Optical testing method and apparatus employing a distortion verification grid

DETAILED DESCRIPTION The need is met according to the present invention by a method and apparatus for testing the configuration of an optical element that includes an optical test-set having a holographic optical element designed to obtain a null wave front at the surface of an optical element under test; an interferometer for viewing the test-set, the interferometer and optical test set having optical distortions; and a distortion verification grid (DVG) located in the optical test-set, the DVG comprising a thin opaque sheet of material having a pre-distorted array of asymmetrically-shaped holes arranged such that the image of the array of holes formed by the interferometer will be regular and the images of the holes will be symmetric when the optical distortions have been correctly understood and accounted for in the design of the DVG and the distortion correction function.
It is possible to design a DVG so that the pattern will look regular at any step in the distortion correction process.
ADVANTAGES The method and apparatus of the present invention have the following advantages: 1.
When used in conjunction with distortion correction software, a DVG can be designed to produce a regularly gridded array of light holes at any given stage of the distortion correction process to provide immediate visual confirmation that all distortion correction calculations were performed correctly.
2.
Once a DVG is produced, it can be used in a given test-set to characterize the distortion of other identical optical elements.
3.
There is no longer a need to remove the optical element from the test-set, or to place a grid of spots on the optical element being tested.
4.
The DVG can be easily inserted or removed from the optical test-set using a kinematic mount.
5.
The DVG can be used to empirically characterize and separate the component of distortion in a commercial interferometer from that of the optical test-set.