I've used a DLSR to check exposure and lighting on Medium format shoots, but I was wondering about using them for LF nighttime shooting, for example if i set the DSLR to f2.8 at 20 sec, what would I set the LF too, is there a scale factor invloved, also on long exposures the DLSR doesn't suffer Reciprocity failure, whereas the film will, again is there a factor to figured i to account for this?
Throwing it out there, as I'm sure someone here will have the answers, before I go off shooting loads of black film!
The exposure would be exactly the same regardless of format, though the DOF and FOV obviously would differ. The reciprocity issue would have to be tackled separately. I simply download the reciprocity charts for my favourite films to my cell phone.
I sometimes spot meter with my DSLR. A DSLR makes a very nice exposure proofing system, because the exposure latitude is crap... (compared to b&w film, at least!)