Moiré Patterns

Moir� Patterns & Fringes

Images by Chester Leeds of a giant reel spool for a coiled tubing unit, a machine for the oil and gas industry. The spool sides, 80 inches apart, are covered with perforated metal sheets having circular holes 5/8� diameter spaced in a hexagonal array.

Daylight shining through both sets of perforations forms a hugely magnified version of the arrays � a Moir� pattern. The camera has frozen it but to the eye Moiré patterns shift, swirl, grow or shrink with the ever moving head.

All images ©Chester Leeds, shown with permission

A close-up of the side sheet with the hexagonal hole array. Holes in the sheet on the far side are visible, sometimes in line and letting through daylight and in other places partially blocking it.

Moiré patterns are generally magnified versions of the hole array - not of the shapes of the holes themselves.

This reel spool at left has sides covered with mesh having a diamond array. The Moiré pattern (below) is likewise of diamonds.

Moiré pattern generation

The two perforated screens act as masks that in places open to reveal daylight and in other places block it.

Daylight is visible when a line to the eye passes through a hole in each screen. Angular directions where the holes do not align at all have light blocked and appear dark.

The conditions for alignment or transmission occur periodically with the result that a moiré pattern forms. The pattern generation is most easily visualised for a pair of simple linear arrays of holes as at left.

The condition of transmission through a given pair of holes in the two screens is extremely sensitive to the position of the eye or camera. The slightest movement shifts the pattern dramatically.

Holes are periodically in-line or out of line. The angles are sensitive to the distance between the screens and the distance to the eye.