The dome has nothing to do with the gray card.
Your distant scene is illuminated from many different angles, including reflections from the area in front of it, like grass, dirt, sand, or water.
The dome integrates light from all different directions and includes that information in the meter reading. It should be pointed directly at the camera lens, not up or down or sideways, from the subject position, or from a position that mimics the illumination environment of the subject.
I normally just hold it above my head, pointed straight back. Works fine in most situations. I know when the subject and lighting are such that a correction may be needed.
Regarding the gray card... Very few people use these correctly.
It should be angled halfway between the camera line of sight and the illumination source. Then you take a reflected reading of the card from the camera position. As an example, if you're shooting a landscape at noon, with the sun directly overhead, the card should be at a 45° angle.
Last edited by Leigh B; 07-23-2011 at 10:12 PM. Click to view previous post history.