The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Rokinon 85mm F1.8 and the Sigma 105mm F1.4 DG HSM 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. Sigma 105mm F1.4 DG HSM is the longer of the two lenses at 132mm. The Rokinon 85mm F1.8 with a length of 81mm, is 51mm shorter. Besides being longer, the Sigma 105mm F1.4 DG HSM also has a larger diameter of 116mm 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, which means it is 1301g (79%) lighter than the Sigma 105mm F1.4 DG HSM which has a weight of 1645g.
Below you can find the dimension and weight table of the Telephoto Prime Lenses in Sony E Mount for size comparison purposes.
Telephoto Lenses in Sony E Mount for Size Comparison
Filter Threads
The Rokinon 85mm F1.8 has a filter size of 62mm whereas the Sigma 105mm F1.4 DG HSM has a 105mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 62mm filters that we recommend you to consider for the Rokinon 85mm F1.8:
And these are the 105mm filters that we recommend for the Sigma 105mm F1.4 DG HSM:
Lens Mounts
Both the Rokinon 85mm F1.8 and the Sigma 105mm F1.4 DG HSM has the same Sony E lens mount. Some of the latest released cameras that are compatible with the Sony E lenses are Sony A6700, Sony FX30 and Sony ZV-E10.
Rokinon 85mm F1.8 is also available in Canon EF-M and Fujifilm X mounts.
Sigma 105mm F1.4 DG HSM is also available in Canon EF , Nikon F (FX) and Sigma SA mounts.
Focal Range
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.
On the other hand, the Sigma 105mm F1.4 DG HSM is a prime lens with fixed focal lenght of 105mm which has an effective (full-frame 35mm equivalent) focal range of 157.5mm when used on a 35mm FF format camera.