The earliest known written record of the camera obscura is to be found in Chinese writings called Mozi, dated to the 4th century BCE. Until the 16th century the camera obscura was mainly used to study optics and astronomy, especially to safely watch solar eclipses without damaging the eyes. In the later half of the 16th century some technical improvements were developed: a (biconvex) lens in the opening (first described by Gerolamo Cardano in 1550) and a diaphragm restricting the aperture (Daniel Barbaro in 1568) gave a brighter and sharper image. In 1558 Giambattista della Porta advised using the camera obscura as a drawing aid in his popular and influential books.
