The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Voigtlander 28mm F2 Ultron and the Voigtlander 21mm F4 Color Skopar II for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is an important deciding factor when comparing two lenses. Voigtlander 28mm F2 Ultron is the longer of the two lenses at 51mm. The Voigtlander 21mm F4 Color Skopar II with a length of 25mm, is 26mm shorter. On the other hand, there is no difference between the max diameters of these lenses, both coming at 55mm.
The 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 21mm F4 Color Skopar II weighs 136g, 44% (108g) lighter than the Voigtlander 28mm F2 Ultron's weight of 244g.
Below you can find the dimension and weight table of the Wideangle Prime Lenses in Leica M Mount for size comparison purposes.
Wideangle Prime Lenses in Leica M Mount for Size Comparison
Lens Mounts
Both the Voigtlander 28mm F2 Ultron and the Voigtlander 21mm F4 Color Skopar II has the same Leica M lens mount. Some of the latest released cameras that are compatible with the Leica M lenses are Leica M11, Leica M10 and Leica M Typ 262.
Focal Range
Voigtlander 28mm F2 Ultron is a prime lens with fixed focal lenght of 28mm. Voigtlander 21mm F4 Color Skopar II is a prime lens with fixed focal lenght of 21mm.