Gravitational deflection of light in the Schwarzschild-de Sitter space-time

Recent studies suggest that the cosmological constant affects the gravitational bending of photons, although the orbital equation for light in Schwarzschild-de Sitter space-time is free from a cosmological constant. Here we argue that the very notion of a cosmological constant independent of the photon orbit in the Schwarzschild-de Sitter space-time is not proper. Consequently, the cosmological constant has some clear contributions to the deflection angle of light rays. We stress the importance of the study of photon trajectories from the reference objects in bending calculations, particularly for asymptotically nonflat space-time. When such an aspect is taken into consideration, the contribution of a cosmological constant to the effective bending is found to depend on the distances of the source and the reference objects.