The first generation of maskless array synthesizers image the mirror pattern on the DMD to the reaction chamber using a 0.08 NA (2.4 µm spatial resolution at 365 nm) Offner relay . The Offner relay is a simple imaging system consisting of two concentric, spherical mirrors. The advantage of Offner relays is that reflectiononly optical systems are achromatic, and the Offner relay system in particular is relatively simple to manufacture as it consists of only two spherical optical surfaces, one concave primary mirror and a second, much smaller, convex mirror. This system was chosen for the MAS 1.0 because of these qualities, as well as because illumination of the DMD requires substantial clearance in front of the DMD, and because readout resolution of the arrays was limited by the resolution of the microarray scanners of the time . The 0.08 NA Offner relay of the original MAS (Figure ) has a diffraction-limited field of view sufficient for the XGA DMD and marginally acceptable for the 1080p DMD (Figure ). Because of these advantages, we explored the possibility to using a 0.12 NA Offner relay (Figure ) which provides 1.6 µm spatial resolution at 365 nm. In addition to the very large size of the mirrors, such a relay results in diffraction-limited imaging only in a thin annulus that is smaller than any of the DMDs (Figure ) and is therefore unsuitable in this application. Other options were explored, including the use of aspherical optics, but simulations found these likely to be inferior to the chosen catadioptric relay, either due to manufacturing difficulty/cost or performance. Nevertheless, an Offnerlike relay with two aspheric mirrors was found to satisfy the design criteria and would have the advantage of achromaticity and having fewer surfaces, an advantage in reducing scattered light (vide infra).