The first steps for learning optics: Ibn Sahl's, Al-Haytham's and Young's works on refraction as typical examples
Optics scholars did not only discover optical phenomena and laws governing them. Some of them also invented impressive optical systems and instruments or offered us techniques to juggle with optical signals and rays. One typical example of the impressive optical systems is the camera obscura invented by Ibn Al-Haytham. For techniques enabling us to easily handle optical rays, one can mention Young's method to handle rays put into play by refraction. Nine centuries before him, Ibn Sahl proposed an elegant method to manipulate refraction related rays. These three examples will be handled in this paper, together with a historical overview inviting the reader to be in the context of this fascinating works.