Product description from Canon. At launch 1991 Canon wrote this regarding Canon EF 100mm F2 USM : "Despite the large maximum aperture, the lens remains compact. Lens group 5 moves for rear focusing, and sharp, crisp pictures are obtained at all apertures. The background blur is ideal for portraits. The USM autofocuses the lens quickly and quietly."
The flash unit clips into a groove around the end of any compatible Canon EF, EF-S or MP-E macro lens or a Macrolite Adapter. Canon's supported macro lenses are: Canon EF 50mm f/2.5 Macro Lens Canon EF-S 60mm f/2.8 Macro USM Lens Canon MP-E 65mm Macro Lens Canon EF 100mm f/2.8 USM Macro Lens (non-USM also supported)NEW: Canon EF 100mm f/2.8 Macro (1990~2000) Full frame, 52mm filters, 20.6 oz./585g, 1:1 magnification, 1'/0.3m close focus. Works great on Canon's newest full-frame mirrorless cameras with an EF to RF adapter, and works flawlessly on all DSLRs and 35mm EOS cameras as well. I got mine used at eBay (How to Win at eBay). 11 May 2021