In addition to the standard 120 (6x7) film back, Mamiya made a 120 (645) back that shoots 6cm x 4.5 cm negatives.
Does anyone know if you get more exposures per role of 120 film? If so, how many? If it gives the same number of exposures as a standard 120 (6x7) back, just with smaller negatives, then why would anyone use it?
645, Also called 6 x 4.5 cm.
Actual image size is about 56 x 42 mm.
16 shots per roll 120, 32 shots per 220 roll.
Used where size and film economy is important.
Not used seriously where image quality is paramount.
~Lifted from Ken Rockwell's web site. http://www.kenrockwell.com/tech/format.htm#120
Thanks for the info. At the time I asked that question, KEH had sent me a 645 back for the RZ67 by mistake and I was trying to decide whether I should keep it. I ended up reaching the same conclusion... and returned it to KEH.
I've bought the '56 x 26mm' back 24 exp.; I love the strange format (there was a url link here which no longer exists) and can use all kinds of 135 film and I think I'm the only one with this item !