Nikon D90 - F4: Assign AE-L;AF-L Button

f4: Assign AE-LI AF-L Button
Choose the role played by the AE-UAF-l button. This option is
available in all shooting modes
Option
~ AE/AF lock
(default)
...... ~ AE lock only
rj;j AF lock only
~@ AE lock (hold)
am AF-ON
Ell! FV lock
Description
i Focus and exposure lock while the AE-UAF-L button is pressed.
•Exposure locks while the
AE-UAF-L button is pressed.
...................................................
•Focus locks while the AE-UAF-L button is pressed.
Exposurelock$whenthe AE-UAF-Lhuttonispressec{andremains locked ...
until the button is pressed a second time or the exposure meters turn
off.
The
AE-UAF·L button initiates autofocus. The shutter-release button can
not be used to focus.
Press the AE-L/AF-L button to lock flash value (built-in flash and SB-900,
SB-800, SB-600, SB-400, and SB-R200 flash units only, pg. 198). Press
again to cancel FV lock.
200