The Canon RF 100-400mm F5.6-8 IS USM is constructed from 12 elements in 9 groups with one UD (ultra-low dispersion) element and one PMo (plastic-moulded) aspherical element. These special elements correct chromatic and other aberrations while Canon’s Super Spectra coating helps keep flare and ghosting at bay.
Focusing is handled by a Nano USM (ultra-sonic motor), which combines the speed of a ring-type USM system with the low noise and smoothness of STM focusing.
Impressively, the RF 100-400mm F5.6-8 IS USM has a minimum focusing distance of 0.88m (88cm) throughout its focal length range and its maximum reproduction ratio is 0.41x.
Canon has included a stabilisation system within the lens and it’s said to enable shutter speeds of up to 5.5EV slower than normal to be used when the camera is handheld. When the RF 100-400mm F5.6-8 IS USM is mounted on a Canon R-series camera with in-body image stabilisation (IBIS), the shutter speed compensation is claimed to rise to 6EV. At 400mm, that could mean using a shutter speed of just 1/6sec rather than 1/400sec.
At the 100mm end, the RF 100-400mm F5.6-8 IS USM has a maximum aperture of f/5.6, while at 400mm it’s f/8. That may sound slow for a telephoto lens that is likely to be used to capture moving subjects, but the advancements made in noise control make it more acceptable than it used to be.
The RF 100-400mm F5.6-8 IS USM is the first non-L series lens to be compatible with Canon’s RF 1.4x and RF 2x tele extenders, enabling the focal length range to be taken to 140-560mm or 200-800mm respectively.