Lensing magnification
= Lensing magnification
{title2=$\mu=1/[(1-\kappa)^2-|\gamma|^2]$}
The signed magnification is the reciprocal determinant of the <Jacobian matrix> of the <thin gravitational lens equation>. Its absolute value gives the flux and solid-angle amplification; its sign gives image parity. <Gravitational lensing> preserves <surface brightness> in the geometric-optics approximation.