A direct comparison between conventional and plenoptic background oriented schlieren imaging

The motivation of this work is to compare results from plenoptic and conventional background oriented schlieren (BOS) systems through two experimental configurations using a buoyant thermal plume to produce the inhomogeneous density field. The first set of experiments fixed the nominal focal plane and varied the plume position along the optical axis. The second set of experiments fixed the position of the plume while varying the nominal focal plane. These experiments were used to observe how measurement performance was influenced by (1) spatial resolution, (2) plume position, (3) focal plane position, (4) depth of field, (5) exposure time, and (6) aperture size. It was determined that both imaging systems follow the trend that the signal is dependent on the distance between the background and the plume but relatively independent of the nominal focal plane position. Conventional BOS images result in high-resolution, single line-of-sight measurements with a high signal-to-noise ratio. These images typically require a small aperture with a longer exposure time in order to achieve an appropriate depth of field. Focused BOS images are a result of lower resolution, multiple line-of-sight measurements with lower signal-to-noise ratios compared to that of the conventional system. Images from this system use a larger aperture to more efficiently collect light while still maintaining an extended depth of field. (paper)