Picture ripples

The following describes the symptoms, cause and prevention of the Moire effect.

Symptoms of the Moire effect

When you are shooting a subject that has a fine regular pattern such as stripes or plaids, a ripple that does not exist on the subject sometimes appears in the image.
An example of this can be seen in the pictures below.
The photo on the left shows the fine plaids pattern on the shirt. The photo on the right is a distance shot of the same shirt. In this photo, you can see a ripple that is not visible in the photo on the left.
This effect is called the Moire effect.

Why does the Moire effect occur?
Digital cameras and camcorders are equipped with imaging devices such as CCD sensors and CMOS sensors that have pixels that are finely aligned horizontally and vertically that convert light into electronic signals. When the pixels and the fine pattern on the subject overlap slightly misaligned, an interference pattern occurs and a ripple that does not exist on the actual subject may appear. This is the Moire effect.
Look at the image above. This image shows red stripes and black plaids overlapped slightly misaligned. When you look at the entire image, you find a ripple that differs from either of the patterns. This is the same principle that causes the Moire effect.

Preventing the Moire effect

You can reduce this effect by changing the distance, zoom setting or the angle of the image. If you are using a camera with manual focusing, the Moire effect can be reduced by simply changing the focus slightly.