Using the convex lens as the example, the main parts of the lens and image formation were sketched and defined. This included the center of the lens, the principal axis, the focal plane, the focal point, the focal distance and twice the focal distance. Rules governing the refraction of light through a lens were reiterated as well as the method used to determine where and how large an image is. Two ray diagrams were sketched, one with the object placed greater than 2f and one with the object placed at 2f. The type of image was explained by the student, eg: inverted or upright, size in relationship to object, same, larger or smaller, type, real or virtual. Each ray diagram was drawn on a separate graph paper.