Comment by primelens

On medium format film - I can't tell if this is 120, 220, or 620, or something like 616 - many cameras can take pictures of varying width. For example, on a camera that makes 6x9, or 6x7 pics, you might be able to put in a masking attachment and make 6x6 pictures. If you forget to put the attachment, you might think you're shooting 6x6 shots and advance the film accordingly, but you'll actually make wider shots which overlap at the edges.