In 1545, Dutch mathematician and astronomer Gemma Frisius observed an eclipse with a camera obscura and was able to illustrate it. The meaning of Camera Obscura comes from “dark chamber” because one needed a completely dark room with only a small peephole for light to enter as to project a picture on a wall. For astronomers, it was impossible to apply the Camera Obscura to solar observations because they needed light to see, but the light would blind their eyes. Frisius was able to make solar observations with the help of a solar eclipse, which protected his eye and allowed him to see.
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Source: Philip Steadman, Vermeer and the Camera Obscura, http://www.bbc.co.uk/history/british/empire_seapower/vermeer_camera_01.shtml (accessed September 22, 2011).