Tōken was certainly the maker of the Crown (6×6) folder in the early or mid-1950s. The name appears as "Token" on the camera (reportedly) and on the ever-ready case. Some sources give the full name "Tohken Kogaku" or "Tohken Optical Works", perhaps corresponding to the Japanese 東研光学 (Tōken Kōgaku, meaning Eastern Research Optics).
- 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).
- 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.