First attempt: trouble with CA on M45

[billyharris72]

Hi all:

It's my first post here, and also my first attempt at a photo. It was taken from a light polluted back garden and was really just an attempt to get used to the setup (Skywatcher Startravel 80 and an EQ5) but I was interested in the high level of chromatic aberration (not so much a halo as stars the wrong colour). I appreciate that this will always be an issue with a fast achromat, but was wondering if there is anything I could do (short of buying a new scope) to reduce it. Baader does a range of CA reduction filters - does anyone know if these would be likely to help or would that be a wasted investment? I have a 120 x 1,300 mm Mak and was wondering if a x0.5 focal reducer might be a better option.

The other thing that is obvious is that the stars on the edge of the image (especially at the top) are very stretched. What causes this - is it an optical thing, or the result of a badly aligned mount?

Any advice much appreciated.

Thanks,

Billy.

[D4N]

Given that the stars in M45 are supposed to have blue clouds around them it isn't that much to worry about

The actual source of the blue is probably out of focus blue light as you are unable to bring the red and blue light to the same focal point.

Unless you use filters to reduce the spectrum to the point where the dispersion isn't noticeable this will always be a problem. Of course unless you have a mono camera this will increase the amount of time it takes to capture an image.

The star shapes could be field curvature, refractors require flatteners to produce a flat field that is well corrected to the edges.

/Dan

Sent from my iPad using Tapatalk

[billyharris72]

Thanks for the tips. Might give one of the filters a go and see what happens. Fingers crossed!