  The Dragonfly Spectral Line Mapper is an innovative all-refracting telescope
designed to carry out ultra-low surface brightness wide-field mapping of
visible wavelength line emission. Equipped with ultranarrowband (0.8 nm
bandwidth) filters mounted in Dragonfly Filter-Tilter instrumentation, the
Dragonfly Spectral Line Mapper maps H$\alpha$, [NII]$\lambda$6583, and
[OIII]$\lambda$5007 line emission produced by structures with sizes ranging
from $\sim$1 to 1000 kpc in the local Universe. These spatial scales encompass
that of the exceedingly diffuse and faintly radiating circumgalactic medium,
which is singularly difficult to detect with conventional mirror-based
telescope instrumentation. Extremely careful control of systematics is required
to directly image these large scale structures, necessitating high fidelity sky
background subtraction, wavelength calibration, and specialized flat-fielding
methods. In this paper, we discuss the on-sky performance of the Dragonfly
Spectral Line Mapper with these methods in place.
