LECTURE 16 THIN LENSES – RAY TRACING
Instructor: Kazumi Tolich Lecture 16
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¨ 18.4 Image formation by refraction
¨ 18.5 Thin lenses: ray tracing ¤ Converging lenses ¤ Real images ¤ Magnification ¤ Virtual images ¤ Diverging lenses Quiz: 18.4-1 18.4 Image formation by refraction
¨ The optical axis is the line through the object and perpendicular to the boundary.
¨ Using Snell’s law and geometry, you can show that the image distance is given by
� � = � � 18.5 Thin lenses: ray tracing
¨ A lens uses refraction of light rays at curved surfaces to form an image.
¨ Ray tracing is a pictorial method used to understand image formation. Quiz: 18.5-1 18.5 Thin lenses: ray tracing – focal point and focal length
¨ The incoming rays parallel to the optical axis converge at (converging lens) or appear to diverge from (diverging lens) the focal point of the lens.
¨ The focal point on the incident-light side is the near focal point; the focal point on the other side is the far focal point.
¨ The focal length � of the lens is the distance of the focal point from the lens. 18.5 Converging lenses
¨ A thin lens is an idealized lens whose thickness is zero and that lies entirely in a plane called the lens plane.
¨ Within the thin-lens approximation, all refraction occurs as the rays cross the lens plane, and all distances are measured from the lens plane.
¨ The special rays for a converging lens: Quiz: 18.5-2 through 18.5-4 18.5 Magnification
¨ The magnification � describes the orientation and size of the image relative to the object and its size.
� � = − �