Yeah! On 8 January 2022 (US time), the Webb telescope team successfully unfolded and locked in the last segments of the primary mirror, which means that the Webb telescope has completed the entire deployment. When Webb telescope is sailing to the second Lagrange point, each of the mirror segments will be adjusted to prepare for the focusing. Future operations are related to the optics, it's time to know more about the Webb's optics first.
Astronomical telescopes focus starlight. A reflective astronomical telescope has primary and secondary mirrors in which the primary mirror reflects light to the secondary mirror, then to our eyes or instruments. How about Webb?
If you have paid attention to our posts, you will know that Webb's primary mirror looks like an egg-waffle. But Webb is more than that. It has a tertiary mirror system, and is a "three-mirror anastigmat telescope" in which the combination eliminates optical defects such as coma, astigmatism or spherical aberration, and provides a sufficiently large and good field of view.
Ellipsoidal primary mirror
The primary mirror has a diameter of 6.5 m and is composed of 18 individual hexagonal segments. The hexagon design facilitates a gapless connection between adjacent components. 6 actuators under each segment adjust the mirror's curvature for the individual parts with an accuracy of 10 nm to achieve a perfect focus.
Hyperboloidal secondary mirror
The secondary mirror is a convex mirror with a diameter of 0.74 m, which the reflected light from the primary mirror hits and then focuses the light to the Aft Optics Subsystem. It is equipped with 6 actuators to adjust the position and direction.
Aft Optics Subsystem
The Aft Optics Subsystem contains a fixed tertiary mirror and a movable fine steering mirror. The tertiary mirror is a concave mirror with a size of about 0.73×0.52 m which reflects the image from the secondary mirror to the fine steering mirror while eliminating aberrations. The fine steering mirror is a flat mirror that stabilises the image by adjusting the horizontal and vertical tilts.
