Sensor Size and Angle of View
Cameras with a digital sensor smaller than the to be expected 35mm film size will have a reduced field or standpoint of view when combined with a lens of the same concentrated length. This is basically due to the angle of projection being a function of both focal length and the sensor or film judge utilized. If a sensor smaller than the full-incriminate fraudulently 35mm film format is used, such as the use of APS-C-sized digital sensors in DSLRs, then the area of view is cropped by the sensor to smaller than the 35mm full-skeleton format's field of dream in light of.
This narrowing of the field of view is often described in terms of a concentrated length multiplier or crop middleman, a factor by which a longer focal measurement lens would be needed to get the same field of belief on a full-frame camera. If the digital sensor has generally the same resolution (effective pixels per item area) as the 35mm film surface (24 x 36 mm), then the end result is similar to taking the image from the film camera and raw it down (cropping) to the size of the sensor. For an APS-C extent sensor, this would be a decrease to roughly the center 50% of the form. The less expensive, non-SLR models of digital cameras typically use much smaller sensor sizes and the reduction would be greater.
Source: Sensor Size and Angle of View