How Instant Cameras Work

In black-and-white instant photography's early dates, the camera user had to pull the exposed instant picture from the camera, wait about one minute, peel off a piece of paper, and use a small sponge to apply a chemical coating to the picture to stop its development. Then, the picture had to dry before someone could safely handle it.

When Polaroid introduced color instant photography in 1963, the technology had advanced to the point that, although users still had to time the picture's development and remove the print from the film sheet, they did not have to apply any chemicals. The film remained sticky for several minutes.

In 1972, Polaroid introduced the SX-70 instant camera, which used what the company called "integral film." As the name implied, the new film was an integrated structure that did not require the user to do any timing or other treatment. There were no excess pieces of the film or paper to discard. The one-piece unit contained all the chemicals necessary for development of the picture. The user still had to wait several minutes for the exposed picture to develop fully.

With integral film, within four-tenths of a second after the user pushed the shutter release button and exposed the film, the camera partially ejected the exposed film unit. A battery contained in the film cartridge powered the camera and the motor that ejected the film. As the camera ejected the picture, the film passed between two metal rollers. These rollers squeezed the film, bursting a small pod at the leading edge of the film. This pod contained chemical reagents that spread between the film unit's receiving and negative layers. The chemicals reacted with the negative layers based on the nature of the layer and the amount of each layer's exposure to light during the exposure process (see Exhibit 3). These reactions determined the lightness, darkness, and color of each area of the final picture. This chemical process was what users saw as they watched the film develop from the plain, grayish-green initial film color to the finished picture. All of this development took place outside the camera in full light. Opacifying dyes in the reagent layer blocked additional light from entering the lightsensitive layers once the film exited the camera.

Because users did not have to peel anything from the film unit or apply chemicals, they were technically able to take another picture immediately. However, because the camera only partially ejected the picture, the user had to take the exposed picture from the camera and find a place to put it, usually a pocket or nearby table. If the user took a second picture before removing the first, the second film unit would simply push the first out of the camera, causing it to fall to the floor. (See Exhibit 4 for a description of Polaroid's camera line.)

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