Vergence

The vergence of light is defined by

Vergence = V = n/L

where n is the index of refraction of the medium and L is the distance in accordance with the Cartesian sign convention. The standard use of vergence expresses the distance L in meters, so the unit of vergence is m-1, often called "diopters".

Since the distance L1 is measured from the wavefront and light is traveling left to right, it is a negative distance and the vergence is negative (divergent). L2 is positive since it is directed to the right from the wavefront (convergent).

The change in vergence when the light encounters a refracting surface is equal to the power of the surface Ps:

V + Ps = V'
Vergence ExampleVergence Tracing in Thick Lenses
Index

Lens concepts

Thick lens concepts

Meyer-Arendt
Ch 1.1
 
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Vergence Example

The example below shows a positive lens followed by a negative one, but the powers can be given any value, positive or negative. At each surface the relationship V + Ps = V' is applied, and the change in vergence between surfaces is calculated.

Index

Lens concepts

Thick lens concepts
 
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