I have recently watched a video by Dylan O'Donnell (StarStuff on YouTube - https://www.youtube.com/c/DylanODonnell) where he really concentrates on only using the best subframes in his stacking.
His rationale for this is "Garbage in, garbage out".
I decided to follow his lead using some existing M42 data (previously posted here from 27th March 2022), and stacked to be 45mins. total.
By the time I had finished with the new techniques I had 24mins. total... BUT the interesting thing is, the image was much easier to process, looked sharper and had less noise!
So, on to what I did. Well, on top of the normal rejection of any subframes that are clearly blurred or have satellite trails, etc. I used two other columns in Deep Sky Stacker called "FWHM" and "Stars" [count].
(These fields are also available in other image processing software.)
FWHM or Full Width Half Maximum is a measure here to show how good the focus is. The lower the number the better the focus.
Stars is a count of the number of stars in the frame.
FWHM or Full Width Half Maximum is a measure here to show how good the focus is. The lower the number the better the focus.
Stars is a count of the number of stars in the frame.
With the light frames ordered using the FWHM value, subtract the smallest from the largest and then divide the result by 2, to get the half way difference point. Then add this result to the lowest value, i.e.
100-40=60, 60/2=30, 40+30=70
You would then reject any subframe over a FWHM value of 70.
Of these remaining light frames, order them by Stars [count] and reject 50% of the lowest value frames.
(I also found using a 10% rule worked just as well when there are not many subframes available).
(I also found using a 10% rule worked just as well when there are not many subframes available).
Here is my result:
(The original is here: https://mmastrogroup.blogspot.com/2022/03/the-end-of-winter.html)
Clear skies.
MJ.
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