Hello Everyone,
I hope everyone is happy and all's well. I've always been interested in wanting to visualize the difference between stacking more and more sub-exposures, with a view to improving the signal to noise ratio in images. In particular how much better do things get for each bit of extra effort.
Well there is plenty of information/theory out there (simplifying) to suggest that given "appropriate" sub-exposures that signal to noise ratio can be improved by as much as the square-root of 2 (an ~41% improvement) for each doubling of the number of sub-exposures.
I set about to try to see what that looks like, not that I tweaked things to the max to achieve sky-limited exposures, but just "reasonable exposures" which were not obviously black clipped on the camera histogram. Using a Modified Nikon D800 with Sigma Art 50mm f/1.4 lens on a fixed tripod/no tracking I imaged the Milky Way from my suburban Melbourne backyard. Unfortunately as this was conducted last year and I've filed/misplaced the original image details, but most likely they were 8 second exposures @f/2 at ISO800. The images were stacked in Sequator, with its Light Pollution processing applied but no specific noise reduction was applied. The final n=1,2,4,8,16 and 30 final images were somewhat adjusted to equalise brightness to facilitate comparison.
The full image is attached of the stack of 30 x 8s images of the Milky Way. There is also a comparison below this image of the Cat's Paw Nebula magnified (Yellow Rectangle) to show detail for n = 1, 2, 4, 8, 16 and 30 sub-exposures, i.e: each time doubling the number of sub-exposures. (Yes i know it should have been 32). There is clearly a benefit with each doubling in the number of sub-exposures and 30 seems a decent/realistic endpoint given the overall image size/FOV and for the conditions. I'd be interested to continue it past 30 images to see the point of no further benefit. I might do that one day. In any event it's important to recognize that some of the benefit seen will also be due to some mild "dithering", given the use of a fixed tripod without tracking.
Happy viewing.
(Image TBA soon)EDIT: Now added
Best
JA
