Film Cartridge.jpg
Wondering how DX coded films work ?
It works just like the bar codes. The white areas are the conducting area while the black are insulated. it has to work in conjunction with the DX contacts in your cameras (Just open the camera back and take a look). Those pin-like contacts that reside in the film cartridge chamber will remit the data relating to the film speed (ASA) to the camera CPU for computation in auto exposures.

Credit: Mr. Richard Yeow of Canon Marketing
for providing the graph chart.

A quick reference graph for DX coded films

DX coded Graph.jpg

There is an external link I found on the web recently that can help
you understand more with further illustrations:

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