What is another word for Rayleigh Disk?
Pronunciation: [ɹˈe͡ɪliː dˈɪsk] (IPA) 
A Rayleigh disk is a device used to test the spherical and astigmatic aberrations of an optical system. It is also known by various other names, such as a Ronchi test, a Foucault test, a knife-edge test, and a split-screen test. The Ronchi test involves projecting collimated light through a periodic grating. The Foucault test uses a knife-edge to observe the variations in a reflected beam of light. The knife-edge test involves observing a beam of light as it passes through a knife-edge placed at a distance from the focus. Finally, the split-screen test uses a screen with a half-circular aperture to separate and observe the two parts of a beam of light.
