6-way Shootout at 35mm: Zeiss ZM 35/1.4 Distagon, 35/2 Biogon, 35/2.8 C-Biogon, Voigtlander Nokton 35/1.2, Leica 35/1.4 Summilux, Leica 35/2 Summicron
Order Zeiss ZM 35mm f/1.4 Distagon for Leica M at B&H Photo. See also gear pages for Leica M cameras / lenses.
This 6-way comparison includes extensive commentary on the practical merits of these six lenses using a subject that is revealing of key lens behaviors.
I found it very useful myself, and for anyone considering a 35mm lens for Leica M, I deem it worth the price of Guide to Leica alone for what it reveals.
6-way Shootout at 35mm: Wyman Cabin (M240)
With HD and UltraHD images, along with large crops, from f/1.4 through f/16.