Pentax's SMC Takumar 15mm f/3.5 — a scarce multi-coated M42 ultra-wide rectilinear prime.
The SMC Takumar 15mm f/3.5 is an ultra-wide-angle prime made by Asahi Optical for the M42 screw mount, dating from the early 1970s in the final SMC-branded phase of the Takumar line. It was among the widest rectilinear lenses Asahi offered in screw mount and represented the mature multi-coated version of their 15mm design.
This is a manual-focus M42 screw-mount lens with a 15mm focal length and a maximum aperture of f/3.5. Focus and the automatic diaphragm are set on the barrel. As a complex ultra-wide of its era it is a large optic that typically used built-in filters rather than a conventional front thread. Element counts are not asserted here beyond the verified focal length and aperture.
At 15mm it produces sweeping rectilinear ultra-wide perspectives for architecture, interiors and dramatic landscapes without the curvature of a fisheye. The SMC coating gives improved flare resistance and contrast. It is a specialist optic prized for the breadth of its angle of view and its solid rendering stopped down.
This is one of the scarcer and pricier Takumars, sought by collectors and ultra-wide users alike. Inspect the large front element for scratches, haze and fungus, verify the automatic diaphragm and built-in filter mechanism work, and check focus smoothness and mount integrity given the lens's bulk. An M42 adapter allows ultra-wide use on mirrorless.