How do you lock focus and exposure during a shoot?

[Fastfwd13]

I have been doing my first tries with an S5 that does not have any form of focus lock as far as I know. Having not so good light I was using a tripod and was trying to press the shutter halfway to get the focus on the eyes, then recompose the image and finally lock the tripod before I press fully and then wait 2 seconds for the timer before the shot is taken.

I already know that I will be able to lock exposure separately on the 50D or I could use M mode instead of Av like I do now. I suppose I can also switch the lens from AF to MF but is there a simpler way?

There is a button that will activate focus without depressing the shutter but will it then refocus when I press the shutter?

Also if I focus once and my model does not move much will focus stay OK or is it better to refocus for every shot? How big a movement will make me lose perfect focus on the eyes?

[aroundlsu]

On the 1d you can assign two buttons by your thumb to alternate and focus between two favorite focus points. If you want to manual focus there is no need to flip a switch as the auto doesn't kick in until you press those buttons.

That's how I focus. I have yet to find another phoographer that does it that way, but it really works for me.