Because it can be useful to operate the MAS 2.0 at lower NA, e.g. to reduce scattered light, or to increase the depth of focus, the system can be equipped with two circular apertures, one each at the Fourier plane of the catadioptric relay and the illumination optics, i.e., the position where the Euclidian representation of the image is transformed to its frequency (Fourier) representation, such that the low-frequency components are near the optical axis and higher frequency components are radially distal . The Fourier plane of the relay is located directly in front of the back lens (Figure ) and that of the illumination system will be shown in an illustration below. The aperture in either position reduces the NA to, e.g., 0.08, but both should be used to minimize stray light reaching the synthesis flow cell. Since reducing the NA also reduces the spatial resolution, by blocking the higher frequency components of the image, it will generally make sense to use an XGA array or to combine blocks of the smaller mirrors of other DMDs to display larger synthesis pixels.