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Tuesday, April 26, 2011

Find Your Wildlife Action Lens


How to pick the right lens to match your photo needs and your budget

Labels: Lenses


This Article Features Photo Zoom

Grizzly bear chasing after Coho salmon in Katmai National Park, Alaska. Photo by Matthias Breiter/Minden Pictures

Wildlife action covers quite a range, from huge bears snagging salmon while standing in a river to quick and tiny birds zipping by. The best lenses to capture wildlife action also cover a lot of range. Primary considerations for wildlife-action lenses include focal length, lens speed, AF performance and cost.


Clockwise from top: Pentax DA* 300mm ƒ/4 ED(IF) SDM; Sony 70-200mm ƒ/2.8 G; Tokina AT-X AF 80-400mm ƒ/4.5-5.6; Tamron SP 70-300mm ƒ/4.5-5.6 Di VC USD
Focal Length
The best focal length depends on your subjects and how close you can get to them. It’s hard to get close to most wild subjects, so wildlife photographers generally use long lenses: at least 300mm for an APS-C DSLR, or 400mm for a full-frame DSLR or 35mm SLR. If you can get fairly close to larger animals, a 70-200mm zoom can work. Zoom lenses do provide some framing flexibility, important when you can’t easily change the distance between you and your wild subject. Keep in mind that changing focal length—zooming—alters magnification and framing, but not perspective; you have to change camera-to-subject distance to change that.

Lens Speed
Faster lenses let you use a faster shutter speed in any given light level, which is obviously important when photographing action. Fast lenses also provide a brighter viewfinder image for easier composing and faster, more accurate focusing. The fastest lenses are generally in the pro lineups from the various manufacturers so they also tend to have rugged construction, superior glass elements and overall more refined designs.

On the downside, fast lenses also usually cost more than slower models for a given focal length or zoom range, and they’re usually bulkier. Because of their size, they’re harder to handhold and to carry around into the field.

Note that many lower-end and mid-level tele-zoom lenses have variable maximum apertures: A 70-300mm ƒ/4-5.6 has a maximum aperture of ƒ/4 at 70mm and a maximum aperture of ƒ/5.6 at 300mm. Keep this in mind when considering a tele-zoom versus a fixed-focal-length lens of the zoom’s maximum focal length. Also, the variable aperture is seldom even across the zoom range (as we showed in a previous OP article, “Get The Most Out Of Variable-Aperture Lenses,” Jan./Feb. 2011). That is, a 70-300mm ƒ/4-5.6 might be ƒ/4 at 70mm, but ƒ/5.6 from 120mm to 300mm. You just don’t get something for nothing.

Teleconverters
A teleconverter, also known as a tele-extender, attaches between the lens and camera body, and increases the lens’ focal length by 1.4x or 2x (there also are a few 1.7x converters out there). Adding a 2x converter to a 300mm lens gives you a 600mm lens for a lot less money than a real 600mm lens. But there are a few things to bear in mind.

First, converters reduce the amount of light transmitted to the image sensor or film (and to the viewfinder): a 1.4x converter, by one stop, a 2x, by two stops. This requires the use of longer shutter speeds or higher ISOs. Longer shutter speeds don’t yield sharp action shots, so you’ll have to increase the ISO—not a big problem with today’s DSLRs, more so with early digital cameras and film. The light loss also makes the image in the SLR finder dimmer, which can be annoying in dim light or when trying to focus manually. The smaller effective aperture also will slow AF performance, and with some lens/teleconverter/camera combinations, you lose autofocusing capability altogether. Many SLRs can’t autofocus with lens/converter combinations slower than around ƒ/5.6.

Second, the converter adds more elements to the optical system, thus potentially reducing image quality. With good converters matched to good lenses, this isn’t a big problem. With lesser converters and lenses, it can reduce image quality noticeably. Pro wildlife photographers often add a top-quality converter to their expensive supertele lenses for more reach, while maintaining pro-quality images.

Converters offer some serious advantages, however. First, of course, they provide access to focal lengths that otherwise wouldn’t be affordable for many. Another benefit is that converters don’t affect the lens’ minimum focusing distance. Attach a 2x converter to a 300mm ƒ/4 lens that focuses down to five feet, and you get a 600mm ƒ/8 that focuses down to five feet—much closer than the 15- to 18-foot minimum focusing distance of a typical 600mm ƒ/4 lens. You rarely get that close to wildlife in the field, but when you do, you definitely want your lens to be able to focus!


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