The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 17-40mm f1.8 and the Tamron 17-70 F2.8 Di III-A 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. Tamron 17-70 F2.8 Di III-A VC is the longer of the two lenses at 119mm. The Sigma 17-40mm f1.8 with a length of 116mm, is 3mm shorter. Besides being longer, the Tamron 17-70 F2.8 Di III-A VC also has a larger diameter of 75mm compared to the Sigma 17-40mm f1.8's 73mm 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 17-70 F2.8 Di III-A VC weighs 525g, 1% (10g) lighter than the Sigma 17-40mm f1.8's weight of 535g.
Filter Threads
Both the Sigma 17-40mm f1.8 and the Tamron 17-70 F2.8 Di III-A VC 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
The Sigma 17-40mm f1.8 has the Canon RF lens mount whereas the Tamron 17-70 F2.8 Di III-A VC has the Sony E lens mount. Some of the latest released cameras that are compatible with these mounts are Canon R50 V, Canon R100 and Canon R50 for the Canon RF Mount and Sony ZV-E10 II, Sony A6700 and Sony FX30 for the Sony E Mount.
Sigma 17-40mm f1.8 is also available in the Sony E , Leica L and Fujifilm X mounts.
Tamron 17-70 F2.8 Di III-A VC is also available in Fujifilm X mount.
Focal Range
Sigma 17-40mm f1.8 has a focal range of 17-40mm and
2.4X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
27.2-64mm when used on a APS-C / DX format camera.
On the other hand, the 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.
