The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon 400mm f2.8L IS II USM and the Canon 85mm f1.2L II USM for their suitability to various photography scenarios:
Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Canon 400mm f2.8L IS II USM is the longer of the two lenses at 343mm. The Canon 85mm f1.2L II USM with a length of 84mm is 259mm shorter. Besides being longer, the Canon 400mm f2.8L IS II USM also has a larger diameter of 163mm compared to Canon 85mm f1.2L II USM's 92mm diameter.
Weight of a lens is as important as its external dimensions, especially if you are planning to hand hold your camera and lens combination for longer periods. Canon 85mm f1.2L II USM weighs 1025g, 73% (2825g) lighter than the Canon 400mm f2.8L IS II USM's weight of 3850g.
Below you can find the dimension and weight table of the 'Telephoto Prime Lenses in Canon EF Mount for size comparison purposes.
Telephoto Prime Lenses in Canon EF Mount for Size Comparison
Lens Mounts
Both Canon 400mm f2.8L IS II USM and Canon 85mm f1.2L II USM has the same Canon EF lens mount. Some of the latest released cameras that are compatible with the Canon EF lenses are Canon 1D X III, Canon 6D MII and Canon 5D MIV.
Focal Range
Canon 400mm f2.8L IS II USM is a prime lens with fixed focal lenght of 400mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides an 35mm (FF) equivalent of 640mm.
Canon 85mm f1.2L II USM is a prime lens with fixed focal lenght of 85mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides an 35mm (FF) equivalent of 136mm.