Ibn al-Haytham (c. 965–1040 AD), an Arab physicist also known as Alhazen, wrote very influential essays about the camera obscura, including experiments with light through a small opening in a darkened room. The invention of the camera has been traced back to the work of Ibn al-Haytham, who is credited with the invention of the pinhole camera. While the effects of a single light passing through a pinhole had been described earlier, Ibn al-Haytham gave the first correct analysis of the camera obscura, including the first geometrical and quantitative descriptions of the phenomenon, and was the first to use a screen in a dark room so that an image from one side of a hole in the surface could be projected onto a screen on the other side. He also first understood the relationship between the focal point and the pinhole, and performed early experiments with afterimage.