Paper size a number of different sizes were defined for large sheets of paper, and paper sizes were defined by the sheet name and the number of times it had been folded. Thus a full sheet of "royal" paper was 25 × 20 inches, and "royal octavo" was this size folded three times, so as to make eight sheets, and was thus 10 × inches. Imperial sizes were used in the United Kingdom and its territories. These sizes are no longer commonly used since the UK switched to ISO sizes. Many of these sizes were only used for making books (see bookbinding),
Sheet film In the mid-20th century, some sheet film sizes, including medium format, were made in "film packs" of 12 to 16 exposures, which are thin sheets of film and folded into a rectangular pack which was placed in a pack holder camera back. Some large format cameras have rotating or sliding reduction backs, which mask off part of the film sheet, allowing several smaller photos to be placed on a single sheet of film. Sheet film Sheet film is large format and medium format photographic film supplied on individual sheets of acetate or polyester film base rather than rolls. Sheet film