From SPTelescope https://twitter.com/SPTelescope on Twitter: A close-up of the SPT-3G focal plane right before installation! It consists of 16,000 superconducting detectors, cooled to 0.25 Kelvin. The white circular pieces are small lenslests https://twitter.com/SPTelescope/status/950231862320001025/photo/1 https://chirp.cooleysekula.net/attachment/47113