Cosina's telephoto for Pentax — the 100mm f/3.5 in PKA mount with auto aperture.
The Cosina 100mm f/3.5 for Pentax PKA is a compact telephoto prime from Cosina in Pentax K mount with A-series auto aperture coupling. The PKA designation enables program and shutter-priority auto exposure on Pentax bodies. At 100mm f/3.5, it provides basic telephoto. Cosina produced affordable lenses — also manufacturing for Voigtlander.
Basic Cosina optical quality. The 100mm provides moderate telephoto. The f/3.5 is slow. The PKA auto aperture coupling adds practical convenience for auto-exposure on Pentax DSLRs. Build quality is basic. Better 100mm options exist in K mount from Pentax and premium third parties.
Pentax K mount with A-series coupling — enables auto-exposure on Pentax DSLRs. Manual focus. Benefits from Pentax body SR. The PKA designation is the practical advantage — auto-exposure on digital Pentax bodies. Filter thread varies. Build quality basic Cosina.
Very cheap. The PKA auto aperture is the practical advantage. Benefits from body SR. Not recommended when better K-mount 100mm options exist. Only at near-zero prices. The auto aperture coupling is the sole distinguishing feature.