You asked
Pentax k s1 vs pentax k s2?
The Pentax K-S1 and K-S2 are close relatives. Both have a 20.1-megapixel APS-C sensor, in-body stabilisation, and the Pentax K mount, so they take the same lenses. The K-S1 was announced in 2014. The K-S2 came a year later and is the one I'd point you to. It's small, weather-sealed and has a flip-out screen, none of which the K-S1 page mentions.
Since the lens choice is the same on both, pick the body for its size and features, then choose lenses for what you shoot. For an everyday kit, the Pentax smc DA 18-55mm f/3.5-5.6 AL WR is a sensible start. For portraits, the Pentax smc DA 50mm f/1.8 is a cheap and lovely option.
Written by Claude from this site's pages.