Cool! I'll look forward to the details when your 150mms as tube lenses review is out (not seeing them on your website as yet).RobertOToole wrote:I need to make sure that I take a look at short focus with future testing!
My testing has been starting to move this way as well, though I've been thinking more in terms of creating something like a 500mm space rather than an infinity space. With stacked enlarger lenses it seems like short focus should suit for that. When stacking with most telephoto or telezooms it's necessary to push the tele off infinity focus to reduce the close focus limit, presumably with extension tubes. The amount of extension needed for full matching seems impractical but perhaps there's some modest benefit to using a bit of extension to nudge the tele's focus range into greater overlap with the enlarger lens. A potentially better corrected approach would be to pull a 150-200mm macro towards its close focus limit and see what happens.
A related configuration is three lens stacks where an enlarger lens provides conjugate translation between a scanner lens and a tube lens. I haven't pursued any math to investigate whether this might be worthwhile, largely because I'm unsure if 1) there's a case where this arrangement would accomplish something not possible with two lens stacks and 2) there's a somewhat affordable yet sufficiently well corrected enlarger lens as not to defeat the purpose of using a scanner lens.
Hi Rik, thanks for the catch; I've tidied the wording above. In general, I think I'm less concerned with the presence of a sign mismatch than the extent of the mismatch as function of subject, image, and aperture sizes. However, it seems something of academic exercise until someone finds with a useful operating point. The short conjugates of most interest are probably scanner lenses of roughly 35-105mm focal lengths. If one chooses a macro capable of focusing down to something comparable to twice a scanner lens's focal length the macro's focal length is too short to yield a magnification above 1x. So one might as well just use the macro on its own and not bother with stacking.rjlittlefield wrote:The absolute powers may match, but the signs are wrong.