Zunow 5cm f/1.1

Zunow 5cm f/1.1

When this lens reached the market in 1953, it became the fastest normal lens available for a 35mm camera, briefly putting a small Japanese maker ahead of the larger optical firms in the postwar speed race [1][2]. Its roots run deeper than its release date suggests: development of an f/1.1 normal lens began in 1943 at Teikoku Optical to meet a wartime requirement from the Japanese Navy for a fast objective usable in low light, such as dawn and dusk aerial reconnaissance [1]. Three prototypes were built, but the factory was destroyed in a wartime air raid, and the project took roughly a decade to complete, with finished prototypes appearing around 1950 before the production lens arrived in 1953 [1][2]. Zunow's name is generally linked to the Japanese word for "brain," and the lens is closely associated with the Teikoku Optical lineage [2].

Optically the lens uses a 9-element, 5-group Sonnar-type layout, likely derived from the 50mm f/1.5 Sonnar, and it was notable for reaching f/1.1 without resorting to rare-earth glasses [1][2]. It was offered in Contax and Nikon rangefinder fittings as well as Leica screw mount, the configuration recorded here [1][2]. The earliest version, the form that matches the 9-element design, earned the nickname "Ping-Pong ball" because its rounded front cell protruded noticeably [1]. Despite the extreme aperture the barrel is fairly compact for an f/1.1 optic, with a reviewer comparing its overall size to a modern MS-Optical 50mm f/1.1 Sonnetar [3]. One practical quirk noted in period testing is that the lens mount can intrude into the corner of some rangefinder viewfinder windows, which led testers to suggest an accessory finder [1].

Zunow revised the design after the original launch. To address flare and wide-open performance issues, the company introduced a Type 2 in 1955 that replaced the protruding front with a flat-rear arrangement reported as 8 elements in 5 groups, with hard coatings on the air-to-glass surfaces to reduce internal reflections [1]. Because the verified configuration here is 9 elements in 5 groups, this entry corresponds to the original 1953 type rather than the later revision [1]. Production was small, and survivors are split across the Contax, Nikon, and Leica thread mounts, so mount type is an important identification point for collectors [1][3].

Optical qualities

Rendering Contemporary and modern accounts agree that the lens is at its most characterful, and least corrected, wide open. Period testing found vignetting at f/1.1 that clears by about f/2.8, acceptable central sharpness, and softening toward the edges and corners, with the sharpest results between roughly f/5.6 and f/11 [1]. A modern user shooting it on film and on a digital Leica described a soft, glowing look at f/1.1, with f/2.8 emerging as a sweet spot where sharpness builds and the subject separates well; the same user noted field curvature that keeps the corners from crisping up even stopped down [3].

Bokeh and transitions The Sonnar-type design produces a busy, radial out-of-focus rendering that one reviewer likened to fireworks and compared to the modern Zeiss Sonnar 50mm f/1.5 ZM, noting it can compete with the subject unless the background is kept clean [3].

Flare resistance The original protruding-front version was reported to suffer from flare wide open, which was among the reasons Zunow reworked the optics and added coatings for the later type [1].

Digital use The lens has been used on a modern Leica M digital body, where its soft, glowing wide-open signature and Sonnar-style background rendering remain evident [3].

History

Development and Launch The f/1.1 project originated in 1943 at Teikoku Optical under a Japanese Navy requirement for a high-speed lens for low-light and reconnaissance use [1]. Design work is associated with Sakuo Suzuki and Michisaburo Hamano, the latter described as having moved from Nippon Kogaku toward the Teikoku Optical effort [1][3]. After wartime destruction of the factory and a long rebuild, prototypes were finished around 1950 and the production 5cm f/1.1 was released in 1953, making it the first ultrafast lens for rangefinder cameras [1][3]. It held the speed lead until Nippon Kogaku matched it with the Nikkor 5cm f/1.1 in early 1956; Canon later went faster with the 50mm f/0.95 in 1961, and Leitz reached f/1.0 only with the Noctilux in 1976 [1].

Production Evolution The original 1953 lens, with its rounded protruding front element, was followed in 1955 by a redesigned Type 2 that adopted a flat-rear layout and added hard coatings to improve flare control and wide-open brightness [1]. The two versions differ in element count and front-cell shape, which is the clearest way to tell them apart [1].

Special editions No major factory special editions are widely documented for this lens. The principal variations of interest are the rangefinder mount fittings, with Contax, Nikon, and Leica thread-mount examples recorded [1][3].

Collector Notes The Zunow 5cm f/1.1 is rare and sought after, with reported sales commonly in the multi-thousand-dollar range and higher for clean or desirable mounts; for reference, its 1956 price was roughly US$450 [1]. Mount type, version (protruding-front original versus flat-rear Type 2), and coating condition are worth verifying before purchase, and buyers should remember that the lens mount may interfere with some camera viewfinder windows [1][3]. Because so few were made, provenance and originality matter, and confirming the LTM fitting against the camera is advisable [1][3].

Sources

• [1] Crafting Pixels. Ultrafast lenses – the Zunow 5cm f/1.1 (and 58mm f/1.2). https://pixelcraft.photo.blog/2025/02/25/ultrafast-lenses-the-zunow-5cm-f-1-1-and-58mm-f-1-2/
• [2] Crafting Pixels. Ultrafast lenses – the Zunow 5cm f/1.1 (and 58mm f/1.2). https://pixelcraft.photo.blog/2025/02/25/ultrafast-lenses-the-zunow-5cm-f-1-1-and-58mm-f-1-2/
• [3] Tahusa (Anson). Zunow Teikoku Kogaku Japan 50mm f1.1 – The First Ultra Fast Lens. https://tahusa.co/lens-review/zunow-teikoku-kogaku-japan-50mm/