This is a groundbreaking wide zoom lens that utilizes Canon’s own 2-group zoom optical system, as in the FD35-70mm f/2.8-3.5 S.S.C. (released in December 1973), which has been highly regarded since its release due to excellent performance on par with a single lens.
In contrast to a normal 4-group zoom optical system, the lens system is divided into two blocks at the front and rear, and each of these moves independently while compensation of aberrations is performed separately for the front group and the rear group. This has resulted in a high-performance zoom lens that is extremely compact despite being a wide-angle zoom lens with a short focal length of 28mm, in addition to having no loss of focus and image quality through zooming.