85mm f1.8 focusing hunting

there's been a lot of posts re: the 85mm recently :P

anyways, i know this bad boy lens focuses fast but i have noticed that when focusing on subjects front and back it will constantly flip between the two hunting back and forth. Is it meant to do this?

I thought holding down the shutter half way is meant to lock it?

Yella Fella wrote in post #2114682
I thought holding down the shutter half way is meant to lock it?

Not if you are in AI-Servo mode -- it never locks.

haha that could be it... need to check but im sure im in normal mode