Canon EOS 5D - Manual (Page 160)

3 Custom Function SettingsN
160
C.Fn-17 AF point activation area
0: Standard
1: Expanded
In the AI SERVO AF mode when the center AF point is selected,
six invisible Assist AF points within the spot metering circle also
become active. Therefore, seven AF points will track the subject
(p.76). This is effective for subjects that move erratically, making it
difficult for only the center AF point to track it.
C.Fn-18 LCD displ -> Return to shoot.
0: With Shutter Button only
1: Also with A etc.
During image playback or the menu display, pressing the <A>,
<E>, <S>, <Q>, <R>, or depth-of-field preview
button will exit the image playback or menu display and make the
pressed button active.
Also, during the image review right after image capture, you can
hold down the <l> button and press the <u> or <I> button
to magnify or reduce the image.
Even during image playback with the <x> button, you can hold down
the <l> button and press the <u> or <I> button to magnify or
reduce the image.
“Easy Printing” (p.142) will not work.