German researchers (left to right) Enrico Pfüller, Manuel Wiedemann, and Jürgen Wolf monitor images from their Fast Diagnostic Camera (FDC), whose main purpose is to evaluate the SOFIA telescope’s optical performance. A beam-splitting tertiary mirror transmits half the reflector’s light to the FDC, mounted in the telescope cavity behind the primary mirror, and bounces the other half through a bulkhead to the pressurized cabin, where it’s fed into the HIPO instrument.