For a given wavelength, the refractive index of a lens at may be computed using the quadratic:

     [ C1 - C2 + C1 * C2 * t ] * k² +
     [ P1 - P2 + C1 - C2 + C1 * P2 * t + P1 * C2 * t ] * k +
     [ P1 - P2 + P1 * P2 * t ] = 0

where:

     C1 is the curvature of the first surface
     C2 is the curvature of the second surface
     t is the lens thickness
     P1 is the inverse of the source distance from the first surface
     P2 is the inverse of the target distance from the second surface
     k is the refractive index minus 1

In this equation, distances to the left are considered negative, and distances to the right are considered positive. The thickness is always positive. Surface radii (or curvatures) are considered negative if the center of curvature is to the left, and surface radii are considered positive if the center of curvature is to the right.

INDEX CALCULATOR

To use this calculator, either the radius of curvature or the curvature for each surface needs to be known. The thickness also needs to be known. These values are entered into the appropriate box and the button under it is clicked, selecting that option.

After the above are provided, the distances of the source and target need to be provided. After these are entered with the clicking of the buttons under them, the refractive index of the lens material is calculated.