It’s been discussed extensively elsewhere that unfortunately DSLR manufacturers do not adhere to an ISO standard as much as one might think (despite the fact that it’s called a standard). In other words, ISO100 sensitivity in Brand X is not necessarily the same (and thus not the same exposure) as in Brand Y bodies, and not necessarily the same as ISO100 film.
If you want to use a DSLR as a meter for your film shooting, you’ll need to figure out the difference between what your digital body shows and what your film body captures, and factor that offset into your film exposure. What a nuisance. I really wish that it wasn’t so, because now that Fuji FP100 instant film is no more, I’d like to be able to buy a DSLR to proof my lighting. Oh well.
Take both cameras, get the settings from the DSLR, write them on a 3x5 card, put the card in the scene, shoot it with both cameras, repeat with a darker scene and a lighter scene. Get the film developed and printed, print the digitals and compare the shots. This will tell you how close the DSLR's metering is to your film cameras settings. Use manual settings in the DSLR for ISO, matching the film ISO.