Hello everyone, I am trying to test the collimation of light emerging from an off-axis parabolic mirror. My mirror has a diameter of 0.5m or so. The focal length is about 5m. The light source I am using is a red laser focused at a pinhole. To test the collimation of this point source, I am using a shear plate. Basically light comes in, reflects from both sides of the thick piece of glass, and produces an interference pattern. The laser is good enough to produce fringe patterns. The angle of the fringe patterns indicates the radius of curvature of the wavefront, and therefore the collimation. What I am finding is that this method is not sensitive enough for me, because I can move the point source by several mm before I notice a change in the pattern angle. Also, my patterns go wavy once in a while, so that doesnt help. Is anyone familiar with this technique, and can give some advice on how to improve this set up. Maybe a different approach all together?