DX Camera Auto Sensing
The outside of film cartridges are marked with a DX Camera Auto Sensing (CAS) code readable by many cameras. Cameras can then automatically determine the film speed, number of exposures and exposure tolerance. The first cameras to use the technology are said to be the Konica TC-X SLR and Pentax Super Sport 35 (PC 35AF-M) in 1984.
The DX Camera Auto Sensing code takes the form of a grid of contact points on the side of the metal cartridge surface that are either conductive or non-conductive. Electrical contacts in the camera read the bit pattern. Most cameras read only part of the code; typically, only the film speed is read, and some cameras aimed at the consumer market only read enough bits to tell apart the most common film speeds. For example 100, 200, 400, and 800 can be detected by reading only S1 and S2 and ground.
Read more about this topic: DX Encoding
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