THE MOIRÉ EFFECT IN COMBINED OBJECTS OFF-AXIS

We investigated the moiré effect in combined objects (such as a planar surface combined with a cylinder) off-axis when the center of the cylinder is not on the axis of the camera which is displaced laterally. This is an example of the 3D moiré effect. The theory is based on projections of both surfaces onto the same screen. The formula for the period of the moiré patterns along the surface of the cylinder was obtained in a form similar to the on-axis case. Experiments confirmed the theory. Compared to objects consisting of parts of similar curvature (for example, planar facets or halves of a cylinder), the moiré patterns in the combined objects differ significantly; in particular, their period can have more than one maximum across the surface of the cylinder. An overall picture of the period of the patterns was built in the parameter space. Five particular specimens of the behaviour are described. In the parameter space, the region most suitable for the measurements is found. This allows the moiré measurements to be taken on vibrating cylinders.