To achieve a high-enough angular resolution for some of the science goals, a telescope with an aperture larger than about 5 meters is needed. To reduce systematic effects which become the dominant source of errors in very-low-noise maps, the Simons Observatory has built a 6-meter telescope and underilluminates the primary mirror to 5.5 meters. At the same time, other science goals require very low noise on large angular scales—something a 6-meter telescope will struggle to achieve. For this reason the Simons observatory has also built three 0.5-meter-aperture telescopes and combines the data sets in analysis.
The Large-Aperture Telescope (LAT) The 6-meter-diameter telescope has a
Crossed Dragone design. At a frequency of 90 GHz, it has a field-of-view over 7.8 degrees. It was built by Vertex Antennentechnik in Germany. This telescope is of an identical design to the higher frequency
CCAT-prime telescope which is still under construction. The detectors on the LAT are housed in a single large cryostat over 2.4 meters in diameter. This can house up to 13 optics tubes consisting of three cooled silicon lenses (to refocus light from the secondary focus of the telescope onto the detectors) and a Lyot stop at an image of the primary mirror (to prevent stray light from the telescope structure reaching the detectors). Currently, of these 13 tubes, one operates at 27 & 39 GHz, four operate at 93 & 145 GHz, two at 225 & 280 GHz, and the rest will be populated within 2 years. This cryostat is one of the largest millimeter-wave astronomical cameras ever built.
The Small-Aperture Telescopes (SATs) The small-aperture telescopes are refracting telescopes with 3 aspheric silicon lenses and a rotating
half wave plate. Each telescope has a field-of-view of over 35 degrees. Overcoming systematic effects, such as picking up signals from the ground in
sidelobes, is critical to the measurement of the very largest angular scales, so each telescope has co-moving screens and is mounted inside a fixed ground screen that reflects diffraction from the co-moving screens to the sky. == Detectors ==