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Tuesday, December 1, 2009

Choose Your Perfect Zoom

The modern zoom lens is a marvel of technology, and it’s the nature photographer’s best friend

This Article Features Photo Zoom

Tamron AF28-300mm F/3.5-6.3 XR Di VC
How A Zoom Works
A single-focal-length lens contains a number of elements, both individual elements and groups of elements cemented together to function as individual elements. The elements establish the focal length and compensate for aberrations and distortions, and some of them move to focus the lens at different distances.

Canon EF-S 10-22mm ƒ/3.5-4.5 USM
A zoom lens must do all of this, but also move some elements to change the focal lengths while moving others to maintain focus and still others to maintain compensation for aberrations and distortions at all focal lengths. “True” zoom lenses maintain focus as they’re zoomed; vari-focal lenses change focus as they zoom and must be refocused after zooming. Autofocus systems take care of that automatically, but keep it in mind if you focus a “zoom” lens manually. Most SLR “zoom” lenses today are vari-focals, not “true” zooms.

The challenge for lens manufacturers is making a zoom lens that performs well throughout its focal-length range. With any lens, designers have to provide excellent resolution, contrast and color rendition, minimize peripheral illumination falloff (vignetting) and flare, and eliminate distortions, aberrations and field curvature. With a prime lens, they need to do this for only one focal length. With a zoom lens, they have to correct these things for the entire focal range, and correcting something at one focal length tends to make that particular problem worse at other focal lengths.

Olympus Zuiko Digital 12-60mm ƒ/2.8-4.0 SWD
Today, thanks to advancements in materials and knowledge, and powerful computers to run simulations, designers are able to create zoom lenses that produce excellent image quality at all focal lengths. As with prime lenses, the more costly pro zooms tend to be better performers in terms of sharpness, contrast, color rendition and autofocusing; and shorter-range zooms (3:1, 4:1) tend to be better performers than “super” zooms (7:1 on up). But today’s zooms, in general, perform very well—so well, in fact, that many landscape and wildlife pros shoot primarily, if not exclusively, with zooms.

That said, pro prime lenses—also having the benefits of advanced materials and computer-aided designs—still outperform even the best zoom lenses. But you’ll have to be a “pixel-peeper” to see it.


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