KMZ MC Zenitar-ME1 50mm f/1.7

Put a plain Zenitar-M and an ME1 side by side and you will probably read the engraving twice. Both came out of KMZ, both are 50mm f/1.7 lenses with an A/M switch, and from the front they could pass for the same lens. The differences sit at the mount and inside the barrel. The ME1 carries electrical contacts at the mount, and its diaphragm has exactly two blades. On paper it is also the sharper of the pair, rated at 48 lines/mm in the centre and 27 at the edge, a small margin over the plain M. Only one camera can read those contacts.

The E stands for electronic. KMZ built the lens for the Zenit-18, and a resistor in the barrel reports the set aperture to that camera's electronic control unit, so the body knows where the ring sits without the lens stopping down. On a Zenit-E or a Spotmatic the contacts sit idle and you have an ordinary M42 fifty, with the A/M switch for stop-down metering. Production ran from 1980 to 1987, and every one was built to serve a single camera.

The diaphragm is the odd part, and you will see it in your pictures. Two blades close to make a square opening; KMZ went that way because it kept the mechanism simple and needed less force to close. At f/1.7 the blades sit clear of the opening, so highlights are shaped by the barrel rather than the square iris. Stop down even a little and they start to square off, and by f/2.8 or f/4 every street lamp and every gap in backlit leaves becomes a small square, which makes a cluttered background look more cluttered still. At small apertures, point sources pick up four-pointed stars instead of the six or eight spikes a normal iris gives. If you want that look on purpose, this is one of the few M42 fifties that gives it to you. Otherwise it means choosing apertures with the background in mind, which matters far less with a Helios and its many-bladed iris.

Optically it is a six-element, five-group multicoated design weighing about 260 g, so it sits with some heft on the front of a Zenit. The gap between those centre and edge figures is the thing to plan around. The middle of the frame holds up and the edges lag well behind, so a flat wall shot wide open shows soft corners. For a head-and-shoulders portrait that hardly matters, since the subject is in the middle and the falloff reads as atmosphere. Landscapes want f/5.6 or f/8, which is also where the square highlights are easiest to spot, so check what sits behind your focus point.

Off the Zenit-18, the lens's one real advantage disappears. You carry contacts that do nothing and an aperture shape you may not want. The Helios-44M is easy to find and cheap. The plain Zenitar-M gives you the same f/1.7 speed with a conventional iris. The ME1 makes sense if you own a Zenit-18 and want the system to work the way KMZ designed it, or if those square highlights are the reason you are shopping.

Dim interiors are where the f/1.7 speed pays off. Take the reading in Zone Light Meter at f/1.7 and set the shutter speed it gives you; that keeps you at the one aperture where the square iris stays out of the highlights. The 52mm thread takes standard filters, so an ND lets you shoot wide open in daylight too.