@Slate I haven't looked at recent mirror prices yet, I'm probably remembering numbers from a 1970's Edmund Optics catalog :-)

@uhoh This is an interesting question, and I'd be curious how the answer's changed! Probably it has changed somewhat with the available technologies, too.

Ex., I know that zonal defects on Newtonian parabolic reflectors are more common nowadays due to patterns in machine grinding, which hand grinding tends to average out. But as the demand increases, the additional hand polishing steps have gotten quite a lot trickier to work into the price point of modern Dobsonians.

Ex 2., I believe but don't quote me, that the increased price of shipping containers from China has seriously impacted the sale of GSO scopes and other scopes manufactured in China. Similar supply chain shortages are impacting prices and availability across the board, as well, independent of the cost of labor itself.

There are definitely a lot more manufactured mirrors lately, not necessarily China's fault, that's just the way the market is. But at the same time iirc the quality of the mirrors that are produced by machine has also risen. GSO certifies their plates for 1/4 wave but that's really a 2- or 3-sigma bound, and -- again, don't quote me on this, I think I just read it on Cloudy Nights - their median is somewhere around 1/6 wave.

I'm definitely not an expert in this topic, though. I'm pretty new to the hobby myself.

@Slate does GSO refer to Guan Sheng Optical gs-telescope.com ? They seem to be here in TW but I won't be surprised if the optics are made on the mainland.

Yeah! GSO is one of the major providers of Newtonian telescopes at the moment. They make a ton of mirrors.