The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 20mm F1.8 EX DG RF and the Samyang T-S 24mm f3.5 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 T-S 24mm f3.5 is the longer of the two lenses at 112mm. The Sigma 20mm F1.8 EX DG RF with a length of 90mm is 22mm shorter. On the other hand, the Sigma 20mm F1.8 EX DG RF has a larger diameter of 89mm compared to Samyang T-S 24mm f3.5's 86mm 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, which means it is 160g (23%) lighter than the Samyang T-S 24mm f3.5 which has a weight of 680g.
Lens Mounts
Both Sigma 20mm F1.8 EX DG RF and Samyang T-S 24mm f3.5 has the same Pentax KAF lens mount. Some of the latest released cameras that are compatible with the Pentax KAF lenses are Pentax KF, Pentax K-3 III and Pentax K-1 II.
Sigma 20mm F1.8 EX DG RF is also available in Canon EF , Nikon F (DX), Sony Alpha and Sigma SA mounts.
Samyang T-S 24mm f3.5 is also available in Canon EF , Nikon F (FX), Sony Alpha and Sony E mounts.
Focal Range
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.
Samyang T-S 24mm f3.5 is a prime lens with fixed focal lenght of 24mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides an 35mm (FF) equivalent of 36mm.