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Guide to Image Stabilisation

We’ve all had great shots spoiled by blur. One of the first jobs most of us do with any new set of images is work through them to discard the technical failures – and poor focus is one of the main reasons for failure.

Some images are blurred because of bad focusing or insufficient depth of field. Many more are blurred, though, because the camera moved during the exposure. The popular theory is that there are ‘safe’ and ‘unsafe’ shutter speeds for handheld shooting. In practice, the boundaries aren’t so clear. Our boxout on Safe Shooting on the next page explains this in more depth and gives a few rules of thumb for working out ‘safe’ speeds.

Camera shake occurs mainly in two key situations; low light and long lenses. Low light means longer exposures and increased risk of shake; longer lenses magnify the effect of any camera movement. You also risk shake when taking night shots with slow flash – the flash-lit foreground will be sharp, but the background may not be. Sharp handheld macro shots can be difficult to achieve, too.

There are other circumstances where camera shake can creep in. If you’re working in a nice, warm interior with all the time in the world to shoot in, it’s possible to get sharp shots even at extremely ‘marginal’ shutter speeds. But outside, in the teeth of a bitter gale, it’s another story. You might struggle to get sharp shots at shutter speeds two or even three times faster than normal.

Sometimes you’re working on a platform that is itself moving. Helicopters, for example, produce a great deal of vibration, and if you’re standing in the back of a Land Rover bouncing over the veldt at 40 miles an hour, you’ll discover just how hard it is to keep your camera steady. Image stabilisation systems are designed to counter this camera movement – but how do they do this?

How they work
Image stabilisers have three main components. The first is a pair of tiny gyroscopes spinning on two mutually perpendicular axes. It’s one of the extraordinary properties of gyroscopes that they are able to ‘detect’ movement. One gyroscope detects ‘pitching’, or vertical movement, while another detects ‘yaw’, which is horizontal movement. Diagonal movements are measured by combining data from both gyroscopes.

A processor then constantly checks, or ‘samples’, the movement of these gyroscopic sensors – Nikon’s SLR lens VR systems check for movement 1,000 times per second. The processor controls tiny motors that counter the detected camera movement by shifting either purpose-built lens elements or the camera sensor itself (depending on the system) to compensate for this movement. In Nikon’s VR system, two VCMs (Voice Coil Motors) are used to produce horizontal and vertical movement respectively, and the two are combined for diagonal movements.

Clearly, this has to happen with exceptional speed. For the system to work, the gyroscopes must pass movement information to the sensor, which then has to drive the motors, which themselves have to respond near-instantaneously – and all this during the exposure itself. There are limits to the amount of movement that image stabilisers can cope with. Manufacturers will typically quote their effectiveness in ‘shutter speeds’. For example, they might say that their system allows you to shoot at shutter speeds two or three times slower than usual.

Image-stabilisation technology continues to advance, though. Nikon reckons that its latest stabilisation systems can produce sharp shots at shutter speeds up to four stops slower than usual. It’s not the same as using a tripod. A tripod will give you sharp shots at any shutter speed, while an image stabiliser simply improves your chances when shooting handheld at ‘marginal’ speeds.   

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