Quote Originally Posted by Kevin Kehler View Post
My Yashica Mat 124G door has a little plate that you slide up for 220 or down for 120. As well, my RZ 6x6 back has a similar feature for 220 film, where you twist and rotate the plate depending on 120 or 220 film. I still have 2 boxes of 220 TXP in my freezer which I love using.

As a side note, is the biggest problem with using 120 film in a 220 back the film flatness or is there something else like spacing I am missing?
The spacing can be off, so you can get fewer frames, but film flatness is generally not an issue, since the 220 pressure plate is closer to the film gate than a 120 one (no backing paper to add thickness). The extra thickness of the 120 film/paper just pushes the pressure plate back into its spring, so the film is still held flatly.

Going the other way (220 in a 120 back), film flatness is not as good as it should be, and you only get to use half the roll (unless you can somehow reset the frame counter).