Aperture-

➤ Aperture Here we'll discuss only those spherical mirrors which are of small aperture i.e., we have to study only those of spherical mirrors which are of small aperture in our syllabus. The circular diameter of reflecting face of a mirror is called aperture. In figures 1.8 (a) and 1.8 (b), MN is denoted by aperture. It is normal to principal axis.