Pentax, lens, limited, hd,

Pentax HD Pentax DA 15mm f/4 ED AL Limited Lens

Recently I have decided to buy a wide-angle lens in order to improve my landscape pictures, some architecture and street pictures. Forasmuch I own Pentax cameras with K bayonets, first, I was trying to make decisions between zoom lens Sigma 6-18 and Pentax12-24.