Do You Know Your SBA?; The “Shake Begins At” Level And Image Quality

sorcadmin's picture

Do you know your SBA? You should. SBA means “Shake Begins At”—the level at which camera movement makes your images lose the sharpness battle. Don’t make the mistake of thinking that you’re shake-proof just because your camera or lens has built-in Image Stabilization (IS). While stabilization technology helps, like all technology, it has its limits. Learn the boundaries and you’ll be a better photographer.

Camera movement—even ever-so-slight movement—can turn a great shot into trash. Camera shake is the number one cause of unsharp and unpleasant pictures. In the late summer of 2003, the now-defunct Minolta Corporation introduced the DiMAGE A1 camera, the first in the world to offer stabilization technology (dubbed “Anti-Shake” by Minolta). I was part of the team that brought the product to market. The feature was a result of considerable research that concluded that photographers needed some mechanical help to hold their cameras steady. Anti-Shake is now the feature de rigueur for all serious digital photographic systems.

Tamron’s Vibration Control (VC) improves sharpness dramatically. The image captured with VC “on” (top) was shot at 1⁄15 sec at 270mm (432mm equivalent), handheld, and is remarkably sharp, while the image shot without VC (above) shows how camera shake can turn a good shot into trash. The compact size and well-positioned center of gravity of the Tamron design contributes to sharpness even beyond the VC feature, making otherwise impossible shots like this child’s play.
All Photos © 2008, Jon Sienkiewicz, All Rights Reserved

Steadiness Factors
Four factors interact to determine your SBA. The first factor is the camera. Models with built-in Image Stabilization, like the Pentax K20D or Sony A700, do their shake dampening in the camera, so you enjoy the stabilizing benefits regardless of which lens you use. But nearly as important as the on-board technology is the shape, weight, and grip comfort of the camera design. A D-SLR with a small, uncomfortable grip can be nightmarish to hold still.

The next factor is the lens. Focal length is most important. Longer lenses are harder to hold steady and long heavy lenses can be nearly impossible to keep immobile. Lenses with self-contained Image Stabilization fight the shakes better than those without, but some examples—like the Tamron 18-270mm VC zoom, for instance—add compact design and an intelligently balanced center of gravity that make them easier to hand hold even with the stabilization turned off.

You are the third factor. The individual steadiness of the photographer is as critical as any other element. Unless you are abnormally shaky, you can improve your contribution to the equation by practicing sound fundamental techniques—keep your feet planted, elbows tucked, and control your breathing. And of course you can use a tripod. More on that later.

We’ll call the forth factor “delta.” Delta is the mystery behind why many photographers discover that even if they are using the exact same camera and lens combination their SBA can differ from day to day. It includes all of the negligible influences—wind, posture, grip strength, fatigue, subject distance, mirror vibration, heart rate, mental state, tummy growl, and so forth.

These four images were shot with a Canon EOS 5D Mark II and a 24-105mm IS lens zoomed to the 105mm position. The top two were shot at 1⁄25 and 1⁄13 sec (left to right), while the bottom two were shot at 1⁄10 and 1⁄8 (left to right). It’s easy to see that the image is still sharp at 1⁄13 sec but begins to break down at 1⁄10 sec. I concluded that my SBA with this combination is 1⁄13 sec. The small inset shows the entire frame.

The SBA Sample
Manufacturers who pack Anti-Shake powers into their cameras and lenses need a quantitative way to explain the relative value that their technology provides, so they often make claims that imply you’ll enjoy a “Two stop improvement” or “Up to four stops better” performance. Even if this marketspeak were true you’d have to ask yourself, “Two stops better than what?” Forget about what the ad copy says and determine your SBA for yourself. It’s easy—here’s how I did it.

Article Contents
Share | |