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Abstract:
Gravitational bending of light influences observations of cosmologically distant sources, e.g. by producing an amplification bias in source counts. To assess the importance of any such effect one has to determine its probability, given a random distribution of lenses. For this purpose, the assumptions underlying the Dyer-Roeder description of light propagation in a clumpy universe are exhibited and its weaknesses are pointed out. Assuming this description as a working hypothesis and combining it with the lens equation, a formula for the probability of lens effects is derived which differs from the one hitherto accepted. It is shown that the previous formula is inconsistent with the assumed law of light propagation in a clumpy universe, and that, compared to the new formula, the former one significantly underestimates the importance of light bending.
