The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Samyang 50mm F1.2 AS UMC CS and the Rokinon 85mm F1.8 for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is a crucial factor to consider when comparing two lenses. Rokinon 85mm F1.8 is the longer of the two lenses at 81mm. The Samyang 50mm F1.2 AS UMC CS with a length of 74mm, is 7mm shorter. On the other hand, there is no difference between the max diameters of these lenses, both coming at 68mm.
The weight of a lens is equally significant as its external dimensions, particularly if you intend to handhold your camera and lens combination for extended periods. Rokinon 85mm F1.8 weighs 344g, 8% (31g) lighter than the Samyang 50mm F1.2 AS UMC CS's weight of 375g.
Below you can find the dimension and weight table of the Telephoto Prime Lenses in Fujifilm X Mount for size comparison purposes.
Telephoto Lenses in Fujifilm X Mount for Size Comparison
Filter Threads
Both the Samyang 50mm F1.2 AS UMC CS and the Rokinon 85mm F1.8 have the same Filter thread size of 62mm.
Below are links to the 62mm filters that we recommend you to consider for these lenses:
Lens Mounts
Both the Samyang 50mm F1.2 AS UMC CS and the 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-S20, Fujifilm X-T5 and Fujifilm X-H2.
Samyang 50mm F1.2 AS UMC CS is also available in Canon EF-M , Micro Four Thirds and Sony E mounts.
Rokinon 85mm F1.8 is also available in Canon EF-M and Sony E mounts.
Focal Range
Samyang 50mm F1.2 AS UMC CS is a prime lens with fixed focal lenght of 50mm which has an effective (full-frame 35mm equivalent) focal range of
75mm when used on a APS-C / DX format camera.
On the other hand, the 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.