Crop factor
![The outer, red box displays what a 24×36 mm sensor would see, the inner, blue box displays what a 15×23 mm sensor would see. (The actual image circle of most lenses designed for 35 mm SLR format would extend further beyond the red box than shown in the above image.)](/Images/godic/202501/23/Crop_Factor4928.JPG")
![A 50 mm lens on an APS-C format (crop factor 1.6) images a slightly smaller field of view than a 70 mm lens on a 35 mm camera.](/Images/godic/202501/23/Full-frame_vs_APS-C.svg4929.png")
![Field-of-view crop in cameras of different sensor size but the same lens focal length.](/Images/godic/202501/23/LensCropFactor4929.png")
In digital photography, the crop factor of an image sensor format is related to the ratio of the dimensions of a camera's imaging area compared to a reference format; most often, this term is applied to digital cameras, relative to 35 mm film format as a reference. In the case of digital cameras, the imaging device would be a digital sensor. The most commonly used definition of crop factor is the ratio of a 35 mm frame's diagonal (43.3 mm) to the diagonal of the image sensor in question; that is, CF=diag35mm / diagsensor. Given the same 3:2 aspect ratio as 35mm's 36mm x 24mm area, this is equivalent to the ratio of heights or ratio of widths; the ratio of sensor areas is the square of the crop factor.