The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon 75-300mm f4.0-5.6 III USM and the Sigma 70-300mm F4-5.6 DG OS 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. Sigma 70-300mm F4-5.6 DG OS is the longer of the two lenses at 126mm. The Canon 75-300mm f4.0-5.6 III USM with a length of 122mm, is 4mm shorter. Besides being longer, the Sigma 70-300mm F4-5.6 DG OS also has a larger diameter of 77mm compared to the Canon 75-300mm f4.0-5.6 III USM's 71mm 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. Canon 75-300mm f4.0-5.6 III USM weighs 480g, which means it is 130g (21%) lighter than the Sigma 70-300mm F4-5.6 DG OS which has a weight of 610g.
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 75-300mm f4.0-5.6 III USM and the Sigma 70-300mm F4-5.6 DG OS 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 75-300mm f4.0-5.6 III USM and the Sigma 70-300mm F4-5.6 DG OS 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.
Sigma 70-300mm F4-5.6 DG OS is also available in Nikon F (FX) , Pentax KAF3, Sony Alpha and Sigma SA mounts.
Focal Range
Canon 75-300mm f4.0-5.6 III USM 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.
On the other hand, the Sigma 70-300mm F4-5.6 DG OS 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.