get the calibration board far enough away to get an A4 sheet to cover around 1/3 of the sensor, I did a quick test in my garden and an A4 page covers about 80% of the sensor, so i'll have to find somewhere else to take the test images.

[almcl]

Coming a bit late to this, but I ran your 'before' image through StarTools' lens module and got this result.  Not sure how much of an improvement it is? Didn't take more than a minute over it, so better may be possible.

[billyharris72]

It might be worth looking at the Astro Art "compress stars" filter (you can downlod the free AA7 demo and check it out). This makes stars smaller, but also has a module that reshapes them, so can help deal with curvature a bit. It's tedious though - the only way to get really good results is to manually select stars in groups (depending on what bit of the image they are in and the extent / direction of elongation), apply the filter and then move onto the next part of the image.

May or may not work for you, but worth a try.

Billy.

[Davey-T]

You can mess about in P'Shop working on a corner at a time with layer mode darken and nudge the stars round with the arrow keys.

Dave

[blinky]

I have often thought that it should be possible to completely fix stars (and anything else in the frame) in software.  CCD Inspector (and other apps) can work out the field curvature, so why after working it out can they not apply the opposite to correct the frame?