Best portrait lens for pentax k?

Here is what the site says about that.

From Pentax K: Pentax K: Pentax's DSLR mount since 1975: decades of lenses still fit the current bodies, which have stabilisation built in. Old manual K lenses fit directly.

From Pentax smc DA 50mm f/1.8: Pentax smc DA 50mm f/1.8: A prime lens by Pentax for APS-C cameras, 50mm f/1.8. The cheapest fast portrait lens for Pentax APS-C bodies.

Quoted from this site's pages.