I've just purchased a second hand Olympus Quick Flash AFL-S and on the front it reads 'ISO Auto Set' and I was wondering how film cameras detected what ISO a film was?

I normally use fully manual cameras, so as my first point and shoot I'm guessing it sets aperture and shutter speed automatically, but I'm confused about how it would detect the ISO of a film.

Also, if anyone has any links to the camera manual online that would be greatly appreciated.


There is a pattern on the side of a 135 film cartridge that the camera "reads" to determine the ISO of the film. The system is called DX encoding.

  • This is true but should be qualified. Some cameras (many compacts) will only read ISO values within a certain range and/or will only recognize films whose box speeds are stated in full stops (100, 200, 400, etc.). Check your manual to understand how it reads the DX codes. – bvy Jul 17 '17 at 3:01

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