SAG Calculator

Sag (mm): --

$$ \text{SAG} = \left| R \right| - \sqrt{R^2 - \left( \frac{D}{2} \right)^2} \approx \frac{D^2}{8 R} $$

R	Radius of Curvature
D	Diameter
	Paraxial approximation is good for $ \tfrac{D}{2}<<R $

Description

Determine the sag of a surface based on radius of curvature and diameter.

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