The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Carl Zeiss Distagon T2,8/21 and the Sigma 20mm F1.8 EX DG RF 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. Carl Zeiss Distagon T2,8/21 is the longer of the two lenses at 109mm. The Sigma 20mm F1.8 EX DG RF with a length of 90mm, is 19mm shorter. On the other hand, the Sigma 20mm F1.8 EX DG RF has a larger diameter of 89mm compared to the Carl Zeiss Distagon T2,8/21's 87mm 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, 13% (80g) lighter than the Carl Zeiss Distagon T2,8/21's weight of 600g.
Filter Threads
Both the Carl Zeiss Distagon T2,8/21 and the Sigma 20mm F1.8 EX DG RF have the same Filter thread size of 82mm.
Below are links to the 82mm filters that we recommend you to consider for these lenses:
Lens Mounts
Both the Carl Zeiss Distagon T2,8/21 and the Sigma 20mm F1.8 EX DG RF has the same Pentax KAF lens mount. Some of the latest released cameras that are compatible with the Pentax KAF lenses are Pentax K-3 III Monochrome, Pentax KF and Pentax K-3 III.
Carl Zeiss Distagon T2,8/21 is also available in Canon EF and Nikon F (FX) mounts.
Sigma 20mm F1.8 EX DG RF is also available in Canon EF , Nikon F (DX), Sony Alpha and Sigma SA mounts.
Focal Range
Carl Zeiss Distagon T2,8/21 is a prime lens with fixed focal lenght of 21mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
31.5mm.
On the other hand, the 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 1.5x crop, it provides a 35mm (FF) equivalent of 30mm.