Back button Focus?

[GeorgieGirl]

I have back button focus on my 7D...if I press it with my thumb it will focus as opposed to pressing the shutter half way with my index. Its ergonomic. It also can do more than that but that is one way it is used.

Cool- i learned something new today Ma!!! Georgie - Is it just for the ergonomics on the 7D for u? Do u this button another way yourself?

The location of the button is ergonomically placed and this was a clue for momo to locate the button with her thumb as noted above. On the 7D this button is multi-function depending upon the way the camera custom functions are set, if desired.

 

[GeorgieGirl]

"makes focus and recompose much easier"

What is the advantage to this vs selecting a point that is on what you want? Is it because the center on most cameras is cross type? It seems like focusing then recomposing would cause you to lose focus, do you need to keep the movement to a minimum?

It Locks focus. Then you can recompose.

 

[iresq]

Excellent article on why to consider using it:

Canon DLC: Article: Back-Button Auto Focus Explained

 

[Joey_Ricard]

In other words
Standard factory set up = when you depress the shutter button it triggers AF and your meter at same time

When you set up Back button focus, you are making the camera trigger AF only when you hit that particular button.
Metering will be done by depressing the shutter button.

 

[Big Mike]

In other words
Standard factory set up = when you depress the shutter button it triggers AF and your meter at same time

When you set up Back button focus, you are making the camera trigger AF only when you hit that particular button.
Metering will be done by depressing the shutter button.

Exactly.

I've been using back button focus for years and years. My old camera's didn't have a specific button, like many of the new ones did, but on a Canon, you could change the * button to activate the focus, taking it away from the shutter release button.

 

[Joey_Ricard]

In other words
Standard factory set up = when you depress the shutter button it triggers AF and your meter at same time

When you set up Back button focus, you are making the camera trigger AF only when you hit that particular button.
Metering will be done by depressing the shutter button.

Exactly.

I've been using back button focus for years and years. My old camera's didn't have a specific button, like many of the new ones did, but on a Canon, you could change the * button to activate the focus, taking it away from the shutter release button.

Mike, same here and truthfully I don't know how I ever shot without it. I'd feel handicapped so to speak.

 

[ph0enix]

In other words
Standard factory set up = when you depress the shutter button it triggers AF and your meter at same time

When you set up Back button focus, you are making the camera trigger AF only when you hit that particular button.
Metering will be done by depressing the shutter button.

Exactly.

I've been using back button focus for years and years. My old camera's didn't have a specific button, like many of the new ones did, but on a Canon, you could change the * button to activate the focus, taking it away from the shutter release button.

Mike, same here and truthfully I don't know how I ever shot without it. I'd feel handicapped so to speak.

I started using BBF on my D90 about a month or two ago and I can't live without it now.

 

[Big Mike]

Yes, I couldn't live without it either. The wired part, is when I pick up a camera that still uses the shutter button to activate focus...it's totally alien to me.

Heck, when I got my 5DmkII, I had to readjust my brain/hand to use the AF-ON button, rather than the * button.

 

[Geaux]

I've never really thought of trying it b/c the half shutter has worked for me, but I'm seriously thinking of giving it a shot after reading through the links in this thread.

 

[ph0enix]

Yes, I couldn't live without it either. The wired part, is when I pick up a camera that still uses the shutter button to activate focus...it's totally alien to me.

That happened to me last weekend. I was at my friend's house for his kid's birthday party and I picked up his D90 to take a couple photos. For a second I thought his camera was broken when I pressed the AF-L button and it didn't focus but then I remembered that most people's cameras aren't configured with BBF.

 

[Carny]

"makes focus and recompose much easier"

What is the advantage to this vs selecting a point that is on what you want? Is it because the center on most cameras is cross type? It seems like focusing then recomposing would cause you to lose focus, do you need to keep the movement to a minimum?

It Locks focus. Then you can recompose.

I guess focus isn't as sensitive as I've thought it to be. I figured if you moved the camera or subject, even a bit, you would need to refocus. Is this not the case?

 

[Big Mike]

I guess focus isn't as sensitive as I've thought it to be. I figured if you moved the camera or subject, even a bit, you would need to refocus. Is this not the case?

Yes and no.

If you are rather close to your subject, and you don't move the camera around the nodal point, then yes, you may see a focus shift when you focus and recompose...especially with a shallow DOF.

But in many 'real world' cases, the difference in distance (from camera to subject) that you get when you focus and recompose, is so slight, that it's isn't going to be noticeable.

So it's not about focus being sensitive, it's about the physics of the situation you're in.

 

[ph0enix]

I guess focus isn't as sensitive as I've thought it to be. I figured if you moved the camera or subject, even a bit, you would need to refocus. Is this not the case?

In some cases it might be. For example if you're really close to your subject like when shooting macro. The slightest move will throw your focus off. The "lock focus and recompose" technique assumes that the distance between the lens and the subject isn't changing in the process.
Play with your camera and see what you end up with.