The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon 100-300mm f4.5-5.6 USM and the Canon 75-300mm f4.0-5.6 III for their suitability to various photography scenarios:
Size and Weight Comparison
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. Canon 75-300mm f4.0-5.6 III weighs 480g, 11% (60g) lighter than the Canon 100-300mm f4.5-5.6 USM's weight of 540g.
Below you can find the dimension and weight table of the Telephoto Zoom Lenses in Canon EF Mount for size comparison purposes.
Telephoto Lenses in Canon EF Mount for Size Comparison
Filter Threads
Both the Canon 100-300mm f4.5-5.6 USM and the Canon 75-300mm f4.0-5.6 III have the same Filter thread size of 58mm.
Below are links to the 58mm filters that we recommend you to consider for these lenses:
Lens Mounts
Both the Canon 100-300mm f4.5-5.6 USM and the Canon 75-300mm f4.0-5.6 III has the same Canon EF lens mount. Some of the latest released cameras that are compatible with the Canon EF lenses are Blackmagic URSA 12K LF, Z CAM E2-F6 II 6K and Z CAM E2-S6 II 6K.
Focal Range
Canon 100-300mm f4.5-5.6 USM has a focal range of 100-300mm and
3.0X zoom ratio . When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of
160 - 480mm.
On the other hand, the Canon 75-300mm f4.0-5.6 III has a focal range of 75-300mm 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 120 - 480mm.
