ABSTRACT
This chapter deals with the "meat" of geometrical optics, namely, imaging by thin lenses. Lenses are usually made of transparent substance such as glass. Lenses usually consist of two curved spherical surfaces. Cylindrical lenses are also used for special applications. Lenses change the vergence of the wavefront that is incident on it and result in the formation of images. Similarly, spherical mirrors also change the vergence of the incident wavefront and form images. The chapter uses the idea of ray optics to study image fromation by lenses and mirrors. When the magnification is negative, the image is inverted in orientation with respect to the object; when it is positive, the image has the same orientation as the object. A clear understanding of how an image is formed by a spherical surface can be obtained only by studying the image formation for various object positions and sizes for a variety of surface powers.
