This equation is used for manufacturing lens. Therefore it is called lens maker's equation.
Following are the important assumptions made for lens maker's formula.
1. The spherical must be very thin
2. The distance from pole to optical centre must be very-very small.
3. The angle made by object, image and normal must be very-very small.
For refracting surface XAY
Using in equation (1)
:. P1 is very-very close to “C”
For refracting surface XP2Y
:. P2 is very-very close to “C”
adding eqn (5) and (10)
Using proper sign-convention,
According to lens equation
Equation (15) is called lens maker's equation,