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How Does a Dark Slide Work in Photography?

The images people see with their eyes are actually waves of light, with slightly different wavelengths marking different colors. Just as the human eye converts the light that hits it into images, a camera records this light as images. Whereas modern digital cameras have chips that turn this light into electronic data, older cameras recorded these images on film. To protect the film from light until the photographer is ready, he uses a dark slide.

Film-Based Photography
- In the cameras that preceeded digital photography, the device captured an image through light falling on film that was coated in a special blend of chemicals. As the light hit the film, each part would change to mimic the light which fell upon it. In this way, the film recorded the image which passed through the lens. This process was irreversible, so once a film was exposed to light, it would permanently record the image that light carried.
Dark Slide Purpose
- Dark slides are the original technology the first cameras used to preserve films for the image the photographer intended. The photographer places the film inside a rectangular cartridge, which will keep the film in complete darkness. The photographer slips this cartridge into the camera, behind the lens, and pulls the wall of the cartridge between the film and the lens out of the cartridge, allowing un-shuttered light from the lens to fall onto the film. After the photographer takes the image, he slides the wall back in to close the cartridge then removes the cartridge from the camera. This removable wall is the dark slide.
Exposure Indicator
- Dark slides have a different color on each side, usually black and white. This allows the photographer to discern if the film inside a given cartridge holds an exposure, or if the cartridge holds a blank film. While the photographer can use either side to indicate either status, the black side facing outwards generally indicates that the film is blank, and the white side facing outwards generally indicates that the film already holds an exposure.
Double Dark Slide
- Film cartridges that use dark slides can either hold one or two pieces of film. Cartridges that hold two pieces of film have dark slides on both sides, and an internal partition that creates two separate chambers for film, are called double dark slides. Rather than having to reach for a new cartridge after each shot, double dark slides allow the photographer to simply flip the cartridge around to take another exposure.

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