The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Voigtlander 20mm F3.5 SL II and the Pentax FA 31mm F1.8 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. Pentax FA 31mm F1.8 L is the longer of the two lenses at 69mm. The Voigtlander 20mm F3.5 SL II with a length of 29mm, is 40mm shorter. Besides being longer, the Pentax FA 31mm F1.8 L also has a larger diameter of 65mm compared to the Voigtlander 20mm F3.5 SL II's 63mm 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. Voigtlander 20mm F3.5 SL II weighs 205g, which means it is 140g (40%) lighter than the Pentax FA 31mm F1.8 L which has a weight of 345g.
Filter Threads
The Voigtlander 20mm F3.5 SL II has a filter size of 52mm whereas the Pentax FA 31mm F1.8 L has a 58mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 52mm filters that we recommend you to consider for the Voigtlander 20mm F3.5 SL II:
And these are the 58mm filters that we recommend for the Pentax FA 31mm F1.8 L:
Lens Mounts
Both the Voigtlander 20mm F3.5 SL II and the Pentax FA 31mm F1.8 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.
Voigtlander 20mm F3.5 SL II is also available in Canon EF and Nikon F (FX) mounts.
Focal Range
Voigtlander 20mm F3.5 SL II 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.
On the other hand, the Pentax FA 31mm F1.8 L 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.