Wilson Tsoi , Dec 17, 2006; 04:27 a.m.
You can program via custom menu to have the AE-L/AF-L button to do both exposure and auto focus lock, or just one of the two. It's a matter of preferance. If you're more accustom to exposure lock, you can program that button to execute AE-L only, and leave the AF-L to your half-pressed shutter release. Some people like to have AE-L and AF-L together since the focused portion is where they want to meter anyway. Just whatever that will make you work more efficiently really.