First approach to characterize tilts through multiple pistons in the classical Ronchi test.

In this work, it is shown how a tilt can be introduced into a segmented surface through several piston terms, by using the classical Ronchi test. We have developed tilt error simulations by adding multiple constant terms to each point on the sagitta surface of a segment using ray tracing. Thereby a comparison between simulated Ronchigrams for piston and tilt has been performed for two adjacent segments, so that it is possible to appreciate the tilt and piston effects on the shape of the patterns. As a result, we show the behavior of the central maximum of the fringes in the presence of tilt and/or piston. Additionally we present evidence of introducing tilting without changing the surface shape by adding multiple pistons, and a description of how to characterize both piston and tilt using the Ronchi test.

Ronchi test can detect piston by means of the defocusing term.

We present simulated results on piston detection applying the classical Ronchi test to a segmented surface. We have found that a piston error in a test segment, induces a change in the transversal aberration, that can be analyzed by mutually comparing the fringes frequency in each segment. We propose that the piston term of the segmented surface can be recovered by geometrically relating the change in transversal aberration with the piston term. To test this, we have simulated some ronchigrams for a known piston error, and we have been able to recover this term for a dynamic range comprised among 57nm and 550 microm. For piston errors > 550 microm a change in the transversal aberration can be appreciated and measured in the ronchigrams although these large pistons are now classical defocusings. Thus we have demonstrated that the Ronchi test can be an alternative method for the piston detection with a large dynamic range.