23.6 x 15.7 mm image area · 70 interactive lens diagrams
Fujifilm X, Nikon DX, Canon crop-sensor, Sony E, Ricoh GR, and many compact digital systems | 23.6 x 15.7 mm reference area in this catalog; production sizes vary slightly by maker
APS-C sits between Four Thirds and full-frame in both image area and lens scale. The name comes from the smaller "Classic" frame idea in Advanced Photo System film, but digital APS-C is not one exact size: Nikon, Fujifilm, Sony, Canon, Sigma, and fixed-lens compact cameras all use slightly different dimensions. This catalog uses a 23.6 x 15.7 mm reference area so field comparisons stay consistent while still representing the broad APS-C class.
The format became the dominant consumer and enthusiast digital camera size because it offered a practical balance: sensors large enough for strong image quality and subject separation, but small enough to keep bodies, shutters, stabilization systems, and lenses more compact than 35 mm full-frame equivalents. It also made telephoto angles easier to package, since a shorter focal length gives the same framing.
Lens design for APS-C can take two paths. Some systems, such as Fujifilm X and many fixed-lens compacts, are built around dedicated APS-C image circles; others adapt or share full-frame mount families, where throat diameter and flange distance were chosen for a larger format. The catalog's APS-C pages make those choices visible by grouping dedicated mirrorless lenses, DSLR crop lenses, and fixed-lens compact-camera optics together.