What is an 18% Gray Card?
An 18% gray card is a standardized tool in photography. It’s usually a flat piece of cardboard or plastic (Lasolite have collapsible one available), that reflects 18% of the light that hits it. This level of reflectance represents a mid-tone gray, which is the standard assumption for light meters when they calculate exposure. This will help you achieve correct exposure settings for your images. Wikipedia has a more technical description of the card here.
Why Use an 18% Gray Card?
It’s a Standard Reference:
Light meters in cameras are calibrated assuming that the average scene reflects 18% of the light. Using a gray card ensures that your meter reading is accurate, providing a reliable reference point.
It will ensure Consistent Exposure:
The 18% gray card helps achieve consistent and accurate exposure across different lighting conditions.
It simplifies Lighting Balance:
It’s essential for balancing ambient and flash light in manual flash photography.
How to Use an 18% Gray Card
- Position the Gray Card:
Place the gray card in the same lighting conditions as your subject. Ensure it is receiving the same amount of light as the subject to ensure accurate readings.
The card should be placed at the subject’s location, facing the camera lens, and perpendicular to the direction of the light source. But for more reliable results, and to emulate Kodak’s recommendations from the Wikipedia article, have the model point it directly to the light source. Then point it directly to the camera. Then move it one third the way back to the light source again. This will ensure there are no reflective hot spots on the card that would affect the readings.
- Meter the light using your camera:
Set your camera Spot metering mode. This means it will take a single exposure reading from the center of the screen.
Move in close, or zoom in and point your camera at the gray card so that it fills the viewfinder or the metering area of the meter. Confirm the card is flat and evenly lit, with no shadows or reflections affecting the reading.
- Take the Reading:
Just press the shutter button half-way to take an exposure reading. This will give you the correct exposure settings (aperture, shutter speed, and ISO) for the scene.
- Adjust Your Camera Settings:
Switch your camera to Manual Mode and, based on the reading, set your camera’s aperture, shutter speed, and ISO to match the values indicated by the meter.
Example of Using an 18% Gray Card
Imagine you’re photographing a person outdoors in the shade. You want to ensure the exposure is correct despite the mixed lighting conditions. Here’s how you would use the gray card:
- Have the person stand in their allotted place holding the gray card. They should hold it close to their body and within the same light conditions.
- Take a reflected light reading using your camera, aiming at the gray card.
- Note the exposure settings from the reading (e.g., aperture f/5.6, shutter speed 1/125s, ISO 100).
- Set your camera to these settings.
- Take your photo, knowing the exposure should be correct.
Pitfalls to Avoid
- Incorrect Placement:
Ensure the gray card is placed in the same lighting as your subject. If it’s in a different light (e.g., shadow while the subject is in sunlight), the reading will be inaccurate. If you are taking the photo in dappled light – for example with the subject standing under a tree with dappled sunlight shining through, you should place the gray card in the shaded portion or the sunlit portion according to which is the most important light for your photograph.
- Angle and Reflections:
The gray card should point to a position between the camera and the light source to avoid reflections and uneven lighting that could skew the reading.
- Using a Dirty or Worn Card:
Over time, gray cards can get dirty or fade, which can affect their reflectance properties. Keep the card clean and replace it if it shows signs of wear.
- Metering from the Wrong Spot:
Ensure your camera or light meter is actually reading the light reflected from the gray card and not from the surrounding area, which could have different lighting characteristics. This means you should move in as close as possible to fill the camera screen with the gray card as much as possible.
Additional Tips
Use in Post-Processing: After exposing for the gray card, take the shot you want with the subject holding the gray card. In post-processing, you can use this shot to set accurate white balance and exposure for the rest of your photos.
Practice Makes Perfect: Regular use of the gray card will help you get a feel for its benefits and how to best incorporate it into your workflow.
In conclusion
You may not understand the need for an 18% Gray Card, because maybe you’ve been happy with the exposures from your camera already. In that case, you obviously haven’t needed the 18% Gray Card, and most likely you never will need it. But by being aware of the card and it’s uses in photography, and by understanding how to use an 18% gray card correctly, you can be prepared in the event some of your photographs are not exposed properly and you will immediately know what’s needed to correct this.