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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.

Labels: LensesGear
This Article Features Photo Zoom

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.

Maximum Aperture
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.

14-50mm Focal Lengths 24-300mm Focal Lengths

These diagrams illustrate the angle of view for focal lengths from 14mm through 300mm. The apparent angle of view changes with different image sensors, typically referred to as the magnification factor or crop factor. Medium focal lengths have an apparent angle of view of about 84º to 20º, so though we refer to a 14mm lens (114º angle of view) as "medium" on a Micro Four Thirds camera, with the crop factor, it has an apparent angle of view of 75º.


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