The Semi Osamo is a Japanese 4.5×6 folding camera made in the first half of the 1940s. It seems that its manufacturer was called Yamanashi Kōki (see below).
The official list of set prices published in January 1941 does not mention the Semi Osamo, but a similar list dated November 1941 has a "Semi Osamo I", attributed to a company perhaps called Yamanashi Kōki (山梨光機). The Semi Osamo is also mentioned in the "Kokusan shashinki no genjōchōsa" ("Inquiry into Japanese cameras"), listing Japanese camera production as of April 1943. The names of the maker and distributor are unfortunately missing from the document. The shutter is registered as an Osamo giving T, B, 1–300 speeds and the lens as a three-element Liebe 75/4.5 made by Riken.
The Semi Osamo is a horizontal folder with straight diagonal struts. There is a small housing in the middle of the top plate, containing a brilliant finder and a direct vision finder placed side by side. There is an accessory shoe above the eye-level finder, a body release on the right and a folding bed release on the left. The advance knob is at the left end of the top plate and there is a film retaining knob at the right end. The back is hinged to the right and the film advance is probably controlled by red windows. The name SEMI OSAMO is embossed in the front leather in capital letters.
Only one surviving example has been observed so far, pictured in Sugiyama. It has a Liebe Anastigmat 75mm f/4.5 lens (no. 1039) and a shutter reportedly giving T, B, 1–300 speeds. The shutter plate has a marking at the top, perhaps reading TOKKYO (meaning "patent" in Japanese) and another at the bottom, ending with SHUTTER.
- "Kokusan shashinki no kōtei kakaku".
- "Kamera no kōtei kakaku kanpō happyō", November 1941, type 3, section 6B. The company name is barely legible in the reproduction consulted. Sugiyama, item 1220, McKeown, p. 1020, say "Yama-ko Optical Co." Yamanashi is the name of a Japanese city and of a prefecture, in the Chūbu region.
- "Kokusan shashinki no genjōchōsa" ("Inquiry into Japanese cameras"), item 53.
- "Kokusan shashinki no genjōchōsa" ("Inquiry into Japanese cameras"), shutter item 18-P-14, lens item Lc12.
- Sugiyama, item 1220.
- "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 6B.
- "Kokusan shashinki no genjōchōsa" (国産写真機ノ現状調査, Inquiry into Japanese cameras), listing Japanese camera production as of April 1943. Reproduced in Supuringu kamera de ikou: Zen 69 kishu no shōkai to tsukaikata (スプリングカメラでいこう: 全69機種の紹介と使い方, Let's try spring cameras: Presentation and use of 69 machines). Tokyo: Shashinkogyo Syuppan-sha, 2004. ISBN 4-87956-072-3. Pp.180–7. Item 53.
- "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 Semi Osamo 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. 1020.
- Sugiyama, Kōichi (杉山浩一); Naoi, Hiroaki (直井浩明); Bullock, John R. The Collector's Guide to Japanese Cameras. 国産カメラ図鑑 (Kokusan kamera zukan). Tokyo: Asahi Sonorama, 1985. ISBN 4-257-03187-5. Item 1220.
The Semi Osamo is not listed in Kokusan kamera no rekishi.