The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Samyang 21mm F1.4 ED AS UMC CS and the Samyang 20mm F1.8 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 Samyang 21mm F1.4 ED AS UMC CS with a length of 68mm is 20mm shorter. Besides being longer, the Samyang 20mm F1.8 also has a larger diameter of 83mm compared to Samyang 21mm F1.4 ED AS UMC CS's 64mm 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. Samyang 21mm F1.4 ED AS UMC CS weighs 275g, which means it is 222g (44%) lighter than the Samyang 20mm F1.8 which has a weight of 497g.
Below you can find the dimension and weight table of the 'Wideangle Prime Lenses in Canon EF-M Mount for size comparison purposes.
Wideangle Prime Lenses in Canon EF-M Mount for Size Comparison
Both Samyang 21mm F1.4 ED AS UMC CS and Samyang 20mm F1.8 has the same Canon EF-M lens mount. Some of the latest released cameras that are compatible with the Canon EF-M lenses are Canon M50 II, Canon M200 and Canon M6 MII.
Samyang 21mm F1.4 ED AS UMC CS is also available in Fujifilm X , Micro Four Thirds and Sony E mounts.
Samyang 20mm F1.8 is also available in Canon EF , Fujifilm X, Micro Four Thirds, Nikon F (FX), Pentax KAF, Samsung NX, Sony Alpha and Sony E mounts.
Samyang 21mm F1.4 ED AS UMC CS is a prime lens with fixed focal lenght of 21mm which has a 35mm equivalent focal range of 33.6mm when used on a APS-C / DX format camera. 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 1.6x crop, it provides an 35mm (FF) equivalent of 32mm.