A plurality of spots forming an M×N matrix can be used in a focus system. Specifically, a plurality of identical spots can be simultaneously projected onto the sample. A V(z) curve can be generated for each spot. A robust focus can be determined based on the generated V(z) curves. Using the spot matrix significantly increases the probability that at least one of the plurality of spots in the matrix can provide an unambiguous V(z) curve. Thus, the spot matrix eliminates the need to search for an appropriate site because the spot matrix increases the probability of landing on a “good” location by a factor of M×N.