The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sony FE 14mm F1.8 GM and the Samyang 12mm f2.0 for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is an important deciding factor when comparing two lenses. Sony FE 14mm F1.8 GM is the longer of the two lenses at 100mm. The Samyang 12mm f2.0 with a length of 59mm, is 41mm shorter. Besides being longer, the Sony FE 14mm F1.8 GM also has a larger diameter of 83mm compared to the Samyang 12mm f2.0's 73mm diameter.
The 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. Samyang 12mm f2.0 weighs 260g, 43% (200g) lighter than the Sony FE 14mm F1.8 GM's weight of 460g.
Below you can find the dimension and weight table of the Wideangle Prime Lenses in Sony E Mount for size comparison purposes.
Wideangle Prime Lenses in Sony E Mount for Size Comparison
Lens Mounts
Both the Sony FE 14mm F1.8 GM and the Samyang 12mm f2.0 has the same Sony E lens mount. Some of the latest released cameras that are compatible with the Sony E lenses are Sony ZV-E1, Sony A7R V and Sony FX30.
Samyang 12mm f2.0 is also available in Canon EF-M , Fujifilm X, Micro Four Thirds and Samsung NX mounts.
Focal Range
Sony FE 14mm F1.8 GM is a prime lens with fixed focal lenght of 14mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 21mm.
Samyang 12mm f2.0 is a prime lens with fixed focal lenght of 12mm which has an effective (full-frame 35mm equivalent) focal range of 18mm when used on a APS-C / DX format camera.