🔦 Schlieren Bench: Knife Edge, Warm Plume, Ray Deflection and Contrast (2D)

A warm air plume bends light a few millionths of a radian; a knife edge in the focal plane of a mirror turns that bending into visible brightness. Set plume temperature and size, light path, mirror focal length, source image height and the fraction cut by the knife, then read the refractive index, ray deflection, focal-plane shift and image contrast. Four numerical checks run in the page.