AF-ON Button

Pete Gl

Pete Gl

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Errr Pete?
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Having recently upgraded to the 50D from a 400D I find myself with a new button. Could anybody help me gain a fuller understanding of what this button does?

Before anybody says RTFM, I have and the manuals precious little help.

Pete
 
It really does what is says - it activates AF!

So you use this button to start autofocus, and the shutter release button is only use to for exposure and actually taking the image.

It allows more fine grained control, and de-couples autofocus and exposure / image taking from being all on the same button.

I always shoot this was on my Nikon bodies.
 
Yup as puddleduck says there is a custom function in the menu which lets you use this as the auto focus button...personally I dont use it as I am too use to half pressing the shutter release. The only time I do use it is in live view, where half pressing shutter doesnt auto focus and you have to use the AF-ON button (well at least you do on the 40D)
 
it does the job that the * button did on a custom function on previous models. i.e - move the focus to the */AF-ON (usually with AI SERVO turned on) and keep exposure lock on the shutter release.
 
I switched to using the AF-ON button about a year ago as it allows me to use all three AF functions (AF-S, AF-C, Manual) through this method without having to change other settings.

For AF-C just keep your finger on the AF-ON button and you will be able to track moving subjects.

For the AF-S function use the AF-ON button to focus on your subject and then release, you will be able to re-compose if you wish.

Manual is exactly as it says, don't press the AF-ON button and focus manually. In all of the above half pressing the shutter release will not make any difference. One thing to note, if you are using a Nikon camera fitted with a VR equipped lens the VR will not kick in until you half press the shutter.

Using AF in this way took a little bit of getting used to but I wouldn't go back to the old method.
 
Hacker,

I appreciate you replying, but, I think you're talking in Nikon. AF-C and AF-S don't mean anything in Canonese.

Pete
 
Think AI-Servo and One Shot (continuous and single, I'm guessing).
 
I presume it will be similar on a McCanon but I don't know what they are called, AF-C (AF continuous, sometimes called continuous servo) is good use when photographing moving objects and AF-S (AF single, sometimes called single area AF) mode, is good for photographing subjects that don't move, such as flowers or portraits etc. It locks the focus on the non moving object that you want to photograph. You can then recompose the shot and take the photograph.

*Edit* I've just done a quick Google and Canon's Single AF equates to Nikon's AF-A and AI Servo AF = AF-C. I think. :D
 
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