Hi Cynthia,
Thank you! I had never heard the term Focus Stacking until you, Bob (@bobdrbob) and (apparently way back at the beginning), Bear (@beargems) mentioned it.
I have stacked multiple low-light frames in astrophotography to integrate weak-signal sources (dim stars, nebulae) for deep-sky field images. After reading the article above, it seems both techniques are setup in similar fashion but use completely different math and algorithms. Very fascinating!
I am now curious if focus stacking can be used with my microscope camera to improve depth of field (DOF) for inclusions. Bear had mentioned image stacking early on in this topic…
… but I had assumed (probably incorrectly) he was talking about illumination balance or something kin to the technique used in astrophotography. It seems he might have been talking about the DOF issue… 
I have a particular specimen that could definitely benefit from improving the DOF, discussed here.
My interests in ancient metal arts and gemstone cutting is a long-winded discussion. 
If you are curious to know more, please send me a PM.
Cheers!