Design considerations for a Nomarski reflection microscope to produce a desired differential interference contrast image and the results are presented. Formulas for tracing of rays through the Nomarski prism and calculation of the optical path difference and the angular separation between the orthogonal linearly polarized components and for determining the position of the ray intersection plane are devised. Techniques for the design and fabrication of a Nomarski prism and a complete differential interference contrast microscope are described.