Of course, you're all a bunch of nutters, and there's no WAY I'm going to be sucked in to going down the same path as all of you… Rolling Eyes
no no, I mean it, really!
The field of microscopy seems to be much more complicated than photography and its measly handful of parameters…
hmmm.... what's that distant sucking sound I hear!If, just by chance, I happened to mention to them that I was looking around for some objectives (in the <8x range) that might be lying around in a bottom drawer
Actually microscope objectives become a real viable (and desirable) option from about 10X and up. There are a few nice 4X and 5X that can be used, but the advantage, if any, over the optics we've discussed is not that great (and there are a couple of possible "downsides" like a fixed aperture, shorter working distances, and questions of coverage on a full frame camera).
Microscope stuff does get a little more complicated. There's much to be found in the forum threads. Be best to spend some time searching through them. But briefly (in terms of putting it on your PB-6)...
Newer Zeiss objectives (infinity design) would require an additional tube lens. Not completely impractical, but almost.
Older Zeiss and most other manufacturers (160mmm, finite type) required corrective eyepieces to complete correction for chromatic aberration. Not practical on bellows.
The best options in used gear (without tackling the tube lens issue) are some Nikon "CF" style objectives. Nothing here bwtween 5X and 10X.
For 10X you would be most interested in:
10/0.30 Nikon CF Plan Achromat
Any of the Nikon CF M Plans (finite 210mm tube length). There were several versions made.
Working distance becomes a critical issue. You'll get about 9-10mm of working space with most of the ones mentioned. Many 10X objectives will have unusably short working distances.
No CF Plan Achromats on eBay now, But here are a few CF M Plans: 200280675991, 110280668140, 350079982121 (20mm working distance... other than that image quality about same)
The BD versions have the same "glass" but shorter working distance unless you remove the darkfield component to the mount. (350104224200)
Lastly, microscope objectives were designed to produce a smaller image than the other optics we've discussed. No problem with the D300, but with the D700 you may want to check the corners to see if it's up to your needs.