Two medieval writers did much to analyse optical effects: Ibn al-Haitham, born in Basra in Iraq ah354 (Islamic calendar) (ad 965) and Roger Bacon, born in Somerset around 1214. Both were jailbirds. Ibn al-Haitham went to Cairo to work as a hydraulic engineer for the Caliph, pretended to be mad and was thrown into jail when he realised he could not carry out the Caliph's schemes. Roger Bacon was locked up in Paris in the 1260s and again for a decade from 1278, because of charges of heresy.
The role of light in God's creation was fundamental to the philosophies of both men. Ibn al-Haitham, known in western Europe as Alhazen, wrote geometrical analyses of the inner workings of the human eye and produced theories of light and vision. He described the camera obscura, explaining how the image of a candle would be inverted when shone through a small hole on to a screen in a dark room.
Bacon translated and publicised Alhazen's theories of light. Writing when spectacles were first used in western Europe, Bacon commented on the amazing ways in which convex glasses or crystals could improve vision and outlined Alhazen's model of the eye.