How do you set a custom white balance using a gray card in-camera?

• A. Use the gray card as a wet filter to adjust color temperature in post.
• B. Place the gray card in the scene, fill the frame with the card, take a WB reference shot or use the card to set a custom WB in-camera; apply the WB to subsequent photos.
• C. Mount the gray card on the lens and shoot with auto WB.
• D. Remove the gray card after composing; WB is automatic.

Answer: (B)

To set a custom white balance with a gray card, you need a neutral reference captured under the lighting you’ll be shooting in. Place the gray card in the scene, fill the frame with it, and take a shot specifically for white balance (or use your camera’s function to sample the card). Then use the camera’s custom white balance option to set that shot as the WB reference; the camera stores the color temperature and tint from the card and applies it to subsequent exposures. This makes all colors balance to the same neutral gray under those lighting conditions. The other approaches don’t provide the same controlled, consistent balance—using the card as a post-filter, mounting it on the lens, or relying on automatic WB won’t give you the reliable on-camera custom WB you get from this method.