Coma Corrector Comparision, with and without

Using a Baader Multi Purpose Coma Corrector.
They were taken through the 4.25” f/4 scope.
The top image is without the coma corrector, the bottom with it.
Mostly look at the stars (though some of the difference in the nebula is due to the corrector).
These are crops of larger images. The center of the frames are near the rigth.
The comparison isn’t quite apples to apple as the top image is slightly out of focus, taken on a slightly hazy night (the day I got the corrector), is a stack of 3 verses 7 (4 min) images for the bottom and no dark/flats for the uncorrected image.
Many more stars are visible in frame edge of the coma corrected image and they are round, not oval.
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This summer I starting thinking about getting an apochromatic refractor and a f/ratio reducer/field flattener. I was looking at a Borg 80mm f/3.9 setup. I wasn’t so keen on spending $2000 though, so I got to thinking about cobbling together a short focus reflector instead. I have three 4.25” f/4 finder scopes that I had build over the years for my 10” scope and a 4.5” f/8 (source of the 2" diag) that I built as a guide scope for the 10” (none of these were currently being used). Among them I had one good 4.25” f/4 mirror and one good 2” diagonal mirror and 2 good tube assemblies. A couple years ago at the Stellafane swap tables I bought a 2” Crayford style focuser with dual speed focus for $80 and this year a couple 8x50 finders with dovetail mounts for about $30 each.
Taking images with the resulting 4.25 f/4 scope (f/4.4 equiv. with the 2" obstruction) worked well except for the coma. Coma correctors range from about $150 to $250. I purchased a Baader Multi Purpose Coma Corrector (MPCC) (the astrophoto setup only) for $145. It is optimized for f/4.5 optics and does not change the focal length (does not reduce or magnify the image).

FYI, the same image brightness requires only 4 minutes in the 4” f/4 (f/4.4 equiv) compared to 7 minutes in the 10” f/5.6 (f5.8 equiv).

I extracted this from an article I wrote for our local club's Winter newsletter.