Leica Summicron-M 50mm f/2 (v3)

Walter Mandler designed this one at Leitz Canada in Midland, Ontario, and it shipped in 1969 as the third Summicron 50. Give the M system a normal lens that was compact, fast at f/2, and clean enough to satisfy people who shot for a living. Mandler's answer was a six-element, four-group double-Gauss. This version held the catalog through its long run, and the six-element redesign that followed it is the formula that is still essentially in production today.

Wide open it has a look that the modern aspherical Summicron deliberately engineered away. There is a faint glow on specular highlights and contrast drops a touch, and that lifts as you stop down to f/4. How much it gains depends on who you ask. The most-cited dedicated review of the v3, at Casual Photophile, argues it holds resolution to the edges of the frame at every aperture from f/2 to f/16, so the "soft corners that snap shut at f/4" story you hear about old double-Gausses may not apply cleanly here. My read is that the change between open and stopped down is more about contrast and that bit of glow than about corner sharpness, but reasonable people disagree on the same lens.

Out-of-focus backgrounds render smooth and quiet, no swirl and no harsh edges, which is what reportage and portrait shooters wanted from a normal lens they carried every day. Rendering is on the neutral side, the way older Leica glass tends to read next to today's lenses. Flare is worth knowing about. Point it at a bright source in or near the frame without the hood and you can pull a flare, though the lens runs high contrast and keeps veiling glare reasonably in check for its era. Single-era coatings do not fight veiling glare the way newer multicoating does.

The honest limitation, beyond flare, is that it is not a clinical lens and was never trying to be. If you want corner-to-corner bite at f/2 for testing charts or copying flat art, the later aspherical version or a modern Zeiss Planar will out-resolve it everywhere. People still reach for the v3 because it costs a fraction of the aspherical, it is small, and the wide-open rendering has a character the sharper lenses can read as flat. It is the fifty that street and documentary shooters cross-shop against the Zeiss ZM Planar 50 and the older rigid Summicron, and it usually wins on the combination of price and that wide-open quality.

One practical note. This is an f/2 lens with no leaf shutter and a 39mm filter thread, so the meter discipline is straightforward. When you are working it open in low light, meter at the taking aperture rather than guessing, since the difference between f/2 and f/2.8 is a full stop you cannot recover later. In Zone Light Meter, set the working aperture and read the shutter the meter gives you. If you screw an ND or a polarizer onto that 39mm thread, dial the filter factor in so the reading already accounts for the light the glass eats.