Film Speeds

If you are over ten years old you might still belong to the generation of people that have used only or at least up to some point a film camera. You might also know that film material has to be exposed to light to create an image on the material and has to be developed to with several chemical processes to actually create a negative and a photo form the negative. But you might not know what film speed is after all. Find here some information about film speed.

One of the important factors while buying film material especially for professional photographers is the Film speed. It is the measure for the light sensitivity of the photographic film. Film material with a lower sensitivity, means a lower speed rating usually requires a longer exposure to the light and is therefore called “slow film”. While on the other hand film material with a higher sesnititvity, means a high speed rating can shoot the exact same picture with a hsorter exposure to light and is therefore called “fast film”.

The film speed rating was established by the International Standardization Organization with the ISO 5800. There are two ISO film speed scales in existence, the ISO linear scale (adopted from the former ASA film speed scale) and the ISO logarithmic scale (adopted from the DIN film speed scale). These scales reach from 1 to 6400 in linear and 39 in logarithmic.

In the development process the film speed is used to find the proper exposure parameters for the material to be developed. The difference in film speed can make a picture or ruin it. Wrong settings with the wrong film speed can overexposure or underexposure the picture.

Film speed is somewhat related to the granularity of the salts used in the film material layer, since the size of the grain plays a role in the light sensitivity of the film paper.

The best film speed for underwater shots depends on the depth the shot is taken. The deeper the underwater shot is the less light there is. Also when using a lighting system or a flash under water film speed needs to be adapted to the longer light waves, which are slowed down through the density of the water. Therefore film speeds in the slow speed range are better for underwater photography.

Besides film speed there are three other options for the photographer to directly influence the outcome of his picture, lighting, f-number and shutter speed.