Most Medium Format cameras don’t have some sort of window on the back of the camera that you can peer into; one of the many way that they differ from 35mm cameras. So then the question becomes how to remember what film you’ve got in that camera? Well, the answer varies but the most consistent one that you’ll find is that you should be using the little note holder on either the back of the camera or the film back depending on what you’re using.
Let’s say that I was shooting some Ilford Delta 400 in my Mamiya 6. What I’d do is take a little tab from the box that clearly notes what film it is and slip it into the little holder. This way, it will stay in place and when I go back to pick the camera up to shoot, I’ll remember that Ilford Delta 400 is in there.
Why not just finish the roll, you ask? Well, 120 film usually has less shots per roll vs 35mm film. Depending on the format, you could have something like 16 shots when shooting at the 645 forma or even 9 at the larger variants like 6×9 format. Because of this, you also tend to be much more heavily selective of your shots. You’ll switch camera backs between color and black and white as well if you’re using an SLR style of camera that allows you to do so. Just to note, a camera like the Pentax 67 won’t let you switch backs but the Mamiya RB67 Pros S will. Otherwise, there’s a possibility that you can go for some time without shooting images with that camera and back, and you’ll just forget that there’s film in there. You may also forget what film you put inside unless you’re the type to really stick to a few emulsions.