DX encoding
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Dx135can.jpg
Dx135can.jpg
135 Film Cartridge DX Markings: 125 ISO, 24 exp., +f/3 -f/1
The DX Camera Auto-Sensing Code takes the form of a common ground and ten areas (bits) on the cartridge surface that are either conductive or non-conductive. Electrical contacts in the camera read the bit pattern.
The first 5 bits represent 32 possible film speeds. But there are only 24 speeds representing the 1/3 "stops" from 25 ISO to 5000 ISO.
Likewise, 3 bits represent possible 8 film lengths, although in practice only 12, 20, 24 and 36 exposures are encoded.
Finally, 2 bits give 4 ranges of film tolerance, or latitude, in ±f-stops.
The full DX geometrical and electrical standard is set by ANSI and I3A.
See also
External link
- http://www.geocities.com/thombell/dx.html (Shows how to read the codes.)