I am looking for a auto focus 50mm lens for my Pentax .I was looking at Sigma 50mm f1.4 EX DG HSM or Pentax smc FA 50mm 1:1.4 , does any one have these or experience with either ? Thoughts on how they find them .I currently have two Pentax 50mm 1.7 manual lenses which I love using but an auto focus prime would be a good addition .Maybe I should just save up for a Pentax smc DA* 55mm f/1.4 SDM ,going by the reviews its the ducks guts off 50 odd mm for the Pentax .