To make these buttons do what you want, press the menu button, go to the "gear" (settings) page 6 and look for "Custom Key Settings".
As a note, I just upgraded my camera from 3.1 to 3.21. Before the upgrade the custom key setting page was a confusing mess. Now with 3.21 it makes sensse.
I have C1 set to "focus magnifier", which is OK by me.
C2 is set to "lock on AF". We will see about that.
I change it to AF/MF Ctrl toggle.
AEL button (AEL hold by default) C1 and C2 (as already mentioned) center button ("standard") left button (Drive mode) right button (ISO) down button (exposure comp)Interestingly, you cannot remap the "up" button (display). Also I find it surprising that you can remap the center button. It seems like once you did that, it would be impossible to work with the menu system.
The options vary for each button.
You can change the default setup in much the same way as you set up custom buttons. You press "menu", then go to the "gear" (settings) page 6, and look for "Function Menu Set".
When you press "Fn" to access the matrix, many of the settings have icons for which you may not have a clue what they mean. For example on my camera, the first (upper left) just shows a rectangle. What could that possibly mean (it is drive mode in single shot mode). It actually tells you in plain english above the matrix, but who would expect that?
Tom's Digital Photography Info / [email protected]