Pentax's legendary fast fifty — the Super-Takumar 50mm f/1.4 in M42 mount.
The Super-Takumar 50mm f/1.4 is one of the most sought-after M42 screw-mount lenses, produced by Asahi Optical (Pentax) in two distinct versions. The earlier 8-element version uses thoriated glass (containing thorium oxide for high refractive index), which yellows with age and emits trace radiation — a known characteristic that de-yellows with UV exposure. The later 7-element version is non-radioactive with a cleaner rendering.
50mm focal length, f/1.4 maximum aperture, M42 screw mount, 8-element (early thoriated) or 7-element (later) construction, Super-Multi Coated.
The Super-Takumar 50mm f/1.4 is prized by portrait and creative photographers for its characteristic rendering — smooth bokeh, warm colour tone in the thoriated version, and a slightly swirly out-of-focus quality. The f/1.4 aperture delivers thin depth of field for subject isolation. Both versions are optically excellent for their era. The thoriated version's yellow cast can be corrected in post-processing.
Determine which version is present (8-element thoriated or 7-element) — the radioactive warning on the thoriated version's description is sometimes present. Inspect elements for fungus and haze. Confirm M42 thread engagement is clean and un-cross-threaded. Aperture blades should be oil-free.