Leica-mount rangefinder lenses have a long history, stretching from the thread-mount lenses of the early 1930s to the modern Leitz and Zeiss/Voigtlander Cosina "M" bayonet lenses of the present day.
More to the point for the contemporary reader, the very earliest thread-mount lenses are still compatible (via adapters, of course) with the thoroughly modern Leica M, Micro Four Thirds, and Voigtlander cameras of today. So, new camera shoppers, this affects you directly.
I shoot with a rangefinder, and I think it's the finest sort of camera out there- but the lens selection can be so extensive that I often wonder what the difference might be between this lens and that one. And for the digital-only bunch out there, how do these lenses work on an affordable Micro Four Thirds camera? Are they worth considering?
So here we go: a quick comparison of seven different "standard" rangefinder lenses, from the 1930s to today. THIS IS NOT SCIENCE! It's curiosity. I think we've got a solid comparison going here, and I'll leave most of the conclusions to you. Full-resolution files are linked below, so have a look and decide for yourself.
And if you think that a 70-year-old lens has no relevance to modern cameras, you might want to keep reading (warning: image-heavy!)