EOS R10 back button focus disengages shutter button focus?

[R10]

Hi I have just purchased a Canon R10. I understand the concept of back button focus, and that you need to disengage the shutter button AF activation so that you can use back button focus. I have not done this adjustment to the shutter button focus disengagement, and yet I seem to be able to use both the shutter button and the AF ON button to focus. When using the back button, the shutter button focus function seems to be disengaged. Is this correct?

[shadowsports]

Greetings,

Yes.  You are correct.  

[p4pictures]

With the factory configuration the shutter and AF-ON buttons are both assigned AF and metering start. In this configuration the following happens. 

When you half-press the shutter the camera focuses and meters the scene. Fully pressing the shutter will take the photo. You can choose not to use the AF-ON button at all. 

You can press and hold the AF-ON button to meter and focus, and if you then press the shutter the camera will see that the AF-ON button was pressed first so continue with that function even if it's the same as the half-press of the shutter button. 

However if you press the AF-ON button to focus, and then release the AF-ON button to effectively lock the AF, the only way to take a photo is press the shutter and since the AF-ON button has been released then the camera will initiate AF and metering as the half press of the shutter is passed on the way to taking a photo.

Many photographers use back button AF to independently determine when focus is active or not, if you leave focus on the half press of the shutter you remove the independence of AF operation that back button offers. 

[R10]

Thanks so much for your comments.

Most reports I have read about back button AF-ON, cite the many advantages of using it. I rather like that option also. Then reports then continue on to instruct that one then needs to proceed through the Menu to assign the shutter button to meter only and to shoot the photo, and to disengage the focus function.

Just to clarify, is this action absolutely required if one wishes to use the back button focus features, whilst still maintaining the shutter button alive as an alternative option. This appears to be the case in my situation. It seems that I am able to use the shutter button to activate the meter and focus and shoot. Alternatively I can use the back button to do the same, without having to assign the shutter button to meter only, which is contrary to what I have already read. So slightly confused. 

[p4pictures]

If you leave the shutter button half press activating AF, then you have no way to interrupt / stop AF since every time you press the shutter to take a photo the camera will simply refocus.

• If AF-ON is pressed and then then shutter is pressed the camera will autofocus at the point the photo is taken
• If AF-on is not pressed and then the shutter is pressed the camera will autofocus at the point the photo is taken

For clarity, let me explain some usage cases so that you can understand the options. In general most photographers using back button AF use it with the camera set to SERVO AF. 

1. Lock focus to allow recomposition while using servo AF

For a many years photographers used back button AF to be able to stop the camera focusing once the subject was in focus. In effect being able to focus, lock, recompose even using servo AF. In this case, the photographer presses the AF-ON button, the camera focuses on the subject, the photographer releases the AF-ON button and recomposes the frame, then presses the shutter to take the photo. In effect this means you can use servo AF mode all the time, and still have the ability to lock (stop focus) as if using one shot AF.

If you still have the shutter set to engage AF, then when the shutter is pressed to take the photo the camera starts focusing again which is not what was required. 

2. Interrupt AF when the AF point is no longer on the subject

When photographing a bird flying through the sky. With the AF-ON button pressed to track the bird using servo AF. If the photographer cannot keep the AF points on the bird, they can release the AF-ON button to stop the lens from hunting for a new subject, and allow the photographer to move the AF point back to the bird. This would not be possible if the shutter button is also activating AF and the photographer was in the mid-part of a sequence of images when the AF point was no longer on the bird. 

Is back button AF still a helpful choice with mirrorless cameras?

The two examples are commonly quoted as good reasons for back button AF, but with a mirrorless camera like your EOS R10 with it's intelligent subject tracking AF I don't think it is beneficial to use back button AF. I have stopped using back button AF myself after many years of using it with DSLRs.

For the focus - lock - recompose case the AF point will move to follow the subject while in servo AF even if you recompose and keep the focus active. For me this is now such a good choice that I use servo AF or manual focus only with my mirrorless cameras, 

For the bird in the sky situation, this is still valid to use back button AF and you should stop the shutter button from activating AF. Though I prefer to reconfigure the AF-ON button with the AF-OFF function, making the AF-ON button a way to interrupt focus when needed. 

Some cameras allow the AF-ON and "star / asterisk" buttons to have a deeper level of settings when you assign the AF & metering start function, you'll see people referring to double and triple back button AF setups. They use this to switch AF areas, subject types, eye detection etc. Your EOS R10 does not support that level of configuration. 

[R10]

Thanks so much Brian for your detailed explanation. It all makes sense now.