The type of photography that you are planning to use is an important decision factor. Here we have evaluated the HD Pentax-FA 31mm F1.8 Ltd and the Rokinon 14mm f2.8 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 14mm f2.8 is the longer of the two lenses at 96mm. The HD Pentax-FA 31mm F1.8 Ltd with a length of 69mm, is 27mm shorter. Besides being longer, the Rokinon 14mm f2.8 also has a larger diameter of 87mm compared to the HD Pentax-FA 31mm F1.8 Ltd's 65mm 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. HD Pentax-FA 31mm F1.8 Ltd weighs 341g, which means it is 211g (38%) lighter than the Rokinon 14mm f2.8 which has a weight of 552g.
Lens Mounts
Both the HD Pentax-FA 31mm F1.8 Ltd and the Rokinon 14mm f2.8 has the same Pentax KAF lens mount. Some of the latest released cameras that are compatible with the Pentax KAF lenses are Pentax K-3 III Monochrome, Pentax KF and Pentax K-3 III.
Rokinon 14mm f2.8 is also available in Canon EF , Nikon F (FX), Four Thirds, Sony Alpha and Samsung NX mounts.
Focal Range
HD Pentax-FA 31mm F1.8 Ltd is a prime lens with fixed focal lenght of 31mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
46.5mm.
On the other hand, the Rokinon 14mm f2.8 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.