For most photographers, Canon’s beefy EF 400mm f/2.8L IS II lens is nothing but a pipe dream. The $10,000 telephoto combines a long focal length with a fast aperture, making it a mainstay of professional sports photography. It also happens to be great for observing the night sky, which is how astronomers Pieter van Dokkum and Roberto Abraham recently put it to use.
While any photographer would be happy with just a single copy of the lens, van Dokkum and Abraham’s project required a few more: 48 to be exact, divided across two 24-lens arrays. That’s — gulp — $480,000 worth of glass. But compared to the programs the astronomers manage in their day-to-day life, this qualified as a “small side project,” according to Symmetry Magazine.
The Canon lenses are particularly good at resolving faint light from distant galaxies that is too spread out, or diffuse, for standard telescopes to detect. Telescopes use mirror lenses, which tend to scatter light, rendering diffuse light sources invisible. Canon introduced a new type of nano coating on the 400mm in 2011, which is specifically designed to prevent light scattering.
Van Dokkum practiced photography as an amateur, shooting mostly macro photos of insects. He was familiar with Canon’s lens technology, and while it wasn’t specifically designed for astrophotography, he realized it may help with the problem of detecting diffuse-light objects.
With help from a few grad students, van Dokkum and Abraham grew their team and began testing the lenses in a dark sky preserve in Quebec. Over time, they added more and more lenses, placing them side by side in a honeycomb arrangement they dubbed the Dragonfly.
By using multiple lenses, the effective aperture of the system is multiplied, allowing more light to be captured. Each lens is connected to a science-grade, eight-megapixel CCD camera, according to DPReview.
In 2014, the then eight-lens Dragonfly detected an entirely new galaxy in the heavily photographed Coma Cluster. Now known as Dragonfly 44, it wasn’t just a new galaxy, but an entirely new class of galaxy, large in mass but with a small number of stars, signaling that it is made mostly of dark matter. The team dubbed this class of galaxy “ultradiffuse.” Galaxies heavy in dark matter aren’t new discoveries themselves, but previously observed examples had all been much smaller.
Thanks to the interest sparked by Dragonfly, more of these galaxies are now being discovered, and Van Dokkum and Abraham continue to point the multifaceted eyes of Dragonfly in their direction.
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