Precision low-tech
We consider whether to build or buy.
In our astronomer’s bookshelf are three volumes with the unlikely title of Amateur Telescope Making (the original, Advanced, and Book Three). A telescope is, after all, a precision optical instrument; how could an amateur make one? The idea seems even more absurd when we get into the numbers: the curve of a lens or a mirror must be the right one, a deviation the size of a wavelength of light making it all but useless. (How big is that? Say, half of a millionth of a meter, or twenty millionths of an inch. Really small compared to anything you can hold in your hand.) But the books give directions on how to do it. And how to do it with very old, low-tech methods. By “very old” we mean technology freely available in the 1920s, when the first of these collected articles was written. And by “low-tech” we mean, not the apparatus of a research workshop or precision machine-shop, but what might be at hand on a farm (roughly half of Americans were still rural dwellers at the time).
The astonishing thing is that it worked, that people with no special skill or tools could (with patience and care) make their own telescopes. It’s less astonishing why they did so. A professional product of any size (main lens or mirror of, say, six-inch diameter upward) was simply out of reach of most incomes at the time, and with the Great Depression became even less obtainable. The materials to do it on one’s own cost little. The main inputs were time and care.
Amateur Telescope Making continued to be a large part of the hobby even in postwar America, with its rising standard of living and greater disposable income. It was easier to buy a ‘scope than it used to be, and more were sold, but it was still much cheaper to make your own. And also easier to make one than it had been: in the later articles collected in the books we see electric bulbs used for testing, rather than kerosene lamps, and there is no longer a need to test and purify one’s pitch and grinding material. Homemade telescopes dominated the larger sizes among amateurs in the 1960s and 70s and into the 1980s. They do so no longer.
Why is that? We think the answer is a matter of economics. Sometime in the 1980s, we reckon, there came to be a sufficient number of people interested in buying a larger telescope and having sufficient disposable income to do it, that it made economic sense for a company to invest in large-scale manufacturing. With a big enough market the price came down, which enlarged the market even more, and commercial eight-inch Schmidt-Cassegrain telescopes proliferated. At the same time, for most people life became more scheduled and busy, so finding the extended periods of time required to grind, polish and figure a mirror became much harder. Buying made more sense.
Our astronomer, dinosaur that he is (with one mirror and part of another to his credit), thinks this is overall a good thing. There are no doubt many wonderful examples of optical engineering that get little use, having been bought rather than painfully made. And many amateur astronomers no longer understand very much about optics. But there are now observers in the hobby that, in the old days, would have been excluded by the mirror-grinding rite of passage; and that can only be good.
