Knife-edge removal in schlieren imaging

TL;DR

This paper introduces a novel method to eliminate the external knife-edge in schlieren imaging by utilizing the camera lens's internal aperture, simplifying the setup and reducing costs while maintaining high sensitivity.

Contribution

The authors propose and validate a technique that replaces the traditional knife-edge with the lens's internal aperture, streamlining schlieren imaging systems.

Findings

Effective removal of the external knife-edge without loss of sensitivity

Simplified setup reduces optical components and costs

Flow visualization confirms maintained schlieren contrast

Abstract

A knife-edge is recognized as a critical component of the schlieren imaging system. This knife-edge serves as a cutoff element, which is required to achieve high sensitivity in the schlieren imaging setup. This article describes a method for totally removing the knife-edge from a normal schlieren imaging system while maintaining the same sensitivity. In this approach, the camera lens's internal aperture acts like the cutoff element making an external knife-edge redundant. This method simplifies the schlieren setup and also reduces the setup cost due to the reduced number of optical or optomechanical elements. We show flow visualization data that clearly demonstrate that schlieren contrast can be obtained by employing a lens's internal aperture as the cutoff.