Photolithographic apparatus and methods are disclosed. One such apparatus includes an optical path configured to provide a first diffraction pattern in a portion of an optical system and to provide a second diffraction pattern to the portion of the optical system after providing the first diffraction pattern. Meanwhile, one such method includes providing a first diffraction pattern onto a portion of an optical system, wherein a semiconductor article is imaged using the first diffraction pattern. A second diffraction pattern is also provided onto the portion of the optical system, but the second diffraction pattern is not used to image the semiconductor article.