Image Stabilization - Application in Still Photography

Application in Still Photography

In photography, image stabilization can often permit the use of shutter speeds 2–4 stops slower (exposures 4–16 times longer), although even slower effective speeds have been reported.

The rule of thumb to determine the slowest shutter speed possible for hand-holding without noticeable blur due to camera shake is to take the reciprocal of the 35mm equivalent focal length of the lens. For example, at a focal length of 125 mm on a 35mm camera, vibration or camera shake could affect sharpness if the shutter speed was slower than 1/125 second. As a result of the 3–4 stops slower shutter speeds allowed by IS, an image taken at 1/125 second speed with an ordinary lens could be taken at 1/15 or 1/8 second with an IS-equipped lens and produce almost the same quality. The sharpness obtainable at a given speed can increase dramatically. When calculating the effective focal length, it is important to take into account the image format a camera uses. For example, many digital SLR cameras use an image sensor that is 2/3, 5/8, or 1/2 the size of a 35mm film frame. This means that the 35 mm frame is 1.5, 1.6, or 2 times the size of the digital sensor. The latter values are referred to as the crop factor, field-of-view crop factor, focal-length multiplier, or format factor. On a 2x crop factor camera, for instance, a 50mm lens produces the same field of view as a 100mm lens used on a 35mm film camera, and can typically be handheld at 1/100 of a second.

However, image stabilization does not prevent motion blur caused by the movement of the subject or by extreme movements of the camera. Image stabilization is only designed for and capable of reducing blur that results from normal, minute shaking of a lens due to hand-held shooting. Some lenses and camera bodies include a secondary panning mode or a more aggressive 'active mode', both described in greater detail below under optical image stabilization.

Image-stabilization features can also be a benefit in astrophotography, when the camera is technically- but not effectively- fixed in place. The Pentax K-5 and K-r can use their sensor-shift capability to reduce star trails in reasonable exposure times, when equipped with a GPS accessory for position data. In effect, the stabilization compensates for the Earth's motion, not the camera's.

There are two types of implementation - lens-based, or body-based stabilization. These refer to where the stabilizing system is located. Both have their advantages and disadvantages.