The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron 20-40mm F2.8 VXD and the Sigma 18-50mm F2.8 DC DN C for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is an important deciding factor when comparing two lenses. Tamron 20-40mm F2.8 VXD is the longer of the two lenses at 86mm. The Sigma 18-50mm F2.8 DC DN C with a length of 75mm, is 11mm shorter. Besides being longer, the Tamron 20-40mm F2.8 VXD also has a larger diameter of 74mm compared to the Sigma 18-50mm F2.8 DC DN C's 65mm diameter.
Below you can find a scaled side-by-side image of Tamron 20-40mm F2.8 VXD and Sigma 18-50mm F2.8 DC DN C to get a better idea of how their sizes compare in real life.
Comparison image of the Tamron 20-40mm F2.8 VXD and the Sigma 18-50mm F2.8 DC DN C Size and Weight The weight of a lens is as important as its external dimensions, especially if you are planning to hand hold your camera and lens combination for longer periods. Sigma 18-50mm F2.8 DC DN C weighs 290g, 20% (75g) lighter than the Tamron 20-40mm F2.8 VXD's weight of 365g.
Lens Mounts
Both the Tamron 20-40mm F2.8 VXD and the Sigma 18-50mm F2.8 DC DN C has the same Sony E lens mount. Some of the latest released cameras that are compatible with the Sony E lenses are Sony ZV-E1, Sony A7R V and Sony FX30.
Sigma 18-50mm F2.8 DC DN C is also available in Leica L and Fujifilm X mounts.
Focal Range
Tamron 20-40mm F2.8 VXD has a focal range of 20-40mm and 2.0X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 30 - 60mm.
Sigma 18-50mm F2.8 DC DN C has a focal range of 18-50mm and 2.8X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27-75mm when used on a APS-C / DX format camera.