Well, this happened to a rangefinder of mine, but since it pertains to all 35mm gear, I thought I'd post it here.

I loaded a roll of Agfa APX 100 into my Contax G2 which had been set to "DX coding". I was shooting with an external viewfinder and a 21mm lens and had not noticed anything amiss until I switched lenses and noticed that the shutter speed reading was out of whack in the camera viewfinder. When I checked the ISO setting, I realised it had been set to 2500 and not 100. The "DX" was lit on the LCD display though, which means the camera had somehow misread the DX code on the film canister.

The batteries are new-ish in the camera, unlikely that they need replacement so soon. And there are no marks or scratches on the film canister that could possibly have caused confusion.

In fact, from the DX code, for ISO 100 the topmost row should read silver-black-silver-black-silver-black.
For ISO 2500, the row should read silver-black-silver-silver-silver-silver.
I have no idea how the camera sensors would have read "silver" when there were blacks.

At any rate, I don't know if my entire roll of film was misrated at 2500 because I'd nearly finished the roll by the time I made the discovery.

Does the camera pick up the ISO every single time the camera is switched on, or only when the film is loaded, and then it holds it in memory? If so, is there a possibility that the DX coding only started to screw up midway through the roll, or...?

I took out the APX roll and put in a fresh roll of Neopan 100, and the camera DX sensor seemed to be working OK again.

Anyone know how to salvage a roll of APX 100 shot at ISO 2500? Won't the results be horribly grainy?