Back Button AF?

Road Dog wrote in post #17809755
I've never used it, and probably never will...

'Never' simply means you have not found yourself in a situation like this...
Try to shoot a picture of a distant animal wandering toward you at a zoo, thru the bars/check of a nearby fence, and you will instantly see the advantage of

• a single focus zone being activated, along with
  
• the use of Back Button Focus
  

jay125 wrote in post #17807680
T-shirts make me appear closer than I actually am.

There's a great t-shirt slogan right there.

Wilt wrote in post #17811689
'Never' simply means you have not found yourself in a situation like this...
Try to shoot a picture of a distant animal wandering toward you at a zoo, thru the bars/check of a nearby fence, and you will instantly see the advantage of

• a single focus zone being activated, along with
  
• the use of Back Button Focus
  

...to assure yourself that you are focused on the moving animal and not the bars/cyclone fence which is close to your position, while still maintaining focus on your target rather than refocusing unpredictably when you press the shutter release.

I don't get that.

How does using BBF make shooting through a fence easier?

Surely this is an example of not using BBF? Animal is walking towards you so you need to keep focusing pressed, maybe changing focus points with your thumb. If you remove your thumb to change the focus point aren´t you more likely to start bouncing around with the fence or bars?

john crossley wrote in post #17812411
I don't get that.

How does using BBF make shooting through a fence easier?

If your AF is coupled to your shutter the AF might lock onto the fence when you don't want it to. With BBF you can pick and choose when to focus. You focus through an opening in the fence and then you can recompose and shoot without having to worry about the camera trying to focus and possibly lock onto the fence with every shot. It is the same principal when shooting a bird that is inside heavy cover. Once you lock focus you don't want to have to worry about the camera locking onto something else every time you want to activate the shutter.

Philihase wrote in post #17812560
Surely this is an example of not using BBF? Animal is walking towards you so you need to keep focusing pressed, maybe changing focus points with your thumb. If you remove your thumb to change the focus point aren´t you more likely to start bouncing around with the fence or bars?

Not really. With BBF you don't need to keep your thumb on the BB constantly focusing. This happens when shooting birds that may be difficult to follow. Once you lock focus, even with a fairly shallow DOF you'll be able to get a number of sharp images before you need to refocus. You stop using focus and follow the birds using your shutter for capture and the advantage is that you get to pick and choose when to refocus. If you couple focus with the shutter your AF will try to re-lock with every shot. Advantage BBF. The same applies with your scenario. One would assume the reason you want to change focus points is because the one you're using isn't working for you. Well with BBF the problem is solved. You just need to focus and recompose without having to worry about changing focus points. Your camera won't try to refocus unless you want it to. If you do need to make some kind of major adjustment things are likely bad enough that you won't be shooting anyway. Lastly, realistically speaking, people use BBF all the time and change focus points with the joystick without introducing unnecessary movement into the shot. It is very, very simple.

Wilt wrote in post #17811689
'Never' simply means you have not found yourself in a situation like this...
Try to shoot a picture of a distant animal wandering toward you at a zoo, thru the bars/check of a nearby fence, and you will instantly see the advantage of

• a single focus zone being activated, along with
  
• the use of Back Button Focus
  

...to assure yourself that you are focused on the moving animal and not the bars/cyclone fence which is close to your position, while still maintaining focus on your target rather than refocusing unpredictably when you press the shutter release.

nqjudo wrote in post #17812596
If your AF is coupled to your shutter the AF might lock onto the fence when you don't want it to. With BBF you can pick and choose when to focus. You focus through an opening in the fence and then you can recompose and shoot without having to worry about the camera trying to focus and possibly lock onto the fence with every shot. It is the same principal when shooting a bird that is inside heavy cover. Once you lock focus you don't want to have to worry about the camera locking onto something else every time you want to activate the shutter.

But WILT said the animal was MOVING towards the photographer. Having focus on the shutter button or using BBF makes no difference whatsoever.

