Glass-making is an ancient art, originally developed in the Middle East. Its secrets have been lost, re-discovered at different times and in different processes, and eventually spread around the world. The magnifying properties of glass were obvious and often remarked upon.
Modern lenses evolved from reading stones — rock crystal, for example, that was shaped into magnifiers, the first step toward creating instruments that would make the minute world visible.
Reading stone
The scientist and mathematician Abu Ali Hasan Ibn Al-Haitham, also known as Alhazen, "the father of modern optics," working in 11th-century Spain, described many of the properties of light, including refraction and color, as well as the magnifying properties of lenses.
In 1604, Johannes Kepler, the great German mathematician, astronomer and inventor, published Optics, an astonishing treatise that covered the nature and action of light, as well as the mechanics of sight. Optics became part of the bedrock of physics.
In 1611, Kepler improved on Galileo's telescope by replacing its concave eyepiece with a convex one. (Candidates abound for the honor of inventing the telescope, around 1600.)
Incidentally, Kepler's mother, Katharina, was accused of witchcraft in 1615, when she was about 70. He handled her defense himself, eventually winning her acquittal. Katharina Kepler reportedly had played a part in her son's lifelong love affair with the heavens: When he was six years old, she took him to "a high place" so he could see the spectacle of the Great Comet of 1577 in the night sky.