So guys i was reading some tips from this section and kept reading back button focus, i'm new to this, so What's the big difference and Advantages??? and How do i do the back button focusing??? Sorry if its a noob question but i had to ask...

Its a custom function which turns one of the 2 buttons where your thumb is into your focus button, instead of pushing down the trigger halfway. Advantages are, that you can put the middle of the frame on the subject and focus, then move the camera around to frame how you want, and the focus wont change unless you bush the back button again.
A word of advice: dont just decide that you are going to try this on a shoot. It takes some getting used to, and I would practice before the shoot. Also remember how to switch it back quickly incase you get over it.
Chris

see these links:

Melissa Jill
or
Chris Humphreys

for a good explanation of back button auto focus and how it helps you get sharper images.

Back Button Focusing has completely changed the way I shoot (for the better). I actually get tons of questions about this from other photographers, and I think most who adapt it have come back to me and told me what a difference it has made for them.

If you have any specific questions feel free to let me know, and I'll do my best to answer them!

I feel like I have more control so, I back focus

I love back button focusing! I would never go back to shutter button focus. I also feel like I have way more control when I back button focus too.

I've been a long time back focuser, But I have to say that lately (the last 9 months) out focus images have been my plague and I can't figure out what the problem is. I'm sick of soft images so if any one has any suggestions on what could be my problem I'd love to hear your thoughts.

Plus, you're already in AI Servo for people coming at you down the aisle (hold the * down instead of release to keep the focus on their face)!

Ok so i read the post and looks like i'm going to try it, i has a 40D but i dont know which custom function is? i think the AF-ON button is that button ? Thanks for helping me

Look at the custom functions in your cameras manual. It will have a list of all CF's and how to change them

i think in the bigger canons, the AF selector button becomes the focus button... and you use the multi-directional mini tiny thing to grab the AF points instead...

cuz that's how it was in the 30D.


'or maybe it was the flash button....




also, i've wanted to know, I can do this with my D70s without using the back-focus function... it's just a two-tier setup. focus using the shutter release, and then lock it with the AE-L button by the rear command wheel (which is placed in a much more ergonomic location behind the shutter release )

HI joseph,
I think you are getting confused with "selecting the AF point" where you press the button next to the * button to select the AF point with the little joystick. Let me tell you I tried that and is not very practical in my opinion.The back button technique is completely different:1)go to custom function. 2)select C.Fn 4. 3)select 1 (for on). 4)select the AF mode: AI servo. 5)now the function of focusing with the shutter button half down is off. In order to focus press the *. 6)when your subject is in focus press the shutter button.
Let me tell you that I tried and the sharpness increase is amazing.Hope it works for you too!

The AF-on button on a 40D is a dedicated back button focus button.. I use the custom function on my 20d's but on my 40 there is no need to set the custom function unless you don't want the shutter button to focus ever.

The af-on button works just like the custom function but I get to keep my * button for exposure lock too.