Pentax SMC Pentax 67 300mm f/4

Telephoto lens for the Pentax 67 system. In 35mm-equivalent terms, 300mm on 6×7 corresponds to roughly 150mm full-frame. The 300mm position is the practical limit before the body's mirror clearance and inner-bayonet mount become problematic for handheld use — 400mm and longer lenses use the larger outer bayonet to handle the additional weight and torque.

Used for distant landscape, sports, wildlife, and any scene requiring strong subject isolation against compressed backgrounds. The lens's f/4 maximum aperture is fast for the focal length on medium format (most LF telephotos at 300mm sit at f/9 or smaller).

A later SMC Pentax 67 300mm f/4 ED variant added extra-low-dispersion (ED) glass for improved chromatic-aberration correction at long focal lengths — sought after for color landscape and wildlife work where LoCA is most visible. Both versions mount on the inner bayonet; 67mm filter thread on most variants.

Mirror lock-up is essentially mandatory on this lens for any tripod work below 1/500s — the long focal length amplifies vibration much more than the 105mm normal does.