Can someone explain the AF modes in my rebel?

[Stilltime]

I've read the manual, as well as some online photo blogs. I've also poked around here, but I'm just not getting it. I don't know what mode to use for what.

 

[Big Mike]

One shot mode will focus and then lock the focus, I think the camera waits until it hits focus before it fires.
AI focus lets you fire the shot while you are still focusing.
AI Servo constantly refocuses while active and it can sort of track a moving subject across the frame.

I think that's how it works...and those are the modes on my Canon...I'm not sure about yours.

 

[tsaraleksi]

Don't bother with AI focus, just use the One shot and AI Servo-- it's just not really as good as using one or the other.

 

[majorpayne66]

Yep, Big Mikes got it right.
Simlified:
One shot=Shooting a still object
AI focus= Shooting a still object that may move
AI servo= Shooting a moving object

 

[dtornabene1]

AI focus in a wedding photographer's dream. It is not that it allows you to shoot while focusing, it predicts where the focus will be between the time you depress the shutter button and the shot is taken.

One shot lets you focus, hold the focus and recompose.

AI Servo is for sports photography because AI Focus does have its limitations.

Don't take my word for it, try it. Have someone stand 25ft away from you and let them walk at you in a fast pace while using AI Focus. You will find the focus is spot on every time. If you use One Shot, the person will be out of focus by the time the shot is taken. If you use AI Servo, you run the risk of the camera focusing on a different point and using less "thinking".

With the latest chips, Dig!c III and faster, you can have them run at you not just fast walk or jog. Try it, it's really cool.

-Nick

 

[Derek Zoolander]

that's awesome. good question!

 

[Kendo]

So lets say that you wanted to take a pic of a horse running by on a trail. What focus would you use as it is running by, or do you have someone stand about where it would be and lock the focus? Or just pan as the horse runs by?

 

[Big Mike]

I would use AI Servo and pan as the horse ran by...but pre-focusing isn't a bad option either.

 

[Stilltime]

If you're going to prefocus, which option would you choose? AI servo?

 

[dtornabene1]

If the horse is running at me, AI Focus. If panning, AI Servo

-Nick