An optical system for variably re-directing light (preferably sunlight) which passes through an input aperture. The input aperture is covered with a flexible optical film such as a Fresnel lens having an optical deflection characteristic which varies as a function of position so as to redirect the light in a direction which varies as a function of such position. The film is supported with a selected portion of the film covering the input aperture, and with the non-selected portion of the film stored away from the input aperture. A control mechanism controllably displaces the film in the aforementioned direction, to position the selected film portion relative to the input aperture. The film re-directs and concentrates the light into an output aperture whose cross-sectional area is less than the cross-sectional area of the input aperture. The output aperture may be a light guide's input port. At any particular point on the selected film portion, the film's deflection characteristic is approximately proportional to the distance, in the aforementioned direction, between the center of the film and the point. The proportionality is further characterized by a constant having a selected sign and a selected magnitude, whereby substantially all of the light is focused onto the output aperture. The system preferably redirects the light in a direction which is substantially perpendicular to the film.