Confused about ISO?
So what the heck is ISO? Well it literally stands for the International Organization for Standardization and it applies to photography as the keeper of the world standard for measuring the sensitivity of film or other light sensitive materials.
ISO film speeds are extremely important in photography because it can make all the difference between getting a correct exposure, with the right level of sharpness to illustrate your image, or blowing it completely.
It works like this. On all or most DSLR and some compact cameras there will be an ISO setting that is adjustable. This can be varied to suit the changing needs of the photographer in shifting light conditions. What this means is the photograph can be made in situations with more or less available light for shooting. Using an ISO number like 100 ISO means the capture medium (either film or digital) is not as sensitive to light as one of 1600 ISO.
So which ISO is good for what situation?
Photographing in a low light situation, such as after dark, on a very stormy day or inside in a windowless building will lend itself to adjusting your ISO to a higher (800 or 1600) setting.
On a bright day, on the beach or snow ski-ing the most suitable ISO to set your camera at is much lower, say 100 ISO.
Of course, because nothing is ever that simple in photography, you will create different effects in your pictures by changing the ISO value. At a lower ISO speed the image will have little or no visible noise (what was known as grain for shots taken on film).
At the higher ISO speeds though, noise and grain become more significant factors in your image making as they determine the innate sharpness and colour integrity of your picture. The higher the ISO, the more chance you have of a loss of definition at the edges of objects. This can upset some people, but it can also add an atmospheric touch to an image as well.
While adjusting ISO to deal with light conditions is the most universal use of this feature in photography, it also has the added benefit of increasing the speed at which an object can be photographed without any blur.
Translated simply this means that if you wish to photograph a moving object at a high speed then your camera shutter, which regulates the amount of light allowed to hit the capture medium over a time period, needs to be set at a very fast speed. This restricts the amount of light reaching the capture medium. Therefore having an ISO that is more sensitive to light will allow you more flexibility to shoot with a less flexible shutter speed!
Clear as mud?
Photography has a habit of throwing up inverses but this is one of the simplest to remember- high speed ISO equals high sensitivity to light while low speed ISO equals less sensitivity to light.
And that is all you need to remember!