We describe the Dragonfly Telephoto Array , a robotic imaging system optimized for the detection of extended ultra low surface brightness structures .
The array consists of eight Canon 400 mm f / 2.8 L IS II USM telephoto lenses coupled to eight science-grade commercial CCD cameras .
The lenses are mounted on a common framework and are co-aligned to image simultaneously the same position on the sky .
The system provides an imaging capability equivalent to a 0.4 m aperture f / 1.0 refractor with a 2.6 ^ { \circ } \times 1.9 ^ { \circ } field of view .
The system is driven by custom software for instrument control and robotic operation .
Data is collected with non-common optical paths through each lens , and with careful tracking of sky variations in order to minimize systematic errors that limit the accuracy of background estimation and flat-fielding .
The system has no obstructions in the light path , optimized baffling , and internal optical surfaces coated with a new generation of anti-reflection coatings based on sub-wavelength nanostructures .
As a result , the array ’ s point spread function has a factor of \sim 10 less scattered light at large radii than well-baffled reflecting telescopes .
As a result , the Dragonfly Telephoto Array is capable of imaging extended structures to surface brightness levels below \mu _ { B } = 30 mag arcsec ^ { -2 } in \sim 10h integrations ( without binning or foreground star removal ) .
This is considerably deeper than the surface brightness limit of any existing wide-field telescope .
At present no systematic errors limiting the usefulness of much longer integration times has been identified .
With longer integrations ( 50-100h ) , foreground star removal and modest binning the Dragonfly Telephoto Array is capable of probing structures with surface brightnesses below \mu _ { B } = 32 mag arcsec ^ { -2 } .
The detection of structures at these surface brightness levels may hold the key to solving the ‘ missing substructure ’ and ‘ missing satellite ’ problems of conventional hierarchical galaxy formation models .
The Dragonfly Telephoto Array is therefore executing a fully-automated multi-year imaging survey of a complete sample of nearby galaxies in order to undertake the first census of ultra-faint substructures in the nearby Universe .