A sheet-fed rotary printing press for selective recto printing and recto and verso printing includes a three-drum reversing device having three cylinders cooperatively disposed behind one another between respective impression cylinders of two adjacent printing units. The interface of the outer sidewall with the outer ring may include a plurality of mechanical hooks on one or both of the upstream face and the outer radial face of the outer sidewall that engage with complimentary structures on the outer ring. The weights x, y and z of the components, and, respectively, have a relationship of 0. The ac-to-dc converter comprises: first and second rectifiers, each connected to a respective first and second portion of the output winding, to the dc link and winding tap; and a series inductor connected to the winding tap. Imaging optics combine portions of the resultant set of diffraction orders to generate an interference pattern that is ultimately imaged by an imager.