I was interested in seeing side-by-side the progression of images and how stacking affects astro photos. So I took some images of M31 Andromeda Galaxy in mid-october and decided to do some comparisons. So here is a single light frame pretty much straight out of camera (just rotation and raw conversion using default settings in DPP). I tried to select the "best" light frame (#37 out of 80 total taken) for the comparison.

2021-10-13_90.00s_0037 by Stephen, on Flickr

Then I took that same best exposure and post-processed it with flats, darks, and bias frames using PixInsight. Did a stretch of the data and adjusted curves, colors, saturation, etc. Generally most of the same things I would do with any stacked astro photo.

M31 Andromeda Galaxy (Single Sub) by Stephen, on Flickr

And finally, I stacked multiple light frames and fully post-processed for a final image. This is 70 light frames (the best chosen out of 80 total taken that session). Again, stacked and calibrated in PixInsight using Darks, Flats and Bias frames.

M31 Andromeda Galaxy by Stephen, on Flickr

Overall, I thought this was a great exercise for me to better understand the difference that comes from stacking multiple images and doing proper stretching and calibration in post-processing. I still find it amazing what can be extracted from what looks like a pretty bland image straight out of the camera.

For those who want the technical details of capture, these are all 90s exposures at iso 1600 taken with an unmodified 5dmk3. Mount was an HEQ5 and scope was a WO Z81 with 0.8FF. No guiding.

Thanks for looking!