The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Zeiss Milvus 18mm F2.8 and the Sigma 20mm F1.8 EX DG RF for their suitability to various photography scenarios:
Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Zeiss Milvus 18mm F2.8 is the longer of the two lenses at 93mm. The Sigma 20mm F1.8 EX DG RF with a length of 90mm is 3mm shorter. On the other hand, the Sigma 20mm F1.8 EX DG RF has a larger diameter of 89mm compared to Zeiss Milvus 18mm F2.8's 73mm diameter.
Weight of a lens is as important as its external dimensions, especially if you are planning to hand hold your camera and lens combination for longer periods. Sigma 20mm F1.8 EX DG RF weighs 520g, 27% (201g) lighter than the Zeiss Milvus 18mm F2.8's weight of 721g.
Lens Mounts
Both Zeiss Milvus 18mm F2.8 has the Nikon F (FX) lens mount whereas the Sigma 20mm F1.8 EX DG RF has the Nikon F (DX) lens mount. Some of the latest released cameras that are compatible with these mounts are Nikon D6, Nikon D780 and Nikon D3500 for the Nikon F (FX) Mount and Nikon D6, Nikon D780 and Nikon D3500 for the Nikon F (DX) Mount.
Zeiss Milvus 18mm F2.8 is also available in Canon EF mount.
Sigma 20mm F1.8 EX DG RF is also available in Canon EF , Pentax KAF, Sony Alpha and Sigma SA mounts.
Focal Range
Zeiss Milvus 18mm F2.8 is a prime lens with fixed focal lenght of 18mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides an 35mm (FF) equivalent of 27mm.
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 an 35mm (FF) equivalent of 30mm.