Pentax's Fish-eye-Takumar 17mm f/4 — an M42 full-frame fisheye prime with strong curved perspective.
The Fish-eye-Takumar 17mm f/4 is a full-frame fisheye prime made by Asahi Optical for the M42 screw mount in the late 1960s. It was the fisheye offering of the Pentax M42 system, giving the strong barrel-curved perspective characteristic of fisheye optics across the full-frame image.
This is a manual-focus M42 screw-mount lens with a 17mm focal length and a maximum aperture of f/4, designed as a fisheye rather than a rectilinear wide-angle. Focus and aperture are set on the barrel, and fisheyes of this type commonly incorporate built-in filters. Detailed optical figures are not asserted here beyond the verified focal length and aperture.
As a fisheye the 17mm produces a wide, curved field of view that bends straight lines away from the centre, an effect used creatively for landscapes, interiors and dramatic perspectives. The very deep depth of field means focus is rarely critical. It is a specialist lens chosen for its distinctive look rather than conventional wide-angle work.
Used copies are collectible and priced above ordinary Takumars owing to the specialist fisheye design. Inspect the curved front element carefully for scratches, haze and fungus, verify the built-in filter mechanism and aperture work, and check the mount and focus. An M42 adapter allows fisheye use on mirrorless, where the effect is easily previewed.