Solutions of the lens equation for axisymmetric power-law lens models. The coloured solid curves show θ − α(θ) as a function of θ for two lenses with the same Einstein radius and different values of the density slope parameter γ. The horizontal dashed line marks the position β of a background source. Its images form at solutions of the lens equation, β = θ − α(θ), indicated by the vertical dotted lines with the colour of the corresponding lens model. For the lens with density profile shallower than isothermal, γ < 2, three images form, while the γ > 2 lens produces only two images. The slope of the θ − α(θ) curve is the inverse of the radial magnification. Stationary points, only visible in the γ < 2 case, correspond to the radial critical curve.