The concept of maskless array synthesis is illustrated in Figure . UV light, generally at 365 nm, illuminates an array of micromirrors. Each micromirror can be selectively tilted at defined angles of ±12° to either reflect the UV light, via a unit magnification optical relay, to a photochemical reaction chamber or flow cell where oligonucleotide synthesis is controlled by the removal of photolabile protecting groups, or away from the synthesis area for absorption on a black surface. For the MAS 2.0, the optic relay was designed de novo to take advantage of modern DMDs, with millions of mirrors, pitches under 14 µm, and array dimensions of several centimeters, thus requiring a very large and undistorted field of view while simultaneously providing spatial resolution sufficient to resolve each of the millions of micromirrors. This was accomplished with 0.12 NA catadioptric (making use of both reflective and refractive elements) relay consisting of one biconvex and one biconcave spherical lens and a concave spherical mirror (Figure ). This relay results in diffraction-limited imaging over a field larger (Figure ) than any currently existing DMD (Figure ). A disadvantage of catadioptric optics is their use of refraction, which can result in chromatic aberrations, which limit illumination versatility. Our design, however, is well corrected for both first order axial and lateral chromatic aberration. Therefore, although the relay was optimized for the light spectrum from 365 nm LEDs, it can be used at other relevant wavelengths, in particular for the 405 nm LED emission, with a minor refocus.