A photographer showed us his picture of a fashion model in front of a dark gray backdrop. The supposedly solid gray backdrop had a mysterious pattern in it. The photographer had seen something similar with the same camera. The question was what was the pattern and where did it come from?
The answer is it is a moire pattern.** What exactly is a moire pattern?
Take two window screens and stack on top of the other. Rotate the top screen. See the pattern emerge and change with the angle? Two patterns combined to give a new pattern. That is a moire pattern. It is essentially an interference pattern and is kind of a cool, but unwanted, effect. Maybe like a kaleidoscope.
Now your digital camera sensor has individual sensor sites for each pixel arranged in a repeating pattern. If you photograph something that also has a fine repeating pattern, a new pattern can emerge where they two patterns interact. This is called moire. You will see it in the image.
This problem shows up more with high-resolution sensors that produce a very sharp image. To reduce the effect, camera manufacturers put an anti-aliasing filter in front of the sensor which is a form of low-pass filter. Unfortunately, the AA filter softens the image. So there is a trade-off between sharpness and moire pattern.
Nikon answers the question: What is moire?
**How do you pronounce moire? I have always said MORE-RAY as in moray eel, but inoglo says it is pronouced MOY-ruh.
