Optical Shop Testing

Chapter 10 - Hartmann, Hartmann–Shack, and Other Screen Tests

10.1.   INTRODUCTION

This chapter has been rewritten and updated by the first author; it includes some of
the materials taken from the chapter in previous versions of the book. The Hartmann
test, as the Ronchi test and lateral shearing interferometry, measures the wavefront
slope instead of the optical path difference (OPD), like the Twyman–Green and
Fizeau interferometers. A very large wavefront deformation may produce small
slopes changes if the extension of this deformation is large. In an analogous manner,
small wavefront deformations may produce large slope changes if their extension
is small. However, since most of the times the final aim is the retrieval of the
wavefront shape, this has to be obtained from these slope measurements. These
slope are measured from the transverse aberrations at some observation plane near
the focal plane using a geometric optics approach.

This chapter is concerned mainly with the methods of sampling a wavefront or
mirror surface through the use of such screens and similar methods. The sections on
applications of these methods and comparison of the various screen tests among
themselves are included in this chapter. Although the methods described are applicable
to most lens systems, the presentation in the rest of this chapter will be made for
large concave mirrors, which are the most commonly tested.

The Hartmann test, invented by Hartmann (1900, 1904a,b and c) to test the
Great Refractor at Postdam and illustrated in Figure 10.1, has its antecedent in the
measurements of eye refractive defects using a screen with two holes in front of the
eye as described by Tscherning (1894). It uses a screen with an array of holes
placed close to the entrance or exit pupil of the system under test. The most
frequent screen has a rectangular array of holes with one at the center as shown in
Figure 10.2.

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