The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Samyang 135mm F2.0 ED UMC and the Rokinon 85mm 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 135mm F2.0 ED UMC is the longer of the two lenses at 122mm. The Rokinon 85mm F1.8 with a length of 81mm is 41mm shorter. Besides being longer, the Samyang 135mm F2.0 ED UMC also has a larger diameter of 82mm compared to Rokinon 85mm F1.8's 68mm 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. Rokinon 85mm F1.8 weighs 344g, 58% (486g) lighter than the Samyang 135mm F2.0 ED UMC's weight of 830g.
Below you can find the dimension and weight table of the 'Telephoto Prime Lenses in Fujifilm X Mount for size comparison purposes.
Telephoto Prime Lenses in Fujifilm X Mount for Size Comparison
Both Samyang 135mm F2.0 ED UMC and Rokinon 85mm F1.8 has the same Fujifilm X lens mount. Some of the latest released cameras that are compatible with the Fujifilm X lenses are Fujifilm X-T5, Fujifilm X-H2 and Fujifilm X-H2S.
Samyang 135mm F2.0 ED UMC is also available in Canon EF , Canon EF-M, Four Thirds, Micro Four Thirds, Nikon F (FX), Pentax KAF, Samsung NX, Sony Alpha and Sony E mounts.
Rokinon 85mm F1.8 is also available in Canon EF-M and Sony E mounts.
Samyang 135mm F2.0 ED UMC is a prime lens with fixed focal lenght of 135mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides an 35mm (FF) equivalent of 202.5mm.
Rokinon 85mm F1.8 is a prime lens with fixed focal lenght of 85mm which has an effective (full-frame 35mm equivalent) focal range of 127.5mm when used on a APS-C / DX format camera.