Pentax's M-series 50mm f/2 — the slower compact standard prime alongside the f/1.7.
The Pentax SMC Pentax-M 50mm f/2 is the slower standard prime in Pentax's compact M-series — alongside the more popular f/1.7 (ID 1763). The f/2 version is slightly more compact. SMC coating.
Optically good — sharp from f/4 with the SMC coating providing good contrast. The f/2 is one stop slower than the f/1.7 version — less popular but even more compact. Same M-series miniaturisation philosophy.
Pentax K mount with 49mm filter thread. Very compact M-series design. Manual focus and aperture. SMC coating. Metal construction. Compatible with modern Pentax DSLRs and adapts to mirrorless.
Available used for almost nothing — less popular than the f/1.7 version. The f/1.7 is generally preferred. The f/2 offers marginal compactness benefit. For vintage lens collectors or budget K-mount normal prime.