Sorry, wrong info - it's actually a Pentax-M 1:1.7 50mm lens...(it's my telephoto that goes down to 2.8) shows how often I look at the figures, but I know some of you good people like to know these details, so I thought I'd better get it right! It's a great lens actually, i've taken some of my better shots with this...and it's nice and fast in low light! :-)>