Back-button focus

[RobertTheFat]

Last week I had an "optional" photo shoot at a civic event in our town, so I used the opportunity to experiment with back-button focus. I'd never used it, but a friend who's a sports photographer had told me how much he liked it (each of us has a 5D Mark III), so I set up the buttons and gave it a try.

Overall, BBF worked pretty much as I had expected; and while I didn't really notice any significant benefit for the kind of photography I do (landscapes, architecture, and events, mostly), I could see where it could be useful in certain circumstances. But one thing bothered me: When I edited the pictures in DPP 4, there were no red squares to indicate which AF points had achieved focus. (I was using the mode that divides the AF points into groups; and if any point in the selected group achieves focus, that's what's used.) I guess I can see the logic to it. With BBF it's assumed that that there's a high probability that you'll recompose, in which case a red square wouldn't necessarily mean that what's behind it is what was in focus. But I found it a bit annoying anyway. After all, you can recompose with shutter-button focus, and that doesn't make the red squares go dark. Is that really how it works, or am I missing something?

[Waddizzle]

You need to be pressing the BBF when you activate the shutter.  It is sort of lik maintaining a half press on the shutter to maintain a focus lock in One Shot Mode.  

The focus point is still reported in EXIF, because Lightroom has an add-in that can distinguish between when you're holding the button, and when you're not, although the info isn't spelled out in that fashion.  It reports multiple states of focus lock.  

One state indicates a focus lock, and AF point was the one you selected.  Another state says focus locked, but you did not have the point selected, which is the case when you have released the BBF button when you activate the shutter.

[ebiggs1]

Bob from Bean Town,

"I didn't really notice any significant benefit..."

Neither did or do I.  Maybe it's because we are too old school as I don't use a lot of the newer functions available.  I am currently content using with a camera that doesn't have all of them!

[Ray-uk]

They don't come much more old school than me, 70yrs old and been playing with cameras since I was 18. One day I might just get that perfect shot I keep trying for.

I wouldn't be without back button focus, it's the perfect way to separate focus lock from exposure lock.

I must admit there are a lot of other new functions I don't care for though.

[ebiggs1]

I still shoot my F1n and I am just fine with it.

[TTMartin]

Instead of BBF, I reprogram the AF ON button to be AF OFF. 

That gives me the ability to press the 'back button' when using AIServo and I need to temporarily suspend focus.

I find that the times I need to suspend focus are a lot less than the times I want continuous focus. So for me BBF would just mean having to press two buttons (back button and shutter button) most of the time. Where having the AF OFF button available just means I occasionally have to press two buttons (back button and shutter button).

To my knowledge all cameras that have an AF ON button allow you to reprogram it to AF OFF. I know the 40D/50D/6D/7D/7D Mk II for sure do.

[Ray-uk]

No, cannot see the point of that. If you use back button for focus then in AI Servo just take your thumb off it and it stops, assuming of course you have also removed the focus operation from the shutter button.

[TTMartin]

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@Ray-uk wrote:

No, cannot see the point of that. If you use back button for focus then in AI Servo just take your thumb off it and it stops, assuming of course you have also removed the focus operation from the shutter button.

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If you use BBF you have to keep pressing the back button for continuous focus.

So if you are shooting a sequence of action shots (moving subject) you have to press both the shutter and the back button at the same time.

As a sports and wildlife photographer I want continuous focus most of the time. I only want to stop focus on rare occasions. So I'm going to have to press two buttons most of the time, so on rare occasions I can remove my thumb and stop focus? Seems silly to me. Why would you want to have to press two buttons most of the time?

[ebiggs1]

"No, cannot see the point of that."

......and here comes a MTF chart to prove it. 

[diverhank]

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@RobertTheFat wrote:

When I edited the pictures in DPP 4, there were no red squares to indicate which AF points had achieved focus. (I was using the mode that divides the AF points into groups; and if any point in the selected group achieves focus, that's what's used.) 

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This is interesting...I've been using BBF for years now.  I had never paid any attention to the red squares and how they work but I can tell you recently I was doing a presentation on photography and needed a couple of pictures showing the red square focus and I used DPP and got the squares.  

Granted I only grabbed a couple of pictures to do that and got the squares.  I don't doubt depending on the settings, sometimes you don't get the squares.  So at least for me, the squares are still there, using BBF.  For these pictures, I did not recompose, if that's making any difference.