photo’s blog

After you’d had your D-SLR a while, you might want to get an extra lens (or two) to complement the kit lens that came with your camera. And when that happens, you probably have some questions. Should you buy a Canon lens for your Canon camera, or perhaps from third-party lenses (from companies like Sigma and Tokina)? Why is one 200mm lens $300 but a seemingly similar model $2000? How do you pick a lens?
First things first. There’s nothing wrong with buying a third-party lens, in principle. Many lenses that have a badge other than Canon or Nikon (or whatever camera you own) are great lenses. Often they’re less expensive, and that’s why they’re popular. As to how to pick a lens and what separates a $300 lens from a $3000 hunk of glass, there are a few really important characteristics to consider when lens shopping

■Maximum aperture. This affects the price more dramatically than perhaps any other lens feature. A fast lens—that is, a lens that can open way up with a large maximum aperture like f/2—is a valuable commodity because it can take pictures in low light. A similar lens that can open only to f/5.6 must rely on a dramatically slower shutter speed
to capture the same picture.

Note:Many zoom lenses have a different maximum aperture at opposite ends of the zoom range, as you can see in Figure 2-5. A typical zoom, like a Nikon 18-200mm, is an f/3.5 at wide angle but a much slower f/5.6 at the telephoto end. A zoom that is a constant f/4 (or faster) through the whole zoom range is priced beyond the budget of most
photographers.

■ Image quality. When we talk about the quality a lens can capture, we’re discussing the lens’s sharpness, to be sure. But we’re also discussing seemingly technical stuff like contrast, chromatic aberration, color fidelity, and vingetting. And it gets worse: all of these values, including overall sharpness, vary through the zoom range for a zoom lens at each f/stop. Most modern lenses are somewhat sharper when stopped down a bit from the lens’s maximum aperture. And there are a lot of factors that contribute to image quality. One example: lenses with more “blades” in the diaphragm (the mechanism that controls the size of the aperture) tend to create a smoother, more pleasing blurred background.

Lens

in photos with a shallow depth of field. It’s almost impossible to judge these kinds of factors yourself. As a result, I recommend that you read lens reviews on the Web. Here are some sites I highly recommend:

■ http://www.bobatkins.com/
■ http://www.photo.net/canon/
■ http://www.slrgear.com/reviews/
■ http://www.the-digital-picture.com/Canon-Lenses/
■ http://www.photozone.de/8Reviews/
■ http://www.photo.net/

■ Zoom control. If you’re shopping for a zoom lens, be sure to handle it yourself (either in a store or borrowing one from a friend) before you pay for it. Why? The control needs to feel comfortable and natural. Some cheaply made lenses use a zoom control that you have to push and pull in order to change the focal length. Ugh. It’s hard to do and
almost impossible to quickly lock in the right magnification. Instead, look for zooms with controls that turn around the lens barrel. It should be smooth and easy, not hard and jerky. Another consideration: some zooms have a completely internal mechanism, so the lens does not change size as you zoom. Other lenses get longer or shorter as you zoom.

■ Image stabilization. Nikon calls its image stabilized lenses “VR.” Canon uses the term “IS.” Either way, these lenses contain small gyroscopes and motors that minimize the sort of blur caused by handholding a lens. Image stabilization can be found on many telephoto lenses, and manufacturers claim that using a stabilized lens allows you to shoot pictures
as much as three stops slower than you normally could without blurring your photo. Now, don’t get me wrong: you should use a tripod for the best results, but image stabilization really does work well and is nothing short of astonishing. If you can afford to get an IS or VR lens, definitely go for it. As you can see in the following illustration, most image stabilized lenses have a control on the lens that lets you turn the effect on or off.