Lights, Camera, Action!

In high school, I had an astronomer friend who liked to make his own telescopes. He learned how to make a telescope through a local planetarium, which included the skill of grinding and polishing mirrors. For beginners, the planetarium had a saying that the quickest way to make a 4-inch mirror is to make a 3-inch mirror first. The reasoning was based on two things. First, it takes a long time to grind and polish glass to make a mirror, and the larger the mirror, the longer it takes to grind. Second, the likelihood of making a mistake is higher the first time you go through the process. Since it is likely you are going to mess up the first mirror, it is better to learn from the failure by making a smaller one.