Using Gray Cards Using A Gray Card Do not tip the card up to the light like the picture on the left. The middle picture is correct. Position the card parallel to the front surface of your lens like this. Do not tip the card down like the picture on the right.
Less light is seen by the meter.
Get the camera close enough so that only the gray card shows in the viewfinder. Once you have the meter reading, back off to frame the view as you like. Be aware that automatic cameras go back to their erroneous ways as soon as the gray card is out of view. With an 18 percent gray card you can get a reflected light reading which is essentially the same as reading incident light. Our gray cards are made from mat board.