Tuesday, April 29, 2014
The Medium Mainstay
Big telezooms get the glory and wide-angle models get the headlines, but the underappreciated middle child in a typical three-zoom kit may be your most useful lens. Learn how to choose the right one for you.
Telephoto zooms are popular with wildlife photographers and wide-angle zooms with landscapists, but the mid-range zooms also have their fans. The 24-70mm to 24-105mm zooms (for full-frame DSLRs and 35mm cameras; 16-50mm to 17-70mm for APS-C cameras) take you from the start of true wide-angle into portrait telephoto (yes, people can be great outdoor photo subjects, too!). Most will focus close enough to do good flower and spider-web still lifes and, of course, that focal-length range covers most of the classic landscape angles of view.
Mid-range zooms come in fast (and bulkier) ƒ/2.8 form and in slower (and more compact) ƒ/4 form. If you like to shoot in dim light, you'll find the ƒ/2.8 zoom more suitable; if traveling light is more important to you, you'll be better off with the ƒ/4s.
Wider apertures produce less depth of field, making the faster zooms better for selective-focus shots, where you want to concentrate the viewer's attention on a specific part of a subject or scene by minimizing depth of field and throwing everything else out of focus. Shooting wide open at ƒ/2.8 also helps blur a busy background so it's less distracting.
The ƒ/2.8 lenses also autofocus more quickly and accurately, in part, because they provide more light for the AF system to work with and, in part, because many mid- and high-end DSLRs have central AF points that provide added precision with ƒ/2.8 (and faster) lenses due to the wider beam of light provided to the AF system (much as wide-base rangefinders are more accurate than narrower-base ones). Within a given brand, the ƒ/2.8 lens also likely has a better AF motor.
On the other hand, ƒ/4 lenses are more compact and less costly, while still providing the focal-length range and delivering excellent image quality. As an example, the Canon EF 24-70mm ƒ/2.8 weighs 28.4 ounces, and the EF 24-70mm ƒ/4, 21 ounces. That's almost a half-pound difference—a lot when carrying the camera and lens on a neck strap all day. The ƒ/2.8 also costs 50% more.
Bottom line: If you specialize in handheld low-light photography or selective-focus work, it's likely you'll be happier with an ƒ/2.8 mid-range zoom. If light weight and low cost are more important to you, an ƒ/4 is a better choice.
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