As best as I can tell, Tomioka Optical in Tokyo has always made the lenses used by Yashica and Yashima. In fact at some point in the late 1960s (I believe 1968) Yashica acquired Tomioka as part of their company. The Tominon name sometimes appeared on lenses that also had the Yashinon name. On occasion, Yashica would also “allow” Tomioka to put their name on the lens. The image attached to this article is an example of that. The Tomioka “branded” 55mm f/ 1.2 lens is to some the epitome of the classic fast lenses of the 1970s. I don’t have that lens in my collection as it almost always appears for sale on auction sites near the $1,000 mark… well out of my range for a lens that I would use infrequently. In addition, the mystique of the lens may outweigh the actual performance of the optics.
No doubt though the lens is fast and did perform well enough for its reputation to grow with an almost cult-like following. It is certainly a good looking lens that any Yashica collector would like to have.
This image is from a recently acquired Yashica publication titled Yashica TL ELECTRO-X, The Creative System of Photography. Some excellent images, illustrations, charts and descriptions of the TL Electro-X ITS and its accessories are spread out over its 45 pages.
Of note, the “model number” of these lenses are included in the serial numbers… they begin with 552 which tells the focal length of the lens (55mm) and the 2 indicates (f/ 1.2) aperture or “speed”. The next four numbers are the production sequence numbers. So when you see a serial number of “No. 5520312” you know that you’re looking at a 55mm lens with a maximum aperture of f/ 1.2 and it was the 312th unit made.