Negative meniscus lens for enhancing depth-of focus in schlieren imaging systems

Non-ideal optical systems inherently suffer from image quality degradation due to geometric aberration. The degradation is often corrected by the use of "meniscus correctors" or negative meniscus lenses. Negative meniscus lenses were introduced into a z-type focused shadowgraph imaging system to enhance the depth-of-focus. Focus was quantified using image processing techniques to determine focus range in the imaging system. High zoom camera lenses were used to image a focusing target within a 4-meter-long test section. Fixed focal length and variable focal length camera lenses were compared to quantify the ability to enhance focus when a meniscus corrector is introduced. Although most schlieren and focused shadowgraph systems do not need these corrections, systems with long distances between the collimating optics almost always require these meniscus lenses.