How Do Old Film Cameras Work

By Shawn McClain

Film cameras use light and chemistry to record an image.
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Before the advent, and then explosion, of the digital camera, old cameras had to use film to record an image. The camera manipulated the properties of light to create an image on a piece of film, called a negative. Then, the negative went through a chemical process to create the end picture.

Manipulating Light

The process of capturing an image begins when light reflects off of an object. If you create a small opening in front of this image, the photons from the reflected light will pass through the opening and align themselves in a way that creates an image on the other side of the opening. By focusing this light with a lens and positioning film a set distance behind the opening, a camera can record that image on the film.

Capturing the Image

The film is covered in an emulsion, made up of silver halide crystals, that will capture the image when exposed to light. When the camera's shutter opens for a fraction of a second and light passes through to the film, the silver halide crystals turn into silver ions. The density of the silver ions, compared with the remaining silver halide, represents the intensity of the light in that area of the picture.

Processing the Film

Turning the exposed emulsion into an image requires using both chemicals and time. First, the film is placed in a developer solution, which converts the ions into black silver. The film is then placed into a fixer, which removes the remaining silver halide crystals, leaving just the dark silver in place. After the film is washed and dried one last time, what's left is called a negative because the film is dark in areas that recorded the most light, and it's white in areas that received no light. Photo developers will then pass light through the negative and onto photographic paper, where the light levels are reversed and the end result is the image that was in front of the camera.

Color Film

Standard film can only capture black and white images because it can only differentiate between light and dark. There is, however, color film, which is actually three different emulsions in one. Each emulsion layer is chemically designed to react to only green, red or blue light, and the three layers are separated by a filter. The three negatives that this film creates are recombined when creating the final image, using those three primary colors to create full-color photographs.

Camera Mechanics

Because the image on an old film camera is stored on an actual piece of film, instead of just residing in memory like on a modern digital camera, the film cameras do have an extra set of mechanics required to take a picture. First, a roll of film, which is stored in a light-proof container, has to be put into a slot on the camera. Some cameras also require the operator to manually unroll the first few inches of the film roll to get the operation started, although many do this automatically. When you press the shutter to snap the picture, the camera then advances the film by one frame, readying the camera for the next shot. Once the roll is completely expended, the film is rewound back into the container, again sometimes automatically and sometimes by pressing a button or turning a crank, so the film can be safely removed from the camera and taken for developing.