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.[1] 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.

A Canon EF 400mm f/2.8L IS II USM lens, the model used in the array

The telescope was designed by Roberto Abraham of the University of Toronto and Pieter van Dokkum of Yale University.[2] It was commissioned in 2013[1] and initially had eight commercially available Canon EF 400mm f/2.8L IS II USM camera lenses.[3] This was first increased to ten lenses, and was extended to two clusters of 24 lenses in 2016.[4][5][6] The array is designed to accommodate the addition of lenses to increase its effective aperture with each additional lens.[3]

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.[7] 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.[8] Further work indicated that NGC 1052-DF2 was closer to the earth than previous thought.[9] If this is the case then the galaxy appears to contain a typical amount of dark matter.[9]