I probably did not make myself clear in the discussions I had with Richard Knoppow the other night. Bear in mind that I am not speaking of amateur astronomers in general, but just with the amateur-telescope-making (ATM) community.
Up to around 1965, there were no inexpensive means of having a mirror aluminized, so ATM's all silvered their mirrors and redid them every few years as the coatings degraded. There were not overcoats: there is a simple process of coating which you did in your own kitchen, though caution was in order as several of the necessary chemicals are a bit toxic. At that time, professional telescopes also used a silver coating: major observatories such as Palomar and Wilson have silvering rooms directly below the telescope so that the mirror can periodically be lowered into the room to have the silver coating replaced. That was then, and this is, as they say, now.
Aluminizing requires a vacuum chamber to deposit the film. The resulting coating is quite long-lasting. A simple aluminized coating provides a better wavelength response for photography and, actually, works even better for most astronomical digitial imaging gear. Silver, though, provides a better response pattern for visual work.
Around 1965, several firms began offering relatively inexpensive aluminium coatings for ATM mirrors. All was well until some ATM's questioned the wavelength issue, and then the coating firms, around 1970, began claiming that they were using an overcoat which allowed an aluminium coating to equal the visual wavelength response of silver. And then the engineers got involved. The ATM community is fascinating: it includes tool-and-die makers and accountants -- and a lot of engineers, many of whom work for firms with sophisticated measuring equipment. So, the 1970's and 1980's saw the literature populated with occasional exclamations of shock and horror one way or the other, but, in the end, the consensus was that an aluminium coating with an overcoat did NOT match an simple silver coating for visual work, but was hellaciously more simple and long-lasting.
There are still ATM's who insist on silver. There are still amateur observers who insist on silver. The commercial purveyors of amateur telescopes switched from silver to overcoated aluminium from 1950 to 1965 -- note that all Questar telescopes, from 1952, to the present have had overcoated aluminium coatings, and even the Fecker Celestars of the mid-1950's came with such.
Richard, I hold your views in very high regard, but I suspect that you are being overly institutionalized in your approach. Perhaps it would do you well to rejoin the amateur astronomy community to witness the depth of discussion, much of it over my head, on issues such as this. On a parallel note, there has been a discussion on pages of the British Astronomical Association JOURNAL for the past twenty years over whether the Rayleigh and Dawes limits are really applicable, and whether or not the Reverend Dawes might not have been a piker! Again, most of the discussions are well over my head, being conducted by optical engineers and the like with far greater command of the subject than this peasant could ever have!
One minor point about the vibrancy of the amateur astronomy community, and of the vibrancy of the camera community. There has been a bit of a dispute for the past decade over who determined that, in voting maps in the US, red stood for "Republican" and blue for "Democrats". This decision was absolutely contrary to a century of US political history, in whch the Democrats normally chose red as their campaign color and the Republicans blue. Well, one claimant is our former host, Brian Reid, who has stated that he made the decision in 1996 while doing a computer simulation for a client. The other person suggested for the honor is Robert Vanderbei, who is given this honor by THE ECONOMIST for work done in the 2000 election. Both fellows acknowledge that they had no experience in politics and did not realize that they were flipping the axes with their choices. It is odd that I know both folks thanks to the Internet.
I need not bore you with Brian's many accomplishments. Robert was the fellow who began aggressively exploring the use of "stacking" astronomical images in the early 1990's to exceed the limits of what could be expected from a small telescope. He know does phenomenal work with a 3.5" (89mm) Questar and a digital camera. It is all far above my head, but it is most impressive!
Me? I take my Questar and my Celestar Four and my Swift 731 76mm refractor out on clear nights onto my dark-sky driveway and enjoy the heavens.
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