The Piotar 4.5cm f/1.9 is the only lens made by Shōwa Kōki in Leica screw mount.
The barrel has a predominantly black finish, with chrome plating on the lens mount and at the bottom of the focus ring. The latter is driven by a tab with an infinity lock. The distance scale is reportedly engraved until 3.5ft, also the closer limit for rangefinder coupling. However the focus ring reportedly turns past this setting, and the lens can focus down to 1.5ft with no coupling. The aperture scale goes from 1.9 to 22, with irregular spacing.
The front bezel is engraved SHOWAKOKI PIOTAR, hence the attribution to Shōwa Kōki. That company made Coral lenses for Aires in the early 1950s. It is said that it was absorbed by Aires in 1953, and became its optical factory. However the Piotar f/1.9 lens was obviously manufactured later, and was perhaps adapted from the H Coral 4.5cm f/1.9, made of six elements in four groups, mounted on the Aires 35 IIIL and IIIC in 1957–8 and later on the Viscount and Radar Eye.
The Piotar f/1.9 lens is very rare, and the only serial number known so far is 570204; the two first digits are perhaps a further indication that the lens was made in 1957.
- Awano Mikio (粟野幹男) and Maeda Daisuke (前田大介). "Kokusan Raika maunto renzu 3: Mezurashii renzu 1" (国産ライかマウントレンズ 3 珍しいレンズ 1, Japanese Leica-mount lenses 3: Rare lenses 1). In Kamera Rebyū: Kurashikku Kamera Senka (カメラレビュー クラシックカメラ専科) / Camera Review: All about Historical Cameras no.32, March 1995. No ISBN number. Leica Book '95 (ライカブック'95). Pp.122–5.
- Hagiya Takeshi (萩谷剛). "Airesu no kamera: Yarūfurekkusu soshite 6×6-han niganrefu, 35mm kamera e (アイレスのカメラ：ヤルーフレックスそして6×6判二眼レフ、35mmカメラへ, The Aires cameras: From the Yallu Flex to 6×6 TLRs and 35mm cameras). Chapter 5 of Zunō kamera tanjō: Sengo kokusan kamera jū monogatari (ズノーカメラ誕生：戦後国産カメラ10物語, The birth of the Zunow camera: Ten stories of postwar Japanese camera makers). Tokyo: Asahi Sonorama, 1999. ISBN 4-257-12023-1. (Originally published in Kurashikku Kamera Senka no.22.)