Tomioka Optical was a Japanese lens manufacturer that supplied fast standard primes to numerous rebadged camera brands through the 1960s and early 1970s, before its acquisition by Yashica in 1968 folded its optical designs into the Yashica and later Contax lens lineage.
The 55mm f/1.4 is a fast double-Gauss standard lens built in M42 screw mount, sold under Tomioka's own name as well as rebadged variants including Porst, Revuenon and Chinon-branded lenses sharing the same optical formula. Some production runs used thorium-doped glass elements, a common practice for fast standard lenses of this period.
Wide open the lens produces soft, low-contrast rendering with pronounced field curvature, sharpening and gaining contrast by f/2.8. Lenses built with thorium glass are noted among collectors for a warm yellow cast that develops with age as the glass browns.
These lenses have gained a following among manual-focus enthusiasts for their fast-aperture rendering and now command higher secondhand prices than typical M42 standard primes. Buyers should check thorium-glass examples with a radiation-aware eye and inspect for the yellowing that affects many surviving copies.