KMZ MC Zenitar-K 16mm f/2.8 Fisheye

The bayonet one came first. Krasnogorsk had already moved its cameras onto the Pentax K mount with the Zenit-Automat family, and those bodies needed a fisheye with an automatic diaphragm. KMZ ran a pilot batch of the K-mount Zenitar 16mm in 1988 and a setup batch in 1989, then started series production in 1990. The M42 Zenitar-M carries the same 180 degree optics, so the screw-mount lens most people picture when they hear the name is really the follow-up.

It's a diagonal fisheye. The 180 degrees run corner to corner, the whole rectangle fills, and there's no black circle anywhere. Lines through the centre of the frame stay straight; everything else bows outward toward the edges. Keep the horizon exactly on the middle line and it stays level. Tip the camera a few degrees and it curves into a smile or a frown. Expect the corners to lag the centre: they tighten up noticeably as you stop down but never quite catch it. Contrast is fair for multicoated Soviet glass. Flare is the real fight. At this angle of view the sun is in the frame more often than not, and the coating only partly holds back the ghosts and grey veil that come with it.

On a K body it handles like any auto-diaphragm prime. The six blades stay open while you frame and close only when the mirror goes up, so the finder stays bright while you compose. Focus barely matters. Set f/8 and focus at a little over a metre (or put the infinity mark against f/8 on the depth-of-field scale), and everything from about half a metre to infinity is acceptably sharp. After that you watch the edges of the frame instead of the focus ring. The 0.3 m close focus earns its keep indoors: in a small room or a packed crowd you can bring the nearest face to within about 30 cm of the camera and still hold it sharp, and that's where the fisheye bend turns into exaggerated scale.

The front element is the weak point. The convex front glass sits exposed, there's no front filter thread, and it scratches easily if the lens rides in a bag without its cap. All filtration happens at the back. The rear thread is M26.5 x 0.5, though some development documents gave M26 x 0.75, so test-fit before you order filters. That thread must always carry a glass, because the optics were computed with one in place. The clear compensator can be swapped for a yellow or orange filter on black and white film, but the slot is never left empty. If you meter with a handheld meter or Zone Light Meter instead of through the lens, enter the filter factor so the reading includes it.

Today it's a direct route to a full-frame fisheye on a Pentax K film body. One lens people weigh it against is its own twin, the M42 Zenitar-M. Same glass, but on a K camera the screw-mount version needs an adapter, and with that you usually lose the automatic diaphragm and end up composing and metering stopped down. The K version skips that compromise entirely.

Soviet quality control was uneven, so check two things before you pay. Look at the front element for scratches and haze under a torch, then look into the back and confirm the rear glass is still sitting in its thread. A copy missing that piece won't render the way the designers intended, whatever the asking price.