35 years ago it would have been unthinkable in my country to mass produce such large, quality mirrors with the technology available at the time, a 10-12 inch mirror tended to be something mounted in a GEM in a small observatory, it's great that this has become affordable for everyone now. One of the enabling technologies I think is laser interferometry (actually digital photography and computers.......laser interferometry existed before but we previously used Polaroid photography and rulers!), it lets factory workers who are not deeply trained to quickly determine the rough figure of a mirror on a computer screen. When making hundreds of mirrors quickly, it is impractical to hire enough expert eyes of specialists with traditional knife-edge based techniques.
The Newtonian mirror-making factories are located I think in two different Chinese-speaking countries, one is smaller (around 40 employees?) and started installing mirror making equipment and laser interferometry in the late 1990's or early 2000's as I understand, and they seem to use more traditional polishing methods to make 6 to 16 inch mirrors. A 10 inch f4 mirror+88 mm secondary mirror set costs around 600 USD, for f/5 it is 330 USD, in the past they provided mirrors for US brands like Orion (up until early 2000's?) and Meade. Photo shows the laser interferometer in the elevator hall, it's hard to tell from the photos, but this is probably designed for fast, quick-look measurements.
A recruitment ad for mirror polishing and CNC jobs at this company? 35 employees, 95% of production exported overseas.
The other company with the much larger market share makes every kind of telescope in a large factory at much lower prices, and tends to utilize more large-scale CNC technology (photos in the other post above). I heard about their technological advances and ramping up of mirror production in the late 2000's, but I'm not very sure.
This includes a bit of guessing, but the higher-priced US products tend to have higher grade glass materials (there are several glass companies providing a spectrum of glasses, even though they may use the same tradename, the expensive grades have less defects buried in the glass, higher homogeneity); better annealing (glass contains internal stress, and this can cause the optic to slightly deform when the temperature changes or very long periods of time pass, but annealing in a furnace tends to relax this stress and reduce some defects), each mirror will be followed through on an individual basis and optimized by an expert, traditional testing methods may be used (this is for me an advantage, though other people may disagree) rather than relying on laser interferometry. Longer times would be spent in polishing. Figure is often just a bit better, though I have seen only a few examples of both types of mirrors. All this may give a subtle improvement at the eyepiece, the rest is up to individual choice.
This is not to say, people must spend a fortune to enjoy a 10 inch telescope, this is absolutely not the case and I agree with what the others on this thread are saying.
It's just a bit frightening, I clearly remember around year 2000, it could cost 200,000 USD to manufacture any new ED lens element of diameter maybe 4-5 inches because of the polishing tools and measurement devices one first had to manufacture for each new lens. Now with the new grinding devices and lower-cost glass materials it seems so much awfully cheaper.... 7 or 8 inches really appears to be no problem.....
Edited by X3782, 12 August 2018 - 04:34 PM.