The depth of focus of the image (focal tolerance) is highly relevant because it determines the necessary positioning accuracy of the glass slide on which photochemical synthesis takes place. Since the image of the DMD on the glass slide measures almost 21 × 12 mm in the case of the 1080p DMD, this entire rectangular area must be constrained within this focal depth. At the small numerical apertures relevant here, the depth of focus ∆𝑧 is given approximately by ∆𝑧~𝜆𝑛/𝑁𝐴 , where λ is the wavelength and n the index of refraction . In air and with 365 nm light, the depth of focus of the 0.08 NA MAS 1.0 is about 57 µm, and is about 25 µm for the 0.12 NA MAS 2.0. This estimate was the basis for the initial choice of a numerical aperture of 0.12 for the new design because numerical apertures significantly greater than 0.12 appeared likely to result in a depth of focus that was too small given the experimental constraint of synthesizing on glass slides with incompletely constrained flatness and thickness. Simulations in Zemax OpticStudio for the 0.12 NA catadioptric relay (Figure ) are consistent with this value of 25 µm. Here, the Strehl ratios at nine representative positions within the footprint of the 1080p DMD image are calculated at focus positions between -25 and 25 µm and all yield values above 0.8, indicating diffraction limited, within a 23 µm range.