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 Tamron 11-20mm F2.8 Di III-A for their suitability to various photography scenarios:
Size and Weight Comparison
tt
Below you can find a scaled side-by-side image of Tamron 20-40mm F2.8 VXD and Tamron 11-20mm F2.8 Di III-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 11-20mm F2.8 Di III-A weighs 335g, 8% (30g) lighter than the Tamron 20-40mm F2.8 VXD's weight of 365g.
Filter Threads
Both the Tamron 20-40mm F2.8 VXD and the Tamron 11-20mm F2.8 Di III-A 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 20-40mm F2.8 VXD and the Tamron 11-20mm F2.8 Di III-A 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.
Tamron 11-20mm F2.8 Di III-A is also available in Fujifilm X mount.
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.
On the other hand, the Tamron 11-20mm F2.8 Di III-A has a focal range of 11-20mm and 1.8X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 16.5-30mm when used on a APS-C / DX format camera.