Therefore only the centre of the lens is used to capture the image. Due to the smaller image circle of the sensor, the field of view changes compared to using a FE lens on a Full Frame camera and therefore the focal length extents by factor 1.5. E.g. when using a FE 50mm lens, the focal length and the field of view on APS-C size sensor will be
Thebest way to think of this is by way of a 50mm f1.4 full frame lens. When placed on a APS-c body, the lens "ACTS" like a 75mm f2.1 lens. I use the word acts because in reality the exposure doesn't change as you would expect it to if you were to manually change the lens from f1.4 to f2. BUT, the f stop difference is seen in the depth of field . 145 479 279 243 125 386 121 439