Camera obscura
In his experiment of the sun light he extended his observation of the penetration of light through the pinhole to conclude that when the sun light reaches and penetrates the hole it makes a conic shape at the points meeting at the pinhole, forming later another conic shape reverse to the first one on the opposite wall in the dark room.  This happens when sun light diverges from point “ﺍ” until it reaches an aperture “ﺏﺤ” and is projected through it onto a screen at the luminous spot “ﺩﻫ”.  Since the distance between the aperture and the screen is insignificant in comparison to the distance between the aperture and the sun, the divergence of sunlight after going through the aperture should be insignificant.  In other words, “ﺏﺤ” should be about equal to “ﺩﻫ”.  However, it is observed to be much greater “ﻙﻁ” when the paths of the rays which form the extremities of “ﻙﻁ” are retraced in the reverse direction, it is found that they meet at a point outside the aperture and then diverge again toward the sun as illustrated in figure 1.   This was indeed the first accurate description of the Camera Obscura phenomenon.