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Galileo's Telescope; the Opera Glass The simplest, and also the oldest form of telescope is Galileo's telescope. This has but two lenses; namely, a convex object glass, and a concave eyepiece (Fig. 1). The eyepiece is placed between the object glass and the image formed by it. Being concave, the eyepiece causes the rays to diverge and appear to the eye to come from ab, which thus forms an enlarged upright image. Opera glasses consist of a pair of these telescopes.