The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Venus 25mm F2.8 2.5-5X Ultra Macro and the Voigtlander 20mm F3.5 SL II for their suitability to various photography scenarios:
Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Venus 25mm F2.8 2.5-5X Ultra Macro is the longer of the two lenses at 65mm. The Voigtlander 20mm F3.5 SL II with a length of 29mm is 36mm shorter. Besides being longer, the Venus 25mm F2.8 2.5-5X Ultra Macro also has a larger diameter of 82mm compared to Voigtlander 20mm F3.5 SL II's 63mm diameter.
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. Voigtlander 20mm F3.5 SL II weighs 205g, 48% (195g) lighter than the Venus 25mm F2.8 2.5-5X Ultra Macro's weight of 400g.
Lens Mounts
Both Venus 25mm F2.8 2.5-5X Ultra Macro has the Pentax KAF2 lens mount whereas the Voigtlander 20mm F3.5 SL II has the Pentax KAF lens mount. Some of the latest released cameras that are compatible with these mounts are Pentax KF, Pentax K-3 III and Pentax K-1 II for the Pentax KAF2 Mount and Pentax KF, Pentax K-3 III and Pentax K-1 II for the Pentax KAF Mount.
Venus 25mm F2.8 2.5-5X Ultra Macro is also available in Canon EF , Nikon F (DX) and Sony E mounts.
Voigtlander 20mm F3.5 SL II is also available in Canon EF and Nikon F (FX) mounts.
Focal Range
Venus 25mm F2.8 2.5-5X Ultra Macro is a prime lens with fixed focal lenght of 25mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides an 35mm (FF) equivalent of 37.5mm.
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.