As far as I know, it is also the only medium format camera that changes from 120 to 220 film without having to buy another back or insert. Considering the fact that backs for most cameras are going in the $500 to $900 range these days, that can save a few bucks
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rollei sl66 backs can take both 120 & 220 films - although Ilford are discontinuing their 220 films, and i imagine that other film manufacturers will follow at some point. And Backs are about 180-200 although are getting rare in UK now