Since the fabulous Roni has made me revisit (and like) the world of lens-reversal close-ups, I thought to push it a little.
Took the standard setup, and inserted 68mm of extension tubes into the stack. Extension tubes help to decrease the minimum focus distance, so you can get even closer. Use with caution; you can get so close that you block light.
(Wobble-focus technique is in play for all of the following. Yes, I did have and carried a tripod, but I really need a focusing stage...)
Anyway, pointed the stack at a known reference: a U.S. quarter dollar coin
Then pointed it at the ever-available Agapanthus bloom:
(this is the same bloom, sans extension tubes)
And then, one for fun
At some point, I will try this with a bellows extension. Definitely need a tripod for that, but the bellows has a built-in slide, so it should be a little easier.
Now excuse me while I go clean my filthy sensors...o.O