The ELT, also known as the "World's Biggest Eye on the Sky", contains a ground-breaking optical system consisting of a total of five mirrors. Each of these mirrors is a technical masterpiece. The M1 main mirror, with a diameter of 30 meters, is a hollow mirror consisting of 798 individual segments. For the high-precision storage and alignment of these segments, PI provides more than 2,000 actuators that are based on a hybrid drive principle, which consists of a motor spindle drive and a piezo actuator. The individual segments collect the light from the night sky and reflect it to the M2 secondary mirror. In turn, this mirror, which hangs above the main mirror and has a diameter of 4.2 meters, directs the light in a bundled form to the M3 tertiary mirror. The M3 is a module made up of three curved half mirrors, enabling the night sky to be imaged in a quality never seen before. From here, the light is transferred to an M4 flat adaptive mirror. To balance out distortions caused by turbulences in the atmosphere, this mirror can change its shape up to 1,000 times per second.