The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Rokinon 85mm F1.4 and the Pentax FA 77mm 1.8 L 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 85mm F1.4 is the longer of the two lenses at 75mm. The Pentax FA 77mm 1.8 L with a length of 48mm, is 27mm shorter. Besides being longer, the Rokinon 85mm F1.4 also has a larger diameter of 78mm compared to the Pentax FA 77mm 1.8 L's 64mm 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. Pentax FA 77mm 1.8 L weighs 270g, 49% (269g) lighter than the Rokinon 85mm F1.4's weight of 539g.
Below you can find the dimension and weight table of the Telephoto Prime Lenses in Pentax KAF Mount for size comparison purposes.
Telephoto Lenses in Pentax KAF Mount for Size Comparison
Filter Threads
The Rokinon 85mm F1.4 has a filter size of 72mm whereas the Pentax FA 77mm 1.8 L has a 49mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 72mm filters that we recommend you to consider for the Rokinon 85mm F1.4:
And these are the 49mm filters that we recommend for the Pentax FA 77mm 1.8 L:
Lens Mounts
Both the Rokinon 85mm F1.4 and the Pentax FA 77mm 1.8 L 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 85mm F1.4 is also available in Canon EF , Four Thirds, Sony Alpha, Samsung NX and Nikon F (FX) mounts.
Focal Range
Rokinon 85mm F1.4 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.
On the other hand, the Pentax FA 77mm 1.8 L is a prime lens with fixed focal lenght of 77mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 115.5mm.