The Optomax 135mm f/3.5 was the slower, more affordable sibling to the brand's f/2.8 telephoto, sold through UK camera shops from the 1970s as one of many near-identical designs shared across budget Japanese lens brands of the period, including close relatives such as the Hanimar 135mm f/3.5.
It was built around the interchangeable T2/T-mount adapter system, most commonly encountered in M42 screw-mount form, with a manual preset aperture ring and a reported ten-to-twelve blade iris on different production runs. Build is all-metal, in keeping with lenses of this class and era.
As a preset design it needs the aperture set on one ring before a second focusing/stop-down ring is used to compose and shoot, a slower workflow than later auto lenses but one that suits video and mirrorless adapter use, where smooth, click-free aperture control is often preferred.
It typically sells for well under forty pounds on the used market. Worth checking: that both preset and stop-down rings move independently and smoothly, that the many-bladed iris is free of oil, and that the T2 thread or fitted adapter matches the mount of the intended camera.