The Oko Semi is not mentioned in the official list of set prices compiled in October 1940 and published in January 1941, but it appears in a later official price list dated November 1941. It was also advertised in the January 1942 issue of Hōdō Shashin, together with the Oko Six. The advertising picture is very small and of bad quality. The only surviving example observed so far is pictured in McKeown. Its lens and shutter are unknown.
The Oko Semi is a vertical folder, whose body and struts are copied from the Ikonta A. The advance knob is at the top left, as seen by a photographer holding the camera horizontally. There is a body release on the left and a folding bed release button on the right. The camera has a small housing in the middle of the top plate, containing an eye-level finder and a waist-level brilliant finder. The back is hinged to the left and the film advance is certainly controlled by red windows.
In the advertisement, the shutter is said to give 1–350 speeds and is perhaps called "Precision". The lens is described as a four-element Tessar-type Okor Anastigmat f/3.5. This lens was probably made by Ōki itself.
The example pictured in the advertisement and the example pictured in McKeown differ by some points.
The advertised camera has an L-shaped finder housing, perhaps identical to the finder unit of the late BB Semi First, BB Semi Rotte and BB Baby Semi First by Kuribayashi. It also has a knob at the right end of the top plate, probably the depth-of-field dial which is mentioned in the advertising text.
The surviving example has a smaller pyramidal-shaped housing, engraved OKO SEMI on the top. This part is identical to the finder unit of the second model of the Semi Mulber, and it has also been observed on a Star Semi. The right end of the top plate is smooth and no knob is visible.
- In the only advertisement observed, the name of the camera is written オコーセミ (with a short "O") but the title is オーコーカメラ (Oko cameras, with a long "O").
- "Kokusan shashinki no kōtei kakaku".
- "Kamera no kōtei kakaku kanpō happyō", November 1941, type 3, section 7B.
- Advertisement reproduced in Kokusan kamera no rekishi, p.61.
- McKeown, p.746.
- The shutter name is written プレジョン (purejon) in katakana but this is perhaps a typo for プレシジョン (pureshijon or Precision). The word PRECISION is faintly readable on the shutter plate of the Oko Six pictured in the same advertisement.
- This name in roman letters is tentatively inferred from the katakana オーコール printed in the advertisement; the actual roman form may differ.
- Semi Mulber: see for example Sugiyama, item 1207. Star Semi: example pictured in Sugiyama, item 1246.
- Asahi Camera (アサヒカメラ) editorial staff. Shōwa 10–40nen kōkoku ni miru kokusan kamera no rekishi (昭和10–40年広告にみる国産カメラの歴史, Japanese camera history as seen in advertisements, 1935–1965). Tokyo: Asahi Shinbunsha, 1994. ISBN 4-02-330312-7. Item 32.
- "Kamera no kōtei kakaku kanpō happyō" (カメラの公定価格官報発表, Official announcement of the set prices of the cameras), November 1941. Extract of a table listing Japanese camera production and setting the retail prices, reproduced in "Bebī Semi Fāsuto 'Kore ha bebī wo nanotta semi-ki da'" (ベビーセミファースト"これはベビーを名乗ったセミ機だ", Baby Semi First, 'this is a Semi camera called Baby'), an article by Furukawa Yasuo (古川保男) in Camera Collectors' News no. 277 (July 2000). Nishinomiya: Camera Collectors News-sha. P. 27. Type 3, section 7B.
- "Kokusan shashinki no kōtei kakaku" (国産写真機の公定価格, Set prices of the Japanese cameras), listing Japanese camera production as of October 25, 1940 and setting the retail prices from December 10, 1940. Published in Asahi Camera January 1941 and reproduced in Shōwa 10—40nen kōkoku ni miru kokusan kamera no rekishi (昭和10〜40年広告にみる国産カメラの歴史, Japanese camera history as seen in advertisements, 1935—1965). Tokyo: Asahi Shinbunsha, 1994. ISBN 4-02-330312-7. Pp.108—9. The Oko Semi does not appear in this list.
- McKeown, James M. and Joan C. McKeown's Price Guide to Antique and Classic Cameras, 12th Edition, 2005-2006. USA, Centennial Photo Service, 2004. ISBN 0-931838-40-1 (hardcover). ISBN 0-931838-41-X (softcover). P.746.
The Oko Semi is not listed in Sugiyama.