I have the Sigma 1.4 and an old Pentax A 1.7 50mm - both purchased second hand off ebay. The Sigma has procuced some lovely shots and of course will auto focus. I actually prefer the IQ I get out of the Pentax - but it is manual focus and you have to use it on manual - so not so quick for a newbie to take random shots of children. Unless I am shooting landscape one or the other is my default lens.