5D mk4 button to the right of Q...

[rgrebby]

Just upgraded to the 5dmk4 from the 3 and there is a button next to the Q button.
Can't see in the manual what it's actually meant to do.

 

[jonoooo125]

It's a custom function button, you can set it to what you want, I change af selection with mine

https://photorec.tv/2016/09/canon-5d-mark-iv-tips-tricks-custom-button-setup/

 

[Andrew Benbow]

AF area selection AND exposure compensation (hold it and turn top wheel).

Go to the 5th menu, 3rd page, “custom controls” and you can see it.

 

[rgrebby]

Thanks guys

 

[Gaz J]

Pages 61 and 497 in the manual!!

 

[jezza8]

This small button is one of the big improvements over the mk3. You can have full manual control along with auto ISO and using this button still set exposure compensation. I use this all the time, can't do that on the mk3