Consider a thick biconvex lens whose magnitudes of the radii of curvature of the first and second surfaces are 45 cm and 30 cm respectively. The thickness of the lens is 5 cm and the refractive index of the material of the lens is 1.5. Determine the elements of the system matrix and positions of the unit planes and use Eq. (67) to determine the image point of an object at a distance of 90 cm from the first surface. On simplification, we obtain (67)