Characteristics
The 120 format is typical of roll film. The spool was originally made of wood with metal flanges, later all metal, and finally plastic. The film is at least 30 inches (76 cm) long, up to 32–33 inches (81–84 cm), attached to a piece of backing paper longer and slightly wider than the film. The backing paper protects the film while it is wound on the spool, with enough extra length to allow loading and unloading the roll in daylight without exposing any of the film. Frame number markings for the three standard image formats (6×4.5, 6×6, and 6×9; see below) are printed on the backing paper.
The 220 format was introduced in 1965 and is the same width as 120 film, but with about double the length of film and thus twice the number of possible exposures per roll. Unlike 120 film, however, there is no backing paper behind the film itself, just a leader and a trailer. This results in a longer film on the same spool, but there are no printed frame numbers. Moreover, it cannot be used in unmodified old cameras that have a red window as frame indicator. Also, since the film alone is thinner than a film with a backing paper, a special pressure plate may be required to achieve optimal focus if the film is registered against its back side. Some cameras capable of using both 120 and 220 film will have a two position adjustment of the pressure plate (e.g. the Mamiya C220 or Mamiya C330) while others will require different film backs e.g. the Pentax 645 or Kowa Six).
The specifications for 120 and 220 film are defined in the ISO 732 standard. Earlier editions of ISO 732 also provided international standards for the now-obsolete 127 and 620 film formats.
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