Gray card: what is it used for in photography?

Gray card: what is it used for in photography?

• A. A card used to measure light for exposure
• B. A card used to calibrate autofocus
• C. A card with a color of halfway between black and white, often called 18% grey. It is what your meter will "see"
• D. A card used to protect the lens

Answer: (C)

The main idea here is using a known mid-tone as a reference for exposure. A gray card is designed to reflect about 18% of the light that hits it, which is treated by camera meters as middle gray. Since meters are calibrated to render that 18% reflectance as a balanced midtone, pointing the meter at the card yields exposure settings that will translate to correctly exposed midtones in the scene. In other words, the card provides a reliable baseline: measure from it, then set your exposure for the rest of the shot. It’s not about autofocus, lens protection, or white balance (though color targets can be used for white balance); its primary purpose is giving the meter a consistent reference for proper exposure.

The main idea here is using a known mid-tone as a reference for exposure. A gray card is designed to reflect about 18% of the light that hits it, which is treated by camera meters as middle gray. Since meters are calibrated to render that 18% reflectance as a balanced midtone, pointing the meter at the card yields exposure settings that will translate to correctly exposed midtones in the scene. In other words, the card provides a reliable baseline: measure from it, then set your exposure for the rest of the shot. It’s not about autofocus, lens protection, or white balance (though color targets can be used for white balance); its primary purpose is giving the meter a consistent reference for proper exposure.