The ratio of the focal length of a digital camera lens to a 35 mm still camera lens. The crop factor is used by experienced photographers, who want to know the field of view of a lens on a digital camera as compared to a lens on a 35 mm camera, because that is what they are familiar with.

For example, the crop factor on most Nikon, Pentax, Sony and FujiFilm cameras is 1.5, which means an 18 mm focal length on the digital camera is equivalent to 27 mm on a 35 mm camera (18 X 1.5). Canon typically has a 1.6 crop factor.

The Sensor Is Smaller
The size of a 35 mm still camera film frame is 36 x 24 mm. Although increasingly being made larger, most sensors in a digital camera are smaller; for example, 24 x 16 mm. The difference in size creates the crop factor, also known as the "lens factor," "focal length conversion factor" and "lens multiplier." See focal length and f-stop.