The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Carl Zeiss Distagon T3,5/18 and the Samyang 20mm 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. Samyang 20mm F1.8 is the longer of the two lenses at 88mm. The Carl Zeiss Distagon T3,5/18 with a length of 84mm, is 4mm shorter. On the other hand, the Carl Zeiss Distagon T3,5/18 has a larger diameter of 87mm compared to the Samyang 20mm F1.8's 83mm 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. Carl Zeiss Distagon T3,5/18 weighs 470g, which means it is 27g (5%) lighter than the Samyang 20mm F1.8 which has a weight of 497g.
Below you can find the dimension and weight table of the Wideangle Prime Lenses in Pentax KAF Mount for size comparison purposes.
Ultra-Wideangle Lenses in Pentax KAF Mount for Size Comparison
Filter Threads
The Carl Zeiss Distagon T3,5/18 has a filter size of 82mm whereas the Samyang 20mm F1.8 has a 77mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 82mm filters that we recommend you to consider for the Carl Zeiss Distagon T3,5/18:
And these are the 77mm filters that we recommend for the Samyang 20mm F1.8:
Lens Mounts
Both the Carl Zeiss Distagon T3,5/18 and the Samyang 20mm F1.8 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.
Carl Zeiss Distagon T3,5/18 is also available in Canon EF and Nikon F (FX) mounts.
Samyang 20mm F1.8 is also available in Canon EF , Canon EF-M, Fujifilm X, Micro Four Thirds, Nikon F (FX), Samsung NX, Sony Alpha and Sony E mounts.
Focal Range
Carl Zeiss Distagon T3,5/18 is a prime lens with fixed focal lenght of 18mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
27mm.
On the other hand, the Samyang 20mm F1.8 is a prime lens with fixed focal lenght of 20mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 30mm.