What is APSH format?

We usually refer to the size of 135 film as 36×24mm Quan Huafu, and APS (Advanced Photographic System) is an outdated photographic system. There are three sizes of APS film: H, C and P. The APS-H model is close to Quan Huafu (30.3× 16.6 mm), and the APS-C model is blocked at the top, bottom, left and right ends, with an aspect ratio of 3:2, which is about (24.0× 16.0 mm).

Digital SLR borrows this standard, and 22.5 x 15.0 mm, 23.6 x 15.8 mm, 23.7x15.6mm and 22.2x14.8mm whose CCD size is close to APS-C are called APS-C frames.

The 28.7x1mm of EOS- 1D and 1DMkII are called APS-H frames.

The frame can also be expressed indirectly by 1.0 times1.3 times1.5 times1.6 times, that is, the multiple of Quan Huafu diagonal size and system diagonal size, that is, the focal length conversion coefficient.