ISO on a Digital Camera?

Legacy_user

Might sound daft but what exactly is ISO? Mine goes from 80 to 1600. What is it purpose?

Robin_T_Cox

In the days when we used film instead of digital, the ISO number indicated the speed of the film, i.e. the rapidity with which the film would react to light. 'Fast' films had high ISO numbers, while 'Slow' films had low ISO numbers. So under poor light conditions you would use a High ISO film, but under bright light you would use a Low ISO film. However, this had a drawback: using a Hi-ISO film meant that your picture was very grainy, whereas using a Lo-ISO film meant that your picture suffered little graininess.

With digital cameras, the same applies. If you want to take pictures in poor light conditions, you may need to adjust ISO to High, at the risk of having more grainy pictures. But in more normal or bright light conditions you can use Low ISO, and have the benefit of relatively little graininess in your photos.

A value of 64-100 ISO probably represents for most films and digicams a medium level ISO. Whereas ISO 200 or 400 would represent a grainy but fast film and digicam equivalent.

The best thing would be to try taking shots on your camera at each ISO that it will do, so that you can use this facility to choose the most appropriate ISO for the scene you are trying to shoot.

Fifer

On both film and digital cameras, ISO is a measure of sensitivity to light. The higher the ISO, the more sensitive to light (faster) the film or sensor is, but high sensitivity is generally accompanied by higher noise too (grain in film and flecks and specks caused by heat, electrical noise and random interference in the sensor of digital cameras).

Marty_J

When you increase the ISO on a digital camera, you increase the gain of the sensor. It's like turning up the volume on your stereo.

Some cameras have better high ISO performance than others, and dSLRs are generally much better than compact cameras.

As noted above, a higher ISO means the sensor is more sensitive to light, so you can use a faster shutter speed in low light, which helps to eliminate cameras shake.

It can also be desirable to use a high ISO when you want to use a fast shutter speed, say for action photography. If the sensor is more sensitive to light, you can use a faster shutter speed but get the same exposure, which can help freeze the action.

Generally speaking though, on a compact camera, you want to keep is as low as possible.

AHAR

The lower the ISO setting, the longer the shutter needs to be open to capture enough light. In gloomy conditions this may result in shutter times long enough to show the effects of slight movements of the camera i.e. blurred pictures.
Each doubling of the ISO halves the time the shutter is open so it may help you get a steadier shot at the expense of noisier images.
These days camera manufacturers tend to try to counteract this noise by smoothing out the variations produced by the sensor which results in un-natural looking smudged details. I'd take film-like grain over that anytime.