Stacking stacked photos

[jackp93]

Hi all

a couple of nights ago I managed 4 hours of M81. However every time I go to stack them in dss my computer takes 3 hours to stack and then crashes before the image is completed. Is it possible to stack say four lots of one hour and then stack the four images together.

 

thanks

 

Jack

[ONIKKINEN]

Sure, its possible. Not sure how that will effect the final signal to noise ratio but i would expect it to be a bit lower than just stacking everything at once, especially if sigma clipping is used. I would stack the 1hr stacks with sigma clipping to remove satellite trails and other outliers and then just a simple average combination for the 4x1hr stacks.

The easiest way to do this would be to use the same single sub frame for all the stacks as a reference frame, that way you dont need registration and the final stacks do not have rotation differences, since they were all stacked on the same sub. Also, the intermediate stacks must be the same size, so mosaic and intersection modes are out of the question, the standard mode (which stacks to your selected reference frame) must be used. Doing this you can just stack the final stacks with no star alignment and average combination, and of course no calibration frames since they were already applied previously.