Measurement of Off-Axis Parabolic Prisms

It is well known that Off-Axis Parabolic Surfaces are offering the advantage of an unobstructed aperture, giving access to the focal plane in system designs. They often can provide the most cost effective answer with no compromise in performance because they produce perfect images for infinite-conjugate off-axis points. But it always appears to be difficult to measure the surface shape of such an optical element. To qualify the optical performance of an Off-Axis Parabolic Prism FISBA OPTIK has been developed a two stage test. The first test is the fully sized measurement of the surface deviation of the Off-Axis Parabola. This is done by using an interferometer together with intelligent software which allows analysing weak aspheric surfaces. The second test inspects the function of the whole optical system. For this we are using a digital microscope which measures the extent of the focal spot generated by the Off-Axis Parabolic Surface. Both measurements are presented exemplary.