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Lately I've been surfing the web and have run across a number of sites with readers' reviews of lenses. After reading some of the comments I'm amazed as to the basis on which equipment decisions are made. One reviewer of a macro lens stated his testing procedure: he hand-held his camera, shot tight closeups with the lens wide open at f/2.8, used ISO 200 speed color negative film, and had it processed at the local WalMart. He then trashed the lens based on the resulting prints. Folks, that is not how you test a lens. In fact, I don't know if you could learn much at all from this "test." If you really want to conduct a proper evaluation, here are the basic steps to take:
- Load your camera with a fine-grained slide film such as Fuji's Provia 100F or Kodak's E100S. Do not use any slide film faster than ISO 100. Definitely do not use color print film. There are too many variables outside your control if you test with negative film. Are the resulting prints off-color and out-of-focus because of the lens being tested or because of the machine that made the prints? Use slide film for all equipment tests since what you look at is the actual piece of film you exposed, not a second-generation copy. You see what was originally recorded on the film.
- Mount your camera on a sturdy tripod that has a stout tripod head. Far too many tripods are not solid and will in fact blow around in the wind. Use something like a Gitzo G1340 or Bogen 3221. If in doubt, hang a heavy weight — your camera bag will work — from the tripod to keep it from moving around. Don't use one of the "pistol grip action heads" as these are too vibration prone, particularly when used in the vertical mode. Make sure all the tripod head controls are locked tight.
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Female upland goose, Falkland Islands. Nikon 80-400mm VR lens set at roughly 400mm. Just to see how well the VR technology works, I took a hand held photo of this upland goose using a shutter speed of 1/125 sec. Hey, it works!
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- Set up a test target with fine detail. Tape some newspaper pages to your garage door, or stack a number of cereal boxes together, or anything along these lines. Ideally you want a variety of colors plus some neutrals (white, gray, black) in your test target and you want it to be a flat surface to photograph.
- Place your camera so that the film plane is parallel to the test target. One thing you want to see is whether the lens shows field curvature wide open, and you can't test this if the film isn't flat to the target. Spend a few extra moments aligning camera to subject.
- Run your test with natural light. Work in a light level so that you can shoot at shutter speeds ranging from about 1/125 second with the lens wide open down to 1/2 second.
- Set your camera to single frame advance. Manually focus on your test subject, meter properly and set the exposure. Lock up the camera's mirror if you can. Now use a remote release — you don't want to poke the shutter release with your finger — and take a frame. Wait about five seconds for all vibrations to stop, refocus the lens just to make sure it really is in sharp focus on your subject, and take another frame. Shoot at least three frames with the lens set wide open, then repeat this entire process at several other apertures on the lens (shooting at every aperture would be even better). If the lens is a zoom, do this all again at both ends of the zoom range and at the middle focal length. If the lens is AF, repeat this whole process once more making the lens refocus for each frame. Ideally you should write a little note as to how the film was exposed and stick it on your test subject, so that you don't have to correlate shooting information with slides after the fact. Placing notes directly on the test target also allows you to come back to your test images months later to re-evaluate them without searching for the information you tossed into the trash long ago.
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Anders Island, Antarctic Peninsula, at first light. Nikon 80-400mm VR lens on tripod. Having the ability to crop is one of the primary reasons to use a zoom lens — any zoom lens — for landscape work.
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- If you own another lens in the same general focal length, take a few shots with it as a comparison. This will help you judge color. All lens lines exhibit a certain color bias. There is Nikon color, Canon color, Pentax color, etc. While these are subtle differences they are indeed there. You want to learn if the lens you're testing — particularly if it's a different brand than your other equipment — merges well with what you already own.
- Get your film processed by a professional lab. (Which is the sort of lab you're already using, right?) When you get the slides back, evaluate. Don't project the images; after all, doing so just means you're testing the quality of your projector lens, and quite frankly most projector lenses are optically not even close to camera lenses. If you don't own one, buy a quality loupe that can be focused for your eyesight. At the minimum I would suggest a 4X one, which you'll need anyway to check slides in the future. Buy a more powerful one if you want, 8X or so. Peak, Schneider, and Rodenstock are all good brands. Don't waste your money on a cheap loupe with plastic elements.
