The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon EF 400mm F2.8L IS III USM and the Canon 400mm f2.8L IS 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 USM is the longer of the two lenses at 349mm. The Canon EF 400mm F2.8L IS III USM with a length of 343mm is 6mm shorter. On the other hand, there is no difference between the max diameters of these lenses, both coming at 163mm.
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 EF 400mm F2.8L IS III USM weighs 2840g, which means it is 2530g (47%) lighter than the Canon 400mm f2.8L IS USM which has a weight of 5370g.
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
Both Canon EF 400mm F2.8L IS III USM and Canon 400mm f2.8L IS 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.
Both lenses have the same focal range of 400mm and the fastest aperture of F2.8.