What is a macro lens?

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I'm just pondering about macro lenses, and when they would be used. Without getting too technical, what do they actually do? For example, do they allow you to magnify a subject (make equal or greater than life size), but with shorter bellows extension and a greater lens to subject distance than a normal lens? I tried to photograph (and fill the frame with) a sea-shell (about 1" in diameter) on my 5x4 with a 90mm and 210mm lens a few months ago, and had extreme difficulty getting enough depth of field, not to mention the trouble I had lighting the subject. I messed around with semi-silvered mirrors, but I gave up in the end.

I'd like to photograph some flower heads, and am wondering if a macro lens would reduce the stress... I have both 5x4" and 10x8" cameras, so I'm not sure about the 'ideal' focal length, if indeed there is such a thing for macro lenses. My current lenses are Rodenstocks (bought new), so I would probably stick with this brand unless some other make was universally declared as being 'better'.

Thanks in advance

David Nash

-- David Nash (nashcom@btinternet.com), March 16, 2001


A macro lens won't give you more depth of field or a shorter exposure than a lens of the same focal length and aperture, but it will be better corrected for short distances than for longer distances.

-- David Goldfarb (dgoldfarb@barnard.edu), March 16, 2001.

David, Unhappily, your optics aren't the best options for macro work. The 90mm, wich I suppose to be a wide-angle, is a unsymmetrical design optimized for reductions, and probably will compare badly with an enlarging lens, for example. The 210mm - a great lens - makes your bellows extension quite unconfortable. At 1:1, 420mm. Going farther on magnification will strech your arms proportionally. I've been working on some 6:1 macro work and having a good time with 105/5.6 and 150/5.6 Nikkor-W. They're almost symmetrical and allow some space for lighting as well. Obviously, an assistant arm is still great value. Have fun. Cesar Barreto

-- Cesar Barreto (cesarb@infolink.com.br), March 16, 2001.

David, Just for laughs, take your enlarger lens out of the enlarger and mount it in a board for your camera. It'll be doing what it's made to do in this application. Chances are that at your bellows extension a very long exposure will be necessary, so just do the lenscap thing. All it'll cost you is a little time and a piece of film. If you've got a 105 or 90 for medium format enlargements, try it too. Have fun. J

-- Jim Galli (jimgalli@sierra.net), March 16, 2001.

I shoot a lot of small things in the studio (coins, stamps, etc.) and have never used a "macro" lense on my 4x5" camera. What i do use is an extension rail and an extra long bellows. I usually like to shoot with a 210 to give a bit of room between the lense and the subject. Depth of feild can be a problem at these distances and careful focusing is a bit tedious. Long arms are nice too. I assisted a photographer one time who was shooting a fabric swatch to show the weave pattern. He had it shot on a scanning electron microscope but was unhappy with the results. We ended up stringing together 5-6 different bellows across the studio and used an enlarger lense (as mentioned above). The length of the whole contraption must have been 15 - 20 ft. but the pictures turned out great. I know that this is probably not practical, but I thought it was a relavent story.

-- Eric Blevins (goat@gloryroad.net), March 17, 2001.

In the same line, is the sharpness of a macro (repro) lens optimized for smaller apertures than for a normal lens? I have recently purchased a FujinonA 240. I took a few shots of flowers at 1:1 on 120 film. The opening used was f 32 and they are very sharp. With another lens, diffraction would have started to degrade the sharpness. The Fujinon smallest aperture is f 90. Would it be reasonable to use apertures as small as 45 or 64 (for maximal DOF) or would the diffraction effect be noticeable?

-- Paul Schilliger (pschilliger@smile.ch), March 17, 2001.

Paul: Diffraction is a fixed law of optical physics, and can't be 'designed out' of a lens. Even an otherwise perfect lens would be subject to diffraction limiting.
In addition, at macro subject distances, the marked aperture of the lens bears little resemblance to the real, or effective aperture. At 1:1 the marked aperture number has to be multiplied by 2; at 2:1 by 3 times, etc.
A marked aperture of f/45 is really f/90 at 1:1, and this is the number you have to use to calculate both the exposure and the diffraction effect.
ANY lens working at f/90 will be diffraction limited to about 15 line pairs per millimetre, whether it has a macro label, or even go-faster stripes on the barrel.

-- Pete Andrews (p.l.andrews@bham.ac.uk), March 19, 2001.

Thanks Pete, this is what I thought too. Most lenses are optimized at f16-22. From 32 and beyond, the drop is significant and at 45-64, they are poor in sharpness even if DOF is maximized. This points the fact that LF close-ups are not always better than medium format close-ups. If the same DOF is attained at f22 with 6x7 and f45 with 4x5, the results may not differ much but the LF approach will bring extra cost and difficulties.

-- Paul Schilliger (pschilliger@smile.ch), March 20, 2001.

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