Lens Maker Equation Calculator

Find a lens's focal length from its radii and refractive index.

Refractive index

Radius R₁

Radius R₂

Focal length 0.2

Power (D) 5

Formula: 1/f = (n − 1)(1/R₁ − 1/R₂)

Step-by-step with your numbers:

1. Values used:

2. Refractive index = 1.5

3. Radius R₁ = 0.2

4. Radius R₂ = -0.2

6. Focal length = 0.2

7. Power = 5D

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The lens maker's equation links a lens's shape and material to its focal length.

The math behind it

1/f = (n − 1)(1/R₁ − 1/R₂). Use sign conventions: convex-toward-incoming-light radii are positive.

n = 1.5, R₁ = 0.2 m, R₂ = −0.2 m → f = 0.2 m (power 5 D).

What is a flat surface's radius?

Infinite — its 1/R term is zero.