Here is a fascinating video of the coating of the 8.4-meter primary/tertiary mirror of the Rubin Observatory, performed on April 27, onsite in Cerro Pachón, Chile.
Using a technique called magnetron sputtering, 4 coats were applied -
Here is an aerial view of the Rubin Observatory site in the scenic mountains of Cerro Pachón, Chile.
First light for the engineering camera is expected in August 2024, while system first light is expected in January 2025, Full survey operations are aimed to begin in August 2025.
The Rubin Observatory Simonyi Survey Telescope consists of 3 aspheric mirrors: an 8.4-m primary mirror M1, a 3.5-m convex secondary mirror M2, and a 5.0-m tertiary mirror M3.
The primary and tertiary mirrors, which were coated on April 27, are fabricated from a single piece of glass.
The secondary mirror (M2) is the largest convex mirror ever made.
Field of view = 3.5°.
The 3.2-gigapixel camera hangs below the secondary mirror. https://www.lsst.org/about/tel-site/optical_design #VeraRubin#astronomy
3/n
@AkaSci@ISibboI engineering reasons. From 8.6m mirror to camera you have competing difficulties of mirror curvature (more curvature is harder to make, finish, support, adjust) and length (end of the telescope supporting detector, and a building big enough to house it).
@Pyrrhlin@ISibboI
Also, in this case, the field of view is very large, which makes it challenging to create a telescope that can remove all the optical aberrations introduced by mirrors.
It require mirrors with a very large focal length - folding the path 3 times helps on that front. Also I think the 3 mirrors help remove aberrations better than 2.
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