In order to evaluate either qualitative or quantitatively the shape of fast plano-convex aspheric lenses, a method to design null screens type Hartmann is proposed. The null screens are formed with non-uniform spots, which allows to have uniform images at detection's plane. The screens are printed on a foil sheet and placed in front of the lens under test, they are illuminated with a collimated monochromatic beam propagating along the optical axis, in such a way that through the process of refraction will form a uniform spot patterns which are recorded at a predefined plane of detection. Finally, processing properly its image recorded we could be able to get a quantitative evaluation of the lens under test. The designs of these null screens are based on the equations of the caustic surface produced by refraction. A preliminary test for a fast plano-convex aspheric lens with F=# = 0:8 is presented in this work. This method could also be applied to alignment of optical systems.
A method to design Ronchi-Hartmann null screens for improved alignment in the testing of fast concave conic mirrors is presented. The designs of these null screens are based on knowledge of the caustic by reflection.