Nikon D40 - Manual (Page 58)

46 Reference: P, S, A, and M Modes/Exposure
If the subject is not in the metered area when center-weighted or spot metering is used,
exposure will be based on lighting conditions in the background and the main subject may
not be correctly exposed. This can be prevented by using autoexposure lock.
Adjusting Shutter Speed and Aperture
While exposure lock is in effect, the following settings can be adjusted without altering the metered
value for exposure.
The new values can be confirmed in the viewfinder and shooting information display. Note that the
metering method can not be changed while exposure lock is in effect (changes to metering take
effect when the lock is released.
12—AE-L/AF-L ( 77)
This option controls the behavior of the AE-L/AF-L button.
13—AE Lock ( 77)
This option controls whether the shutter-release button locks exposure.
Autoexposure Lock
Controls used AE-L/AF-L button
1 Select mode P, S, or A and choose center-weighted or spot metering (exposure lock has
no effect in mode M).
2 Position the subject in the selected focus area (when using
center-weighted metering, position the subject in the center
focus area). Press the shutter-release button halfway and con-
firm that the in-focus indicator (z) appears in the viewfinder.
Then, keeping the shutter-release button pressed halfway and
the subject positioned in the selected focus area, press the AE-
L/AF-L
button to lock exposure.
While exposure lock is in effect, an EL indicator will appear in
the viewfinder.
3 Keeping the AE-L/AF-L button pressed, recompose the photo-
graph and shoot.
Mode Setting
Programmed auto Shutter speed and aperture (flexible program; 40)
Shutter-priority auto Shutter speed
Aperture-priority auto Aperture