I'm thinking of acquiring a fast prime lens in the range 30mm-35mm (45-50mm 35 equiv.) for mainly portraits (indoor babies & children). I narrowed down to 3 options: Pentax 35mm f2.4, 35mm f2.8, & Sigma 30mm f1.4. I think only the Sigma qualifies as a fast prime. Would like to solicit some feedback from fellow Pentaxians who have used the Sigma 30mm f1.4. Market price is about $700+. Are there other alternatives that I've missed? Thanks.