Thanks, Zoeff. The last one is one of my favorites, too. Believe it or not, the image is techincally "overexposed." If we had the capacity to view diatoms, we wouldn't be able to see the honeycomb structure beneath the sheath. It's a little wild to think about the different forms and how they're constructed. Little living organisms with that honeycombing, overlayed with a band of tissue round the center. Very strange.
popo, not sure about macro photography. Greg's fractal-sharpened butterfly wing
is the closest I've ever seen someone get to the individual scales using something other than a microscope. I don't know how your setup differs from his, nor am I knowledgeable enough to comment on the actual resolving power of a macro DSLR lens + TC.
Just as an example, though, most snowflakes
are somewhere between 7000 and 10000 um in diameter, whereas butterfly wing scales are on the order of 100 um or less. I'm curious about it, though, so it would be great for you to give it a shot!
Nikon D300 / 35mm f1.8 / 300mm f4 / TC-14E II
Pentax K200D / DA 18-55mm / DA 55-300mm