Optimum contrast in single mirror off-axis Schlieren system

Abstract

Schlieren technique reveals the refractive index variations caused by temperature or pressure gradients to visualise fluid non-uniformities and dynamics, quantitatively measure gas density, and observe transparent solid deformities. The simplest and relatively least expensive Schlieren setup is the single-mirror off-axis Schlieren apparatus with knife-edge. We investigate the physical conditions of Schlieren parameters that will result to maximum gray-level contrast. In the setup, the distance measured from the concave mirror's vertex to its focal point is F = 64 inches. To achieve high contrast images, experiment revealed that the object distance must be ≈F and the knife edge is positioned at ≈2F while camera is focused within the range 0 to F.