The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Rokinon 24mm f1.4 and the Canon 20mm f2.8 USM for their suitability to various photography scenarios:
Size and Weight Comparison
The 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. Canon 20mm f2.8 USM weighs 405g, 30% (175g) lighter than the Rokinon 24mm f1.4's weight of 580g.
Below you can find the dimension and weight table of the Wideangle Prime Lenses in Canon EF Mount for size comparison purposes.
Wideangle Prime Lenses in Canon EF Mount for Size Comparison
Both the Rokinon 24mm f1.4 and the Canon 20mm f2.8 USM has the same Canon EF lens mount. Some of the latest released cameras that are compatible with the Canon EF lenses are Canon 1D X III, Canon 6D MII and Canon 5D MIV.
Rokinon 24mm f1.4 is also available in Nikon F (FX) , Four Thirds, Pentax KAF, Sony Alpha and Samsung NX mounts.
Rokinon 24mm f1.4 is a prime lens with fixed focal lenght of 24mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of 38.4mm.
Canon 20mm f2.8 USM 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 a 35mm (FF) equivalent of 32mm.