Analysis of key parameters in schlieren systems for microscale flow-field measurements

Abstract This study systematically investigates the effects of image resolution, optical resolution, schlieren contrast, and depth of field (DOF) on the imaging performance of a microscale schlieren system through experimental methods. Image resolution and optical resolution jointly constrain the sharpness of microscale schlieren flow field images, but as imaging magnification increases, optical resolution becomes the dominant factor in determining image clarity. When no significant diffraction occurs, the optical resolution of the microscale schlieren system is primarily determined by the parameters of the second lens. Schlieren contrast is found to be largely independent of both image and optical resolution. Furthermore, DOF analysis indicates that, for microscale flow fields, even when the flow field dimension along the optical path exceeds the DOF by a factor of six or more, the defocusing effect on image clarity remains negligible.