The Largest Optical Lens in the World: One and a Half Meters in Diameter

The Large Synoptic Survey Telescope (LSST) started its construction in 2015 and will begin operations at the end of 2020 or the beginning of 2021. LSST will become the home of the largest digital camera in the world, combining 189 sensors under a single 3.2-gigapixel frame. However, every camera needs a lens that lives up to the task. That means the sensor network will be equipped with the largest optical lens in the world. It measures a little over one and a half meters in diameter, and will be accompanied by its smaller siblings of 1.2 meters and 72 centimeters, respectively.

Studying the sky is a fascinating process, but it also presents giant challenges. Only a handful of places on the globe have enough clarity for experts to obtain images without noise or external distortions. One of those privileged regions is Cerro Pachón in Coquimbo, Chile, where the Large Synoptic Survey Telescope (LSST) is being built. There, the largest digital camera in the world will be installed, a beast with 189 sensors of 16 megapixels each, operating at 100 degrees below zero.

Unlike telescopes such as the Hubble, the LSST's work will be to create a "movie" of the night sky, with 15-second exposures separated by intervals of twenty seconds. The LSST will only need a couple of nights to obtain a complete record of the sky in the southern hemisphere, and it will devour data like crazy: a session is calculated to demand on average 15 terabytes. Now, the camera is barely half of the equation. The other half comes through the lens.

The largest lens in the world

Not just any lens, of course. The largest on the planet, designed by the Lawrence Livermore National Laboratory, and built jointly by Ball Aerospace of Colorado and Optical Systems of Arizona. The lens, identified as L-1, measures 1.57 meters in diameter, and comes accompanied by a smaller lens, L-2, of 1.2 meters. Both units were installed in a carbon fiber structure and transported to the SLAC laboratory of Stanford University in Menlo Park by land. The truck trip took 17 hours.

Designing the LSST is a job that has spanned more than a decade, while the construction of L-1 and L-2 took about five years. A third lens of 72 centimeters in diameter will join them, with delivery scheduled within the next 30 days. The LSST's main mission will last ten years, and it is expected to detect about 20 billion galaxies.

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