Studies and experiments to obtain contour lines of a non-topographic object have been conducted for some time, especially in the use of Moiré Pattern techniques by H. Takasaki and D. M. Meadows etc. In these days, an evaluation of Moiré Pattern's photographs and a standardization of Moiré Pattern techniques must be considered. The author plans to study these problems and will be concerned with a contrast of Moiré fringes. To analyze slit (or grid) geometry, a rectangular wave function is adopted for the transmission function. There are two reasons for adopting the rectangular wave function; namely, there exists a ratio between the width of the string and the space, and the distribution of light through a series of slits onto the object is observed as a rectangular wave. If only a sinusoidal function for a series of slits is used to express the transmission function, the effect of the ratio mentioned above can not be discussed in detail. The ratio K affects the brightness of the picture of Moiré Pattern and the noise introduced by these slits, or the grid. In this paper, the ratio K mentioned above is defined by [Gap's width] / [Black line's width], and if K is contained within the transmission function, then the effect of the ratio K on the contrast can be discussed and some results shown.