Images formed by convex lenses If the incident rays are parallel(that is come from infinity),they will be converged upon a single point on the other side of the lens;at this point the image will be formed...This point is known as the principal focus,and its distance from the lens is called the focal length. Fig.The incident rays are parallel,coming from infinity;the focus (F)is called the principal focus. In practice,an object which is 6 meters or more away,is considered to be at infinity,and the rays of light issuing from it are parallel 8 Images formed by convex lenses If the incident rays are parallel (that is come from infinity), they will be converged upon a single point on the other side of the lens; at this point the image will be formed… This point is known as the principal focus, and its distance from the lens is called the focal length. 8 Fig. The incident rays are parallel, coming from infinity; the focus (F) is called the principal focus. In practice, an object which is 6 meters or more away, is considered to be at infinity, and the rays of light issuing from it are parallel