WestCoastCannuck wrote in post #18515445
Thanks SO much for jumping in here with an excellent and knowledgeable reply!!
The question had been addressed to me, because I stack fewer images.... and when it works well, I am using sharp low ISO images. In THEORY, and as you so well explained, I should get little benefit. But, I think I do. I may not get much more detail, but a stacked file of 10-15 images shot on a clear night (say 10-15 BEST out of 50 or so) nets me a nicer result when processed with the tools in Astra Image. (deconvolution being the most important) I end up with a cleaner, "deeper" file for lack of a better word. Better IQ. Nicer image.
On poor seeing nights.... no. Too much variation between frames.
When I get time, I will look through my files for a good example comparing - and post.
Very best regards
Hi Mike, [IMAGE'S LINK: https://flic.kr/p/PxjZNs]GassendiCrater_MareHumorum_12102016
What's happening when you stack 10~15 images (or any number) is you're reducing random noise and increasing signal to noise ratio (10 is 3.2 times the signal, 15 is 3.8 times the signal, not much difference). So, because of that, the resulting image will be cleaner (less random noise) which makes it a lot easier to process and sharpen it without it looking messy, noisy, etc (as you will not be sharpening different random patterns of noise) with different sharpening methods. And the reason the file seems deeper, is because of the increased signal to noise ratio which allows you to stretch the histogram so that more of the dynamic range is represented (instead of an all grey looking flat image, you can stretch the histogram and get more contrast without clipping highlights or losing detail in shadows). Having more signal to noise allows more processing latitude. It's just slightly better when stacking 10~15 images compared to a single still image. Is it enough to warrant the extra work involved to capture the images and stack? That's a personal thing. But strictly from a data stand point, it's usually not worth it at that scale compared to the benefits of stacking 4 times that amount or more.
In terms of comparing, be mindful that if you show two different moments in a comparison, you could be simply comparing good seeing to poor seeing in the same few seconds.
For a comparison, I would suggest you show a single frame unstacked from your captures, and then a several-frame-stacked image of the same thing, at 100% crop scale, in two areas: 1) where the deepest shadow is on a group of craters, such as the terminator, with noise, and 2) areas that are relatively smooth and blank such as a mare to see if noise is removed. Ideally use the best still frame to represent the best seeing you captured, compared to stack which will represent variable seeing from several captures. The only difference will be the seeing blur captured, the noise present and the higher potential to stretch the histogram to have more processing latitude.
A lot of times, in general, folk compare a great moon shot and wonder what lens, scope, camera, etc, settings, etc, are used, are really just chasing two things (1) seeing (2) aperture. Seeing is the ultimate limitation of blur. Aperture is the limitation of resolution. Any of us shooting the moon and its details would give everything for the best seeing all the time, rather than the biggest aperture or best equipment.
To show a representation of excellent seeing, here's an example of how really good seeing at near zenith orientation with a small 6 inch aperture allowed me to capture fine detail within a crater, along with craterlets throughout the maria which are normally not seen at all due to blur and low resolution. This is 2,000 frames captured, and 20% of that stacked with excellent seeing conditions.
by Martin Wise
, on Flickr