Hi I am Jeremy. I am a 7th grade student and I need some help is science. Hi Jeremy, Most telescopes built these days use mirrors instead of lenses. The mirrors are concave. The mirrors and lenses are made the same basic way as they were three hundred years ago - they are ground into shape from large chunks of glass.
Molten glass is poured into a mold that is the basic shape as the desired mirror or lens.
Then, various machines are used to carefully grind off extra glass and form a perfectly-shaped mirror. Please let me know if you have more quiestions. Sincerely, Kurtis Back to the Ask An Astronomer page.