USING AE-L BUTTON
When your subject is off-centre or very small against an extremely bright background, your subject may come out too dark (underexposed) in the picture. Or, with a background that is too dark, the subject may be washed out (overexposed) . In such situations, to correctly expose your subject in the auto exposure mode, use the AE-L (Auto Exposure Lock) button.
1 Compose your subject so that the circle in the viewfinder is fully covered by the subject.
2 Lightly press the shutter release button to activate autofocus operation and the exposure meter.
Confirm . (in-focus indicator) and exposure.