Canon 5D IV back focus

[Sparts99]

Been working my way through the options on my new body (ooh err). I can't find a way to make the back focus button focus only, it seems to be focus and exposure. Few tutorials on the web haven't really helped as they seem to be workrounds, any one worked it out?

[Wallace]

I can't say for sure but on my camera, which is not a 5D it is Custom function menu 5, Custom Controls shutter button half press to metering start and the AF ON button to AF, first icon.

[Sparts99]

On my 5DII and 7D I can make the button focus only, but not on the IV, seems like I'm missing something. Bizarrely you can set it to disable the focus, so a workround is to use the shutter button to set the focus, then hold to the back focus button, release the shutter, re-compose and shoot, seems awkward and wrong.