Birds Back button focus? I don't understand the full benefit.

[Dave Williams]

I believe that is why it is being requested as an option so you can choose what works for you.

I think it's this one, EyeDetect.
And he had his * set to "register/recall shooting function" I believe.

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That's the one but I have it assigned to AF-on button as well as that one. Sorry for the delay in replying I have been out of contact in Kruger National Park. The eye af is great with birds but not so clever with all animals it seems from the last two weeks experience however, it's a huge leap forward.
If you just have the shutter button assigned to single spot and the back AF-on, (and the other next to it too ) to eye detect it is far less complicated than having to fumble for the right back button in my opinion, especially the buttons are small and close together.

 

[BradS]

Personally, I find the flexibility and utility of having 3 AF methods available by quickly sliding my thumb across the 3 buttons works for me. It is very fast to find what is working best in any situation. It probably took only one or two times out shooting to remember which button is for each function.