The maths of how to achieve accurate focusing.

[Dan Fromm]

Leonard Evens wrote "Also, as I noted, many of us have learned intuitively just where to put the ground glass as we focus without having to think about it. But it is hard to tell someone how to do something you do instinctively."

Written like a landscape photographer. I get the very strong impression that you focus by moving the rear standard. When working close up, normal practice is to set the magnification by setting extension and then focus by moving the camera fore and aft, not by changing magnification by moving either standard.

I agree with you that for many purposes approximating the lens' principal planes' positions is good enough. But I'm spent a little time designing, making, and testing optimised lens-specific versions of the Spiratone MacroDapter. When doing that, if one gets the principal planes' positions wrong by much (in terms of percent of focal length, not absolute distance) the brackets won't give the calculated results. To be fair to you, errors due to misplaced principal planes can be swamped by errors in flash placement and by the false but handy assumption that a small flash can be treated as a point source.

Cheers,

Dan

[Leonard Evens]

Leonard Evens wrote "Also, as I noted, many of us have learned intuitively just where to put the ground glass as we focus without having to think about it. But it is hard to tell someone how to do something you do instinctively."

Written like a landscape photographer. I get the very strong impression that you focus by moving the rear standard. When working close up, normal practice is to set the magnification by setting extension and then focus by moving the camera fore and aft, not by changing magnification by moving either standard.

I agree with you that for many purposes approximating the lens' principal planes' positions is good enough. But I'm spent a little time designing, making, and testing optimised lens-specific versions of the Spiratone MacroDapter. When doing that, if one gets the principal planes' positions wrong by much (in terms of percent of focal length, not absolute distance) the brackets won't give the calculated results. To be fair to you, errors due to misplaced principal planes can be swamped by errors in flash placement and by the false but handy assumption that a small flash can be treated as a point source.

Cheers,

Dan

You are correct. I don't do much close-up work, but even when I do, I usually do most of my focusing by moving the rear standard because my Toho only allows fine focusing there. But for me close-up usually means about 5-10 times the focal length. Were I to be using larger magnifications, I would do it your way, and I would locate the position of the principal plane. Setting the magnification in advance by setting the bellows extension is a trick I hadn't thought of. Thanks for the tip.

My back has been acting up a lot and winter has arrived, so I am thinking of doing a lot more close-up work. I expect to find some surprises about the technical aspects, but I think those will pale in comparison to the esthetic challenges.

[Dan Fromm]

Leonard, I hope your back acts up less.

All aspects of closeup work are difficult, and the larger the format the more so. I moved up from 35 mm to 2x3 for closeup work to be able to cram more in the frame without losing detail in the main subject. With 35 mm, I had to give up detail in the main subject or give up the setting.

I suggest that you buy copies of:

Gibson, H. Lou. Close-Up Photography and Photomacrography. 1970. Publication N-16. Eastman Kodak Co. Rochester, NY. 98+95+6 pp. The two sections were published separately as Kodak Publications N-12A and N-12B respectively. Republished in 1977 with changes and without the 6 page analytic supplement, which was published separately as Kodak Publication N-15. 1977 edition is ISBN 0-87985-206-2.

and

Lefkowitz, Lester. 1979. The Manual of Close-Up Photography. Amphoto. Garden City, NY. 272 pp. ISBN 0-8174-2456-3 (hardbound) and 0-8174-2130-0 (softbound).

You'll probably enjoy reading both and they contain, um, limitative theorems about closeup photography and photomacrography that photographers who work at normal distances are rarely aware of. I've incorporated some of the scarier ideas in a spreadsheet I wrote to help me design my flash rigs. If you'd like a copy of it, send me a PM with your e-mail address.

Cheers,

Dan