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Tuesday, February 25, 2014

Super Telephoto Zooms

We decipher the technobabble behind these nature photography mainstays

Labels: Gear
This Article Features Photo Zoom
Sigma 150-500mm F/5-6.3 APO DG OS HSM
This has been the go-to lens for wildlife photographers on a budget, the only telezoom with built-in stabilizer to go out to 500mm until the just-introduced Tamron 150-600mm. We know several bird photographers who use the Sigma 150-500mm lens with very good results, and we liked our test example when we tried it. A good stabilized zoom that goes out to 500mm for a bit over $1,000—very nice. If you're a wildlife photographer on a budget, we suggest that you check them both out.

If you use a Pentax or Sigma DSLR and need a long lens, this is your best option. Pentax's only lens longer than 300mm is a 560mm prime that costs thousands more, and the Tamron 150-600mm isn't available in Pentax or Sigma mounts.

AF Motor
Most newer telezooms incorporate AF motors. The best ones are quick, smooth and quiet: Canon's USM, Nikon's AF-S, Olympus' SWD, Pentax's SDM, Sigma's HSM, Sony's SSM II and Tamron's USD. The main thing to check regarding a telezoom's AF motor is whether you can change focus while in AF mode. If you're photographing a bird in flight, for example, and the AF system loses focus and focuses down to its minimum focusing distance, it's a lot quicker if you can just turn the focusing ring back to infinity and press the button to start AF again, rather than have to switch to manual focusing mode, reset focus, then re-enter AF mode. It's also helpful to be able to "ballpark"—focus on the flying bird manually before activating the AF system—something you can't do if the lens won't let you focus manually in AF mode. (With some lenses, rotating the focusing ring manually while in AF mode can damage the AF motor; you don't want this type of lens if you're photographing birds in flight.)

Built-In Stabilization
Many Canon, Nikon, Sigma and Tamron telephoto zooms come with built-in optical image stabilization (Canon's designation for this is IS, Nikon's is VR, Sigma's is OS and Tamron's is VC). This feature moves a group of lens elements as you shoot to minimize the effects of handheld camera shake. Olympus, Pentax and Sony DSLRs have built-in sensor-shift stabilization, which moves the image sensor rather than lens elements to compensate for camera shake. This has the advantage of being available with any lens you put on the camera, not just special stabilized ones. The drawback is that you don't see the stabilizing effect in the eye-level optical viewfinder. If you work handheld with a long lens, stabilization is a wonderful boon; if you work from a tripod, check the instructions for the lens or camera to see whether you should switch the stabilization off.

Each glass/air interface in a lens causes a loss of light due to reflections, and telezooms generally have lots of elements. So, manufacturers coat the surfaces of the elements to reduce reflections, minimizing this light loss. A telezoom with good coatings on all element surfaces can transmit a much greater percentage of the light than a lens with uncoated elements. The coatings also help to produce good color rendition. The newest coatings (found, naturally, on the newer lens designs) are even more effective than older coatings.


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