Sun Optical Co. Sun Sola 7.5cm f/3.5

Sun Optical Co. Sun Sola 7.5cm f/3.5

The Sun Sola 7.5cm f/3.5 is an early Japanese short-telephoto lens made in Leica Thread Mount during the post-war reconstruction of the Japanese optical industry. Surviving examples are extremely scarce. Leitz Photographica Auction has documented original lenses as mechanically rangefinder-coupled M39 optics, confirming that the Sola belongs directly within the Leica-compatible rangefinder system.

The lens was produced by Sun Koki, later known internationally as Sun Optical Co., a successor to the pre-war Kajiro Optical Laboratory and Gojo Koki operations. Early Sun products reused several brand names inherited from the pre-war company, including Sola and Xebec.

The 7.5cm Sola uses a long, narrow focusing barrel strongly influenced by contemporary Leica telephoto lenses. Early examples combine black and chrome components, while later surviving specimens are predominantly chrome-plated brass. A minimum focusing distance of approximately 1 metre is documented for the closely studied production form.

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Optical qualities

Rendering

Reliable modern optical testing of the Leica Thread Mount Sun Sola 7.5cm f/3.5 is extremely limited because so few examples survive.

A four-element 75mm Sola design is documented in earlier pre-war use, and collector research suggests continuity between that lens and the post-war Prominar, Hectar and Sun Sola 7.3/7.5cm family. However, an exact optical diagram for the Leica Thread Mount Sun Sola has not been sufficiently verified to assign a definitive elements-and-groups specification.

For that reason, claims about sharpness, contrast, bokeh and aberrations should remain conservative until stronger technical documentation becomes available.

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History

Development and Launch

Sun Optical traces its roots to Kajiro Optical Laboratory, founded before the Second World War. The company produced lenses under several names, including Sola.

Following the war, operations were reorganized under Sun Koki. The company continued using the Sola name and produced a small group of lenses for Leica-compatible screw-mount cameras.

The earliest post-war 7.5cm lenses appear under names such as Prominar and Hectar before the Sun Sola engraving became established. Serial-number research places the known lenses in closely grouped 71xxx and 72xxx sequences.

Production Evolution

The earliest known Sun Sola lenses include both 7.3cm and 7.5cm engravings.

Early barrels combine black-painted and chrome-plated sections. Later examples adopted an almost entirely chrome finish.

Minor barrel revisions are documented, particularly around the diaphragm ring and front engraving.

Known serial numbers are concentrated within an extremely narrow range. Collector research suggests that total production of the related Prominar, Hectar and Sola 7.3/7.5cm family may have been fewer than 500 units, although an exact Sun factory production figure is not available.

Special Editions/Variants

7.3cm engraving: A very rare factory version engraved 7.3cm f/3.5 is documented. It is mechanically and stylistically closely related to the 7.5cm lens. It is not known whether the true optical focal length differed or whether the alternative engraving was primarily a naming decision.

For LeicaLensList, the 7.3cm version can either be treated as a closely related variant or, preferably, receive a separate database entry if engraved focal length is used as the primary version boundary.

Black/chrome early barrel: Early lenses exist with a combination of black and chrome finish.

All-chrome later barrel: Later surviving examples use a predominantly chrome-plated brass construction.

No separate catalogue numbers for these variants are confirmed.

Collector Notes

The front engraving is essential for identification because 7.3cm and 7.5cm examples exist within closely related serial-number batches.

Original rangefinder coupling should be verified. Leitz Photographica Auction specifically identifies surviving Sun Sola 7.5cm lenses as coupled M39 optics.

Collectors should also distinguish the Sun Sola from earlier Prominar and Hectar 7.5cm lenses. They are historically related and probably came from the same manufacturing lineage, but their engravings and production identities differ.

Original rear caps and period accessories are particularly desirable given the lens's rarity.

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Sources

• Leitz Photographica Auction. Sun Sola 3.5/7.5cmleitz-auction.com →
• Leitz Photographica Auction. Sun Sola 3.5/7.3cmleitz-auction.com →
• Camerapedia. K.O.L. and Sun lenses in Leica screw mountcamerapedia.fandom.com →
• JAPB. Company Profile: Sun Opticaljapb.net →
• Japan Camera Hunter. Eastwest Photo's Collection of War-era Japanese Camerasjapancamerahunter.com →

Special editions

7.3cm f/3.5 variant: Extremely rare closely related factory version with 7.3cm engraving. No separate catalogue number is confirmed.

Early black/chrome barrel: Early production finish variant.

Later chrome barrel: Later predominantly chrome-plated production form.