Crop factor is useful for understanding a field of view changes in cropped sensors with respect to a full-frame sensor. In cameras, with less than 35 mm film format the images clicked will be from a smaller area compared to the standard film, because of which they are referred to as cropped sensors. If you use the same lens on two sensors of different sizes, a smaller field of view will be captured in the smaller sensor. Example: A lens of 50 mm in the APS-C sensor with1.5x-1.6x crop factor will provide the same filed view as a 70 mm lens on a sensor of full-frame.