2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/480We apply elliptical isothermal mass models to reproduce the point source properties, i.e. image positions, flux density ratios and time delay ratios, of the quadruple lens B1608+656. A wide set of suitable solutions is found, showing that models that only fit the properties of point sources are under-constrained and can lead to a large uncertainty in the prediction of Ho. We present two examples of models predicting Ho=100 km/(s Mpc) (chi^2=4) and Ho=69 km/(s Mpc) (chi^2=24).2 pages, 1 figure. To appear in "Gravitational Lensing: Recent Progress and Future Goals", Boston University, MA, July 1999, eds. T.G. Brainerd and C.S. KochanekAstrophysicstext