An optical device is provided, including two dual-fiber collimators, two single-fiber collimators, two filters connected respectively to the two dual collimators, and two mirrors. Further, a device for guiding a continuous belt-shaped carrier material in an electrographic printer or copier is provided, in which a roller element can be displaced andor tilted transversely to the carrier material. Thereby, a person captured by the suction force at the drain will be released and the person is free to move away from the drain essentially instantaneously upon contact with the drain. A subblock interleaver interleaves each subblock and outputs a plurality of interleaved bits.