VSHOT measurement uncertainty and experimental sensitivity study

The video scanning Hartmann optical tester (VSHOT) is a slope-measuring tool for large, imprecise reflectors. To study the accuracy of the VSHOT as well as its sensitivity to changes in test setup variables, a series of experiments were performed with a very precise, astronomical-grade mirror. The slope errors of the reference mirror were much smaller than the resolution of the VSHOT, so that any measured slope errors were caused by the instrument itself rather than the mirror. The VSHOT exceeded its accuracy goals by achieving less than 0.8% error in the determination of focal length and approximately 0.1 mrad error in the determination of RMS slope error with minor restrictions on the test setup. Displacement of the test mirror from the optical axis caused the largest source of measured errors.