Degeneracies in parameter estimates for models of gravitational lens systems

It is noted that observations of gravitational lens systems can yield useful estimates for characteristics of the lenses and for cosmological parameters. However, the nature of these observations restricts the types of characteristics that can be determined. This paper demonstrates some of these inherent restrictions (i.e., degeneracies in parameter estimation) through an analysis of the effects of prismatic, similarity, magnification, and combined transformations. These transformations show that changes over continuous ranges in the values of parameters describing the source and the lens models can leave unchanged the predicted values of observable properties (relative positions, luminosities, magnifications, and time delays) of gravitational images. 32 references.