Leica APO-Summicron-M 50mm f/2 ASPH

Wide open at f/2 this lens resolves like most fifties do stopped down to f/5.6. That is the whole pitch. When Leica released it in 2012 it was, by the magazine bench tests of the day, widely regarded as one of the sharpest fifties available for a 35mm camera, and it held that reputation for years. Corner to corner contrast at maximum aperture, no focus shift to chase, and an apochromatic correction that kills the purple and green color fringing you see on almost every other fast normal lens at high-contrast edges.

The optical formula is the unusual part. Leica went with a floating element design and aspherical surfaces to flatten the field and hold the correction across the focus range, which is why edge performance does not collapse when you focus close. The trade is a rendering that some people find too perfect. Bokeh is smooth and neutral rather than characterful. Out-of-focus highlights come back as clean discs, with none of the swirl or cat-eye stretching at the frame edge that older fast normals give you. If you want the dreamy fall-apart look of an old Summilux or a Sonnar, this is the wrong lens, and that is a deliberate choice on Leica's part.

Who buys it: shooters who want the glass to get out of the way. Documentary and reportage photographers who work wide open in available light and need the subject crisp the instant they nail focus. Portrait shooters who want pores and stray hairs to actually show up in the file instead of being softened away. It draws with high microcontrast and accurate, slightly cool color, so a face reads as the person in front of you and not a retouched version of them. On Leica M bodies it is small and light, takes a 39mm filter, and balances the way a normal M lens should.

The honest weakness is twofold. First, the price. This is one of the most expensive normal lenses ever sold, and you are paying a steep premium over the regular Summicron-M 50mm f/2, which is already excellent and renders with more warmth. For a lot of work the cheaper Summicron is the smarter buy and nobody will see the difference in a print. Second, the rendering can read as sterile. On color negative the files look almost digital. People cross-shop it against the Zeiss ZM Planar 50 and the standard Summicron, and the APO only wins if you genuinely need that last bit of wide-open bite.

One metering note for the way most people use it. The reason you bought an f/2 with this kind of correction is to shoot it wide open in low light, so you will be metering at the edge of your film's latitude with no margin to spare. Meter for the shadow you actually care about and let the highlights do what they do. In Zone Light Meter, place that shadow on Zone III and read off the f/2 exposure directly; with this lens there is no focus shift or softness penalty for staying wide open, so the aperture you meter is the aperture you shoot.