Nikon D700 - Focus Lock

Focus Lock
Focus lock can be used to change the composition after focusing,
making
it possible to focus on a subject that will not be in a focus
point in the final composition. It can also be used when the
autofocus system
is unable to focus (pg. 80).
1
Focus.
Position the subject in the selected focus
point and press the shutter-release
button halfway to initiate focus.
2 Check that the in-focus indicator
(e) appears in the viewfinder.
78
Single-servo AF
Focus will lock automatically
when the in-focus indicator
appears, and remain locked
until you remove your finger
from the shutter-release
button. Pressing the
AE-UAF-L button while the shutter-release
button is pressed halfway will lock both focus and exposure
(an AE-L icon appears in the viewfinder when exposure is
locked; see page 126).
• SeeAlso
If On is selected for Custom Setting c1 (Shutter-release button AE-L,
pg. 296), exposure will lock when
the shutter-release button is pressed
halfway.