Camera shake is the name given to camera movement during exposure. This movement will lead to blurry photographs that appear out of focus and are not very pleasing to look at. Camera shake becomes a problem when taking hand held photographs using slow shutter speeds. There is a rule of thumb that states in order to reduce the chance of camera shake it is necessary to use a shutter speed that is at least the reciprocal of the lens’ focal length. So, when using a 100mm lens that shutter speed should be at least 1/100 seconds. So, when using long lenses the shutter speed needs to be even faster to avoid camera shake. This rule of thumb is fine in theory but it can be difficult in practice. There may be times when light levels are not sufficient enough to achieve fast shutter speeds. This can be overcome by opening the lens up (affecting the depth of field) or by cranking up the ISO (which my lead to unwanted noise) although there will be times when even these methods won’t work.
Image stabilisation was developed to eliminate camera shake and allow photographers to use slower, and readily achievable shutter speeds, and still get tack sharp images. The image stabilisation technology can be in either the camera body or the lens and works by moving the optical plane to counteract the movement of the camera and the lens. Sounds complicated right? Well it is, but in a nutshell here is how it works;
Inside the camera body or the lens there is a series of acceleration motion sensors, often referred to gyroscopes. These tiny sensors measures the movement of the camera or lens, collates the data and submits it to a series of small motors, commonly referred to as actuators, that compensates by moving the internal optical elements or the lens itself, to redirect the optical path to reduce the blur.
Image stabilisation technology is most commonly found in camera lenses where the sensors are built in to the body of the lens. The additional sensors make the lens heavier and more bulky, as well as more expensive, however they do help to eliminate camera shake. As with all things in life a compromise has to be made and having to use a larger and heavier lens is a small price to pay for sharp shots. Historically, image stabilisation technology was only found in the top end professional grade lenses, however it is moving down in to the more affordable consumer level market.
Most manufacturers produce lenses with image stabilisation technology so there is something for most photographers. Image stabilisation in Canon lenses is identified with the letters “IS”. For example, the EF 70mm – 200mm f/4 L IS USM, contains image stabilisation. When using Nikon lenses the image stabilisation technology is identified by the letters “VR”, which stands for vibration reduction but it is the same thing. When using Sigma lenses the image stabilisation is identified by the letters “OS”, which stands for optical stabilisation, and so on.
Image stabilisation is also found in some camera bodies whereby the same style of motion sensors and accelerators are used. However, rather than moving the lens it is the actual sensors that are moved to redirect the optical path and compensate for any movement. One of the biggest advantages of having the image stabilisation technology in the camera body is that every shot will have image stabilisation regardless of the lens used. This means a cheap and cheerful lens can be used and the photographer will still benefit from image stabilisation technology.
One of the biggest disadvantages of having the image stabilisation technology in the camera body is that it doesn’t work very well on lenses with long focal lengths. Up to around 200mm the images stabilisation technology works very well but on lenses longer than this the performance does degrade somewhat.
Image stabilisation technology is fantastic and it really does help to achieve sharper shots at slower shutter speeds. The level of image stabilisation technology varies from lens to lens and whilst some lenses will provide a one stop advantage others, such as the Canon EF 70mm – 200mm f/4 L IS USM, provides a four stop advantage which is very useful.
Image stabilisation technology is a fantastic tool however it is not a substitute for poor technique. It is naive to buy a lens with image stabilisation technology and automatically assume that every shot is going to be pin-sharp. You still need to learn how to use the lens in order to get the most out of it.
Image stabilisation technology does require energy to work efficiently therefore the battery life of the digital camera will decrease so this needs to be borne in mind. Image stabilisation technology is not required when using a tripod therefore it should be switched off. Leaving the image stabilisation technology on when using a tripod will actually lead to blurry shots as the sensors and motors will over compensate and create movement. It should also be noted that image stabilisation technology will only reduce blurring when it is caused by camera shake. If the blurring is created by subject movement image stabilisation technology will not help and there is no other option other than increasing the shutter speed and adjusting the aperture or ISO (or both) to compensate.