In a method for converting a light beam to a line focus, wherein the line focus extends according to its length along a first direction (y) and is narrow in a second direction (x) perpendicular to the first direction (y), the light beam is directed onto at least one conical optically operative surface, by which it is converted to the line focus. The light beam is directed onto the at least one optically operative surface with a ring-segment-shaped cross section transversely with respect to the light propagation direction. A device, in particular for carrying out the method, and an optical arrangement for generating a light beam with a ring-segment-shaped cross section are likewise described. In accordance with a further method and a further device, a line focus is generated only with spherical and/or cylindrical elements.