https://www.youtube.com/watch?v=npuaDOtEQco
What was suppose to be the final telescope to answer the final Astronomical questions was quickly obsolete!
The first reflecting telescopes, of Hamilton, were not silvered. They were just polished to a certain amount of metallic shine, enough to reflect some light. Silvering didn't come till the 1800's If I'm remembering correctly.
Not only was the Palomar mirror so big that it took the engineering of new manufacturing tools, but the glass was made of a low thermal expansion material. They of course, at the time, just silvered the mirror.
Today, the silvering is of another material, but what's really exciting is they use quantum optics science to determine maximum reflectivity. I know the ESO four 10-meter optical interferometer has to take out those mirrors and re-silver them quite a bit often - to keep the dust off the mirrors(this is down in South America).
I think they now use the same quantum optics technology for silvering the Palomar telescope now.
When this original documentary was done, the idea of ccd astronomy wasn't even anyone's pipe dream. This is the same technology you see in digital cameras. At the time of this documentary, they used photo-graphic plates. Now, ccd cameras are universal. They've yet to reach billions of elements; so, we can expect to see even better astronomical pictures in the future!
As hinted above, astronomical telescopes have gone beyond just single mirrors; they have a way of combining the light of multiple telescopes, called interferometry. At one time, Astronomers thought interferometry can only apply to radio telescopes; it took a mathematical breakthrough to make optical interferometry possible - hence great telescopes like the twin Keck in Hawaii, and the ESO four telescope interferometers mentioned above.
And, then of course we've put one optical telescope in orbit - the Hubble space telescope. But, there's new astronomical telescope innovations in the offing. I keep forgetting what they called ; but, there's a rather exotic diffraction disk idea, that once build and placed i space, will make space telescopes like Hubble, and even optical interferometers obsolete as much as Galileo's little telescopes are today or even the Palomar telescope.
