Pictured with the vintage (1975) Pentax K2 are all of the single focal length, auto diaphragm lenses released for this camera in 1975-1976. This was when Pentax switched from the screw mount of the Spotmatics to the bayonet mount known as the K mount. The lenses are tank-like and smooth as silk.
Lenses shown are:
15mm f/3.5, 17mm f/4 fisheye, 18mm f/3.5, 20mm f/4, 24mm f/3.5, 28mm f/3.5, 28mm f/2, 30mm f/2.8, 35mm f/3.5, 35mm f/2, 50mm f/4 macro, 50mm f/1.4, 50mm f/1.2 (on camera), 55mm f/2, 55mm f/1.8, 85mm f/1.8, 100mm f/4 macro, 105mm f/2.8, 120mm f/2.8, 135mm f/3.5, 135mm f/2.5, 150mm f/4, 200mm f/4, 300mm f/4
In 1977, Pentax came out with the M series cameras including the legendary MX. Along with these cameras, M series lenses were released which were generally miniaturized. They were not built as well, nor were they better optically. The original K lenses are hardest to find with some being very rare whereas the M series are easily obtainable. It took 12 years to accumulate the set shown.