  Several recent papers have suggested that the cosmological constant Lambda
directly influences the gravitational deflection of light. We place this
problem in a cosmological context, deriving an expression for the linear
potentials which control the cosmological bending of light, finding that it has
no explicit dependence on the cosmological constant. To explore the physical
origins of the apparent Lambda-dependent potential that appears in the static
Kottler metric, we highlight the two classical effects which lead to the
aberration of light. The first relates to the observer's motion relative to the
source, and encapsulates the familiar concept of angular-diameter distance. The
second term, which has proved to be the source of debate, arises from cosmic
acceleration, but is rarely considered since it vanishes for photons with
radial motion. This apparent form of light-bending gives the appearance of
curved geodesics even within a flat and homogeneous universe. However this
cannot be construed as a real lensing effect, since its value depends on the
observer's frame of reference. Our conclusion is thus that standard results for
gravitational lensing in a universe containing Lambda do not require
modification, with any influence of Lambda being restricted to negligible
high-order terms.
