Optomax — budget 135mm f/2.8 M42 telephoto, sold as preset and auto versions across several fits
Optomax was a trade name used from the 1970s for Japanese-made third-party lenses sold through independent UK camera dealers. The 135mm f/2.8 was among the brand's faster telephotos, distributed alongside near-identical optics badged by houses such as Carsen, Spiratone and Telesar, a common OEM arrangement of the era.
Sold in both manual preset form, built around a 16-blade iris on early copies, and a later automatic-diaphragm version. Recorded fittings include M42 screw mount, Pentax K, Canon FD and Exakta bayonets, alongside T2-adapter examples. Barrels are all-metal with a manual focus collar typical of period telephotos.
Preset copies need aperture set on a separate ring before stopping down, a two-step process some find fiddly but which adapter users on mirrorless bodies now find handy for click-free control. The Auto version instead couples to the camera's stop-down lever, easing handling on period SLR bodies.
Prices on the used market are modest, typically well under thirty pounds. Worth checking before buying: smoothness of the preset or auto-diaphragm ring, absence of oil on the aperture blades, and haze inside the rear elements, common on lenses of this age.