How does photographic film work?

Answer:Light is focused on to a light sensitive chemical deposited on a thin film. The light is allowed to strike the film surface for a short time by the use of a shutter. The shutter acts as a valve for the light. When light strikes the film, the light sensitive chemical undergoes a chemical change. The amount of light makes a proportional amount of change in the light sensitive material (within limits). Too much light can 'overexpose' the film, causing too much of the light sensitive 'grains' to change and not leaving enough of them unexposed to make a discernable image. After exposure, the film is chemically treated to 'develop' the image. The chemical treatment causes a permanent change in the light sensitive grains, and renders them insensitive to light. It also makes them visible.

The lens focuses the light on the film. The 'focal length' of the lens determines how large the focused image will appear on the film.

The shutter acts as a light valve. A longer exposure allows more light, and a shorter exposure allows less light.

The iris acts to reduce the amount of light, and it also affects the focus. This is called the 'field of focus'. A smaller aperture in the iris produces a larger field of focus, allowing object closer and farther away from the actual point of focus to appear sharper.

The camera's light meter measures the amount of light coming from the direction of the subject.

A computer in the camera can control the aperture, shutter, and lens focus to make the act of taking a picture completely automatic, needing little thought by the photographer. The photographer is free to concentrate on the subject.

Filters can be used to correct for differences in light source color balance, reflections off of objects, ultraviolet light, and create different artistic effects.