Dragonfly Telephoto Array
The Dragonfly Telephoto Array is a ground-based optical telescope array developed at the Dunlap Institute for Astronomy & Astrophysics of the University of Toronto in Canada. The array uses a combination of telephoto lenses to observe extragalactic objects.
Its main purpose is to take images of ultra-low surface brightness galaxies at visible wavelengths of light. It is well suited for this purpose because its lenses have specially-coated optical glass that reduces scattered light.
The telescope was designed by Roberto Abraham of the University of Toronto and Pieter van Dokkum of Yale University. It was commissioned in 2013 and initially had eight commercially available Canon EF 400mm f/2.8L IS II USM camera lenses. This was first increased to ten lenses, and was extended to two clusters of 24 lenses in 2016. The array is designed to accommodate the addition of lenses to increase its effective aperture with each additional lens.
With 48 lenses, the instrument has the light gathering power equivalent to a 99 cm diameter refractor, with a focal length of 40 cm.
Astronomers used the Dragonfly Telephoto Array to discover Dragonfly 44, a galaxy that is roughly as massive as the Milky Way, with 99.9% of its mass composed of dark matter. At the other end of the scale it was also used to discover NGC 1052-DF2 which measurements with other instruments initially suggested was a galaxy with very little dark matter. Further work indicated that NGC 1052-DF2 was closer to the earth than previous thought. If this is the case then the galaxy appears to contain a typical amount of dark matter.
