Introduction To ISO
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Beginner's Guide To ISO - What's ISO, how and when can it be used? We answer these questions here.
Digital cameras use a sensor that converts light to analogue signals, which are then processed in the camera to create a digital image. You can adjust how sensitive the camera's sensor is to the amount of light that's around by changing the ISO. The higher you make the ISO, the higher the sensitivity of the sensor is which means you can still produce images in low-light situations, for example.
Most digital cameras now have a wide sensitivity range that reaches from ISO100 right up to and beyond ISO1600. For example, the Pentax K-3 which is currently featured in a trade-in offer has an ISO range from 100 to 51200. You can also expand the ISO range of some cameras when needed.
NoiseIncreasing the ISO of your camera so you can take images indoors or at night is great but by increasing the ISO your images can be more susceptible to noise, which appears as randomly-spaced, brightly coloured pixels. Having said that, camera companies have made vast improvements when it comes to controlling noise at higher ISO levels but as Robin Whalley suggested in a previous article, it's still worth taking a series of identical shots at various ISO levels to compare how much noise is in them. That way, you'll find what limit your camera has and what level is best to use. You can also check the quality of your shots while out shooting on your camera's screen and reshoot if necessary. Use your camera's magnifying option to zoom in part of the image as it makes it easier to spot noise. Also, it's good to remember that there may be times when it's better to have noise and a sharp photo than no noise and a blurred subject because of camera shake or movement.
In most situations it's best to fix the camera on a lower ISO setting, however there are some situations when a higher ISO is needed.
|A shot without noise||The same shot with noise|
When To Use a Higher ISOAs mentioned, when working in low light it can be difficult to achieve a quick shutter speed but by increasing your ISO, you'll get the quicker shutter speed you're looking for. At concerts where you can't use flash and won't have a tripod because they're not allowed, slow shutter speeds will result in camera shake spoiling your shots so increasing your ISO to give you a faster shutter speed will mean you can shoot photos of whoever is on the stage hand-held.
It's also a useful tool for when you're photographing a subject such as close ups of flowers in the shade. You may have set the exposure manually using a small aperture to ensure maximum depth of field but the resulting shutter speed is too slow to prevent the wind movement blurring the subject. But by switching to a faster ISO it will help increase the shutter speed to freeze the movement of the flower giving you a still, blur free shot.