The problem:

As you shoot with longer and longer shutter speeds, the slight shakiness/movement of the camera starts to become visible as blurring of the picture. The following is an example:

A rule of thumb is not to go below 1 / focal length (35mm equivalent) for the shutter speed. For example, if you are shooting with a 30mm lens, you should not have a shutter speed below 1/30s. Conversely, if your focal length is 200mm, then the minimum shutter speed would be 1/200, so much faster because the focal length is longer. I have often found in practice that one can shoot 1 stop slower quite easily, and usually also 2 stops slower if you have a steady hand and a good handholding technique.

How image stabilisation helps:

Image stabilisation counteracts the the vibration by shifting the sensor or the lens to compensate for the movement of the camera. This means you can shoot at slower shutter speeds without the blurry effects of camera shake. This is very useful in a variety of situations. For low light, if you are already using the largest aperture and high ISO, image stabilisation can allow you to shoot at a lower ISO for better image quality. Or, if you have a long lens, where the shutter speeds needed for sharp images are very fast, image stabilisation can extend the range of shutter speeds you can use by 2-3 stops.

There are two main caveats to know about image stabilisation:

Firstly, image stabilisation is not magic and does not replace a tripod.

Image stabilisation only slightly extends the shutter speed range which you can use. In other words, just because your camera has image stabilisation, you cannot expect to shoot with a shutter speed of 1 second at night and expect sharp pictures, that won’t happen. But you probably can shoot at 1/15 instead of 1/60 seconds and get more light. You could get reasonably good results at 1s only if you have a very steady hand and some sort of fixed support (not necessarily a tripod).

Secondly, image stabilisation does not stop subject motion.

If you are photographing a still scene, this does not matter. Image stabilisation will work to make sure the image is sharp and that will be that. But if you are shooting a scene with motion, the following problem arises: With image stabilisation, you usually pick a slower shutter speed to get enough light for a proper exposure, but you can end up with a shutter speed which is too low to freeze the motion. Then you get the ghosting of moving subjects in the picture. While usually not desired, it can also be used to create a “ghost-city” type of effect, try photographing a busy city street at night with a low shutter speed. In the end, if you need more light and to stop subject motion at the same time, you need a faster lens, image stabilisation won’t help you there.

In the picture above the background is borderline usable in terms of sharpness and camera shake, but the people walking and the tram are blurred because of the low shutter speed. If you wanted to freeze the motion here, you would need either higher ISO settings or a faster lens, image stabilisation won’t help you here.

Don’t be fooled by the advertising:

There are different types of image stabilisation on the market today. There is sensor shift stabilisation, which is the most common type in compact cameras. Next, there is lens stabilisation, which is popular in DSLRs and is usually claimed to be more effective especially at longer focal lengths. Both of these are good, and you can find one or the other depending on the brand of camera or lens.

There are also some camera makers which claim that high ISO settings are a type of “Image Stabilisation!”, which is just… not true. Watch out for “Digital Image Stabilisation” or similar terms when you are looking for a camera. The camera in question very probably does not have actual stabilisation, hence the “digital”.

Do you need image stabilisation on your next camera or lens?

Well, if you are shooting in low light or at longer focal lengths, it is a very useful feature to have. Even though it is not a replacement for a tripod or a faster lens, it is still very helpful. I must admit I have gotten quite used to image stabilisation and now find it hard to use a non stabilised camera in low light. It is not a must have feature, but if you can get it for a reasonable price, go for it, I bet you will find it useful. It simply makes it easier to get good images in low light.