Oude Markt
Z9 Voigtländer Color-Ultron 50/1.8 (42M) wide open.
According to the Pentaxforum: "The Voigtländer Color-Ultron 50 mm f/1.8 is a vintage standard prime lens produced in the 1970s and early 1980s, primarily in M42 screw mount and QBM (Rollei bayonet) versions. Designed by Dr. Albrecht Tronnier, it’s the third-generation Ultron and shares its Planar-type optical formula with Carl Zeiss lenses of the era. It features a 6-element/5-group design, a 6-blade diaphragm, and multi-coating (MC) for improved contrast and flare resistance.
With a fast f/1.8 maximum aperture, it delivers excellent low-light performance, shallow depth-of-field, and creamy bokeh—especially from f/2.8 to f/5.6. The lens focuses down to 0.45 m, uses a 49 mm filter thread, and weighs around 230 g, depending on the mount. It’s fully manual, and the M42 version lacks an A/M switch, requiring a flanged adapter or aperture pin modification for digital use.
Engraved as Color-Ultron 1.8/50, it’s praised for its sharpness wide open, micro-contrast, and distinctive rendering. Some versions have a concave front element, while later ones are slightly convex. Though not as well-known as its Zeiss cousins, it’s a hidden gem among vintage 50s—offering a unique blend of German optical heritage and character-rich performance."
https://www.pentaxforums.com/userreviews/voigtlander-50mm-f18-m42.html