In
digital photography, a
crop factor is related to the ratio of the
dimensions of a camera's imaging area compared to a reference format; most often, this term is applied to
digital cameras, relative to
35 mm film format as a reference. In the case of digital cameras, the imaging device would be a
digital sensor. The most commonly used definition of crop factor is the ratio of a 35 mm frame's diagonal (43.3 mm) to the diagonal of the
image sensor in question; that is, CF=diag
35mm / diag
sensor. Given the same 3:2 aspect ratio as 35mm's 36mm x 24mm area, this is equivalent to the ratio of heights or ratio of widths; the ratio of sensor areas is the
square of the crop factor.