A device concept utilizing a rotating optical flat to degenerate the fringe visibility for simultaneously holographic multiplexing purposes is presented. The device basically consists of a rotating slanted optical flat. The rotation induces a periodically varying phase shift to a transmitting wave, which causes a specific degeneration of the maximum achievable time-average visibility. This property can be used to expose independent gratings simultaneously into one photopolymer film with a single coherent light source. Theoretical investigations of the resulting time-average visibility are carried out and presented in detail. Experimental results are compared to the theoretical findings and discussed. The presented device is capable of decreasing the visibility to the desired degree. Thus, it is well suited for holographic multiplexing purposes. A conceptual setup utilizing the device for holographic angular multiplexing is suggested.