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Reflector Primary Mirror Coatings

Started by ivanong, 08/21/2003 10:21AM
Posted 08/21/2003 10:21AM Opening Post
Hi there,
I am looking at some options for a primary mirror for a large reflector.
Where do I get information on the longevity of various mirror coatings? Some have "enhanced dielectic" coatings with significant reflectivity, but are these truly durable? Which are generally regarded as the best coatings? Are durability and reflectivity the two major considerations?
Thanks in advance,
Posted 08/21/2003 10:45AM #1
Ivan,Let me tell you what I was told by Steve Swayze about enhanced coatings.

Steve said that the enhanced coatings are rather thick and will actually ruin the figure on a perfect mirror. He said that several great scope and mirror makers refuse to use them because of this. They go out for coatings as a 10 and come back as a 7-8 at times. This does not imply that it is impossible to get an enhanced coating that would be good, but he said that he had seen this many times and would never advise to use them.

Also, I have read where dielectric coatings are put on with high temperatures. A manufacturer of diagonals has just gotten a patent on a process where he coats both sides of the mirror. Why? Because they said that coating one side only causes the mirror to warp or loose its figure. According to the article I read the diagonal mirror can see a change of 1/20 wave down to 1/4 wave after dielectric coatings are applied to only one side.
They stated that this is why no one states wave readings on dielectric coated diagonals.

These are things I have read or been told by reliable sources and are expressed as an opinion by me! ;^) Pardon the CYA, but you have to cover your self in this forum.

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