For the life of me I cannot find the custom function to disable this feature. I dont want the shutter button to focus if depressed halfway. Pardon my ignorance, but why or when would you want to not focus on half press?
It's not a ignorant question, a lot of people will wonder why would you want to do this....until you've tried it and realize what an awesome function it is.
Example: multiple focus points active is going to give the camera the power to select a focus point. Guess what? When you depress the shutter button it's going to AF and possibly grab a point you don't want. Worse, if you're using flash you just told it "hey, light up this point way over here".
Example: AI Servo. No need to 1/2 depress the shutter to track. Just push the AF start button and track away...fire when you want to...release the AF start and you can keep shooting without the camera attempting to do an AF.
Example: AF then re-compose. Push the AF start to lock the focus...recompose the shot...press the shutter.
Example: Lock focus and keep shooting. Push the AF start to lock focus. Then shoot all you want. Camera will not attempt to refocus.
You'll never have to do a 1/2 press balancing act again.