As I have observed lately, most of the small telescope mirrors available right now are out of China, most of those produced by one company, Guan Sheng Optical or GSO. If you want a small mirror, say a 6″ or 8″ mirror, there is not a lot of choice, the mirror makers in the US generally do not do anything smaller than 10″.
The GSO mirrors range from decent to pretty bad, with no way of knowing what you will get when you order, just luck of the draw.
But how do you tell?
Continue reading “Testing a Mirror”