Parameters
n : refraction index
R1 : radius of curvature of the first surface
R2 : radius of curvature of the second surface
e : center thickness
fi : effective focal length in the image space
l : distance from the vertex of the first surface to the primary principal plane
li : distance from the vertex of the second surface to the secondary principal plane
L : distance from the primary principal plane to the secondary principal plane
ft : front focal length
fb : back focal length
