Glass is used because it is more stable at a wider temperature range. Pretty important when you are focusing things that are light years away. It's a proven FACT that acrylic provides better clarity for the aquaria than glass.rrviper201;1001325; said:The highest quality optical medium for viewing is proven every time the Keck, Gemini, or Hubble telescopes take a picture. NASA spent $65,000,000
on a 2500 lb, 8ft diameter disc of GLASS so we could see across the universe. Polished over an 8 month period, the mirror was declared to be the smoothest surface ever created by man. Telescopes, cameras, webcams, binoculars, and everyday glasses made with plastic optics are garbage. Plastic is a solid.........Glass is a liquid this makes a difference.
Glass is a liquid?
That is one of the oldest legends around.