6d mk2 back button focussing

[Georgezx9]

Hi all, love the camera, however can anyone explain back button focussing.

the camera af-on button works as a default back button focus,

the manual states 

From the manual On page 131 3rd bullet it states, that After achieving focus with on shot Af the image can be recomposed, and the focus is locked, therefore is the difference using servo ai. 

I am still confused

gy

[Georgezx9]

Thanks for very comprehensive and informative answer, I am more than happy now.

what caused me to look at BBF was, my wife does a lot of dog agility, and when I tried to get the dogs in focus over jumps/tunnels at speed, most shots were out of focus.

i played with this and struggled, in the end because I could never get crisp focus of the dog, as often it focused on the jump I changed my approach to give greater depth of field and hopefully catch more in focus dog, this often meant high ISO.

a friend suggested BBF as a method of keeping focus on the moving subject.

lets tryit and experiment.

[jrhoffman75]

For the situation you describe my recommendation would be to use AI Servo (not AI Focus) and auto AF point selection.

See pages 132 and 140-141 in your camera manual.

See page 484 for initail focus point selection options - select a single point..

AI Servo will acquire focus at the initial point and it will follow your subject as it moves through the frame.

If you select single shot mode press BBF the camera will achieve focus on your selected subject and maintain focus as it moves. When its where you want press the shutter button.

If you select continuous shooting get your inital focus and then press the shutter. The camera will shoot multiple images.

Its important that you keep the subject within the autofocus point frame.

This guide for the 1D Mark III may be useful.

 https://cpn.canon-europe.com/files/product/cameras/eos1dmark3/EOS_1D_Mark_III_Guide_to_AI_Servo_AF_C...

Here's a tutorial video:

https://www.bing.com/videos/search?q=canon+6d+mark+ii+af+guide&view=detail&mid=C13E9D3D25075EBC4A80C...

[Waddizzle]

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@Georgezx9 wrote:

Thanks for very comprehensive and informative answer, I am more than happy now.

what caused me to look at BBF was, my wife does a lot of dog agility, and when I tried to get the dogs in focus over jumps/tunnels at speed, most shots were out of focus.

i played with this and struggled, in the end because I could never get crisp focus of the dog, as often it focused on the jump I changed my approach to give greater depth of field and hopefully catch more in focus dog, this often meant high ISO.

a friend suggested BBF as a method of keeping focus on the moving subject.

lets tryit and experiment.

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The problem is two fold.  One is focusing a subject whose distance to the camera is changing.  One is tracking a subject that is moving across the viewfinder.  These are two separate, but inextricably intertwined problems.  It is all too easy to conflate the two concepts.

Using BBF will not help you, at least not yet.  BBF is for far more experienced users.  I used to have a neighbor who trained dobermans for dog shows.  He had a neat little obstacle course set up in his backyard.  I think I have a pretty good idea of what you might be trying to do.

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I suggest that you select “SCN” on the shooting mode dial.  Press the [Q] button, choose the leftmost menu option, which should be the default selection.  Use the up/down arrows on the function disc to select “Kids” as the shooting mode.

The camera will be ready to focus and track randomly moving subjects.  But, you may need to select active AF points.  I suggest enabling multiple AF points to assist you with tracking the moving dogs.  Keeping a single AF point on a moving subject takes lots of practice, months and years of it.

Press the [Q} button, and choose the right most menu selection.  I think default is “Large Zone AF”.  Use the small button [ - - - ] with the dots next to shutter to change the AF point selection option to “Large Zone AF”.  There is a picture of the button icon in the menu.  You might want to try “Auto Selection AF” mode, too.

What lens are you using to photograph the running and jumping dogs?  How far away are you from the dogs?

[Georgezx9]

Thanks, I am an experienced photographer, just new to this camera, and as always, we blame the tools first rather than my technique, however if I can maximise tool capability it will help.

The pictures vary, sometimes running straight at me, others are right to left.

again distance varies, from say 5yds to 20 yds.

my two lenses are 28-135 and 70-300 zooms, with both these when I get it right, picture quality is exceptional

[amfoto1 · Accepted solution]

For action photography such as you describe I would use:

- Back Button Focusing

- Single Point AF, manually selected (usually the center point)

- AI Servo continuous focus

- USM lenses are the fastest to acquire and best tracking

- f/4 to f/8 aperture for added depth of field (minor focus error won't matter)

I use a pair of 7D Mark II, which are excellent with active subjects. Like the 1D/1DX-series cameras, 7D-series use a discrete chip to run the AF system. Dual processors handle images separately. The rest of the Canon cameras use their main processors for everything... incl. both AF and image handling. Lenses I use a lot on my 7DIIs include 70-200mm f/2.8 & f/4 (both IS, USM), 24-70mm f/2.8 USM, 28-135mm IS USM, 300mm f/2.8 IS USM, 300mm f/4 IS USM, 100-400mm IS USM "II", among others.

I typically shoot  between 1000 and 4500 images at an event and have less than 1% images that miss focus... and I bet that at least half of those are my fault, not the camera's or lens'. For example, I might shoot too fast, before focus has been acquired.... or I may to keep the AF point on the subject, where I want camera & lens to focus.... or sometimes I  just press the wrong button with my thumb!.... or other mistakes. It's pretty rare that I think the camera and lens miss focus.

Part of getting a high success is knowing your subjects and what they are going to do.

I haven't shot dog agility, but do shoot some similar equestrian events. A few examples:

Occasionally I'll use Expansion Points for some types of events, where the subjects change direction less predictably. Gymkhana "Pole Bending" for example, where the horse and rider zig zag through a series of poles.

I use Zone Focus occasionally too, but mostly for birds in flight, against a very distant background or clear sky.

I never use All Points/Auto. It would make for a lot of missed focus shots, I'm afraid.

Besides the camera, lens, settings and familiarity with your subjects, the other thing that's needed is practice, practice, practice! Early in the shooting season I don't get as low percentage of missed focus shots as I do later when I've been doing it a lot.

My dog photos tend to be more "posed"...

And my cats are just plain lazy!

***********

Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2) some other cameras, various lenses & accessories
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