How to hack DX Encoding to make a 400ASA film can tell the camera that it is rated 1600ASA or 3200ASA: Just take a knife or a pair of scissors and scrape the black paint off the appropriate square in the top row. See the pictures above. Note that you have to remove one square of paint for 1600ASA, but two for 3200.
How it works: DX coding is a system to allow cameras so equipped to read the film speed and other information from a 135 (35mm) film canister. The left hand row as shown above is the common contact and the conductivity of the other squares give the data. The top of the two rows of DX coding tells the camera the film speed. By if you don’t like the code, just adjust it by altering the surface conductivity of the squares.
Why?: Not all cameras have a way to override the automatic DX setting, making it hard to push film or re-load the canister with faster film than the original factory load.
Bonus: If you take out the last square as well, technically you can re-code it up to 5000ASA, but not all cameras can read this last digit and would just read it as 3200ASA and in any case, you may not get good results pushing film as far as 2 2/3 stops.
Tip: If you recover the squares with sellotape, a sticker, or nail varnish (anything non-conductive) then you restore the coding. If you cover the common contacts, the camera will assume the can has no coding and will default to (usually) 100ASA.
BOSS LEVEL: Recover the squares with tape, mark the relevant setting and set the film speed you want in the street when you load the film!
*Dan K is a photographer based in Hong Kong. He is old school and collects film compact cameras. This original article was published on his Tumblr here.