For refraction through a spherical interface (from medium 1 to 2 of
refractive index n1 and n 2, respectively)
2
1
2
1
n
n
n
n
v
u
−R
−
=
Thin lens formula
1
1
1
v
u
f
−
=
Lens maker’s formula
1
1
1
2
1
1
1
2
f
n
n
n
R
R
=
−
(
)
−




R1 and R2 are the radii of curvature of the lens surfaces f is positive
for a converging lens; f is negative for a diverging lens The power of a
lens  P = 1/f The SI unit for power of a lens is dioptre (D): 1 D = 1 m–1