More on Lensing by a Cosmological Constant
  The question of whether or not the cosmological constant affects the bending of light around a concentrated mass has been the subject of some recent papers. We present here a simple, specific and transparent example where $\Lambda$ bending clearly takes place, and where it is clearly neither a coordinate effect nor an aberration effect. We then show that in some recent works using perturbation theory the $\Lambda$ contribution was missed because of initial too-stringent smallness assumptions. Namely: Our method has been to insert a Kottler (Schwarzschild with $\Lambda$) vacuole into a Friedmann universe, and to calculate the total bending within the vacuole. We assume that no more bending occurs outside. It is important to observe that while the mass contribution to the bending takes place mainly quite near the lens, the $\Lambda$ bending continues throughout the vacuole. Thus if one deliberately restricts one's search for $\Lambda$ bending to the immediate neighborhood of the lens, one will not find it. Lastly, we show that the $\Lambda$ bending also follows from standard Weyl focusing, and so again, it cannot be a coordinate effect. 
Mustapha Ishak, Wolfgang Rindler, Jason Dossett (The University of   Texas at Dallas)