Sun Optical Co.

Est. 1945

Sun Optical Co.

Sun Optical Co., also known as Sun Kōki K.K., was a Japanese lens manufacturer active after the Second World War. The company produced photographic lenses for Leica screw mount rangefinders, Exakta cameras, M42 screw mount SLRs, cine cameras, and later Japanese and international SLR systems. Sun is best known among rangefinder collectors for a small group of rare Leica screw mount, LTM, and M39 lenses sold under names such as Xebec, Sophia, Sola, and Sun Telephoto.

For LeicaLensList, Sun Optical Co. is relevant because the company produced confirmed Leica screw mount lenses, including the Sun Xebec 5cm f/2, Sun Sophia 5cm f/2, Sun Sola 7.3cm f/3.5, Sun Sola 7.5cm f/3.5, Sun Sola 9cm f/4, Sun Xebec Telephoto 9cm f/4, and Sun Telephoto 13.5cm lenses. These lenses belong to the early post-war Japanese Leica-compatible lens market, alongside makes such as Canon, Nikon, Kyoei, Komura, Tanaka, Tōkyō Kōgaku, and other specialist optical makers.

History

Founding / Early Years

Sun Optical Co. appeared shortly after the Second World War as Sun Kōki K.K., written in Japanese as サン光機. The company is generally described as the successor to Gojō Kōki Seisakusho, the wartime maker of K.O.L. lenses. Gojō Kōki had produced Leica screw mount lenses during the war, including the rare K.O.L. Xebec 5cm f/2 for the Nippon Leica copy.

After Gojō Kōki ceased activity in 1945, Sun Kōki continued the general lens-making line. Early Sun lenses reused or inherited names from the K.O.L. period, especially Xebec and Sola. This makes the early Sun lens history closely tied to wartime and immediate post-war Japanese attempts to produce Leica-compatible cameras and lenses.

Early Leica Screw Mount Production

The most important early Sun products for LeicaLensList were Leica screw mount rangefinder lenses. These lenses were made for Japanese Leica-copy cameras and for photographers using Leica-compatible M39 systems.

The earliest Sun-related Leica screw mount lenses included the Sun Xebec 5cm f/2 and Sun Sophia 5cm f/2. The Xebec name had already been used by K.O.L., while Sophia appears to have been an early post-war Sun lens name. These 5cm lenses are rare and are connected to the same historical environment as the early Nippon and Nicca Leica-copy cameras.

Sun also produced uncommon short telephoto lenses such as the Sun Sola 7.3cm f/3.5 and Sun Sola 7.5cm f/3.5. These lenses appear to have been made in very small numbers and are among the more obscure Japanese Leica screw mount lenses.

Sun Sola 9cm f/4 and Telephoto Lenses

The best-known Sun Leica screw mount lens is the Sun Sola 9cm f/4. It was introduced around the late 1940s or early 1950s and became the most common Sun lens in Leica screw mount. Its focal length and aperture placed it in the same practical category as the Leica Elmar 9cm f/4, a compact short telephoto lens for portraits, travel, and general rangefinder photography.

Later versions included the Sun Xebec Telephoto 9cm f/4, which reused the Xebec name. Sun also produced longer 13.5cm telephoto lenses, including f/3.8 and f/3.5 versions. Some were rangefinder-coupled Leica screw mount lenses, while others were made for reflex housings or other camera mounts. Because of this, each Sun 13.5cm lens should be checked carefully before being listed as a standard Leica rangefinder lens.

Expansion into SLR and Cine Lenses

During the 1950s and 1960s, Sun Optical Co. expanded beyond Leica screw mount lenses. The company produced lenses in Exakta mount, M42 screw mount, and other SLR mounts. It also made lenses for cine cameras and later became associated with third-party zoom lenses for 35mm SLR cameras.

This broader production reflects the changing camera market. As rangefinder systems gave way to SLR cameras, Sun moved into interchangeable SLR lenses, telephoto lenses, wide-angle lenses, and zoom lenses. In this later period, Sun was one of several Japanese third-party lens makers supplying affordable alternatives to first-party camera-brand lenses.

Later Period and Disappearance

By the 1970s, Sun Optical Co. appears to have been using the name Gotō Sun or Goto Sun in some contexts. The company was still present in the early 1980s, but it disappeared during that decade. Some collector sources suggest that Sun was absorbed into or connected with Goyo Optical, a Japanese maker of CCTV and industrial lenses, but the exact corporate transition is not fully documented.

For LeicaLensList, the most important period remains the early post-war era, when Sun produced Leica screw mount lenses under the Xebec, Sophia, Sola, and Sun Telephoto names.

Product Lines

Leica Screw Mount Lenses

Sun Optical Co.’s most important LeicaLensList product line is its group of Leica screw mount, LTM, and M39 rangefinder lenses. Known examples include the Sun Xebec 5cm f/2, Sun Sophia 5cm f/2, Sun Sola 7.3cm f/3.5, Sun Sola 7.5cm f/3.5, Sun Sola 9cm f/4, Sun Xebec Telephoto 9cm f/4, Sun Telephoto 13.5cm f/3.8, and Sun Telephoto 13.5cm f/3.5.

