Testing a fast off-axis parabolic mirror using tilted null-screens

We propose the design of tilted null screens in order to test the off-axis segments of conic surfaces. Furthermore we reduce the size of the screen in order to increase the performance of the test. The sensitivity is increased while the size of the screen is reduced in the saggital caustic region and vice versa in the tangential caustic region. Further analysis and experimental results are presented, for an off-axis concave parabolic mirror which has an elliptical aperture, with a distance offset Xc=25.4mm, the radius of curvature at the vertex R= 20.4mm, major axis of the mirror DM=49.4mm and minor axis Dm=29.5mm.