DO try 2-2.5µm, you should see a slight improvement if you look hard.What step size would you normally use at 20x? I've been using 5 um and end up stacking about 30-40 shots. Would there be any disadvantage in going down to 2um apart from storage and time? I'd like them to be as sharp as possible and show as much detail as possible.
Look at Rik's Zerene Stacker page on DOF or use his speadsheet from Here: DOF Two Ways
Are you using flash at the end of an extended exposure (2 seconds?) to be free of shutter vibrations? Try a 4 second exposure without the flash. If there's nowt to see, no worries!How dark should the room be? I have curtains and blinds drawn, but there is some light from the computer screen.
Try turning off the Scale option in Zerene's Setup.I have noticed that if I do a larger stack through more of the depth of the image, then objects appear flattened. Is this normal, or is it something that I'm doing?
The view you have is fairly telecentric so you don't get much perspective. Then it's "just" lighting - the hardest thing. A second, low power slave flash may help.
An adjustable iris interposed right behind the objective. 52mm (eg jinfinance on ebay) so it'll NOT need adapters. I expect you could make a little black paper "hat" to slide over the objective very carefully, to create a small aperture. One frame will do if all you want is to make the foreground and background less out-of-focus. Stack it separately with all possible scale etc setting enabled, and be prepared to retouch a lot - objects will move! You'll need to turn the flash up, or combine several frames exposure-wise. I've never tried the latter-you'd need zero movements I guess. If you can get 3 stops brighter flash for the reduced aperture shot, that should do. Of course you can do more stopped-down steps.What's the best way to blend between the focused area and the unfocused area?