You cannot focus and recompose when the animal is moving towards you, can you?

john crossley wrote in post #17812680
But WILT said the animal was MOVING towards the photographer. Having focus on the shutter button or using BBF makes no difference whatsoever.

You cannot focus and recompose when the animal is moving towards you, can you?

Yes. It makes a HUGE difference and yes you can focus and recompose with the animal moving toward you. Even with the animal moving you still have DOF on your side. With BBF you need to focus once, recompose and you can take unlimited shots using that same focus. With a slow moving animal you can get a fair number of shots off before that animal moves out of focus or better yet an animal that stops moving momentarily as they often do. With the focus on the shutter the camera will try to refocus with every shot. If there are possible obstructions for the AF in that scenario you don't want the camera in charge of focus. Period. As for focusing and recomposing it is the same principal. With the focus on the BB you focus and recompose till you really need to refocus again. With focus on the shutter button you don't have a choice. The camera will try to AF with every shot. You'd have focus and recompose with every shot. BBF wins every time in these scenarios.

Look, if you look at the poll, 84% of respondents use BBF. It isn't by accident. These arguments about BBF with all of these theoretical situations thrown in remind me of children in a playground arguing about some kind of never-ending fight between superheroes where there is an endless stream of theoretical attacks that are survived with the use of some defence and super-powered counter attack. You can go on forever. If you can believe it, years ago similar arguments used to occur about JPEG vs RAW. It just took people a while to catch on. I bet if we started another poll to see how many people really understood the benefits of BBF or even liked using it when they first tried it the numbers would be pretty low. There are very, very few scenarios where BBF is not beneficial. The biggest one is if you ask people to take a picture of you often with your camera. Now THAT should tell you something. Give it a try. Once you become adept with it you'll never go back.

john crossley wrote in post #17812680
But WILT said the animal was MOVING towards the photographer. Having focus on the shutter button or using BBF makes no difference whatsoever.

You cannot focus and recompose when the animal is moving towards you, can you?

nqjudo already addressed your concern: "Once you lock focus you don't want to have to worry about the camera locking onto something else every time you want to activate the shutter." If you need to refocus because DOF no longer will keep the moving animal in focus, you press BBF button exactly when the AF point is seeing your target in the spaces of the fence, and the sensor locks onto your target...and then by you not pushing BBF again (until your target as moved even closer to you and again exceeded DOF zone) you can fire as many shots as you want -- and NEVER worry that pressing the shutter button will cause the AF zone to lock onto the fence that is 3' from your lens.

In the days of MANUAL FOCUS, the photographer had total control of focusing (which was slow)...AF makes it convenient and speedy (especially if AF tracking is being used) but the total control is taken away from the photographer, UNTIL you use BBF rather than leaving focus on the shutter button. Take Back Control!!!

One other point, not all focus points are equal in precision. But no matter which camera you have the center point is of the highest precision type. Like using the central spot in the film days , focus then compose. Funny I think I had fewer mis focused shots back then, But back then my eyes were much better and film more forgiving.

nqjudo wrote in post #17812714
Yes. It makes a HUGE difference and yes you can focus and recompose with the animal moving toward you. Even with the animal moving you still have DOF on your side. With BBF you need to focus once, recompose and you can take unlimited shots using that same focus. With a slow moving animal you can get a fair number of shots off before that animal moves out of focus or better yet an animal that stops moving momentarily as they often do. With the focus on the shutter the camera will try to refocus with every shot. If there are possible obstructions for the AF in that scenario you don't want the camera in charge of focus. Period. As for focusing and recomposing it is the same principal. With the focus on the BB you focus and recompose till you really need to refocus again. With focus on the shutter button you don't have a choice. The camera will try to AF with every shot. You'd have focus and recompose with every shot. BBF wins every time in these scenarios.

