This lens has a focal length of 31mm, which is approximately midway between the conventional 28mm and 35mm wide-angle lenses. This unique focal length draws out the best visual effect of each conventional focal length, depending on the way an image is framed.
The lens features glass-molded, aspherical elements and high-refraction, low-dispersion glass elements to define the main product concept — a lens that delivers sharp, fine-detailed images of small subjects, such as tips of the branches of a bare, leafless in winter.
Thanks to its unconventional focal length, this lens accepts 58mm-diameter filters — a rather large filter size for a compact, wide-angle lens with an open aperture of F1.8.
The lens also features a flower-shaped lens hood, which makes it easier to mount and remove a PL (polarizing) filter. This hood is designed to perfectly integrate with the lens.
While retaining the outstanding optical performance of the smc PENTAX-FA 31mmF1.8AL Limited, PENTAX has upgraded the imaging power by adding HD coating and the round-shaped diaphragm, in the hope that this lens will remain a favorite of PENTAX camera users for many years to come, in both digital and film photography.