There was a question about the value of having a ground glass on a PH/ZP camera I found this information on the Photo Technical Group site. There are PDF's for the camera and an exposure calculator.
Ground Glass Back: Due to the small size of the pinhole and zone plate apertures, using the ground glass to compose or frame the image can be somewhat difficult. The view is REALLY dark! To use the ground glass back, a dark cloth with an elastic band that fits tightly around the camera body and your head is required. All light must be shielded from the rear of the ground glass! When using this method, use the zone plate instead of the pinhole for viewing, then orient the desired aperture when you are ready to make the shot. Happy Trails, Kurt Norlin
