Virbhadra–Ellis lens equation

Template:Technical 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.

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

This approximate lens equation is useful for studying the gravitational lens in strong and weak gravitational fields when the angular source position is small.

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