- Place your slides on a color-corrected light table to view them. How else can you evaluate if the lens has good color transmission than by viewing slides with the proper lighting? Look for: sharpness, color rendition, barrel or pincushion distortion (bowing out or curving in of lines on the frame edges), flatness of field, and light falloff in the corners (particularly wide open). If some specific apertures don't seem sharp, note what shutter speeds were used for those frames. Almost all cameras are most vibration prone at 1/15 and 1/8 second, so, if the slides shot at those speeds are not sharp, you need to decide if the camera and/or your tripod caused the problem or the lens. You might have to run another test just to be sure.
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Adlie penguin on iceberg. Nikon 80-400mm VR lens at 400mm, taken handheld from a Zodiac. This photo was proof to me of the value of VR technology. Will I shoot all wildlife photos handheld? Definitely not, but VR allows me to gain a few extra sharp images for my files.
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No lens is perfect in all respects. The steps outlined above should give you answers about the optical quality, but you still face some choices. Is the lens ergonomically designed to fit your hands and working circumstances? Does it seem to be well made mechanically? Can you afford it? Is it the best you can afford? And most of all, do you really need it? Remember that no lens by itself takes pictures. Photographers do that, not the equipment they carry.
As I said at the beginning, this column was precipitated by my cruising some web sites. Besides the website example I noted in the opening of this essay, one particular forum caught my attention. It was a discussion of the new Nikon 80-400mm VR (Vibration Reduction) lens compared to the Canon 100-400mm IS (Image Stabilized) zoom. There were 37 entries on the forum, both pro and con for each lens, and one fact leaped out at me. Not one person — let me repeat, not one person — who was making claims (positive or negative) about the Nikon lens had physically touched the lens, let alone gone out and actually shot a picture using it. There were comparisons about the published specs, writers who were avidly pro-Canon or pro-Nikon, arguments about push-pull zooms versus two-touch...but not one user report. So I ask, of what value was that forum?
I also found it rather strange that no one brought up points that could apply to both lenses. Instead most forum participants were adamant about their camera brand being the best while the other brand was obviously deficient. But there are some facts about both these lenses, which should be considered. For example: both the Canon 100-400mm and the Nikon 80-400mm lenses are f/5.6 wide open. Is this a fast enough maximum aperture for your type of photography, regardless of the fact that both lenses are "vibration stabilized?" That is, would you be interested in one of these lenses if they did not have IS or VR technology? No matter how "image stabilized" a lens may be, it will not stop subject motion. If the lens is too slow for your kind of photography, then only a faster lens will do. This past summer I photographed side-by-side with a Canon user who was shooting the 100-400mm while I was using my 300mm f/2.8 wide open. We were both using the same film, ISO 100 pushed one stop, and we were both hand-holding our lenses while photographing from a small boat. Simply because I had a faster lens I could always use two higher shutter
speeds to stop subject motion. Yes, he had the ability to zoom...but my pictures are sharp and his were not. IS or VR may stop some of your movement, but not that of the subject. Since these lenses cover many focal lengths, the potential problem I see is the loss of all those focal lengths if the lens breaks. Case in point: I once led a Kenya safari on which, to save weight, a participant brought two Canon lenses, a 24mm and the 35-350mm. Early on in the trip she dropped the 35-350mm, so for her trip of a lifetime she was restricted to photographing with a 24mm lens. Another case in point: on our recent Antarctica trip, on the first full shooting day, the wind blew a tripod over, smashing a brand-new Nikon 80-400mm. What lenses were left? The client could use a 35-70mm or a 500mm, but that's a mighty big gap. If you have a wide-range zoom, carry backup. "One lens does everything" also means "no lens does anything at all if it's broken."
Do these thoughts mean I would not use nor recommend an 80-400mm or 100-400mm zoom? No, not at all. I bought the first Nikon 80-400mm I could get my hands on, and I definitely like it for my style of work. I realized, however, that like all lenses it has both good and bad points, and is not the perfect answer for all subjects. Choose equipment for your own kind of photography and for your own reasons. But be suspiciously discerning when reading web forum test results.
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