120 film

120 is a popular film format for still photography introduced by Kodak for their Brownie No. 2 in 1901. It was originally intended for amateur photography but was later superseded in this role by 135 film. 120 film and its close relative, 220 film, survive to this day as the only medium format films that are readily available to both professionals and amateur enthusiasts.

The 120 film format is a roll film which is nominally 60 mm wide (in fact, about 61 mm, or 2.4 inches). The film is held in an open spool originally made of wood with metal flanges, later with all-metal, and finally with all-plastic. The length of film is typically 30 inches (760 mm) up to 32–33 inches (810–840 mm), 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 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 Pentax 6x7, 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 127 and 620 film formats.

...
Wikipedia