Bronica's 6x6 portrait tele — the leaf-shutter Zenzanon-S 180mm f/4.5 for the SQ system.
The Bronica Zenzanon-S 180mm f/4.5 is a telephoto lens for the Bronica SQ 6x6 medium-format system, from the early SQ era around 1980. The S designation marks the earlier generation of SQ Zenzanon optics that came before the later PS lenses. On the square 6x6 frame a 180mm serves as a portrait and medium-telephoto focal length.
This manual-focus lens uses the Bronica SQ leaf-shutter mount and provides a focal length of 180mm at a maximum aperture of f/4.5. It contains the in-lens Seiko leaf shutter shared across the SQ system, so flash synchronisation is available at all shutter speeds. Optical construction, weight and filter thread are not listed here because they cannot be confirmed from the sources at hand.
A 180mm on 6x6 works well for portraits taken at a flattering distance and for landscape details and general subjects that need reach. The focal length compresses perspective and isolates the subject against a smoothly rendered background from the larger negative. A tripod or firm support helps given the slower shutter speeds common in medium-format work.
On the used market the S 180mm is a fairly common SQ telephoto and generally sells at a moderate price. Check the leaf shutter fires evenly at fast and slow speeds and inspect the longer barrel for internal haze or fungus. Confirm the aperture blades are dry and responsive and that the mount and body coupling engage securely without play.