Question

1. Compare the image formed by a "pinhole camera" (pupil of your eye) to the object from which the image is formed. (video)

2. What is dispersion of visible electromagnetic radiation (light). Explain. Why would reflecting telescopes not have a dispersion problem?

Answer 1

1. The difference between the image formed by a pinhole camera to the object from which the image is formed will be

• Pinhole image will have nearly infinite depth of field. Hence, the image will be always focused
• As there's no lens distortion, wide angle images will remain absolutely rectilinear
• The image of the fast moving object will be blurred
• Multiple images with multiple pin holes can be obtained

2. Dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency or wavelength. One of the consequences of dispersion is the change in the angle of refraction of different colors of light from a refractive medium. In other words, the refrective index varies with wavelength of the light and gets separated. It also happens with lens. The image formed by the blue light will be separated laterally by the image formed by the red light. This is one of the reasons that the reflecting telescopes not have a dispersion problem. Mirrors does not causes dispersion.