Sola Lenses

The Sola name was one of Sun’s key early lens brands. It was used on Leica screw mount lenses such as the Sola 7.5cm f/3.5 and Sola 9cm f/4. The Sola name had earlier connections to K.O.L. lenses, which reinforces the continuity between Gojō Kōki and Sun Kōki.

Xebec Lenses

The Xebec name was used on K.O.L. and Sun lenses. In Leica screw mount, the most important examples are the K.O.L. Xebec 5cm f/2, Sun Xebec 5cm f/2, and Sun Xebec Telephoto 9cm f/4. Because the Xebec name appears across the transition from K.O.L. to Sun, exact markings should be checked before assigning a lens to the correct make.

Sophia Lenses

The Sun Sophia 5cm f/2 is a rare Leica screw mount lens from the early post-war period. It appears to be separate from the Xebec design and is one of the lesser-known Japanese fast normal lenses for Leica screw mount cameras.

SLR and Exakta Lenses

Sun produced lenses for Exakta and M42 screw mount systems, including telephoto lenses and later wider SLR lens families. These lenses are usually outside the LeicaLensList scope unless they were converted to Leica M or otherwise became historically relevant to Leica-compatible rangefinder use.

Zoom Lenses and Later Third-Party Lenses

In the 1960s, 1970s, and early 1980s, Sun Optical Co. produced a wide range of third-party SLR lenses, including zoom lenses. These products contributed to the company’s later market presence, but they are less important for LeicaLensList than the early LTM lenses.

Cine and Specialty Lenses

Sun also made lenses for cine cameras and other formats. These products show that Sun was not only a Leica screw mount lens maker, but a broader Japanese third-party optical manufacturer.

Technical Characteristics

Feature Description
Company Type Japanese third-party photographic and cine lens manufacturer.
Historic Names Sun Kōki K.K., Sun Optical Co., Ltd., Gotō Sun or Goto Sun.
Predecessor Gojō Kōki Seisakusho, maker of K.O.L. lenses.
Known Base Ichikawa, Chiba Prefecture, Japan, in the Sun Optical Co. period.
Main Products Leica screw mount lenses, Exakta lenses, M42 lenses, SLR lenses, cine lenses, telephoto lenses, and zoom lenses.
LeicaLensList Relevance Confirmed Leica screw mount and M39 rangefinder lenses from the early post-war Japanese market.
Important Leica-Compatible Names Xebec, Sophia, Sola, Sun Telephoto.
Important Leica-Compatible Lenses Sun Xebec 5cm f/2, Sun Sophia 5cm f/2, Sun Sola 7.5cm f/3.5, Sun Sola 9cm f/4, Sun Telephoto 13.5cm lenses.
Lens Mounts Leica screw mount, Exakta, M42, cine mounts, and later SLR mounts.
Rangefinder Coupling Present on confirmed Leica screw mount rangefinder lenses.
Optical Character Early post-war Japanese rendering, moderate contrast, compact telephoto designs, and simple mechanical construction.
Collector Caution K.O.L., Sun, Xebec, Sola, and Sophia markings should be checked carefully because the names overlap across the Gojō Kōki and Sun Kōki transition.
Later Corporate Status Disappeared in the 1980s, possibly absorbed into or connected with Goyo Optical.

Market Reception

Sun Optical Co. is a niche but important make for collectors of early Japanese Leica screw mount lenses. It is not as widely known as Canon, Nikon, Minolta, or Komura, but its early LTM lenses represent a significant part of the post-war Japanese effort to build Leica-compatible camera systems.

The Sun Sola 9cm f/4 is the most recognized Sun Leica screw mount lens. Collectors often compare it to the Leica Elmar 9cm f/4 because of its focal length, aperture, compact telephoto purpose, and similar early rangefinder handling. Surviving examples are uncommon, and condition varies because these lenses were made in the early post-war period.

The Sun Xebec, Sun Sophia, and Sun Sola 7.3cm / 7.5cm lenses are rarer and more specialized. Their appeal is mainly historical and collector-oriented rather than based on modern optical performance. They are valuable for understanding the transition from wartime K.O.L. lens production to post-war Japanese third-party Leica screw mount manufacturing.

For LeicaLensList, Sun Optical Co. should be included as a valid make. Its confirmed LTM production, connection to K.O.L. and Japanese Leica copies, and rare Sola/Xebec/Sophia lens families make it directly relevant to collectors of Leica-compatible rangefinder lenses. However, entries should be precise, because many later Sun lenses are SLR or cine lenses and should not automatically be treated as Leica-compatible.

Sources

Lenses (1)

Filters 1 results
Make Model Price Focal Length Aperture Release year Diameter (mm) Length (mm) Weight (g) Min focus distance Elements Groups Filter diameter (mm) MountModel number(s)Actions
Sun Optical Co.Sun Sola 9cm f/4 LTM€106904—————4334LTMSun Sola 9cm f/4, Sun 9cm f/4, Sun Xebec Telephoto 9cm f/4