Pentax SMC Pentax 67 600mm f/4 ED [IF]

Extreme-telephoto refractive design with extra-low-dispersion (ED) glass and internal focusing (IF). In 35mm-equivalent terms, 600mm on 6×7 corresponds to roughly 300mm full-frame — extreme long-tele territory shared with the 1000mm f/8 Reflex but with a full-aperture refractive design rather than catadioptric.

f/4 maximum aperture at 600mm focal length on medium format makes this one of the highest-light-gathering super-telephotos ever produced for the system — very large front element, very heavy (multiple kilograms), and very expensive at retail. ED glass is critical at this focal length: without it, longitudinal chromatic aberration would dominate the image character at any aperture wider than f/11.

Mounts on the outer bayonet. Tripod use is mandatory; even a heavy tripod requires careful technique to manage the long lever arm. Used for distant wildlife, sports at long range, and astrophotography where the f/4 aperture provides a meaningful exposure advantage over the 1000mm f/8 Reflex. Notably scarce on the used market — production runs were small and the lens commands premium prices when it does appear.