The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Samyang 135mm F2.0 ED UMC 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. Samyang 135mm F2.0 ED UMC is the longer of the two lenses at 122mm. The Pentax FA 77mm 1.8 L with a length of 48mm, is 74mm shorter. Besides being longer, the Samyang 135mm F2.0 ED UMC also has a larger diameter of 82mm 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, 67% (560g) lighter than the Samyang 135mm F2.0 ED UMC's weight of 830g.
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 Samyang 135mm F2.0 ED UMC has a filter size of 77mm 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 77mm filters that we recommend you to consider for the Samyang 135mm F2.0 ED UMC:
And these are the 49mm filters that we recommend for the Pentax FA 77mm 1.8 L:
Lens Mounts
Both the Samyang 135mm F2.0 ED UMC 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.
Samyang 135mm F2.0 ED UMC is also available in Canon EF , Canon EF-M, Four Thirds, Fujifilm X, Micro Four Thirds, Nikon F (FX), Samsung NX, Sony Alpha and Sony E mounts.
Focal Range
Samyang 135mm F2.0 ED UMC is a prime lens with fixed focal lenght of 135mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
202.5mm.
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.