Virbhadra–Ellis lens equation

The Virbhadra-Ellis lens equation in astronomy and mathematics relates to the angular positions of an unlensed source $$\left(\beta\right)$$, the image $$ \left(\theta\right)$$, the Einstein bending angle of light $$(\hat{\alpha})$$, and the angular diameter lens-source $$\left(D_{ds}\right)$$ and observer-source $$\left(D_s\right)$$ distances.


 * $$\tan \beta = \tan \theta - \frac{D_{ds}}{D_s} \left [\tan \theta + \tan \left (\hat{\alpha}-\theta\right ) \right ]$$.

This lens equation is useful for studying gravitational lensing in a strong gravitational field.