Image Stabilisation Lenses

Introduction If you’re not careful, camera shake can ruin your photos. Pressing the shutter button whilst hand-holding the camera/lens may cause slight camera/lens movement during exposure and thus could blur the image. Much of the time, you won’t notice the effects of camera shake. If you are shooting with a fast shutter speed or a wide-angle lens, the blurring may not be significant− but it will still be there, and might appear if you have a big enlargement made from the image.

Overcoming Camera Shake The only way to overcome camera shake is to eliminate the movement of the camera and lens during the exposure. The two obvious ways to do this are by using a shutter speed that is faster than the reciprocal of (your sensor crop multiplied by any fitted extender multiplied by the focal length of your lens) or by attaching the camera to something that will not move, such as a heavy tripod or professional beanbag.

Another Way Fortunately, lens manufacturers do offer another method of reducing, if not eliminating, the effects of camera shake. Image stabilised (IS), vibration reduction (VR), optical stabilised (OS) lenses, approach the problem laterally. They all work slightly differently but essentially rather than trying to stop the movement of a hand-held camera, they seek to introduce an opposing movement within the lens. Their aim is to keep the image static on the sensor or film, despite the movement of the camera.

Power for these lenses comes from the camera battery, so there will be fewer exposures per battery charge when an IS lens is attached to the camera and switched on.

IS types There are basically two types of IS lenses:

  • Type 1 detects movement in the pitch axis (raising or lowering of the lens relative to the camera) or yaw axis (spinning yourself around a central point also known as panning) and will try to correct these movements.
  • Type 2 just detects movement in the yaw axis i.e. when you are panning and switches off the IS correction in that direction (horizontal or vertical). IS correction in the direction of perpendicular to the panning movement continues as normal to help give a sharper image.

Performance IS lenses are usually effective with camera movement from 0.5Hz to 20Hz (1Hz is one movement cycle per second). This will cope not only with situations from simple camera shake (0.5Hz to 3Hz), but also the engine vibrations encountered when shooting from a moving vehicle or helicopter (10Hz to 20Hz). There is no reduction in the optical performance of an IS lens.

Fitting to a tripod Whilst some lenses detect being fitted to a tripod and will automatically turn the IS off, generally, you should turn the IS off when attaching the camera & lens to a tripod. You can leave it turned on whilst connected to a monopod as as it is unlikely you will be able to keep this type of support perfectly still.

How effective is IS on a lens? The earliest IS lenses manufactured in the 90s offered a gain of up to 2 stops, i.e. if you can obtain a sharp image without image stabilisation at a shutter speed of 1/60th of a second, you will produce results of similar sharpness at 1/15th of a second with image stabilisation, other factors staying the same.

  • More recent IS lenses have improved their effectiveness, giving a three-step, four-step or a five-step gain. A four-step gain means that shooting with a shutter speed of 1/15th of a second with image stabilisation gives the same image sharpness as shooting at 1/250th of a second without image stabilisation, other factors remaining constant.
  • One of these factors is focal length. Increasing focal length not only magnifies the subject − it also magnifies the effects of camera shake. A useful guide is that you should use a shutter speed at least equal to the reciprocal of (your sensor crop multiplied by any fitted extender multiplied by the focal length of your lens) when holding the camera and lens by hand. If the focal length of the lens is 200mm with a 1.6 crop sensor and a 1.4x extender, then the shutter speed should be at least 1/448th of a second, so 1/500s is ok. Don’t forget that telephoto lenses are heavy and as such, difficult to be handheld. This is one advantage of using an IS lens over a non-IS lens.

Where can you find IS lenses IS used to only be found on the super telephoto lenses but have now worked their way across a number of lenses including 70-200mm, 24-105mm, 100mm macro and 16-35mm wide angle plus lots more lenses.

Cost Naturally, the costs of an IS lens vs a non IS lens is as you would expect much more expensive as the manufacturers will attempt to recover their development costs.