Rainbow holography with a synthesized double slit is proposed. Diffuse three-dimensional objects are translated uniformly in the x(0)-y(0) plane. The propagation direction of the coherent plane wave illuminating the objects is situated in the x(0)-z(0) plane. As a result of this process, a sinc function that modulates the complex-amplitude distribution of the objects is presented on the back focal plane of the lens, and the synthesized slit is formed. The central position of the synthesized slit depends on both the direction of motion of the object and the spatial frequency of the illuminating wave in the x(0) direction. Therefore the synthesized double slit is generated with a two-exposure method that has two illuminating waves of different spatial frequencies. The theoretical analysis and some experimental results are presented.