18% gray reference for white balance and exposure — hold in frame before the take, focus camera on it. Prevents color casts and exposure errors across the entire setup.
On set, you hold the gray card in front of the first shot – a simple, gray piece of plastic or cardboard that reflects 18 percent of the incident light. This is the standard to which camera systems are calibrated. You focus on it, shoot a short take of two to three seconds, then remove it. In the edit or directly on set, this frame becomes the reference material: the colorist pulls the correct white balance from it, and the gaffer checks the light meter. What sounds trivial is your guarantee that all 15 takes of a scene under different artificial light or changing daylight will look color and brightness consistent in the end.
Placement is paramount. The gray card must be in the same plane as your talent or subject – not behind it, not in front of it. It receives exactly the light that falls on the scene. If you are shooting with three cameras, you take a separate gray card shot for each position; the cameras see different lighting conditions depending on the angle. On exterior shoots – especially with changing clouds – you immediately realize why the system works: what appears constant on the visual monitor is actually constant readjustment by the gray card. Without it, you'll be juggling color temperatures in post-production that will tear your footage apart.
A few practical pitfalls: The gray card itself must be clean – fingerprints, dust, or scratches falsify the reference. Some crews tape a white and black stripe next to it (reference strip) to also have reference points for black and white points. Honestly, this is a luxury if the gray card is optimally placed. Digital cameras today sometimes have internal white balance modes, but these are quick fixes – a real gray card is the foundation for color grading, especially in a DCI workflow. And one more thing: Don't confuse it with exposure metering. The gray card is NOT for finding your aperture. It serves solely for color temperature and as a reference brightness value for post-production.