Understanding the DX Code System

The DX (Data eXchange) code system revolutionized film photography by allowing cameras to automatically detect film speed (ISO), the number of exposures, and exposure latitude. This system uses a pattern of conductive and non-conductive patches on the film canister.

How It Works

The DX code consists of several key areas:

ISO Speed Detection (6 squares)

The primary function of the DX code is to communicate the film’s ISO rating to the camera. Six metallic squares arranged in a specific pattern represent different ISO values from 25 to 5000.

Frame Count Detection (4 squares)

Three additional squares tell the camera how many exposures are available on the roll - typically 12, 24, or 36 frames.

Exposure Latitude (2 squares)

These squares indicate the film’s exposure tolerance, helping cameras make more informed metering decisions.

Manual Modification

Advanced photographers sometimes modify DX codes by covering squares with tape or scraping away conductive material to “trick” the camera into using different settings. This technique can be useful for:

• Push/pull processing experiments
• Using expired film at different speeds
• Creative exposure experiments

Warning: Always test modifications on less important shots first, as results can be unpredictable.

Common DX Code Patterns

• ISO 100: Standard daylight film
• ISO 400: Versatile indoor/outdoor film
• ISO 800: Low light situations
• ISO 1600: Very low light or high speed needs

Understanding these patterns helps photographers make informed decisions about film selection and camera compatibility.