Helios — 135mm f/2.8 M42 telephoto prime, Japan-made (not the Soviet KMZ lens).
The Helios 135mm f/2.8 was a Japanese-made manual telephoto sold in Britain and the Netherlands under the Soviet-sounding Helios badge, historically the trademark of USSR maker KMZ. UK importer TOE, the main dealer of Russian Zenit gear, commissioned it when Soviet stock ran short, reportedly from Chinon.
Built as a 4-element, 4-group auto-stopdown design for the M42 screw mount, it stops to f/22 through 6 blades, weighs around 330g, and takes 55mm filters. Minimum focus is 1.5m, and the metal barrel carries a fixed built-in hood with no auto/manual switch.
Wide open it renders softly with swirl-edged bokeh and rippling backlit flare that sharpens by f/5.6-f/8, falling short of the genuine Helios-44's rendering despite the shared name. Some examples even carry spurious Soviet-style factory stamps, adding to buyer confusion.
UK examples surface in M42 job lots and house clearances, usually priced under genuine Soviet Helios glass once the Japanese origin is spotted. Cheap M42 adapters keep it usable on mirrorless bodies; check the aperture blades snap cleanly and the focus ring isn't gritty.