1. A computer-implemented method for detecting defects in a reticle design pattern, comprising: acquiring images of the reticle design pattern using a sensor disposed on a substrate arranged proximate to an image plane of an exposure system configured to perform a wafer printing process using the reticle design pattern, wherein the images illustrate how the reticle design pattern will be projected on a wafer by the exposure system at different values of one or more parameters of the wafer printing process, wherein said acquiring comprises acquiring the images using two or more sensors disposed on the substrate and monochromatic light of the exposure system, wherein the two or more sensors are arranged at different heights on the substrate corresponding to different illumination focus conditions of the exposure system, and wherein the two or more sensors and the substrate are not tilted with respect to the image plane; and detecting defects in the reticle design pattern based on a comparison of two or more of the images corresponding to two or more of the different values.