How Does Camera Film Work?
The Physical Construction of Camera Film
Camera film is typically manufactured and shipped as an encased roll of celluloid, a thin plastic sheet. Both sides of this celluloid are treated with special chemical blends; one side is coated with chemicals that aid in the development of film negatives, while the other is coated with multiple layers of chemicals that help to form the images that eventually become photographs.
The Photochemical Mix
The chemical coatings that allow the creation of images in film are predominantly made up of silver halide crystals. Silver halide is sensitive to both visible light photons and invisible infrared light photons, and each light photon frequency has a different chemical effect on the crystals. This effect changes them forever, and because they are so stable, the images can remain suspended in the film for years before they are developed.
Silver nitrate and halide crystals are mixed and chemically altered to make them sufficiently small and more sensitive to light photons than they would otherwise be. When they're at the proper stage, they're layered onto the celluloid with additional chemical layers that help to filter and control light photon exposure. All of these layers are attached with thin layers of gelatin.
The Photo Capturing Process
For a photo to be taken, the film must be placed inside of the camera and wound into place. Winding mechanisms vary from one camera type to the next, but in any case, the film is pulled from its encased roll and stretched across the interior of the camera directly behind the shutter, which is directly behind the lens.
When the shutter button on the camera is pressed, the shutter opens and closes in a fraction of a second. During this brief moment, light photons are reflected off of the objects in front of the lens, and these photons are absorbed by the silver halide particles on the surface of the film. The brighter and more well-lit objects create areas of greater exposure, while the darker and poorly lit objects result in less chemical change.
From Exposure to Development
To process exposed film, it is first immersed in a liquid developing agent in a darkroom environment. If left in the bath for too long, this agent will turn the exposed areas of the film into pure silver. At the appropriate time, the film must be transferred to a "stop bath," which will neutralize the developing agent and freeze the development process. The film then goes into a "fixing bath," which rinses away any unused silver halide particles that remain. When it is removed, it is rinsed with water, allowed to dry and finally cut into film negatives. Film negatives have long shelf lives and can be used multiple times to create original photo prints.
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