This telephoto macro lens is capable of focusing to life-size (1X) without attachments. Although it replaces the EF 100mm f/2.8 MACRO lens marketed in 1991, it is a completely new design. It incorporates a ring type USM giving quiet, high-speed autofocus. The full-time mechanical manual focus gives very smooth manual focusing. For the first time in a 1X focusing telephoto macro lens, inner focusing is used. The lens length remains constant and a long working distance of 149mm makes worrying about getting too close to the subject unnecessary. Also, during focusing the front ring does not rotate making use of front-mounting accessories like macro ring lites simple and effective.
Three-group floating focusing construction uses three independently moving groups, which holds focusing-related changes of aberrations to a minimum giving excellent image quality all the way from infinity to life size.