Photographic Myth Buster #10

#10. DX-coded Film Canisters

True or False?

The maximum emulsion (film) speed available in a DX-coded film canister is ISO 5000.


DX-coded film canisters have 12 metallic contacts on their sides that indicate to the camera the film speed, the exposure latitude, and the number of available exposures. Five of the contacts encode the speed as a binary number. Rearranging the order of the contacts, they can be read as binary numbers that increase with speed. The highest binary number (11111, that is, decimal 31) is associated with the highest film speed (ISO 5000). Film speeds that fall outside of the range 25 to 5000 in steps of one third stop must be handled manually.

A table of DX Codes is presented in the book Photographic Exposure Calculations and Camera Operation.

Copyright 2008 Michael G. Prais, Ph.D.

For a readable but in-depth analysis of this concept along with many other concepts associated with photographic exposure, take a look at the book Photographic Exposure Calculations and Camera Operation. This book provides insight into the equations that govern exposure, exposure meters, photosensitive arrays (both solid-state and emulsion) and the Zone System as well as concepts associated with resolution, dynamic range, and depth of field.

The book is available through (ISBN 978-1-4392-0641-6) where you can Search Inside!™.

Check under Photography for the table of contents, an extensive list of the topics and subtopics covered, the preface describing the purpose of the book, and a diagram central to the concepts in the book.

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