21mm Rangefinder Lenses
Here are comparisons of 21mm lenses for Leica M and other rangefinder cameras, roughly in alphabetical and then chronological order.
Most of the measurements are my actual measurements, so they won't agree with the manufacturers claimed figures most often repeated elsewhere.
Click the links for detailed reviews on each lens.
THe best lens is the Contax G 21/2.8. It has the lest distortion, it's the sharpest, and it's also the smallest and lightest. It does this because it works only on the Contax G camera, which affords its designers a shorter backfocus with TTL metering, than the Leica lenses. Sorry, but you'll have a cow of a time getting it to work on your Leica.
THe best lens in sprit for the Leica is the Voigtländer 21mm f/4. It has the same optical quality as the Leica lenses, but unlike the Leica lenses, it's still small enough not to block your finder and takes Leica's standard 39mm filters.
I have not tested them yet, but the best lens also might be the Zeiss 21mm f/4.5 because it's also small enough not to block your viewfinder. If you prefer 46mm filters, this Zeiss lens (or the larger, finder-blocking Zeiss 21mm f/2.8) is probably your best choice.
All this said and done, I bit and bought a used Leica 21mm f/2.8 ASPH and even though it's bigger and heavier than the other practical 21mm lenses, it performs just fine and takes the same 55mm filters as the Leica 90mm f/2 APO ASPH with which I often shoot it.
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