KMZ MC Zenitar-M 50mm f/1.7

Forty-three lines per millimetre in the centre, twenty-four at the edge. That is the centre and edge rating KMZ gave the MC Zenitar-M in its own factory specification. It is a lopsided pair of numbers, and it predicts most of what you will see on the negative. Whatever sits in the middle of the frame resolves well. The corners trail a long way behind.

Work on it started at KMZ in 1975 and the lens arrived in 1977. The formula is an Ultron-type derivative of the double Gauss, six elements in five groups, so it comes from a different branch of the family than the Biotar layout behind the Helios-44. The brief was a faster, more modern normal for M42. That meant f/1.7 instead of f/2, a true 50mm instead of a 58, and a pin-actuated automatic diaphragm that keeps the finder bright at full aperture until the shutter fires. An A/M switch on the barrel covers the older Zenits that meter through a stopped-down lens: set it to M and the blades close to whatever the ring says. It shipped as the kit lens on the Zenit-19.

Wide open the picture is softer and flatter, and stopping down a few stops evens out the frame. For portraits the weakness barely matters. A face usually lands in the middle, where the resolution is, and the gentle loss toward the corners does a face no harm. Architecture and flat copy work at big apertures are where it lets you down. Out-of-focus backgrounds have their own character, and this is not the lens for the Helios swirl, so anyone chasing that look should buy a Helios. Six blades also mean that once you close down a little, highlights in the background turn into hexagons.

It weighs about 280 g and takes 52mm filters (M52 x 0.75). Minimum focus is 0.45 m, which frames roughly 17 x 25 cm on 35mm: a face filling the frame, or a hand-sized object. Real close-up work, a single flower or a watch dial, still needs an extension tube.

The weakness that matters is the edges. Line a group up across the frame at full aperture and the people at the ends come out noticeably softer than the person in the middle. You can stop down to even it out, but then you are not using the f/1.7 you paid for. Many of these lenses are now several decades old, too, so work the aperture pin and the A/M switch before you hand over money. A sticky iris on a pin-driven lens means the camera exposes at whatever aperture the blades happen to reach, which is rarely the one you set.

Today it is an easy lens to find on the used M42 market. Against the Helios-44M it gains real ground: almost half a stop (f/1.7 against f/2) and the field of view of a proper 50mm instead of a short 58. The Super-Takumar 50mm f/1.8 is a different argument. The speed is effectively the same, and the choice between them comes down to the condition of the copy in front of you and what it costs. One practical point: f/1.7 on ISO 400 film in full sun needs shutter speeds far beyond any Zenit body. Screw a 52mm ND onto the front, let Zone Light Meter fold the filter factor into the reading, and you can keep the background soft on a bright afternoon.