The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Carl Zeiss Distagon T2,8/25 and the Sigma 20mm F1.8 EX DG RF for their suitability to various photography scenarios:
Size and Weight Comparison
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. Carl Zeiss Distagon T2,8/25 weighs 480g, which means it is 40g (7%) lighter than the Sigma 20mm F1.8 EX DG RF which has a weight of 520g.
Filter Threads
The Carl Zeiss Distagon T2,8/25 has a filter size of 58mm whereas the Sigma 20mm F1.8 EX DG RF has a 82mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 58mm filters that we recommend you to consider for the Carl Zeiss Distagon T2,8/25:
And these are the 82mm filters that we recommend for the Sigma 20mm F1.8 EX DG RF:
Lens Mounts
Both the Carl Zeiss Distagon T2,8/25 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 T2,8/25 is also available in Nikon F (FX) mount.
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 T2,8/25 is a prime lens with fixed focal lenght of 25mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
37.5mm.
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.