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Proceedings Paper

Schlieren unwrapped: distortion correction in digital focusing schlieren
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Paper Abstract

Digital focusing schlieren relies on accurate mapping between a camera and a digital modulator or display system. Our early development of the technology was challenged by higher-order distortions in the optical systems. A simple perspective transform was adequate for lower-power lenses and smaller fields of view, but for wide fields and for highly sensitive configurations such as dark-field schlieren, correction terms were necessary. The Brown-Conrady model fitting implemented by OpenCV offered little improvement, so we developed a new distortion correction method that empirically optimizes the schlieren filter performance and constructs a map with phase unwrapping techniques borrowed from interferometry. This approach allows operation even with wider-angle lenses and finally makes dark-field schlieren practical. It also appears to improve the resilience of the grid generation with lower resolution camera systems, which is important for implementation in high speed schlieren imaging.

Paper Details

Date Published: 3 September 2019
PDF: 9 pages
Proc. SPIE 11102, Applied Optical Metrology III, 111020R (3 September 2019); doi: 10.1117/12.2528081
Show Author Affiliations
Benjamin D. Buckner, Spectabit Optics, LLC (United States)
Drew L'Esperance, Spectabit Optics, LLC (United States)

Published in SPIE Proceedings Vol. 11102:
Applied Optical Metrology III
Erik Novak; James D. Trolinger, Editor(s)

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