The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 20mm F2 DG DN C and the ZEISS Loxia 21mm F2.8 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. Sigma 20mm F2 DG DN C weighs 370g, which means it is 24g (6%) lighter than the ZEISS Loxia 21mm F2.8 which has a weight of 394g.
Filter Threads
The Sigma 20mm F2 DG DN C has a filter size of 62mm whereas the ZEISS Loxia 21mm F2.8 has a 52mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 62mm filters that we recommend you to consider for the Sigma 20mm F2 DG DN C:
And these are the 52mm filters that we recommend for the ZEISS Loxia 21mm F2.8:
Lens Mounts
Both the Sigma 20mm F2 DG DN C and the ZEISS Loxia 21mm F2.8 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.
Sigma 20mm F2 DG DN C is also available in Leica L mount.
Focal Range
Sigma 20mm F2 DG DN C 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.
On the other hand, the ZEISS Loxia 21mm F2.8 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.