The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Voigtlander 21mm F1.8 Ultron and the Leica Summarit-M 35mm f2.5 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. Voigtlander 21mm F1.8 Ultron is the longer of the two lenses at 92mm. The Leica Summarit-M 35mm f2.5 with a length of 34mm, is 58mm shorter. Besides being longer, the Voigtlander 21mm F1.8 Ultron also has a larger diameter of 62mm compared to the Leica Summarit-M 35mm f2.5's 51mm 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. Leica Summarit-M 35mm f2.5 weighs 220g, 46% (192g) lighter than the Voigtlander 21mm F1.8 Ultron's weight of 412g.
Below you can find the dimension and weight table of the Wideangle Prime Lenses in Leica M Mount for size comparison purposes.
Wideangle Lenses in Leica M Mount for Size Comparison
Filter Threads
The Voigtlander 21mm F1.8 Ultron has a filter size of 58mm whereas the Leica Summarit-M 35mm f2.5 has a 39mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 58mm filters that we recommend you to consider for the Voigtlander 21mm F1.8 Ultron:
And these are the 39mm filters that we recommend for the Leica Summarit-M 35mm f2.5:
Lens Mounts
Both the Voigtlander 21mm F1.8 Ultron and the Leica Summarit-M 35mm f2.5 has the same Leica M lens mount. Some of the latest released cameras that are compatible with the Leica M lenses are Leica M11 Monochrome, Leica M11 and Leica M10.
Focal Range
Voigtlander 21mm F1.8 Ultron is a prime lens with fixed focal lenght of 21mm.
On the other hand, the Leica Summarit-M 35mm f2.5 is a prime lens with fixed focal lenght of 25-35mm.