The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 20mm F1.8 EX DG RF and the Tamron AF 18-270mm f3.5-6.3 II VC LD 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 AF 18-270mm f3.5-6.3 II VC LD is the longer of the two lenses at 101mm. The Sigma 20mm F1.8 EX DG RF with a length of 90mm, is 11mm shorter. On the other hand, the Sigma 20mm F1.8 EX DG RF has a larger diameter of 89mm compared to the Tamron AF 18-270mm f3.5-6.3 II VC LD's 80mm 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. Sigma 20mm F1.8 EX DG RF weighs 520g, which means it is 40g (7%) lighter than the Tamron AF 18-270mm f3.5-6.3 II VC LD which has a weight of 560g.
Filter Threads
The Sigma 20mm F1.8 EX DG RF has a filter size of 82mm whereas the Tamron AF 18-270mm f3.5-6.3 II VC LD has a 72mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 82mm filters that we recommend you to consider for the Sigma 20mm F1.8 EX DG RF:
And these are the 72mm filters that we recommend for the Tamron AF 18-270mm f3.5-6.3 II VC LD:
Lens Mounts
Both the Sigma 20mm F1.8 EX DG RF and the Tamron AF 18-270mm f3.5-6.3 II VC LD has the same Canon EF lens mount. Some of the latest released cameras that are compatible with the Canon EF lenses are Canon 1D X III, Canon 6D MII and Canon 5D MIV.
Sigma 20mm F1.8 EX DG RF is also available in Nikon F (DX) , Pentax KAF, Sony Alpha and Sigma SA mounts.
Tamron AF 18-270mm f3.5-6.3 II VC LD is also available in Nikon F (DX) mount.
Focal Range
Sigma 20mm F1.8 EX DG RF is a prime lens with fixed focal lenght of 20mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of
32mm.
On the other hand, the Tamron AF 18-270mm f3.5-6.3 II VC LD has a focal range of 18-270mm and 15.0X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 28.8-432mm when used on a APS-C / DX format camera.