Cameron 32" Reference 18% Gray Disc

This Cameron 32" Reference 18% Gray Disc uses the standard 18% reflectance reference for exposing photographs. As white would reflect close to 100% of the light, and black somewhere near 0%, the gray that reflects 18% of the light is the standard for taking meter readings, going back at least to Ansel Adams. This gray card is a disk, 32" in diameter.