How exposure meters work

 

   
This is a photo of an 18% gray card. Auto exposure

Exposure is f3.5 1/20sec

A photo of a white card. Auto exposure

Exposure f3.5 1/3sec

White card, manual exposure

Exposure f3.5 1/15sec

 Black card, auto exposure

Exposure f3.5 1/60sec

Black card, manual exposure

Exposure f3.5 1/13

All three cards (Black, gray and white) Auto exposure

Exposure: f3.5 1/20sec