Moire Tell Tales

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Moire patterns are created when two regular, but different, patterns are superimposed. The most common place to see them is looking through the fences on brides where you see dark and light bands as you drive through. Here they are caused by perspective making the far fence appear to have closer spaced railings than the near one.

More spectacular patterns appear in the photographs in estate agent's windows. The dot pattern of the printer and that of the camera, combine with the regular patterns of bricks and tiles to produce quite strange patterns.

Moire patterns have been used in measurement for many years, but new applications keep appearing. Moire Tell Tales will shortly be available from Bill Harvey Associates Ltd (our sister company) they carry patent GB 2 386 189. They can be read from considerable distances using binoculars or telescopes. Best of all telephoto lenses and digital cameras allow an immediate and permanent record. Indeed, these gauges can be used with video cameras to show very small dynamic movements if a crack (eg in a bridge) moves under traffic.

The picture here will allow you to experiment with the sensitivity of the gauges. Moving the scroll bars shows the effect of displacement. The units are millimetres. Note how the pattern shows both magnitude and direction of movement.