If I press the AE Lock (*) button on my Canon XTI it will lock the exposure, but how do I un-lock it? I usually just end up turning the camera off and then back on. After playing with my camera a minute ago I found that if I wait 4 seconds the display inside the viewfinder turns off and when I wake it back up by half pressing the shutter button the AE lock indicator is off. So do I just have to wait? I know 4 seconds is not that long but it could also mean getting or missing the shot.
From the Canon article Using Auto Exposure (AE) Lock :
Clearing a locked exposure:
Once you’ve pressed the AE Lock button, the camera holds the meter reading in place. If you change your mind and want to totally eliminate AE Lock, don’t press the AE Lock button again. That simply takes a new meter reading and locks it in.
When AE Lock is in use, an asterisk will be visible in the camera's viewfinder. Instead, either pull your finger off the shutter button and wait 4 to 6 seconds, and wait for the finder display to go blank. Then, press the shutter button back down again. If you’re in a hurry and don’t want to wait a few seconds for the reading to clear, press the AF point select button (right next to the AE Lock button, on the back of the camera), and then immediately let it go and press the shutter button again. You’re back to live metering that’s not locked in place.
Yes, you wait for the meter operating time to go off.... or you simply take a picture.
It would be preferable if it turned off with another press, but it does not.
I am not sure, but I believe changing the exposure mode (from A to P for example) also cancels it. You can try that too and it should be quick enough to just turn the mode dial and back when you want to cancel AE-L.