Choosing a film with a high ISO number allows the motion of an image like this to be frozen.
The ISO number of film, also known as its speed, measures a film's sensitivity to light. The higher the ISO number, the more sensitive it is to light, and therefore is able to produce quality images under low-light conditions. Although digital cameras obviously do not use film, you can still set the ISO higher to amplify its intake of information.
Identification
ISO stands for International Organization for Standardization, though older cameras may use the same film speed number values marked as ASA (American Standards Association). European-made older cameras may be listed under DIN (Deutsches Institut für Normung) values, which consist of two-digit numbers followed by a degree symbol.
ISO Numbers and Light
As the ISO number increases, the less light it requires to make an image. This means film of ISO 100 requires a lot of light, and is best used outdoors. A film rated ISO 1600 requires much less light, and may be able to produce an acceptable image under low-light conditions or indoors. Film speeds range generally from 50 to 3200, with specialty films that go higher, lower, or at speeds in between standard numbers. The standard numbers include 50, 100, 200, 400, 800, 1600 and 3200.
Relationship to Shutter Speed
A shutter speed of 1/30 of a second or longer is considered slow, since a tripod would need to be used to prevent the image from blurring. A film rated at 1600 would be considered a fast film. Because a fast film requires less light to make an image, it also allows for faster shutter speeds to be used, since they inherently let in less light. For situations where action needs to be frozen, or in low-light situations where a flash is not available, film of a high ISO is the best choice.
Film Grain
To capture light quickly, the light-sensitive chemical of high speed film consists of large visible dots, or grain. Grain can be an advantage or disadvantage, depending on the photographer's style. As film speed increases, so does the graininess of the image.
Contrast and Noise
Films of a higher ISO have more contrast than slower films. Digital cameras set to a high ISO will also create images with more contrast and more noise. Noise is like film grain in that it shows up as large visible dots of many colors. In this case, noise is more apparent in the shadows of the image.
Pushing Film
Pushing film refers to it being purposely underexposed and overdeveloped. Some films are more adaptable to pushing than others, with some having the ability to be pushed to three stops faster or more. The result is a grainier image with more contrast.
Tags: less light, more contrast, able produce, fast film, film rated