The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Samyang 20mm F1.8 and the ZEISS Loxia 21mm F2.8 for their suitability to various photography scenarios:
Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Samyang 20mm F1.8 is the longer of the two lenses at 88mm. The ZEISS Loxia 21mm F2.8 with a length of 72mm is 16mm shorter. Besides being longer, the Samyang 20mm F1.8 also has a larger diameter of 83mm compared to ZEISS Loxia 21mm F2.8's 62mm 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. ZEISS Loxia 21mm F2.8 weighs 394g, 20% (103g) lighter than the Samyang 20mm F1.8's weight of 497g.
Below you can find the dimension and weight table of the 'Wideangle Prime Lenses in Sony E Mount for size comparison purposes.
Wideangle Prime Lenses in Sony E Mount for Size Comparison
Both Samyang 20mm F1.8 and 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 A7R V, Sony FX30 and Sony A7 IV.
Samyang 20mm F1.8 is also available in Canon EF , Canon EF-M, Fujifilm X, Micro Four Thirds, Nikon F (FX), Pentax KAF, Samsung NX and Sony Alpha mounts.
Samyang 20mm F1.8 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.
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 an 35mm (FF) equivalent of 31.5mm.