Born approximation in cosmological lensing
= Born approximation in cosmological lensing
{c}
{title2=$\Psi(\eta,\mathbf x)\simeq\Psi(\eta,\mathbf x_{\rm background})$}
In a first-order light-deflection calculation, evaluate the <Weyl lensing potential> and its gradients on the unperturbed <null geodesic>. The position correction is first order, so inserting it into an already first-order potential produces a second-order correction. This approximation omits repeated deflection and lens-lens coupling.