Image Rectangle Dimensions
There is always some confusion in the actual dimensions of the image rectangle. Obviously a 2 ¼-wide film cant have a 2 ¼ x 2 ¼ image due to the necessity of the film width overlapping the film aperturethe window in the camera or film holder. The film aperture can vary slightly from maker to maker.
The Wikipedia page is useful, but doesnt really give the actual dimensions of the image rectangle. Actual sizes vary due to variations in the dimensions of the film aperture chosen by each maker. Usually theyre about:
56mm x 42mm (nominally 6cm x 4.5 cm)
56mm x 56mm (nominally 6cm x 6cm)
56mm x 69.5mm (nominally 6cm x 7cm)
This link provides more comments, particularly on the variations in the length of the 6 x 7cm format:
http://www.kenrockwell.com/tech/format.htm
Mamiya always specified the dimension of the image rectangle for its MF cameras in its advertising literature. It specifies 56mm x 69.5mm for its 6 x 7 cm cameras. I believe that 56mm is the dimension across the width of 120 and 220 films for all Mamiya MF cameras.
A similar situation exists for sheet film holders. Further, they produce a wider image where the hold-down rails are cut out for film loading.
The most accurate way to determine the dimension is to simply measure the film aperture of
your camera or film holder.