I almost didn’t post this because I can’t quite believe the results are so poor for the second image, but here it is. I’ll try again tomorrow if the weather holds out. A stack of 60 images, processed from RAW in PIPP, stacked in Registax v6 and finished in Photoshop. Identical processing other than the exposure time.
The first one is 1/1000th @ ISO100 which is what I normally use. This gives me a histogram peak about one third of the way across the graph in APT. The second is 1/320th @ ISO100, which I chose because it gave me a peak about two thirds of the way across.
To me, this second one looks out of focus but I didn’t touch anything but the APT controls between taking the two:
And a comparison of the sunspot area at the bottom left:
I don’t know if the brighter image caused Registax to have trouble aligning the frames, or if there’s some other processing issue, but clearly the 1/320th sec exposure image looks awful. I’ll post another test when I can do one, but on the the basis of this result I shall be keeping my histogram output well to the left.