Medium format has traditionally referred to a film format in still photography and the related cameras and equipment that use[1] film. Generally, the term applies to film and digital cameras that record images on media larger than 24 by 36 mm (full-frame) (used in 35 mm photography), but smaller than 4 by 5 inches (which is considered to be large-format photography). Medium format refers either to cameras adapted from medium-format film photography uses, or to cameras making use of sensors larger than that of a 35 mm film frame. Often, medium-format film cameras can be retrofitted with digital camera backs, converting them to digital cameras, but some of these digital backs, especially early models, use sensors smaller than a 35 mm film frame. As of 2013, medium-format digital photography sensors were available in sizes of up to 40.3 by 53.7 mm, with 60 million pixels for use with commonly available professional medium-format cameras. Sensors used in special applications such as spy satellites can be even larger, but are not necessarily described as medium-format equipment