In this work, we will show the procedure to design a null screen to evaluate a convex surface without symmetry of revolution, which is of great interest in developing optical devices. The process to obtain the shape of the surface without symmetry of revolution from images reflected from the null screen by the surface under test will be presented. In addition, we will present the experimental results of the test applied to a free-form surfaces. We will show the advantages of the method compared to others and its drawbacks.
We derive simple formulas for the caustic produced by a positive convex-plano and plano-convex conic lens
by considering a plane wave incident on the lens along the optical axis. By using these equations a paraxial
approximation for the caustics are provided in both configurations. Also, by using these equations it is possible
to obtain the third order coefficient of spherical aberration. Changing the parameters of the lens (refraction
index, conic constant, radius of curvature, thickness of the lens, etc.) we can modify the shape of the caustic,
furthermore there are cases where the spherical aberration changes from positive to negative when we vary
exclusively the conic constant. A formula for the Principal Surface as a function of the height also is given. We
believe that the method to obtain the caustic that we report is straightforward, obtaining a relationship between
caustics, wavefronts, and measurements of the spherical aberrations.
A new design of a null Hartman's screen to test quantitatively a fast plano-convex conic lens is presented. The
design of the null screen is based on the caustic produced by refraction through the lens. Additionally, the null
screen can be used to improve the alignment in optical systems. A quantitative evaluation of medium precision
by using a trapezoidal integration method is presented.
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