Which innovative manufacturing technique did Celestron pioneer in the 1960s that revolutionized the telescope market by making Schmidt-Cassegrain telescopes more affordable for amateur astronomers?

Before the 1960s, quality telescopes were primarily handcrafted, expensive, and accessible mainly to professional astronomers and wealthy enthusiasts. Then came a product innovation that changed amateur astronomy forever, making quality optics available to the masses through manufacturing innovation and new distribution channels. Test your knowledge of this pivotal moment in consumer astronomy!

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Mass production of precision-ground mirrors using computer-controlled grinding
Vacuum deposition of aluminum on glass substrates
In-house production of Schmidt corrector plates using a specialized vacuum process
Outsourcing all optical components to Japanese manufacturers