  We calculate the deflection angle of light from a distant source by a galaxy
cluster in Weyl's conformal gravity. The general method of calculation is first
applied to calculate the deflection angle in Schwarzschild-de Sitter (Kottler)
spacetime. The deflection angle calculated in Kottler spacetime includes the
contribution of the cosmological constant, which quantitatively agrees with one
work and disagrees with many works in the literature. We then calculate the
deflection angle in Mannheim-Kazanas spacetime in two conformally related
coordinate systems and find that the result includes contributions from both
the cosmological constant and the Mannheim-Kazanas parameter. There are
conflicting results on the deflection angle for light in Weyl gravity in the
literature. We point out a possible reason for the discrepancy between our work
and the others.

General Relativity and Quantum Cosmology