Canon EOS 77D Telephoto Lens Kit Owner's Manual

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q
 Changing the Metering ModeN
e
 Center-weighted average metering
The metering is averaged for the entire scene 
with the screen center weighted more heavily. 
This metering mode is for advanced experts.
With q (Evaluative metering), the exposure setting will be locked when you 
press the shutter button halfway and focus is achieved. In the w (Partial 
metering), r (Spot metering), and e (Center-weighted average metering) 
modes, the exposure is set at the moment the picture is taken. (Pressing the 
shutter button halfway does not lock the exposure.)