Sensor Size and Lens Loss
What photographers refer to as “full frame” means the sensor is the size of 35mm photographic film: 24x36mm (43.3mm diagonal). On a full frame camera a 50mm lens gives the field of view expected of a 50mm lens.
A crop frame (a.k.a. crop sensor) camera has a sensor roughly 50% smaller than a full-frame sensor, so lenses appear to give an image 50% longer than their actual focal length. (They have a 1.5 crop factor, here referred to as "lens loss".) A 50mm lens on a crop frame camera gives the same field of view that a 75mm lens would on a full-frame.
Olympus and Panasonic 4/3 systems use still smaller 17x13mm sensors which have a crop factor of 2X: a 50mm lens shot on a 4/3 camera would give the same field of view as a 100mm lens shot on a full frame camera.
And just for total chaos, Canon’s 1D III and 1D IV have 1.3x crop cameras--right between full-frame and crop-frame.
Sensor sizes of the commonly used video SLRs
- Full Frame: Canon 5DMk II, Nikon D3s
- 1.3x crop frame: Canon 1DMk IV
- 1.5x crop frame: Canon 7D, 60D, T2i; Nikon D300s, D90; Sony A550, A580 (Note Canon cameras actually crop to 1.6, rather than 1.5. But close enough.)
- 2x crop frame: All Panasonic and Olympus cameras