US Patent 7532403 Optical system for transforming numerical aperture

A system and method are used to form illumination light beams having desirable divergence and directivity. The illumination light beams are shaped using a pupil defining element and a field defining element. Then, divergence or numerical apertures of the light generated by these elements is modified using an optical element that either re-images the light onto planes conjugate to one or both of the pupil defining element and a field defining element or transforms a numerical aperture of light produced by one or both of the pupil defining element and a field defining element.