Mamiya's updated RB67 portrait tele — the leaf-shutter K/L 180mm f/4.5 with better coatings.
The Mamiya Sekor K/L 180mm f/4.5 is the updated short-telephoto lens for the Mamiya RB67 medium-format system, from the K/L generation introduced around 1990. It refined the earlier C-series 180mm with a revised optical design and improved coatings. On the 6x7 frame it remains a favoured portrait and general telephoto.
This is a manual-focus lens native to the Mamiya RB67 bayonet mount, with a focal length of 180mm and a maximum aperture of f/4.5. It carries a built-in leaf shutter, with the aperture set on the barrel and focusing by the camera bellows. The K/L formula was intended to improve contrast and flare control over the C version.
At 180mm on 6x7 the perspective corresponds to roughly an 88-90mm lens on 35mm, a strong portrait length with useful compression. The improved coatings help contrast in mixed light, and the leaf shutter permits flash sync at all speeds for studio and location portraiture. It became a preferred telephoto for later RB67 users.
The K/L 180mm f/4.5 is later and better specified than the C version and usually commands a higher price. Test the leaf shutter across all speeds for clean firing, and inspect the glass for haze and fungus. Confirm the aperture blades are dry and close cleanly, and verify the bayonet and shutter-cocking coupling engage correctly before purchase.