Electrographic copier document transport - carriage moves forwards and back below exposure window

The forwards movement of the document transport carriage causes an exposure of the document image via means conducting the image rays onto a receiving surface in the interior of the copier, and moved in the same sense in synchronism with the carriage. During the return movement of the carriage, the means conducting the image rays are modified such that a negative of the document can be obtained, with the receiving surface continuing being displaced in the same direction, or using a second receiving surface. An optical system (8, 9) using two sets of mirrors or prisms behind an objective (66) can be displaced relative to the image beam. The first mirror or prism set (8) has its edges perpendicular to the image aperture.