Micro stage movement

[rjlittlefield]

Thanks Chris. I'm hopeless with formulas. But if I understood, after spending some time in one of those pupillary magnification threads (huge if) is that the aperture is figured for the 160mm extension or whatever standard it's spec'ed for. A macro lens' specified aperture is presumably spec'ed for infinity focus with no extension. If true, that 40mm 4x f/2 objective compares with an f/4 macro lens that ends up with an effective aperture more like f/17.

That's using this formula: "multiply the f-number on the lens ring by magnification plus one", I used a different one before...

That should be f/20, not f/17. The formula requires adding the one to the magnification before multiplying by the f-number. Hence it is 4*(4+1)=20 as opposed to (4*4)+1=17.

You're correct that the objectives are specified in terms of their nominal tube length. They're also specified in terms of aperture as seen by the subject, not the camera. From the standpoint of the camera, that 4X NA 0.2 objective gives effective f/10, just like the equivalent f/2 macro lens. Similarly the 4X NA 0.1 objective gives effective f/20, just like the equivalent f/4 macro lens.

--Rik

[ChrisR]

Good, convergence. Perhaps I need slightly smaller steps in some cases.
One sobering constant-ish is that for a subject as deep as it is wide, something like 500 steps are needed.
Another column for your spreadsheet Charles?

[PaulFurman]

Thanks again guys. Believe it or not I did notice I messed up the order of that formula after posting <g>.

So yeah I'm convinced those fine steps are needed for optimal work now although it's amazing how few you can get away with sometimes just 3 frames widely spaced looks great.

I figured out a way to use the micrometer dials described above on my bellows and just posted that setup: Micrometer Control of Bellows