The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron 70-300 F4.5-6.3 Di III and the Sigma 100-400mm F5-6.3 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 100-400mm F5-6.3 OS is the longer of the two lenses at 197mm. The Tamron 70-300 F4.5-6.3 Di III with a length of 148mm, is 49mm shorter. Besides being longer, the Sigma 100-400mm F5-6.3 OS also has a larger diameter of 86mm compared to the Tamron 70-300 F4.5-6.3 Di III's 77mm diameter.
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Below you can find a scaled side-by-side image of Tamron 70-300 F4.5-6.3 Di III and Sigma 100-400mm F5-6.3 OS to get a better idea of how their sizes compare in real life.
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 70-300 F4.5-6.3 Di III weighs 545g, which means it is 590g (51%) lighter than the Sigma 100-400mm F5-6.3 OS which has a weight of 1135g.
Filter Threads
Both the Tamron 70-300 F4.5-6.3 Di III and the Sigma 100-400mm F5-6.3 OS have the same Filter thread size of 67mm.
Below are links to the 67mm filters that we recommend you to consider for these lenses:
Lens Mounts
Both the Tamron 70-300 F4.5-6.3 Di III and the Sigma 100-400mm F5-6.3 OS has the same Sony E lens mount. Some of the latest released cameras that are compatible with the Sony E lenses are Sony A9 III, Sony A7C Mark II and Sony A7CR.
Sigma 100-400mm F5-6.3 OS is also available in Leica L and Fujifilm X mounts.
Focal Range
Tamron 70-300 F4.5-6.3 Di III has a focal range of 70-300mm and
4.3X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
105 - 450mm.
On the other hand, the Sigma 100-400mm F5-6.3 OS has a focal range of 100-400mm and 4.0X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 150 - 600mm.