Advanced Photo System type-C (APS-C) is an image sensor format approximately equivalent in size to the Advanced Photo System "classic" negatives of 25.1 × 16.7 mm, an aspect ratio of 3:2.
Sensors approximating these dimensions are used in many digital single-lens reflex cameras (DSLRs), Mirrorless interchangeable-lens cameras (MILCs), and a few large-sensor live-preview digital cameras. These include the Sony DSC-R1, Sigma DP1 and Leica X1. APS-C size sensors are also used in a few digital rangefinders (e.g., the Epson R-D1).
Such sensors exist in many different variants depending on the manufacturer and camera model. All APS-C variants are considerably smaller than 35 mm standard film which measures 36×24 mm. Because of this, devices with APS-C sensors are known as "cropped frame", especially when used in connection with lens mounts that are also used with sensors the size of 35mm film: only part of the image produced by the lens is captured by the APS-C size sensor. Sensor sizes range from 20.7×13.8 mm to 28.7×19.1 mm. Each variant results in a slightly different angle of view from lenses at the same focal length and overall a much narrower angle of view compared to 35 mm film. This is why each manufacturer offers a range of lenses designed for its format.