Kumagai left Seiki Kōgaku in the late 1930s because the company's main activity was shifting to military contracts, whereas he was mainly interested in camera production. He hired a small workshop in the same building as the company Ishii Shōkai, distributor of the Echt products, and specialized in the repair and transformation of high-end cameras, notably adding a coupled rangefinder to viewfinder-only Leica models. Some of these converted Leica might still exist today, but none has been identified so far.
Kōgaku Seiki period
After some time, Kumagai was ordered by Ōmiya's boss Noro Hikota (野呂彦田) to set up a repair workshop for the Canon models, together with seven other former employees of Seiki Kōgaku. This was run as a semi-independent business called Kōgaku Seiki, with Ōmiya's funds and at the first floor of one of Ōmiya's buildings. In parallel to the repair activity, Kumagai began to work on his own Leica-like design, and made the first Nippon in the early 1940s. Kumagai later related that during that period, German people working at Schmidt Shōkai, the importer of the Leica, offered him to set up a company using the Leitz patents, but this was probably an informal offer, with no prior approval of the German company.
Kumagai's workshop moved to another building belonging to the distributor Ōsawa Shōkai in March 1945, and escaped Tokyo's fire bombings unscathed. The workshop moved again in 1946 and in 1947, while the production of the Nippon was slowly restarting. Kumagai left the company in 1948, shortly after the model name was changed to Nicca.
Later camera production
Kumaga apparently returned to the small-scale production of modified Leica and hand-built Leica copies. It is said that he participated to the development of the Phoenix (predecessor of the Miranda T), supplying various shutter parts to its maker Orion Seiki. One of his Leica-like designs was adopted by Daiichi Kōgaku, and became the Ichicon-35, of which a handful were made before the company closed its doors; the camera was then rescued by someone else and sold as the Honor S1, without noticing him (see Honor S1).
Kumagai's last attempt at camera production was the Jeicy, a Leica copy with opening back and 1/1000 top speed, which has some parts in common with the Ichicon-35. The name Jeicy Camera Works engraved on the camera's top cover was invented by Kumagai Genji, and did not correspond to an actual company.
- The name is given in the Japanese order: Kumagai is the family name and Genji is the given name. The family name may also read "Kumatani"; the reading "Kumagai" is found in this page by Nekosan.
- Shirai, p.21 of Maboroshi no kamera o otte.
- Shirai, p.22 of Maboroshi no kamera o otte.
- Shirai, pp.22–3 of Maboroshi no kamera o otte.
- Shirai, pp.21 and 23 of Maboroshi no kamera o otte.
- Shirai, pp.23–4 of Maboroshi no kamera o otte.
- Shirai, p.26 of Maboroshi no kamera o otte.
- Shirai, p.24 of Maboroshi no kamera o otte.
- Shirai, p.25 of Maboroshi no kamera o otte.
- Shirai, p.25 of Maboroshi no kamera o otte: また熊谷氏が改造したライカ、模造したライカも、戦後のライカファンの話題となった. The sentence comes immediately after Shirai said that the viewfinder-only Nippon made during the war for military use appeared on the postwar camera market, and it is unclear if the "modified Leica and Leica copies" were those made by Shirai before and during the war, or others made after he left Nicca.
- Japanese Wikipedia page on Miranda products: シャッタ−部分にはニッポンカメラの熊谷源二氏からスローダイヤル、ガバナー、ドラムの提供を受け[...].
- Shirai, p.25 of Maboroshi no kamera o otte: さらには、ニッポンカメラの製造を譲りうけたいといって、カメラを持っていったゼノビア光学は倒産して、だれかがそこから持ち出したカメラが、「オーナー」という名で熊谷氏にことわりなく作られた.
- Shirai, p.26 of Maboroshi no kamera o otte: これはカメラ界で最後に作ろうとして果たせなかった会社の名である.
- Shirai Tatsuo (白井達男). "Nippon Kamera" (ニッポンカメラ, Nippon Camera). Pp.17–26 of Maboroshi no kamera o otte (幻のカメラを追って, Pursuing phantom cameras). Gendai Kamera Shinsho (現代カメラ新書). Tokyo: Asahi Sonorama, 1982. ISBN 4-257-08077-9. (First published in Kamera Rebyū / Camera Review no.2, February 1978.) Contains an interview of Kumagai Genji.
- List of Miranda products at the Japanese-language Wikipedia (Kumagai Genji is mentioned in relation with the Phoenix prototype)