  The Dragonfly Spectral Line Mapper (DSLM) is the latest evolution of the
Dragonfly Telephoto Array, which turns it into the world's most powerful
wide-field spectral line imager. The DSLM will be the equivalent of a 1.6m
aperture $f$/0.26 refractor with a built-in Integral Field Spectrometer,
covering a five square degree field of view. The new telescope is designed to
carry out ultra-narrow bandpass imaging of the low surface brightness universe
with exquisite control over systematic errors, including real-time calibration
of atmospheric variations in airglow. The key to Dragonfly's transformation is
the "Filter-Tilter", a mechanical assembly which holds ultra-narrow bandpass
interference filters in front of each lens in the array and tilts them to
smoothly shift their central wavelength. Here we describe our development
process based on rapid prototyping, iterative design, and mass production. This
process has resulted in numerous improvements to the design of the DSLM from
the initial pathfinder instrument, including changes to narrower bandpass
filters and the addition of a suite of calibration filters for continuum light
subtraction and sky line monitoring. Improvements have also been made to the
electronics and hardware of the array, which improve tilting accuracy, rigidity
and light baffling. Here we present laboratory and on-sky measurements from the
deployment of the first bank of lenses in May 2022, and a progress report on
the completion of the full array in early 2023.
