How Camera Films Work

1. Every film (including color films) consists of two basic components: a single or multiple layers of light-sensitive emulsion, and a support for the light-sensitive emulsion, the base. The emulsion is made up of microscopic light-sensitive particles suspended in a gelatin medium. The gelatin on the film is similar to the gelatin used in some foods.

2. The photosensitive substance suspended in the gelatin is silver halide particles. This particle is so fine that it can only be observed under a high-power microscope. In 1 square inch of the usual photographic film emulsion, the silver halide crystals contain as many as about 40 billion.

Silver halide crystals have the property of changing their structure upon exposure. The mechanism of this change in chemical properties is not important to us; it is the end effect of the change that is important. How is this change produced? When you take a picture, light passes through the lens of the camera and hits the emulsion layer of the film, and when the light reaches the silver halide crystals, the clumps formed by the agglomeration of the silver halide crystals are still extremely fine. The amount of light received by the emulsion layer depends on the changes in the crystals and the agglomeration. That is to say, different intensity of light irradiation to the film, the film emulsion layer of the microscopic field, there are different numbers of crystals in the structure of the change and mutual agglomeration.

3. Once the film is exposed, a latent image - an invisible image - is produced immediately. The film must be developed to convert the latent image into a solid visible image. When the film is developed, the structure of the silver halide crystals has changed into an agglomeration of black metallic silver particles, resulting in an image - a negative image. Those portions of the film that are not light-sensitive, i.e., crystals that have not undergone structural changes, are washed away by a chemical called a fixer, which makes these portions appear light gray or transparent. The result is a negative image in which the dark (thick) portion is the more exposed portion, the bright (thin) portion is the less exposed portion, and the fully transparent portion is the portion not exposed to light. This is the basic process of recording an image on black-and-white film.

4. Color film has three photographic emulsion layers, in which they also contain different organic compounds capable of generating dyes, called color coupling agents (colorants). They are themselves colorless, but can couple with the oxides of the color developer to become colored dyes during color development. For negative films, the coupling agent contained in the upper blind emulsion forms yellow in color development, the middle layer forms magenta, and the lower layer forms cyan, which is the processed color film we get. Through the expansion or enlargement and then project the image to the photographic paper or reversal of the reversal of the film processing, the upper layer of yellow film into its complementary color blue, the middle layer into green, the lower layer is turned into red, we get the same as the natural state of the color photograph or transparent reversal of the film. This is the basic process of recording images on color film.