Left: the top panel shows the background-subtracted [S II] image, focused on the eastern edge of the nebula. The image has been normalized by the “nebula background.” The middle panel shows in gray the perpendicular profile for dozens of 4″ cross sections placed across visible filaments and knots. The perpendicular direction is defined with respect to the nebula center. The locations and orientations of these profiles are shown in the upper panel with the short gray lines. The flux in all profiles is background subtracted and normalized to the peak. We measure a filament FWHM by fitting a Gaussian (in red) to the median profile (in black). We find a median filament cross section of FWHM = 0﹩\mathop{.}\limits^{{\unicode{x02033}}}﹩68 ± 0﹩\mathop{.}\limits^{{\unicode{x02033}}}﹩02, larger than the empirical PSF (0﹩\mathop{.}\limits^{{\unicode{x02033}}}﹩50 ± 0﹩\mathop{.}\limits^{{\unicode{x02033}}}﹩01). In the lower panel, we show the background-subtracted median profile for all RHT filaments found in the [S II] GMOS imaging (in black). The profile has been normalized by the “nebula background.” The nebula background, indicated with the dotted–dashed horizontal line, is an empirical detection of an additional “background” between filaments, which is in excess over the sky background (see Figure 6). We again fit a Gaussian (in blue) to the profile and recover an FWHM = 0﹩\mathop{.}\limits^{{\unicode{x02033}}}﹩81 ± 0﹩\mathop{.}\limits^{{\unicode{x02033}}}﹩03. Right: similar to the left panels, but for [O III]. We omit a fit to the image filaments (middle panel) but fit the full median RHT profile in the lower panel, finding an FWHM = 1﹩\mathop{.}\limits^{{\unicode{x02033}}}﹩07 ± 0﹩\mathop{.}\limits^{{\unicode{x02033}}}﹩22.