A novel concept on the construction of high-resolution objectives is outlined. Although similar to binary optics technology, this approach brings additional degrees of freedom to the optical design as far as achieving a finer balance of phase curvature via refractive properties and relative thickness of the multilayer stack. The differential coating objective can be used in conjunction with diffractive surfaces to optimize the transmission efficiency and control the secondary spectrum correction. The basic equations describing the monochromatic and three- color achromat predesign are presented.
"Differential coating objective", Proc. SPIE 1527, Current Developments in Optical Design and Optical Engineering, (1 December 1991); doi: 10.1117/12.48644; https://doi.org/10.1117/12.48644