EQUIVALENT FOCAL LENGTH

Photographers using 35mm cameras are used to judging the angle of view of a lens by its focal length. However, with a couple of exceptions, digital SLRs have physically smaller sensors, so that the angle of view of the lens is reduced and it appears to have a longer focal length. You need to multiply the actual focal length by a factor of 1.5 or 1.6 to get its ‘effective’ focal length. For example, on a digital SLR a 50mm lens effectively becomes an 80mm lens.