Canon PowerShot SX10 IS User Manual page 25

J131
_Locking the Exposure Setting (AE Lock)
You can set the exposure and focus separately. This is effective when
the contrast is too strong between the subject and background or when
a sub act is backlit.
To ReJease the AE Lock:
Operate a button other than the control dial.
® In movie mode, AE lock can also be set/canceled (p. 90).
® You can use the FE lock when using the flash.