Lenses optimized for close up vs. diffraction limitsgreenspun.com : LUSENET : Large format photography : One Thread
I'm shooting a lot of close-ups with very 3 dimensional objects on 4x5 film with a Schneider Symmar-S 150mm lens extended out to nearing 1:1 reproduction. At least printing on 16x20" paper (4-5x enlargment) the resolution is looking a bit vague. I'm assuming that much of this is from the diffraction which comes from a typical *effective* aperture in the neighborhood of f64 or even f90. Of course, this lens is not optimized for close up work, but I wonder whether or not such a lens would really offer appreciably higher resolution at such apertures anyway.
In my comparing lenses for 35mm equipment and at effective apertures around f16-22, the macros (not just "close focussing consumer lenses", but lenses like the Zuiko 80mm macro lens on bellows) clearly have higher resolution than normal lenses with lots of extension. But I'm curious whether this would hold for LF lenses stopped way down. In other words, is macro optical design irrelevant and diffraction limited, or is the nature of close-focusing distortion with standard lenses distinguishable from diffraction? I'm unlikely to use an LF lens at less than effective f32 for most subjects. (I don't have an optimized-for-close-focusing LF lens to run my own tests.)
-- Eric Pederson (firstname.lastname@example.org), February 07, 2002
just a few remarks based upon my experiences: I've used an 150mm Apo- Ronar MC at about 1:2 and compared with 180mm Sironar-N MC. Both results were very good and you couldn't tell the difference. Both lenses are not optimized for that 1:2 ratio, for the Apo-Ronar it isn't large enough, and for the Sironar-N it's to close. I used both with f 22 because the Apo-Ronar is optimized for that f-stop and the newer lenses like the Sironar-N are optimized for f 16 to 22. I don't know how old and good your Symmar-S actually is; I've used a mid50's with good results. Distortion could be a problem for normal lenses, but LF-Lenses are nearly symmetrical except Tessar-types. If you have a look at mtf- charts you will see that contrast and resolution will always be lower in the macro-range. But macro-lenses will still perform better than normal lenses. Designs like Apo-Ronar will be better at 1:1 ratio but are still very good at infinity. (They are designed for a flat field in cases of reproduction but can of course take 3D-objects as well.) So I think diffraction at small f-stops is the point as you already mentioned. You can computize the effects generally, but lens design will affect it too. Even my Repro-Claron is realy bad at 1:1 if stopped down below f 32, as other lenses I've tried, too. If you can use the f-stops your lenses are optimized, that will normally be 16 for newer, 22 for Apo-Ronars and the like and 22-32 for older, and effective f-stops at 1:1 will be 32-64, and the results are not as you excpet then try a macro-, copy- or repro-lens. If you have an enlarger, the use of enlarging-lenses is actually discussed on this form (works good for me, too).
-- Thomas Vaehrmann (TVaehrmann@web.de), February 08, 2002.
In my case I tested a New 150mm G-Glaron against a 135mm Sironar N, f 22 was used and I saw a difference in sharpness the Glaron was the winner but it was almost 2:1. I tested it on a old watch and I state the G-Glaron is fantasic for this! It is the cheapest macro lens thad I know!
-- Armin Seeholzer (email@example.com), February 08, 2002.
Thanks for the replies. It sounds as though a different lens would indeed be sharper at least to an indicated f22 (effective f45). I'll keep an eye out for something I can afford. In the meantime, I'll probably assume that with an effective f64-90 aperture, diffraction is probably the great equalizer.
-- Eric Pederson (firstname.lastname@example.org), February 12, 2002.