Canon's FD circular fisheye — the 7.5mm f/5.6 S.S.C. casting a round 180-degree image.
The Canon Fish-Eye FD 7.5mm f/5.6 S.S.C. was a circular fisheye lens introduced in 1973 for Canon's FD manual-focus system, part of the first generation of chrome-nose FD optics carrying Canon's Super Spectra Coating. It produced a full circular 180-degree image within the 35mm frame and sat at the extreme wide end of the FD line alongside the rectilinear ultra-wides of the period.
This is a manual-focus lens for the Canon FD mount with a fixed 7.5mm focal length and a maximum aperture of f/5.6. As a circular fisheye it renders a round 180-degree field of view rather than filling the frame, and it uses built-in filters selected via a turret rather than a front filter thread. Focusing and aperture are set manually on the lens barrel in the usual FD fashion.
A circular fisheye of this type produces the characteristic round image with strong barrel distortion, bending straight lines toward the edges of the circle. It suits creative wide perspectives, architectural interiors, skyscapes and any subject where the extreme curved field is used deliberately rather than corrected, and depth of field is very deep at all apertures given the short focal length.
On the used market this is a specialist and relatively scarce FD lens, so condition and completeness matter. Check the built-in filter turret operates cleanly, inspect the front element for scratches given its exposed bulging shape, and look for haze, fungus or oily aperture blades common to lenses of this age. Adapting to mirrorless is possible but the FD-to-mirrorless adapters must not use corrective optics for a fisheye of this kind.