I used to own a Bronco SQ-Ai 6x6cm roll film camera. This camera had removable backs so that you could fairly easily switch between say 64 ISO slide film and 400 negative film mid roll. To be able to do this, each film back had two dials on it: one for ISO and one for exposure compensation. When you attached the back to the camera, the information was communicated by a set of contacts to the metering prism. There is something so delightful about that window of time when cameras were becoming electronic but still using film. So many clever things were happening. I think about the Canon T90 that the presenter in this video mentioned: it was a technical marvel with lots of different metering modes, a digital display, etc. ...or cameras like the Rollei 6008, which had incredibly sophisticated light metering and film handling, yet still used an analog waist level finder.
Bought a Canon EOS-3 year ago and it's funny how it almost feels like DSLR but with film. The amount of electronics and what in can do is amazing. Well DSLRs are basically film SLRs but with a sensor instead of film + some R&D improvements throughout the years. Also DSLRs got the back display which is a lot more better than the configuring late-90s SLRs with some weird function button setups with super small display on top of the camera. If my memory serves me right the last pro camera, EOS-1V had some serial link cable and a desktop software to configure things properly and get the exposure data for the film rolls. Like exif data but before exif data :D
FYI, Bronica. And the fun detail about the ISO and exposure compensation is I beleive they were concentric dials (they are on my Bronica GS-1) so they were just adjusting a single contact. In other words, ISO 100 with no compensation is the same value as ISO 200 with a +1 stop compensation.
