The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 105mm F1.4 DG HSM and the Sony FE 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. Sigma 105mm F1.4 DG HSM is the longer of the two lenses at 132mm. The Sony FE 85mm F1.8 with a length of 82mm, is 50mm shorter. Besides being longer, the Sigma 105mm F1.4 DG HSM also has a larger diameter of 116mm compared to the Sony FE 85mm F1.8's 78mm 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. Sony FE 85mm F1.8 weighs 371g, 77% (1274g) lighter than the Sigma 105mm F1.4 DG HSM's 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 Sigma 105mm F1.4 DG HSM has a filter size of 105mm whereas the Sony FE 85mm F1.8 has a 67mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 105mm filters that we recommend you to consider for the Sigma 105mm F1.4 DG HSM:
And these are the 67mm filters that we recommend for the Sony FE 85mm F1.8:
Lens Mounts
Both the Sigma 105mm F1.4 DG HSM and the Sony FE 85mm F1.8 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.
Sigma 105mm F1.4 DG HSM is also available in Canon EF , Nikon F (FX) and Sigma SA mounts.
Focal Range
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.
On the other hand, the Sony FE 85mm F1.8 is a prime lens with fixed focal lenght of 85mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 127.5mm.