Canon EOS R3 Advanced User's Manual page 934

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AE Microadjustment
Caution
Normally, this adjustment is not required. Perform this adjustment only if
necessary. Note that performing this adjustment may prevent you from
obtaining suitable exposure.
You can fine-tune the standard exposure level. Effective if images in autoexposure shooting
without exposure compensation usually seem underexposed or overexposed.
OFF: Disable
ON: Enable
To access the adjustment screen, select [Enable], then press the <
Standard exposure can be adjusted in a range of ±1 stop, in 1/8-stop increments. Set on
the positive side if shots tend to be underexposed and on the negative side if they tend
to be overexposed.
Caution
The effective exposure compensation range available in movie recording remains
unchanged if you adjust standard exposure with AE Microadjustment, and only the
standard exposure level is changed. An exposure compensation amount equivalent
to the AE Microadjustment amount is not applied to resulting images if the effective
exposure compensation range in movie recording is exceeded (for example, an
exposure compensation amount of +1 stop is not applied if AE Microadjustment is
set to +1 stop and exposure compensation to +3 stops).
Note
Exposure compensation can be set up to ±3 stops from the adjusted standard
exposure when shooting.
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> button.