The left image was my reference standard with no filter, auto exposure, auto focus, AV mode.
The right image was focus stacked using 4 manual focus exposures, Linear polarizer, auto exposure, AV mode with the same lens opening as the reference image.


The auto exposure is "fooled" in the left image by the bright reflection in the water.
Since the polarizing filter eliminated the reflection in the right image, the overall auto exposure is increased and, in my opinion, more accurate.