Optically, both lenses will outperform their predecessors through the use of two fluorite elements over the previous one fluorite and two UD glass elements. More fluorite results in better image quality as it reduces chromatic aberration to a greater degree than UD glass. The reduction of chromatic aberration contributes to superior resolution, contrast, and color fidelity; this is especially evident when used in conjunction with Canon’s Type III EF Extenders. In addition to the fluorite lens elements, the new super-telephoto lenses also include a nine-blade circular diaphragm for a smoother appearance in areas outside the depth of field of the main subject. In addition, Canon’s SWC (Subwavelength Structure Coating) is applied to four internal groups in each lens to improve resistance to flare and ghosting.
A convenient and useful feature when shooting in the often adverse conditions professionals find themselves in, these new lenses are treated with Canon’s new fluorine anti-smear lens coating. The fluorine layer is highly oil- and water-repellent so that any oil smears or water droplets on the lens can be wiped off quickly and easily, without the aid of solvents, using a soft dry cloth.
The new Series II EF super-telephoto lenses can correct camera shake up to four full shutter speed steps, compared with two shutter speed steps with their predecessors. This improvement is made possible by a new low-friction stabilizer mechanism that is not only more efficient than the previous design but also smaller and lighter. Other enhancements to the IS systems of both new super-telephoto lenses have enabled quieter operation; ideal for use during video capture.
Canon has developed a third Image Stabilization mode option for its super-telephoto EF lenses. First introduced in late 2010 with the EF 400mm f/2.8L IS II USM, and EF 300mm f/2.8L IS II USM lenses, and now available on the new EF 500mm f/4L IS II USM and EF 600mm f/4L IS II USM lenses, IS mode 3 is designed to provide professional sports and wildlife photographers with greater tracking flexibility. When mode 3 is selected on the lens, the Image Stabilization effect will not occur until the shutter is pressed, making the viewfinder image more natural in appearance while tracking a subject. In mode 3 when the shutter button is pressed halfway, the lens will begin detecting camera or lens movement and only during exposure, when the shutter is fully depressed, will the Image Stabilization engage.
Helping filmmakers achieve smoother and more appealing focus shifts when filming on EOS DSLR cameras, Canon has included a new Power Focus (PF) mode on the Company’s new super telephoto lenses. This mode allows manual rack focusing to be operated smoothly by turning a playback ring that is normally used for the focus preset function. Both low-speed and high-speed focus shifting are available.