OPTICAL SYSTEM WITH A FILTER ELEMENT

An optical system with an entrance pupil, has a first aperture diameter, an exit pupil and a reflective or transmissive filter element spaced at a distance from the entrance pupil, which is designed and arranged such that a second diameter is illuminated on the filter element by a beam passing through the entrance pupil and spreading divergently from this. The second diameter corresponds to n times the first aperture diameter, and n is a number greater than 1, as a result of which the local angular spectrum at each point on the filter element is n times smaller in comparison to the entrance pupil. The filter element selectively reflects or transmits to the exit pupil at each point only a predetermined spectral range. An optical imaging unit comprising the filter element is provided, which images the entrance pupil onto the exit pupil.