X10 - can shutter release lock focus but not metering?

Seems awkward to have to toggle to mf by hitting the afl/ael button and then reposition (if I've understood that correctly). There's no way half depressing the shutter can be set to af lock only? This applies equally to the x100. Also, can the afl/ael button be used to focus while in auto-focus mode? I ask because in the x100 focus distance is closer using this button that the shutter release. A different post perhaps.