Photographs are art created by capturing and recording light. Light enters the camera body when the shutter is opened, and goes through the aperture to hit a light sensitive plate. In film cameras, the film undergoes a chemical reaction upon being exposed to light; in digital photography, there is an image sensor whose function digitally mimics that of film.
ISO is one of three fundamental tools a photographer has at their disposal for how light is “painted” to create a photographic image. ISO stands for International Organization for Standardization and instituted standardization across films to convey their sensitivity to light.
How ISO Works
ISO was a necessary component of understanding how photographic films would react to light. When the shutter of a camera was pressed, film would pass through the lens and strike the film plate, thus exposing the film to light and beginning a chemical reaction. There were (and are still) a great variety of films, each having its own unique properties, one of which was just how quickly the film reacts to light.
A “fast” film reacts to light very quickly, not unlike how a bone dry sponge readily absorbs water. A slower film takes longer to “soak up” the sunlight.
ISO in digital cameras work in a very similar manner. While there isn’t the physical limitation of a chemical reaction with which to contend as with film, there is still a need to control and measure how sensitive we want the camera to be to light.
How ISO Affects Photographs
The lower the ISO number, the less sensitive to light. But digital cameras don’t have the limitations of film, and some might wonder why incorporate ISO into digital photography at all.
However, being able to manipulate the camera’s sensitivity to light allows the photographer to create an image with the least amount of “noise” possible. “Noise” refers to graininess and lack of detail.
The general rule is that the lower the ISO, the less noise. In the days of film, this was an absolute; if a photographer wanted a smooth, non-grainy image, they would select the lowest ISO that would work within the available light conditions.
Similarly, in digital photography the ISO can be changed to achieve the desired results. So ISO 50 is less sensitive to light than ISO 100, which in turn is less sensitive than ISO 400, etc. Of course, the advantage in digital photography is that the ISO can be switched from one photograph to the next (unlike the days of film when the photographer had to finish the roll).
ISO's function in manipulating and controlling light to create a photographic image is one of the three fundamental tools for photographers.
Christine Farnum - Christine has been writing since her age was in the single digits; as the years went on she added editing, photography, and graphic design ...
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