Null geodesics in a Schwarzschild space-time reaching an observer on the far right. According to their winding number, geodesics can make up the inner shadow (brown), the n = 0 image (orange), or the n = 1 photon ring (light blue). We represent the projections of the black hole (black), the photon sphere (blue), and the equatorial plane for different polar directions on the screen: ψ = 0° (pink), 45° (red), and 90° (violet).