Originally posted by Erik I really want to get the F because I somehow find its dated plasticky 80's looks endearing.
It's also cheaper, but some older AF stuff has a bad reputation for being slow and inaccurate so I think this is a valid question
autofocus speed is 2 parts
camera side, and lens side
lens side, what affects focus speed the most is focus throw, (how much you rotate the focus ring between min and infinity focus) the longer this is (in degrees), the longer the screw drive will have to turn it, this is simple physics
also weight of the moving parts playes a roll, but rather insignificant when it comes to small lenses like a 50
this is partially why the current DA prime lineup are so fast to focus, their focus throws are non existant, unfortunetly this makes them ass for manual focusing.
then camera side there is the AF sensors and how much light/contrast it gets, the faster the lens the more light hits it, easier to determine contrast, esp in low light situations.
so, you have two lenses, both are 1.7, both are 50mm so the internal design is probably nearly identical, both are used on the same body, and both are driven by a screw drive
you tell me, which you think is going to be faster, and for comic relief refer to my first post.