Digital cameras have two primary sensor formats: full frame (or 35mm) cameras where the sensor is roughly the same size as a 35mm film frame and crop sensor (or APS-C) cameras where the sensor is just under 2/3 the size. Lenses designed for full frame cameras work on crop sensor cameras, but using crop sensor lenses on full frame cameras is either impossible (Canon) or comes with some serious compromises (Nikon and Sony). If you’ve got a crop sensor camera, it can be tempting just to buy crop lenses, but it’s not always the best idea.
Source: How-To Geek
