Photography - Understanding How Image Stabilizing Lenses Work
If you have not yet purchased an image stabilizing lens, you might nonetheless have heard the term "image stabilization" or "vibration reduction" bandied about in reference to various point-and-shoot cameras and SLR lenses. In that case you probably understand that IS or VR technology supposedly results in sharper images. But does the technology really work, and how well? What actually happens to make it work? In what situations does it not work at all? And most important of all, do you really need it?
The answer to the first question is yes, image stabilization technology not only works, it works well. If it did not, the remainder of this article would be entirely unnecessary. But it is useful to understand exactly what image stabilization is, and when it can be used to improve your photography before you shell out the extra few hundred dollars for a lens that has IS built into it.
Note: While the term "image stabilization" is used more frequently by writers when discussing this topic, "vibration reduction" is the term that Nikon uses to describe the same feature in its lenses, and it also happens to better describe what is going on. You should consider the two terms as interchangeable.
To understand how vibration reduction works, let's consider for a moment the effect that it corrects for. When a camera is hand-held, and the shutter is open for a duration longer than the camera can be pointed in one direction without moving, then the resulting image is seen to be blurred. What happens is that as the camera lens tilts upwards, sideways, or a combination of the two, the focused image shifts position on the image sensor. A focused point of light ends up being rendered as a line. The accumulation of all the shifted points of light that make up an image results in a blurred image.
The obvious correction therefore would be to shift the image sensor by the same amount that each point of light is shifted, so the image and the image sensor move together in relative lock-step. Some camera manufacturers implement this exact solution, and float the image sensor so that it can track the image if the camera shifts during exposure. But this is the exception, rather than the norm. Generally the solution is achieved by adding the vibration reduction to the lens, rather than the camera body.
So how does this work? Actually it is fairly simple to understand. Instead of a floating image sensor, the lens body contains floating lens elements. The position of these lens elements is controlled by motors that are coupled to sensors which detect how much the lens body is rotated vertically or horizontally during exposure.
If the lens body rotates upward, the sensors compensate by telling the motors to drop the floating lens elements down a little to maintain the optical path of light traveling through the lens elements. If the lens body is rotated to the left, the lens elements shift to the right to compensate. The end result is that the image maintains its position on the image sensor during the exposure, creating a much sharper image than if the vibration reduction system had been deactivated (which it can be).
It might seem remarkable that the system can track camera shake so well. In fact, it is remarkable, but it all works because camera motion can be monitored about every 1/1000th of a second, while the camera wobble occurs on a time scale of, say, 1/30th, 1/15th, or even 1/4th of a second.
Vendors of these image stabilizing lenses claim that the technology allows you to gain about 3 to 4 stops on your exposures. This means that if, for a given photographic situation, the slowest hand-held shutter speed that consistently results in an OK image is 1/125th of a second, then by adding vibration reduction you ought to be able to shoot at 1/15th or perhaps even 1/8th of a second. This is a big deal if you are forced to shoot into shadow, or the light is fading, or you need to close down the aperture to improve depth of field.
But image stabilization only proves itself in a range of shutter speeds that are neither too great, nor too small. If you try to hand-hold a 1 second exposure it's unlikely your VR compensation will be able to keep up with the erratic motions you supply it. Likewise, if you are shooting at 1/500th of a second or higher, the camera won't have a chance to experience any wobbling, so the VR system will not add any improvement.
Another thing to remember about vibration reduction is that it has to do with compensating for camera motion during exposure. It has nothing to do with the speed of the object you are trying to photograph. So that fast-moving baseball will still be rendered as a blur unless you capture it at 1/500th of a second.
Do you need IS or VR lenses to improve your photography? This one is fairly easy to answer. If you regularly find yourself shooting at speeds less than 1/250th of a second then there is a very good chance you can rid yourself of a substantial number of those blurred, or unsharp, shots by investing in a good VR lens. Better yet, when you buy your next digital camera, simply go for a point-and-shoot with vibration reduction built in, or if you purchase a digital SLR, try to grab a model with vibration reduction built into the supplied kit lens.
Interchangeable Lens Camera
