AF-On Button

Would like to know about the function of AF-On button . How does it differ from half pressed shutter button and in what situations it should be used ?

Thanks
Jai.

Situation: when you want to meter and focus separately.

To follow on from Lowrider, use of the AF-On button is commonly-known known as back button focusing. Useful in all situations and especially in sports where you track your subject and shoot with the shutter button thus metering at the right moment.

J R Mohan wrote in post #15149522
Would like to know about the function of AF-On button . How does it differ from half pressed shutter button and in what situations it should be used ?

As mentioned above it puts focus and metering on separate buttons. Not only useful for shooting sports but also for shots where you may want to meter off one area (and keep that meter settings) but then recompose and focus on another.

Dan Marchant wrote in post #15151272
As mentioned above it puts focus and metering on separate buttons. Not only useful for shooting sports but also for shots where you may want to meter off one area (and keep that meter settings) but then recompose and focus on another.

Actually isn't what you said backwards? I thought pressing the button focuses, and then you can recompose and meter when you shoot.

Dan Marchant wrote in post #15151272
As mentioned above it puts focus and metering on separate buttons. Not only useful for shooting sports but also for shots where you may want to meter off one area (and keep that meter settings) but then recompose and focus on another.

Moose408 wrote in post #15151323
Actually isn't what you said backwards? I thought pressing the button focuses, and then you can recompose and meter when you shoot.

Dan's comment is for the default setting (AF-On for exposure lock, shutter for focus and meter - unless exposure locked) (at least, it's the default on my 600D), but the usual change to back button focussing swaps the functions (focus on the AF-On button, meter on the shutter button). There are other combinations that you can use.

That being said, I guess that you could meter by half-pressing the shutter, then recompose and focus using the back button. Sounds clunky, but probably because it is not normally done that way.