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Published online by Cambridge University Press: 19 July 2016
The generalisation from circular to elliptical mass distributions acting as gravitational lenses produces a number of interesting effects. These effects include an extra indeterminacy in predictions of the time delay between the two brightest images, if only the relative brightness and separation of these images is known. This indeterminacy is removed if further information about the system (such as a measurement of the astigmatism of the lens) is available.