What is a gray card in photography?
A gray card is exactly as it sounds: A card that is gray. More specifically, a gray card is generally middle gray, or 18% gray. They tend to be small, portable, light, and easy to whip out of a camera bag when necessary.
Certain types of photographers never photograph with gray cards, such as street photographers, wildlife photographers, and (most) landscape photographers. But other photographers, including portrait photographers and product photographers rarely leave home without one.
It’s interesting that even today, a lot of good photographers seldom use it, but, if they want things to be perfect, a gray card is a must.
Why are gray cards important?
Remember how I said that a gray card is middle gray, also known as 18% gray?
This number is important because 18% gray is what your camera’s meter is trying to calculate when it determines a correct exposure for a scene. If you put a gray card in front of your subject and take a meter reading, you will get a balanced exposure regardless of any tonal contrast in the scene.
Now, you might be wondering: What about my camera’s meter? Why can’t I rely on it for a good exposure?
Camera meters are very, very good, but they make mistakes, especially when faced with significant tonal contrast, as well as scenes that are naturally very light (e.g., a snowstorm) or very dark (e.g., a black rock).
One thing to remember about the GRAY CARD, is if you want a perfect exposure, there is no other way around this. A GRAY CARD is what you need to use.
The scene below is a tricky one for a camera meter to handle, thanks to the bright highlights on the food and the dark wood of the table:
Do you need a gray card?
Gray cards are helpful, but they don’t work for every type of photography. For one, if the subject is moving, then a gray card calculation is essentially worthless; within a few moments, the scene will change, and you’ll need to take another reading, and another, and another, which is more than a little annoying. Imagine a street photographer, who goes back and forth from shadow to sunlight while photographing subjects on the move. A gray card would be useless, as the exposure and white balance would need recalibrating from moment to moment.
Additionally, a gray card only works if your subject and the gray card are illuminated by the same light. Yet in certain genres of photography – bird photography and sports photography, for instance – the subject may be far off in the distance. That’s why bird photographers and sports photographers pretty much never use a gray card; there’s really no point, given the distance to the subject!
On the other hand, gray cards are perfect for controlled shooting scenarios. If you’re photographing food, products, or portraits, then a gray card is incredibly helpful. You can get close to your subject, take a gray card reading, and rely on it for an entire shooting session. Plus, gray cards are often necessary in these scenarios, as you must accurately represent the product and food colors.
How to use a gray card for perfect exposures
A gray card is the closest thing you’ll get to a magic bullet; it will give a near perfect exposure in almost any situation. So how does it work?
First, set your camera to spot metering mode, which tells your camera to meter off a small spot in the center of the frame. While this is not absolutely necessary, it will help a lot, especially in circumstances where you cannot fill the entire frame with the gray card.
Next, put the gray card in your scene, right at the center of the frame. Switch your camera over to Manual mode and set the exposure (based on your camera’s meter reading).
Then take the gray card away. As long as the light doesn’t change, you will now have an accurate exposure for all subsequent shots you take of the scene.
Next time you take a portrait, or product photography, consider using a gray card. It amazes me every time I see a portrait where a gray card was used. The exposure is just so perfect, you too will be amazed. Just another tool that will help you become a better photographer.