Experimental investigation of third-order binodal astigmatism in Nodal Aberration Theory (NAT) with a Cassegrain system

In this study, we present a simulation and experimental investigation of binodal astigmatism in NAT with a Cassegrain telescope. The high-precision telescope system utilizes a piezo-actuated flexural mechanism to introduce secondary mirror misalignments and generate aberrations intentionally. The induced aberrations are measured interferometrically and quantified for a grid of field points on the image plane of the telescope. For this purpose, a coma-free pivot point of the secondary mirror was simulated for isolating the binodal astigmatism field response. A simulation of binodal astigmatism was generated using a real ray trace model of the Cassegrain system and analyzed to compare to the experimental results. The experimental results were consistent with the simulations, hence experimentally validating NAT for binodal astigmatism for the first time.