Re-processing my image of M31 from 26/8/2019 today 27/8/2019

I used Roger’s suggested Ian’s noise reduction in GIMP and rounded stars although I did not subtract sky background as image went strange when I tried that on this image as I appeared not to be able to properly deal with very bright M31 core in creating frame of sky background.


Image as I previously processed it:

Newly processed image:

7 Responses

  1. I am not that familiar with Deep Sky Stacker, although I have used it occasionally. My preferred option is Registax, and of the various options I like Registax 5 rather than Registax 6. Mind you R5 won’t recognise the video Codec from from the Mikrokular (the PD is fine), so it might not with your camera. R6 does, and that is what I always use with the Mikrokular. A sequence of png or jpg stills should be fine with either.

  2. Star trails must be caused by less than perfect tracking during a single exposure.
    3 obvious possibilities for improvement.
    1) Improve tracking
    2) Use guidance using a guide scope for example.
    3) Shorten the individual exposures and use more of them to compensate. Then let the stacking program sort it out. Both Registax and Deep Sky stacker will compensate for rotation.

    All my “Box Brownie” images do not use individual frames longer than 20 seconds. Either with the SCT which is on an alt-az mount that produces image rotation, or with the window-sill scope that is on an only VERY approximately aligned equatorial.

    1. When I tried multiple exposures on M31 (60 secs) each and then tried stacking in Deep Sky Stacker it said it could not detect enough stars to stack more than one image. I was surprised with that. What do your think?

  3. Yes, I am afraid that background subtraction method only works when the objects you want to retain are small with respect to the background. In this case, it thinks that the extended M31 is background and subtracts it. You could probably get around it if you get an image of a nearby part of the sky (without M31 in it!) and use that for your background subtraction. Assuming, of course, the background IS light pollution. If it is amplifier glow, you need dark frames.

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