Like many observers I’ve talked to through the years, I always have had a special place in my heart for a small refractor. Refracting telescopes use lenses to bring light to a focus and are the oldest type of telescope. While the inventor of the refractor is a matter of debate, Hans Lipperhey, a German-Dutch spectacle maker, filed the first known patent application October 2, 1608.
Early refractors typically required a large (or slow) focal ratio — which translates to a really long tube — to keep false color under control. Such instruments were a bit unwieldy, especially if there was any wind. Major improvements followed: the achromatic lens (in 1733), the apochromatic lens (in 1981), and various formulas for types of low-dispersion glass.
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