AF is automatically adjusted at the sensor (ie. as you pan from light to dark areas the exposure will automatically change, but you can prevent the camera from doing this by pressing the AE-lock button).

Also, you can select Auto or manual for the aperture. In manual you can change the depth of field by turning the aperture dial during the movie capture, but this does not effect the exposure unless you have pressed the AE-Lock button.
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John C.