Identical Gratings Research Articles

Disparity processing of spatial frequencies in man.

1. Adaptation to a high-contrast sine-wave grating has been shown previously by Blakemore & Campbell (1969) to raise the modulation required to detect a low-contrast grating that has the same or similar spatial frequency as the adapting grating.2. A similar adaptation effect occurs when the adaptation and test gratings are seen binocularly and are presented off the plane of fixation. When the gratings are not located on the plane of fixation, however, the greatest rise in threshold following adaptation occurs for test gratings presented in the same plane as the adapting grating. Thus, the neural mechanisms adapted to the high contrast patterns must be processing disparity information.3. The spatial frequency response of the disparity adaptation effect has been measured by adapting to gratings of different spatial frequencies presented at a given disparity, and comparing threshold elevations for identical test gratings presented in the same (disparate) plane as the adapting grating or in the plane of fixation.4. The unbiased adaptation effect specific to disparity is greatest for gratings whose periods are twice the disparity.5. There is no adaptation effect specific to disparity for individuals possessing only convergent or only divergent disparity mechanisms.6. The results suggest that disparity mechanisms make bar by bar correlations as opposed to edge by edge correlations and that narrow bar detectors feed small disparity mechanisms whereas wide bar detectors feed large disparity mechanisms.

Vibration measurements by the moire method

A simple and versatile, but also sensitive and accurate method of determining vibration amplitudes is presented. The method consists of observing the slow motion of a moire pattern formed by the image of a signal grating projected on to an identical reference grating, illuminated by stroboscopic light. The pitch of the image of the signal grating can be suitably adjusted to yield an optimum relation between line frequencies of the two gratings. Full control over the sensitivity of the system is therefore possible. The accuracy and resolution of the method are comparable with those of other known methods based on sophisticated vibration measuring equipment.

Double Diffraction in the Fresnel Region

Double diffraction pattern of two identical gratings placed in the Fresnel region is sensitive to the relative displacement of the gratings, and this phenomenon can be used as a method of displacement measurement. Experimental studies and computer analyses on the contrast revealed that a very high contrast (over 90% modulation depth) can be obtained for the zeroth order beam when the separation of the gratings satisfy the Fourier image conditions. The contrast is also affected by the finite radius of coherent component of the incident laser beam, which was shown by the simultaneous measurement of the spatial coherence factor of the source.

モアレ法による表面形状の測定について

A moire method is described for measuring partial slope contours of flat surfaces of transparent plates. A reference grating is projected by means of a collimated light beam on the surface of a specimen. The light beam passing through the specimen forms a distorted image of the reference grating on the surface of an identical grating, and produces moire fringes which yield partial slope contours of the specimen.A formula for obtaining the slope contour from the inclination and the spacing of the moire fringe is introduced theoretically. Experiments made with a straight line grating of 0.025 mm spacing show that this method has nearly the same precision as the optical interference method.In this paper few applications are shown. As an example, the slope contours are calculated from moire pattern produced by an acrylyte plate which is supported at both ends and loaded at mid point. And also a moire pattern produced by the fractured surface of acrylyte plate is shown.The method described in this paper is applicable for the transparent materials, but for the reflecting materials their slope contours are derived by the somewhat different moire technique.

Two moir instruments

Two simple instruments are presented in which moire fringe effects were used to determine the relative displacement of the instrument components. The magnification of displacement produced by the moire fringes reduced the number of moving parts and hence increased the reliability of the instruments. A moire extensometer employing sets of vernier gratings and utilizing the principle of direct measurement of displacement was fabricated. Experiments showed that with higher quality gratings extensions of the order of 10-4 in. could be attained over a range depending on the length of the scale gratings. A moire displacement gauge capable of operating submerged in a hot bath was fabricated employing two angularly displaced identical gratings. Displacements of the order of 10-3 in. were easily attainable from changes occurring in the density of the moire fringe pattern, over a range of about 0.100 in.

Multiple Source Moiré Patterns with Photographic Diffraction Gratings

Moiré patterns of the multiple source type can be used in the evaluation of line shape, line spacing, and grating plane separation of two nearly identical gratings. For line spacing analysis, the location of the MP indicates which of the gratings has the greater line spacing in a particular region. A difference in the average spacing of the order of one part in 107 between adjacent lines has been detected.