Hacking DX Codes

January 13, 2026

In my last post, we covered the Golden Rule of expired film: Overexpose by 1 stop per decade.

If you are shooting with a manual SLR (like a Pentax K1000 or Canon AE-1), this is easy. You just turn the ISO dial from 400 to 100. Done.

But what if you are using a compact "Point-and-Shoot" from the 90s? These cameras read the barcode on the film canister (the DX Code) and set the ISO automatically. They don't have a manual dial. If you put a roll of expired ISO 400 in there, the camera will shoot it at 400, and your photos will come out dark and muddy.

To fix this, we have to get physical. We have to "hack" the canister.

What is a DX Code?

Look at a roll of 35mm film. On the side, near the lip, you will see a checkerboard pattern of silver and black squares.

Silver (Metal): Conducts electricity (The "On" switch).
Black (Paint): Insulates electricity (The "Off" switch).

When you load the film, tiny pins inside your camera touch these squares to read the ISO. By changing which squares are black and which are silver, we can trick the camera into thinking the film is slower than it actually is.

Here are the three ways to do it, ranked from easiest to hardest.

Method 1: The "Default" Hack (Easiest)

Best for: Expired ISO 200 or 400 film.

Most point-and-shoot cameras are programmed to default to ISO 100 if they cannot detect a DX code at all. This is a failsafe from the days before DX coding became standard.

Since ISO 100 is often exactly what you want for expired film (it gives 1 stop of overexposure to ISO 200, and 2 stops to ISO 400), this works perfectly for about 80% of situations.

The Fix:

Take a piece of electrical tape (or regular scotch tape).
Cover the entire DX code checkerboard on the canister.
Load the film.
The camera will likely assume it is ISO 100 and give you that juicy overexposure you need.

Note: Check your camera manual (often found online) to confirm its default ISO. Some rare cameras default to ISO 25, which might be too slow.

Method 2: The Sticker Solution (Cleanest)

Best for: Frequent shooters who want precision.

If you shoot a lot of expired film, or if you bulk load your own film, scraping and taping canisters gets tedious. Several companies sell pre-made DX Code Stickers.

The Fix:

Buy a pack of ISO 100 or ISO 50 stickers online (eBay or dedicated camera shops).
Peel off the existing label or simply stick the new DX code over the old one.
Your camera now reads the film exactly as the sticker dictates.

Method 3: The "Scrape and Tape" (DIY)

Best for: Specific ISOs (like shooting ISO 800 at 200) or if Method 1 fails.

If you can't use the default hack, you can manually alter the code. You will need a knife (to scrape paint off) and electrical tape (to cover metal up).

You will need to look up a DX Code Chart online to see the specific pattern you need, but here is the logic:

To turn a "Black" square into a "Silver" square: Use a knife or sandpaper to scrape away the black paint until the shiny metal underneath is revealed.
To turn a "Silver" square into a "Black" square: Cut a tiny square of electrical tape and place it precisely over the metal square to block the connection.

Common Conversion (ISO 400 -> ISO 100):

Top Row, Position 2: Scrape paint off (Make it Silver).
Top Row, Position 3: Tape over metal (Make it Black).

(Note: The "Top Row" is the row closest to the flat end of the canister, not the protruding spool end).

A Final Warning

When using Method 1 or Method 3, ensure your tape is flat and secure. You do not want a piece of sticky tape peeling off inside your camera and gumming up the delicate shutter mechanism or the film advance motor.

Happy hacking!