Look, if you look at the poll, 84% of respondents use BBF. It isn't by accident. These arguments about BBF with all of these theoretical situations thrown in remind me of children in a playground arguing about some kind of never-ending fight between superheroes where there is an endless stream of theoretical attacks that are survived with the use of some defence and super-powered counter attack. You can go on forever. If you can believe it, years ago similar arguments used to occur about JPEG vs RAW. It just took people a while to catch on. I bet if we started another poll to see how many people really understood the benefits of BBF or even liked using it when they first tried it the numbers would be pretty low. There are very, very few scenarios where BBF is not beneficial. The biggest one is if you ask people to take a picture of you often with your camera. Now THAT should tell you something. Give it a try. Once you become adept with it you'll never go back.

Wilt wrote in post #17812764
nqjudo already addressed your concern: "Once you lock focus you don't want to have to worry about the camera locking onto something else every time you want to activate the shutter." If you need to refocus because DOF no longer will keep the moving animal in focus, you press BBF button exactly when the AF point is seeing your target in the spaces of the fence, and the sensor locks onto your target...and then by you not pushing BBF again (until your target as moved even closer to you and again exceeded DOF zone) you can fire as many shots as you want -- and NEVER worry that pressing the shutter button will cause the AF zone to lock onto the fence that is 3' from your lens.

In the days of MANUAL FOCUS, the photographer had total control of focusing (which was slow)...AF makes it convenient and speedy (especially if AF tracking is being used) but the total control is taken away from the photographer, UNTIL you use BBF rather than leaving focus on the shutter button. Take Back Control!!!

Well I have to disagree with both of you.
In the scenario provided by Wilt, of an animal moving behind a fence, I personally would use AI Servo as the focusing mode, and if the camera/lens combination supported it, Spot-Focusing. Also I would be shooting at as large an aperture as I could which would help to diminish the effect of the fence on the image. It still makes no difference as to whether the focusing is activated by the shutter button or by BBF.

john crossley wrote in post #17813027
Well I have to disagree with both of you.
In the scenario provided by Wilt, of an animal moving behind a fence, I personally would use AI Servo as the focusing mode, and if the camera/lens combination supported it, Spot-Focusing. Also I would be shooting at as large an aperture as I could which would help to diminish the effect of the fence on the image. It still makes no difference as to whether the focusing is activated by the shutter button or by BBF.

When I wrote that comment I only had AI servo in mind. There's no better way to go with BBF. It is one shot and AI servo in one. If you do not separate focus and shutter when using AI servo you are cutting yourself off at the knee by limiting your focus option to AI servo when it could potentially work as AI servo and one shot. For this alone - advantage BBF. It absolutely does make a difference where your focus is. With the focus on the shutter button in AI servo (or otherwise) your camera will try to focus when you press the shutter button. With the focus on the BB you get to choose when the camera focuses and when the shutter is activated separately. This is extremely valuable when trying to focus in situations where there are obstructions. Your attempt to diminish the effect of the fence by using a large aperture means nothing if your AF grabs the fence or another unwanted obstruction when you try to release the shutter.

When I changed to back button focus the trouble I had was that I kept pressing the AEL button by mistake as it is close to the AF button...I now have both the AF button and the AEL button set to focus so it doesn't matter if I press the wrong one

don1163 wrote in post #17813074
When I changed to back button focus the trouble I had was that I kept pressing the AEL button by mistake as it is close to the AF button...I now have both the AF button and the AEL button set to focus so it doesn't matter if I press the wrong one

I still do that too, but I usually see it in the viewfinder and hit AEL again without having to remove my eye from it.

john crossley wrote in post #17813027
In the scenario provided by Wilt, of an animal moving behind a fence, I personally would use AI Servo as the focusing mode, and if the camera/lens combination supported it, Spot-Focusing.

Well, yes, of course you, or anyone, would be using AI Servo in that scenario. . That is what back button focus is all about, using BBF with AI Servo. . I have never heard of anyone using BBF with one-shot mode (although I'm sure someone has done it at some point in time). . It's pretty much assumed that when someone mentions BBF that they are doing it in conjunction with AI Servo.