DX coding and Lab Processing

For cameras that do not have exposure compensation or DX override, I

have read that I can change the ISO of a film by scratching and taping

the DX coding. In itself this is quite straightforward but do the

minilab machines read the altered DX coding and then develop the film

differently as a result. I want to "overexpose" the film not pull it,

and so want it processed as if it were exposed at its box speed.

 

Any thoughts? Thanks.

AFAIK, C-41 film is processed identically, regardless of film speed or DX coding. Unless you specifically request a pull or push, the minilab development time is independent of film speed.

 

Others more knowledgeable than I can offer more details.

Rather than going at the film casing with something sharp and run the risk of piercing the canister (or worse, slipping and stabbing yourself in the hand) you could just put a small strip of black electrical insulation tape over the DX code. It's thin enough that it won't make the canister too big to fit in the camera, but remember to take it off again before you give the film to the lab. That little strip of tape could come off in the machine and cause merry hell for the lab - and possibly land you with a chit for the subsequent repair.

 

As I write this, I remember that you can buy DX coding stickers from photographic shops - like Jessops (Don't know if you're in the UK or not. if not, read some other photo-shop.

 

I think you'd have to tell your lab what ISO you've rated the film at, as surely they'd have to tell the computer what ISO the film is so it can adjust the developing time accordingly? Not sure about that, but in black & white developing you have to adjust your dev time to how the film has been rated.

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AFAIK, C-41 film is processed identically, regardless of film speed or DX coding.</cite>

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That's correct. It's a standardized process. Film speed is only relevant at exposure time, not at processing time. The lab doesn't read DX codes at all.

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If you want to have C-41 film pushed or pulled as it's processed, then you need to request special processing, where they change the time and/or temperature of the developer. But the original query asked how to have it processed as standard, and for that, you just have it processed normally, and don't worry about what you did or didn't do to the DX coding.

The lab doesn't 'do' anything with the DX code, so if you just change the dx code and make the film 'slower', you'll get the overexposure you're looking for. Don't scratch, just use some tape and take it off after you've finished the roll. What camera do you use? There might be an easier way if, apart from the dx coding, it's not an all-auto camera.

Thanks guys. The processing side obviously isn't a problem. I use a Nikon F90x, but override the DX on the camera. I also have a Samsung P&S which doesn't have override or exp. comp. I understand the use of tape to cover the silver areas, but how do you turn the black areas silver/metal without scratching? Thanks again.

If you Google "DX coding labels" you'll find hints to a few sources. Check out http://www.bythom.com/dxcodes.htm for some good background on the code with a link to Porter's Camera Store which sells labels.

 

I don't see any information on how much of each area needs to be either conductive or insulated, but you might be able to figure it out by looking at the contacts in your camera. I suspect that most cameras only read positions 1-6, as I don't recall two rows of contacts. My Nikon F4 only has contacts for six of the twelve pads, and that's the only DX-aware camera here that doesn't have film in it at the moment. (Of course, this isn't part of my cameras that I often really look at for some reason!)

 

You could find some foil tape and try that to make a connection. I assume that the contacts aren't trying to put a whole lot of current through, so as long as it is foil (metallic, not mirrored Mylar) and doesn't have a coating on it, it should work.

 

I'm also assuming that for each position in the code there are two contacts in the camera. If the set of contacts in my F4 is actually making contact with twelve positions (one contact each) with at least one of them being ground or a common return, then a foil label would only work if it covered the entire area and you created a full replacement label on one piece of foil. On the other hand, that would mean that positioning any label would have to be very precise.

 

Do not worry even slightly about leaving either foil or black tape on the casettes. The lab will fish the leader out of the casette, run the film into the processor, and cut the end off. The casettes never end up in the soup so the little bits of labels you might fabricate are not going to end up compromising anything.

 

I just tried scraping the black ink off pad 6 on a roll of Sensia, and it seems to come off pretty easily with a sharp X-Acto blade. I wouldn't hesitate to do that. If you don't trust your right hand to not jab your left hand while scraping, you could put a bit of masking tape over the tip of the blade, or hold the casette in a gloved hand.

 

To respond to your original question, the DX coding is only used in your camera, the lab doesn't use it at all.

 

Van

You might try using a thick black marker, something like a sharpie. The dx code is actually read by the bare metal on the film canister. If you compare the dx coding for each film type, you can actually fool the camera by coloring in the blocks where the bare metal is showing. This way if you forget to remove any black tape that some of the other replies have suggested there shouldn't be any problems with the lab that processes the film.

 

Paul

Paul, does Sharpie ink prevent electrical conduction? These DX codes

are electrical, not optical. I've always used electrician's tape

and a knife to scrape off black paint.

You do bring up a good point Bill, I would coat the the dx code area really well and since we are talking about minimal voltages and current there shoudn't be any reason this would not work. If for some reason it doesn't then the black tape method would be the best option.

 

Paul