The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron 17-70 F2.8 Di III-A VC and the Sigma 50-100mm F1.8 A 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 50-100mm F1.8 A is the longer of the two lenses at 171mm. The Tamron 17-70 F2.8 Di III-A VC with a length of 119mm, is 52mm shorter. Besides being longer, the Sigma 50-100mm F1.8 A also has a larger diameter of 94mm compared to the Tamron 17-70 F2.8 Di III-A VC's 75mm diameter.
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Below you can find a scaled side-by-side image of Tamron 17-70 F2.8 Di III-A VC and Sigma 50-100mm F1.8 A 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 17-70 F2.8 Di III-A VC weighs 525g, which means it is 965g (64%) lighter than the Sigma 50-100mm F1.8 A which has a weight of 1490g.
Filter Threads
The Tamron 17-70 F2.8 Di III-A VC has a filter size of 67mm whereas the Sigma 50-100mm F1.8 A has a 82mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 67mm filters that we recommend you to consider for the Tamron 17-70 F2.8 Di III-A VC:
And these are the 82mm filters that we recommend for the Sigma 50-100mm F1.8 A:
Lens Mounts
The Tamron 17-70 F2.8 Di III-A VC has the Sony E lens mount whereas the Sigma 50-100mm F1.8 A has the Canon EF lens mount. Some of the latest released cameras that are compatible with these mounts are Sony A6700, Sony FX30 and Sony ZV-E10 for the Sony E Mount and Canon T8i, Canon 90D and Canon SL3 for the Canon EF Mount.
Tamron 17-70 F2.8 Di III-A VC is also available in Fujifilm X mount.
Sigma 50-100mm F1.8 A is also available in Nikon F (DX) and Sigma SA mounts.
Focal Range
Tamron 17-70 F2.8 Di III-A VC has a focal range of 17-70mm and
4.1X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
25.5-105mm when used on a APS-C / DX format camera.
On the other hand, the Sigma 50-100mm F1.8 A has a focal range of 50-100mm and 2.0X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 80-160mm when used on a APS-C / DX format camera.