Thanks for the comments, folks!
Laurie, I'm with you on that "objective shot". Maybe I'll see what I can do today.
Betty, I am honored by your imagination!
But the fact is, I shot some test images at f/4, f/5.6, and f/8 and just looked at 'em. The ones at f/4 were less clear, and I couldn't tell the difference between f/5.6 and f/8. So I went with f/8 to save some time and because I speculated it might make the corners a hair better.
Then I tuned back to the forum just in time to see Charlie's
advice that "
You can use f8 for magnifications up to about 2.5X", so I felt better about my decision...
Normally I would use one of my Olympus bellows lenses for a shot like this. But I wanted a test/demo image shot with a more available lens, so I went with the EL Nikkor for this one.
Using my 80 mm Olympus wouldn't have made much difference in the settings. My notes for the Olympus (based on test images) say that its "sweet spot" is at f/8 for 1:1 and f/5.6 at its highest magnification of about 2.2X. All of those tests were done on a 6.3 Mpixel sensor, and "sweet spot" means the smallest aperture where I couldn't see any degradation. With a higher resolution sensor, the sweet spot might happen at a slightly larger aperture.
--Rik