Canon EOS-3 Instructions Manual page 122

Custom Function Settings
Using Custom Functions CF-4 and CF-7 Together
If Custom Functions CF-4 and CF-7 are used together, the availability of
electronic manual focusing will be as follows:
Custom Function
No.
Setting
0
1
CF-7
2
Before focus/After focus
O: Electronic manual focusing enabled.
×: Electronic manual focusing disabled.
122
CF-4
0, 2
× / O
× / ×
× / ×
1, 3
O / O
O / ×
× / ×