Two photon trajectories emitted at different radii, r₁ and r₂, and emission angles, α₁ and α₂, with their corresponding impact parameters, b₁ and b₂. Trajectory 1 is for a direct photon, while trajectory 2 has a turning point, i.e., passes through periastron p, the minimum distance between the trajectory and the BH. The observer is at infinity, and photons geodesics lie in a single invariant plane.