The use of moire interference fringes in biostereometrical applications has the advantage that contour fringes on the surface of an object are visible to the unaided eye and that these fringes may be recorded photographically. The movement of such fringes as would accompany the motion of the human body can be recorded by movie or video camera when the fringes are used to study human subjects. One of the limitations of this moire method using noncollimated light is that the value of the contour interval increases with the increase of the order number of the fringes as counted from the grating. To overcome this limitation, a new moire technique using parallel light has been developed. An optical system, which includes a field lens, provides the parallel light which makes it possible to obtain equal valued contour intervals, independent of fringe order. Any desired contour interval is obtained by choosing a grating with suitable pitch and/or an appropriate angle of incidence for the parallel light at the grating. Analogue data from the moire pattern is automatically fed into the central processing unit of a computer by means of a TV camera and an A/D converter. Examples of the line printer output of this conversion system are given.
"Photogrammetric Application Of Moire Fringes Produced With A Parallel Beam Of Light," Optical Engineering 18(4), 184399 (1 August 1979). https://doi.org/10.1117/12.7972394