What a $5,900 lens says about photography

The camera industry is in the throes of a digital photography revolution. But a new version of Nikon's 300mm telephoto lens announced this week, a $5,900 model intended for professionals, shows at least some parts of the photography market are constant even as the rest is overhauled.

Digital photography is profoundly different from the film era for many reasons. Here are some: new image sensors can enable photography in conditions too dark for film. The same camera can shoot video and still shots. Cameras can record not just when you took a photo, but where you took it. It's easy to publish photos globally on the Internet or to alter them significantly with software. And steadily increasing computing power lets cameras do everything from detect smiling faces to correct lens shortcomings.

And yet islands of stability remain. The high-end lens, with its complex optical engineering and premium pricing, is one of them.

Many SLR users don't venture beyond the kit lens that comes with their camera--an 18-55mm zoom that's reasonable for indoor shooting and basic tourist photography. Those who want to photograph the kids' soccer matches can step up with a telephoto zoom--usually one reaching to 200mm or 250mm and costing a few hundred dollars.

So why all the extra price for a bit more focal length to reach 300mm?

At the top of the list is speed.

Entry-level telephoto lenses typically don't have very wide apertures at full zoom--F5.6 is common--meaning that it's harder to shoot fast action or in dim conditions. The smaller the aperture number, the more light a lens can gather, and the F2.8 aperture of Nikon's AF-S Nikkor 300mm f/2.8G ED VR II means it can shoot with a shutter speed four times as fast as an F5.6 lens.

The model is appropriate for sports photographers who often need close-ups of action on the far side of a field. There's a big difference in sports photography between 1/500 sec and 1/2000 sec. To support all that light gathering, though, the lens needs much larger optical elements, and that makes the lens more expensive to build.

The lens also has to be larger to enable photography using higher-end full-frame cameras whose image sensor area is the same size as a frame of 35mm film. Most digital SLRs have smaller image sensors, and point-and-shoot cameras have ones smaller still, which permits smaller lenses.

But here's a thought: With SLRs' low-light shooting ability progressing by leaps and bounds as sensors get better, do you really need to pay for that super-fast lens? Can't you just goose the ISO a notch or two and get by with an F4 or even F5.6 lens?

After all, Nikon's newest SLR, the D3S, can shoot at a whopping ISO 102,400, and new image processing software is getting gradually better at removing image noise from high-ISO shots.

My current SLR shoots cleaner images at ISO 6,400 than my last one did at ISO 1,600. And I'm not trying to start a religious war here, but I do appreciate that Canon offers some higher-end but more affordable F4 lenses to bridge the price gap between mainstream lenses and pro-grade F2.8 models.

So you can use a higher ISO rather than a faster lens--but there are consequences.

For one thing, today's SLR autofocus systems work better with wide-aperture lenses. Wider apertures also mean a shallow depth of field, enabling photographers to blur out the background to better focus attention on the subject of the photo. Primarily, though, a wider aperture means you'll still be able to shoot with that much faster a shutter speed or in that much dimmer light.

Another feature that sets professional lenses apart--particularly fixed focal length models--is image quality. They typically provide better sharpness, lower distortion, less vignetting that causes corners of the frame to darken, higher contrast, better colors, and less chromatic aberration--an unpleasant side effect of the different paths that different color light takes through lens optics.

Here, too, digital photography is changing things. Software such as Photoshop can correct many optical problems--but increasingly, so can cameras themselves. Canon's new high-end S90 compact camera corrects barrel distortion of its lens, fixing parallel lines that otherwise look bowed. And many camera models these days correct vignetting on their own. Hasselblad's high-end cameras treat software as part of the photography process, correcting several issues with lenses after the photo is taken.

But there are advantages to getting the image right before the light strikes the image sensor.

For example, although software can correct many problems for still images, SLRs these days can take video too. Correcting the optical properties of anywhere from 24 to 60 frames per second of video is a daunting challenge--especially given that focal lengths and focus distance settings can change continuously throughout the video so corrections aren't necessarily constant.

There are plenty of other features that set professional lenses apart. Some details on the 300mm lens: weather sealing, a setting to quickly return to a preset focus distance, special glass to protect the large front element, three extra-low dispersion (ED) glass elements for sharpness and minimum chromatic aberration, one aspherical lens element to minimize distortion, a magnesium housing, and Nikon's Nano Crystal Coat to cut down on internal glare in the lens. These are the kinds of things that cost real money to research, engineer, and manufacture.

There are electronics systems such as autofocus that predate the mainstream digital era, too, of course. Another is image stabilization, called vibration reduction (VR) by Nikon. Although in the case of Canon and Nikon it predates digital SLRs, it's still undergoing changes. The technology uses small gyroscopes to detect how a lens is moving and then small servomotors to move a lens element to counteract some of that shaking.

Compared to its predecessor, Nikon's 300mm lens has more effective vibration reduction technology. By Nikon's measurements, it can compensate for four F-stops' worth of camera shake--in other words, to let somebody who ordinarily could shoot at 1/400 sec. shoot at 1/25 sec. instead, as long as the subject matter is equally unmoving, too.

For comparison, Nikon's earlier 300mm F2.8 model offered three stops of improvement, which would get that shutter speed down only to 1/50 sec. Many reviewers find that company measurements are overoptimistic about the real-world effect of the stabilization technology, but there's no question it helps significantly.

The upshot here is that image processing hardware and software is dramatically changing how cameras work. The computer science gang is ascendant, but old-school lens design skills still pay dividends.