Then it occurred to me that if I use the sequential drive mode on my DSLR, I could shoot the sreries of stack images quite rapidly. I set the camera up in sequential drive mode and using fine focus, find where the top sharp focus point is on the organism. I use a USB wired remote as a shutter release. I hold the down the shutter button on the release and rack the focus using the fine focus knob on the scope through the thickness of the organism. I can then do the stack in Combine ZP.
Here is a shot of a Naupilus stacked from 18 images.

If you have observed Naupilus and copepods, they skitter about and then stop for a few seconds. This is long enough to shoot a stack series.