Position of Object and Image - (Fig.8.1.5) The positions of object (u) and image (v) are related to the radius of curvature (R) of the surface and the refractive indices (n₁n₂) of two media as

                                                                        (2)

Where R is the radius of curvature of curved surface.

If the object is brought closer to the primary focal point, the image is shifted away from the vertex.

For Objects placed at infinity ( ) the image is formed at secondary focal point (v=f ').

                                                (3a)

Similarly if the object is placed at the primary focal point (u=f), the image is formed at infinity .

                                                   (3b)