What's the point?? (AF Modes)

Ok so while trying to understand the different AF modes, i have come to another learning stump, where i can't figure out when to use what..

One Shot AF: still subjects and snapshots..

AI Focus AF: used for unpredictable motion; Focsues as ONE shot, but swithces to AI Servo AF if the subject moves?? And focuses continously on the moving subject...Is this only if the Focus button is held down??

AI Servo AF: used for moving subjects and focuses continuously??

My questions are:
1) not clear when to use what??
2) Why not ALWAYS use AI FOCUS AF if it changes based on the subject, Automatically??
3) when is says, "focuses continously" is that only if i keep the button pressed, or does it lock the focus from when i first set up the shot??

Don't bother with AI Focus, everyone has had trouble with it.
Use AI Servo for moving subjects.
Use one shot if you want to focus and recompose or if using a tripod with a stationary subject. You can use it handheld as well as long as you don't sway a lot.
Focuses only if you keep the button pressed.

What if i have my * button focusing?? Can i focus then release it? or does it still have to be pressed??

izzy35 wrote in post #5995950
What if i have my * button focusing?? Can i focus then release it? or does it still have to be pressed??

Set the camera for * focusing and set it to AI servo and you'll have the best of both worlds. Holding down the * button gives you AI servo, pressing the button to get the initial focus then releasing it is the same as single shot focus and switching between the two is just that easy.

AI servo lets you release the shutter even if focus hasn't been acheived. one-shot won't release the shutter unless its acheived focus.

So you may end up with soft/Oof shots using servo mode. Although you will get a beep/flash to confirm focus, it'll still release.

I'm still trying to get used to this AF-on button for focus, shutter for release. seems like I'll like it, but not sure yet.

mrklaw wrote in post #5998601
AI servo lets you release the shutter even if focus hasn't been acheived. one-shot won't release the shutter unless its acheived focus.

this is only in the auto zones though right?? if I'm shooting in "M", won't the shutter always allow me take the shot also, regardless if focused or AI servo or whatever???

MANUAL EXPOSURE HAS NOTHING TO DO WITH MANUAL FOCUS!!!!

Are you reading the posts people are writing? You can still use Manual focus in Av mode, or AI Servo, or One Shot.....The Auto focus mode doesn't care what exposure mode you are using.

If you are in M and One Shot, it will NOT take the shot until it locks focus (just like One Shot in ANY other mode)

Reagrding AI-Servo focus mode for all around use ...

Does anyone have thoughts on the accuracy / consistency of ai-servo vs one-shot mode?

I started using ai-servo all the time but I am getting the feeling my focus is sometimes a little off - compared to when I was using one-shot mode. I am using af-on for focus, press till I see the focus point light up, release and shot.

It is probably my technique - using shallow DoF, and getting recompose or camera shift errors.

Anyone one have thoughts on this? Is Ai-Servo just as accurate as one-shot, or is it worth while to switch between the two modes?

I don't use that feature. I don't want to have hold anything down when I'm shooting action & the cam stays on AI Servo.

In good/average light with the 20D, which ARE a factor, it works well. Some AIS shots from this weekend of backlit black cars:
POTN at Waterford Hills - Open Wheel Club Racing.