The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon 100-400mm f4.5-5.6L IS II USM and the Tamron 70-300mm f4-5.6 VC USD for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is an important deciding factor when comparing two lenses. Canon 100-400mm f4.5-5.6L IS II USM is the longer of the two lenses at 193mm. The Tamron 70-300mm f4-5.6 VC USD with a length of 143mm, is 50mm shorter. Besides being longer, the Canon 100-400mm f4.5-5.6L IS II USM also has a larger diameter of 94mm compared to the Tamron 70-300mm f4-5.6 VC USD's 82mm diameter.
The 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. Tamron 70-300mm f4-5.6 VC USD weighs 765g, 51% (825g) lighter than the Canon 100-400mm f4.5-5.6L IS II USM's weight of 1590g.
Below you can find the dimension and weight table of the Telephoto Zoom Lenses in Canon EF Mount for size comparison purposes.
Telephoto Zoom Lenses in Canon EF Mount for Size Comparison
Lens Mounts
Both the Canon 100-400mm f4.5-5.6L IS II USM and the Tamron 70-300mm f4-5.6 VC USD 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.
Tamron 70-300mm f4-5.6 VC USD is also available in Nikon F (FX) mount.
Focal Range
Canon 100-400mm f4.5-5.6L IS II USM has a focal range of 100-400mm and 4.0X zoom ratio . When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of 160 - 640mm.
Tamron 70-300mm f4-5.6 VC USD has a focal range of 70-300mm and 4.3X zoom ratio . When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of 112 - 480mm.