The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon EF 600mm F4L IS III USM and the Tamron 18-400mm F3.5-6.3 VC for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is a crucial factor to consider when comparing two lenses. Canon EF 600mm F4L IS III USM is the longer of the two lenses at 448mm. The Tamron 18-400mm F3.5-6.3 VC with a length of 124mm, is 324mm shorter. Besides being longer, the Canon EF 600mm F4L IS III USM also has a larger diameter of 168mm compared to the Tamron 18-400mm F3.5-6.3 VC's 79mm diameter.
The weight of a lens is equally significant as its external dimensions, particularly if you intend to handhold your camera and lens combination for extended periods. Tamron 18-400mm F3.5-6.3 VC weighs 710g, 76% (2340g) lighter than the Canon EF 600mm F4L IS III USM's weight of 3050g.
Filter Threads
The Canon EF 600mm F4L IS III USM has a filter size of 52mm whereas the Tamron 18-400mm F3.5-6.3 VC has a 72mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 52mm filters that we recommend you to consider for the Canon EF 600mm F4L IS III USM:
And these are the 72mm filters that we recommend for the Tamron 18-400mm F3.5-6.3 VC:
Lens Mounts
The Canon EF 600mm F4L IS III USM has the Canon EF lens mount whereas the Tamron 18-400mm F3.5-6.3 VC has the Canon EF-S lens mount. Some of the latest released cameras that are compatible with these mounts are Blackmagic URSA 12K LF, Z CAM E2-F6 II 6K and Z CAM E2-S6 II 6K for the Canon EF Mount and Canon T8i, Canon 90D and Canon SL3 for the Canon EF-S Mount.
Tamron 18-400mm F3.5-6.3 VC is also available in Nikon F (DX) mount.
Focal Range
Canon EF 600mm F4L IS III USM is a prime lens with fixed focal lenght of 600mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of
960mm.
On the other hand, the Tamron 18-400mm F3.5-6.3 VC has a focal range of 18-400mm and 22.2X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 28.8-640mm when used on a APS-C / DX format camera.
