Osawa — 75-150mm f/3.8 constant-aperture manual telephoto zoom for vintage SLR mounts
Osawa & Co. was a Japanese trading company distributing cameras and lenses under its own name internationally from the 1960s through the 1980s, contracting optical manufacturers to build lenses sold across multiple SLR systems. The 75-150mm f/3.8 was a compact mid-range telephoto zoom in that catalogue.
The 75-150mm f/3.8 is a manual-focus, manual-aperture zoom with a constant f/3.8 maximum aperture across its range, offered in several common SLR mounts of the period in keeping with Osawa's practice of selling one mount version at a time into different markets. Specific optical construction, weight and filter thread are not confirmed from available sources.
The constant-aperture design keeps exposure consistent while zooming, a practical advantage over cheaper variable-aperture rivals, though sharpness and contrast remain modest by the standard of contemporary first-party zooms.
Osawa lenses are uncommon on the current used market compared with better-known trade names. Check the zoom and focus rings turn smoothly, confirm the aperture blades are oil-free, and verify the mount before buying.