Abstract: In a mixing projector, a guide element for the slide magazine extends transversely with respect to the optical axes of the objective lens systems of the optical assembly. Disposed between the two projector units for projecting the respective slides is a main slider member which is displaceable parallel to the optical axes of the optical assembly, for transportation of slides between the magazine and a slide turning mechanism which turns the respective slides through 90.degree.. Transverse slider members then provide for transportation of the turned slides into and out of the positions thereof for projection through the objective lenses of the optical assembly.