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
The size of a lens is a crucial factor to consider 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 the Rokinon 85mm F1.8's 68mm diameter.
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, 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 Canon EF-M Mount for size comparison purposes.
Telephoto Lenses in Canon EF-M Mount for Size Comparison
Filter Threads
The Samyang 135mm F2.0 ED UMC has a filter size of 77mm whereas the Rokinon 85mm F1.8 has a 62mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 77mm filters that we recommend you to consider for the Samyang 135mm F2.0 ED UMC:
And these are the 62mm filters that we recommend for the Rokinon 85mm F1.8:
Lens Mounts
Both the Samyang 135mm F2.0 ED UMC and the Rokinon 85mm 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 135mm F2.0 ED UMC is also available in Canon EF , Four Thirds, Fujifilm X, Micro Four Thirds, Nikon F (FX), Pentax KAF, Samsung NX, Sony Alpha and Sony E mounts.
Rokinon 85mm F1.8 is also available in Fujifilm X and Sony E mounts.
Focal Range
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 1.6x crop, it provides a 35mm (FF) equivalent of
216mm.
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 136mm when used on a APS-C / DX format camera.