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 15mm F4 ED AL L for their suitability to various photography scenarios:
Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Pentax 15mm F4 ED AL L is the longer of the two lenses at 40mm. The Voigtlander 20mm F3.5 SL II with a length of 29mm is 11mm shorter. On the other hand, there is no difference between the max diameters of these lenses, both coming at 63mm.
Weight of a lens is as important as its external dimensions, especially if you are planning to hand hold your camera and lens combination for longer periods. Pentax 15mm F4 ED AL L weighs 189g, 7% (16g) lighter than the Voigtlander 20mm F3.5 SL II's weight of 205g.
Below you can find the dimension and weight table of the 'Wideangle Prime Lenses in Pentax KAF Mount for size comparison purposes.
Wideangle Prime Lenses in Pentax KAF Mount for Size Comparison
Lens Mounts
Both Voigtlander 20mm F3.5 SL II and Pentax 15mm F4 ED AL L has the same Pentax KAF lens mount. Some of the latest released cameras that are compatible with the Pentax KAF lenses are Pentax KF, Pentax K-3 III and Pentax K-1 II.
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 an 35mm (FF) equivalent of 30mm.
Pentax 15mm F4 ED AL L is a prime lens with fixed focal lenght of 15mm which has an effective (full-frame 35mm equivalent) focal range of 22.5mm when used on a APS-C / DX format camera.