Sensor Size and Angle of View

Cameras with a digital sensor smaller than the typical 35mm film size will have a reduced field or angle of view when combined with a lens of the same focal length. This is basically due to the angle of view being a function of both focal length and the sensor or film size utilized. If a sensor smaller than the full-frame 35mm film format is used, such as the use of APS-C-sized digital sensors in DSLRs, then the field of view is cropped by the sensor to smaller than the 35mm full-frame format’s field of view.

This narrowing of the field of view is often described in terms of a focal length multiplier or crop factor, a factor by which a longer focal length lens would be needed to get the same field of view on a full-frame camera. If the digital sensor has approximately the same resolution (effective pixels per unit area) as the 35mm film surface (24 x 36 mm), then the result is similar to taking the image from the film camera and cutting it down (cropping) to the size of the sensor. For an APS-C size sensor, this would be a decrease to roughly the center 50% of the image. The less expensive, non-SLR models of digital cameras typically use much smaller sensor sizes and the reduction would be greater.