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A comment on The $11B Webb telescope aims to probe the early universe. Parent comment

Re:The $11B Webb telescope aims to probe the early universe by gadnuk on Wednesday December 08, 2021 @03:18PM (#29489915)
The whole Hubble mirror fiasco was fascinating. The before and after images of the galaxy M100 in the following link outlines the extent of the error:

https://www.nasa.gov/content/hubbles-mirror-flaw

One may assume that maybe the error was simply too big and that's why the aberration. Here's the root cause and the magnitude of the error would be dismissed as nothing by most people on this planet but ultimately turned out to be huge!

"Ultimately the problem was traced to miscalibrated equipment during the mirror's manufacture. The result was a mirror with an aberration one-50th the thickness of a human hair, in the grinding of the mirror."

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Re:The $11B Webb telescope aims to probe the early universe by a9h74j on Wednesday December 08, 2021 @03:51PM (#29490324)
That's huge. Everyday profile accuracy can be spoken of in "quarter wavelength"-like terms.
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Re:The $11B Webb telescope aims to probe the early universe by xxpor on Wednesday December 08, 2021 @07:42PM (#29492510)
Was that true in 1979?
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Re:The $11B Webb telescope aims to probe the early universe by HPsquared on Thursday December 09, 2021 @04:42AM (#29495498)
Accuracy less than a wavelength has been possible for a long time:

https://en.wikipedia.org/wiki/Foucault_knife-edge_test

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Re:The $11B Webb telescope aims to probe the early universe by xxpor on Thursday December 09, 2021 @11:53AM (#29499745)
Huh wow, that's brilliant! I was expecting something super complicated with extremely high tech sensors.
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Re:The $11B Webb telescope aims to probe the early universe by a9h74j on Sunday December 12, 2021 @01:07AM (#29527533)
Spherical-against-spherical and flat-against-flat grinding can be self-truing, so in effect centuries-old clever results required clever testing to verify.

High tech in those days? Rumor I heard in the mid-1980s was that LLNL had [vertical?] lathes which could mechanically cut mirrors to optical-profile accuracy. Supposedly 100gpm liquid flows were required to keep the part temperatures uniform.

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