The black circle with radius \(R_s\) represents the event horizon of the black hole.
Photons arrive from the right (\(x=+\infty\)
and \(y=b\)) with an impact parameter value \(b\)
that gives a deviation of \(4\pi\)
(2 full revolutions).
The figure is plotted with Cartesian coordinates \(x=r\cos\varphi\) and \(y=r\sin\varphi\),
considering a hypothetical black hole of the mass of the sun \(M\odot\)
that is, \(R_s=2 \ 953\ m\), \(b_{crit}=7\ 672.73\ m\) and with \(b_{4\pi} = 7\ 672.75\ m\).
The value of \(b\) can be obtained by choosing the value of the final variation \(\Delta\varphi\) = deviation + \(\pi\) (target value in an Excel spreadsheet or input data in a Python script).
Here, it is \(b_{crit} + 2\ cm\)
A deviation of \(8\pi\) (4 full revolutions) is obtained with \(b_{8\pi} = b_{crit} + 7\ 10^{-8}\ m\).
For a black hole with a different mass \(M\), the plots are kept by applying the scaling factor
\(\frac{M}{M\odot}\).