Crop factor
Since the year 2000 the big camera makers Nikon, Canon and Pentax continued their Autofocus SLR camera systems mainly based on the APS-C image sensor format. Since then the crop factor is mentioned when using old system lenses for 35mm film frame format on such modern cameras with APS-C sensor. The crop factor for APS-C-sized sensors is 1.5. That means that an old 50mm normal lens lens works like a 1.5×50mm=75mm portrait lens on the camera with the smaller sensor. µ4/3 system cameras make a crop factor 2 since the diagonal sensor diameter is just half of the 35mm film image frame. The latter frame size is not described by a crop factor 1 but as "full format", of course meaning somehing else than "full format" film plates.
The higher the crop factor, the more depth-of-field is gained with good lenses.
