A method of determining at least one of focus and coma of a lens at a selected location in an imaging field, includes the step of forming a predetermined pattern on a mask for transference to a wafer through a lens. The pattern including a plurality of features such that a first of the plurality of features is situated adjacent a first side of a first phase shift region formed on the mask, and a second of the plurality of features is situated adjacent a second side of a second phase shift region formed on the mask, the second side being substantially opposite the first side. The method further includes the steps of transferring the pattern formed on the mask to the wafer, measuring a dimension of each of a first structure and a second structure formed on the wafer, the first structure being formed as a result of the first feature being transferred from the mask to the wafer and the second structure being formed as a result of the second feature being transferred from the mask to the wafer, and using the measured dimensions to determine the at least one of focus and coma of the lens at the selected location.