I'm struggling to figure out how to provide the best help.
You started this thread by writing
Deanimator wrote: ↑
Mon May 03, 2021 1:11 pm
In the below image (unused coffee grounds), I notice some haze in the upper portion.
Any clues on the cause?
The cause of that problem is now clear: you accidentally omitted some source images while running PMax to make that first picture.
So, moving forward I see two main directions.
First is to figure out exactly how those source frames got omitted, and more generally to figure out how to more quickly spot similar problems if they occur again. For that, I still recommend "play like a filmstrip" as the best available technique. I suggest to practice on stacks that are behaving well, so the differences will stand out more for stacks that do not. Again, with a checkmark on "Show as adjusted", you should see focus moving smoothly all the way from one end of the stack to the other. Any jumps, either laterally or in focus depth, will indicate a problem.
Second is to address your other questions about the effect of extra frames on the front or back. For that, the main guideline is that extra frames seldom have any big effect but it's always safer to remove them. Extra frames will usually increase pixel noise with PMax, and they can cause shifts in overall framing and contrast/brightness. However, extra frames at the front and back will not
cause loss-of-detail problems like your first image showed.
Please see the single coffee ground image for the radical difference.
Without guidance, what I see appears to be a much shallower scene, with no obvious problems except some softness at lower right.
When you say "radical difference", what aspects are you referring to?