An LED wall is a grid of tiny lights. Pixel pitch is the distance from the centre of one light to the centre of the next, in millimetres. A smaller pitch means more pixels in the same area, a sharper image and a higher price. It also decides how close the camera can get to the wall before the grid becomes visible.
What moiré is
Camera sensors are grids too. When a camera focuses on a repeating pattern, here the LED pixels, the two grids can interfere and produce wavy bands or coloured shimmer that is not on the wall. That is moiré. It is much easier to avoid on set than to remove afterwards.
Three things that control it
Distance from camera to wall. The farther away the wall is, the finer its pixels look to the sensor.
Focus. Moiré needs the wall to be sharp. If the wall sits well behind the subject and the lens is wide open, the wall goes soft and the pattern dissolves.
Pixel pitch. A finer pitch lets you stay closer or focus nearer to the wall.
A rule of thumb, and its limit
For people looking at a wall, a common guide is that the comfortable viewing distance in metres is roughly the pitch in millimetres. A camera that is focused on the wall needs more room than that, and the right figure depends on the lens, the sensor and the content, so we test with the actual camera rather than trusting a number.
Choosing a pitch
Wall far behind the subject, shallow focus: a larger pitch often works and costs less.
Wall close behind the subject, or close-ups with the wall in focus: choose a finer pitch.
Product shots or glass with reflections of the wall: a finer pitch helps, because the reflections can be sharp.
Ways to shoot around it
Move the subject farther from the wall
Use a longer lens or a wider aperture so the wall softens
Rotate the camera slightly, or change its height, since the pattern depends on the angle
Choose environments with soft, organic detail rather than fine regular patterns such as grids, stripes or fabric
Always test
Bring your camera and lenses to the stage and shoot the environment you plan to use at the distances you plan to use. Ten minutes on the day of the test saves a conversation in post.
Not sure how close you will be shooting? Send us the boards at wlab@wlab.tech and we will say what the wall can handle.
Cover image: an illustration generated for this article, not a photograph of a WLAB shoot.
