a lens's focal-range optimization

greenspun.com : LUSENET : Large format photography : One Thread

General purpose large-format lenses are often designed to yield optimal results when photograping subjects at medium-to-far distances, or within a focal range of 1:10 to infinity, and sometimes as close as 1:5 to infinity. It seems that it is not too unusual to encounter situations where it is desirable to photograph a person or thing closer than 1:10--for example 1:7--or even closer than 1:5--say 1:4 or 1:3. Is a process or flat-field lens the better or proper lens to use in such situations? I am not a still-life photographer, but is a process/flat field lens what still-life photographers typically use for such ranges, or do they just use general purpose lenses? And what exactly happens when a lens is used outside of its optimal focus range? For instance, does sharpness and resolution markedly decrease? Do any other problems occur?

-- nick rowan (nrowan@vf.com), January 08, 2001


Nick, You have two chances: read all you get in hand and find you'll problably be in trouble going far too close, or try to relaxe and use a good symmetrical lens. If you find something so terrible happening in the near world, you've pretty good eyes! I haven't found myself yet. Have fun! Cesar B.

-- Cesar Barreto (cesarb@infolink.com.br), January 08, 2001.

I have an old Schneider 90/6.8 that I use within 1 foot that resolves all the detail I could ask for. Bellows draw up the ying yang though. James

-- lumberjack (james_mickelson@hotmail.com), January 08, 2001.

To try and answer your question: To a very small extent the correction of both chromatic and spherical errors is compromised by using a lens away from its design parameters, but then lens design is all compromise anyway. In fact it's a complex series of inter-related compromises, the aim being to balance one abberation against another and to acheive an acceptable, or even exceptional, standard of optical performance.
Now, this juggling trick only works at one set of conjugate focii, in the same way that a car engine only develops maximum power at a fixed RPM. This doesn't mean that the lens, or engine, is unuseable at other ratios, simply that it's been optimised at one particular ratio.
In practise, you have to go a long way outside those design parameters before the lens quality becomes unacceptable, or the engine stalls. With large film formats, this point of acceptabiltiy is much less critical than with smaller formats, in the same way, (to continue the analogy) that a large capacity engine is more forgiving of working in the wrong gear than a smaller one.

I can't really understand the obsession with lens quality currently being expressed on this forum. Large format photography is surely about using film sizes large enough to make lens abberations, film grain, etcetera, totally trivial.
Am I wrong in my assumption that large format work should actually give us some freedom from a total dependence on high technology, and on having the latest 'this' or the most expensive 'that'?

-- Pete Andrews (p.l.andrews@bham.ac.uk), January 09, 2001.

No no! LF is about getting MORE PIXELS!!!

-- John H. Henderson (jhende03@harris.com), January 09, 2001.


I couldn't agree with Pete more! We seem to get consumed in the "process" at the expense of "art" and "creativity." I suggest trying the lens in the real-word application and see if it meets your requirements. I use a 305mm process lens at infinity and get incredibly sharp negs/chromes. I've also used it at 1:1 and can't tell a difference. I don't have the bellows for much greater than 1:1.

Regards, Pete

-- Pete Caluori (pcaluori@hotmail.com), January 10, 2001.

Moderation questions? read the FAQ