Elimination of Moiré Effects in Tr-Color Kinescopes

Moiré effects which may arise in aperture-mask tricolor kinescopes are spurious intensity variations in the picture in the nature of beat patterns between the scanning lines and the aperture array in the shadow mask. The visibility of these effects depends on the relative mapitudes of the scanning-line width, mask-aperture size, aperture spacing, and line separation, on the orientation of the scanning pattern relative to the mask, and, finally, on the picture content. For the narrow aperture spacing normally employed (e.g., 215,000 apertures in a rectangular picture area of 104 square inches or 195,000 apertures in the somewhat smaller area defined by the framing mask) and for the preferred orientation of the scanning pattern, however, the moiré effects are negligible. They may become noticeable, in the form of dot or bar patterns, if the aperture spacing is increased or the orientation of the scanning pattern relative to the mask is changed. The variation in the line transmission of the mask indicates directly the degree to which the mask may distort transmitted intensity values. It increases with a reduction in the ratios of line width and aperture diameter to aperture spacing and with a departure from the preferred orientation of the scanning pattern relative to the mask. Again, for the preferred orientation and within the range of spot sizes required for optimum resolution, the variation in line transmission is negligible-1 per cent or less.