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Tuesday, May 24, 2011

The Promise Of Stabilization


Between image-stabilized lenses, in-camera stabilization and high-ISO technology, the game has changed for photographers seeking the freedom to shoot handheld



This Article Features Photo Zoom

The AF-S Nikkor 70-200mm ƒ/2.8 ED VR II lens features in-lens stabilization.

Image-stabilized lenses and cameras let you capture sharp, handheld photos at lower shutter speeds than ever before, while supersensitive sensors let some DSLRs shoot in the dark. So is it time to retire your tripod?


Sony SLT-A55, Olympus E-5 and Pentax K-5 cameras provide sensor-shift stabilization.
Most experienced photographers agree that a sturdy tripod is the best tool to use when shooting in low-light situations without a flash. Because tripods reduce camera shake and other vibrations, they enable you to use slow shutter speeds to balance exposures or extend the depth of field in your photos by using small apertures—all while keeping your ISO setting low to maximize image quality. But now that image-stabilized lenses and camera bodies are readily available, and supersensitive, low-noise sensors are appearing in the latest DSLRs, are tripods losing their mass appeal?

That's a trick question, since another key tripod benefit is to support the mass of equipment pros and advanced shooters truck with them, including heavy cameras, long lenses, WiFi adapters and battery packs. With the arrival of HDSLRs, the load increases with accessory microphones, rack-focusing devices and video lights. Add the benefits that fluid heads provide for video panning and tracking, and tripods actually may increase in popularity.

Which Is Better: Lens IS Or Camera IS?
If you're a dedicated DSLR still shooter who likes to travel light, a tripod may soon be the last option you choose for improving your low-light photos and depth of field. Your most affordable and lightweight option is either an image-stabilized lens or a camera body with built-in sensor-shift IS.

How well do these two systems reduce vibrations, and is one better than the other? The answers depend on a number of factors, including the camera brand you own, your physical traits and the subject you're photographing. Currently, manufacturers such as Canon, Nikon, Panasonic and Sigma only offer lens-based image stabilization (called IS, VR, Mega O.I.S. and OS, respectively) for their DSLRs. On the other hand, Olympus, Pentax and Sony only offer DSLR models with sensor-shift IS. Note: Even if you purchase third-party IS lenses from Sigma, Tamron or Tokina to use with a sensor-shift body, only one IS system will work at a time.

Claims for both types of image stabilization range from two to four stops of improvement over the maximum recommended shutter speed for cameras and lenses without IS (see "The Reciprocal Shutter Speed Rule" sidebar). That means that if the slowest recommended shutter speed is 1⁄200 sec., without IS, you may be able to capture sharp handheld shots all the way down to 1/12 sec. with a lens or camera, providing a four-stop advantage. In my experience, however, and based on several lab and field tests I've done, improvements from the best IS lenses and IS cameras are rarely higher than three stops—and that advantage is only reachable when using telephoto lenses with focal lengths over 100mm. With normal and wide-angle lenses, IS improvements are less noticeable and not as obvious on either system. The benefits of IS also decrease at higher shutter speeds, so if you dial in 1/400 sec. with a 200mm lens to reduce vibration from a moving vehicle (or from the four cups of coffee you drank), or chose 1/600 sec. to freeze action in the scene, the IS won't significantly improve the shots.

The Reciprocal Shutter Speed Rule

Before turning on image stabilization, what's the lowest shutter speed you should use while handholding a camera in order to prevent visible camera shake blur in your photos? (Subject motion blur is a different problem.) The answer varies based on the focal length of the lens being used and is calculated using the Reciprocal Shutter Speed Rule: 1/Focal Length. For example, if you're shooting with a full-frame camera and your zoom lens is set to 200mm, your lowest shutter speed should be 1⁄200 sec. Of course, that assumes there's enough light for the camera to set an aperture that produces a proper exposure. (If not, you'll have to dial up your ISO.)

At that suggested shutter speed and faster, most images should appear sharp in a 4x6 or an 8x10 print (assuming correct focus and a stationary subject). Below that speed, images probably will show unwanted blur caused by the photographer (or environment) shaking the camera.

Several factors can modify the rule. If your DSLR uses a smaller APS-C or Four-Thirds sensor, you have to use the 35mm-equivalent focal length in the equation (multiply the actual focal length by 1.5x, 1.6x or 2.0x, depending on the sensor). For example, on a Nikon D5100 with a 200mm lens, the reciprocal shutter speed would be 1/(200 x 1.5) = 1⁄300 sec.

Camera shake also varies by body weight, breath control, physical traits and environmental factors, so use the suggested speed as a starting point and then consider increasing your shutter speed if you've had more than one coffee, and you're cold and tired, or if you're shooting from a vibrating car or platform.

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