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> It was ground very precisely into the wrong shape It was said at the time that the aberration made the Hubble near-sighted and, indeed, was corrected with le

> It was ground very precisely into the wrong shape It was said at the time that the aberration made the Hubble near-sighted and, indeed, was corrected with lenses. I had suspected, apparently incorrectly according to yours and others comments indicating that spy satellite mirrors are interchangeable with and used for astronomy without alteration, that the mistake was one of habit, because I figured they were ordinarily making near-sighted mirrors to specification to focus up to a few hundred miles rather than stellar or galactic distances. I am honestly am still having trouble accepting that a mirror designed for a telescope to look no further than a few hundred miles is identically focused to infinity precisely like similar telescopes that are designed to peer with a lower bound of at least millions of miles. But if you say so.

travisjungroth 4y ago
> I am honestly am still having trouble accepting that a mirror designed for a telescope to look no further than a few hundred miles is identically focused to infinity precisely like similar telescopes that are designed to peer with a lower bound of at least millions of miles. Consider the 2.4m lens to be the base of an isosceles triangle with a height of 100km, the edge of space and much lower than the satellite's orbit. This triangle has two angles of 89.9993 degrees. If the lens was 10cm thick and you wanted to taper the edges to match this angle, you'd need to bring in the near edge one micron, or about 1/50 of a human hair. 100km or 100,000 lightyears, they're still effectively straight away (focused to infinity).