KMZ Industar-50-2 50mm f/3.5

Thirty millimetres. That is about how far the Industar-50-2 sticks out from an M42 mount, which makes it one of the flattest normal lenses you can put on that thread. Published weights run anywhere from 75 to 126 g, and on a Zenit the difference is easy to feel: it takes a lot of the bulk off the front of the camera. KMZ supplied it as a standard lens on Zenit bodies, so it often turns up still mounted on one.

The optics are a Tessar type, four elements in three groups. And the engraving rounds things off. The factory measured the focal length at 52.48mm, not 50. You will never see that in a print, but it tells you the "50" on the barrel is a class name rather than a measurement. Stop down to around f/8 and you get the even, sharp results the Tessar formula built its reputation on. Wide open the corners soften and darken a little, as you would expect from a slow Tessar-type.

Handling is where it parts company with most M42 normals of its day. There is no auto pin and no preset ring, only a plain manual iris with seven blades running from f/3.5 to f/16. Turn the ring and the blades close right then, so the finder dims as you go. On a Zenit's modest screen, focusing at f/11 is guesswork. The habit that works is to focus wide open, then turn to the taking aperture without nudging the focus ring. Metering at working aperture through a dark finder is no fun either; a reading taken in Zone Light Meter gives you the aperture and speed up front, so you set the ring once and skip squinting at a stop-down needle. Minimum focus is 0.65 m, roughly a head-and-shoulders framing.

The real weakness is the filter thread. It is M35.5 x 0.5, an odd size, and ordinary filters will not fit without an adapter ring. If you want a yellow filter for black-and-white or an ND for slow shutter work, you are hunting down a step-up ring first. A hood is worth having in bright side light, and it goes on the same shopping list.

Nobody buys an f/3.5 lens to melt a background. At portrait distances you get gentle separation and not much more. Where it makes sense is zone-focused street work at f/8, or any day the camera has to come along for hours and a heavy normal would have stayed at home. Landscape shooters who stop down anyway lose nothing to the slow maximum aperture. On mirrorless bodies with a simple M42 adapter it still makes a compact normal lens, even with the adapter's added length.

It is usually one of the cheaper M42 normals, and the obvious alternative is a Helios-44, which gives you more than a stop and a half of extra speed at the cost of a much longer barrel. Choose based on whether speed or depth matters more on the camera you carry. KMZ's production of the Industar-50 line ended with this version in 1986, so most copies are decades old. Before buying, turn the helicoid through its full range to check that it moves smoothly, and look at the blades with the iris stopped down. They should be dry, with no oil shine.