We calculate analytically and numerically the Dyer-Roeder distance in perfect fluid quintessence models and give an accurate fit to the numerical solutions for all the values of the density parameter and the quintessence equation of state .
Then we apply our solutions to the estimation of H _ { 0 } from multiple image time delays and find that the inclusion of quintessence modifies sensibly the likelihood distribution of H _ { 0 } , generally reducing the best estimate with respect to a pure cosmological constant .
Marginalizing over the other parameters ( \Omega _ { m } and the quintessence equation of state ) , we obtain H _ { 0 } = 71 \pm 6 km/sec/Mpc for an empty beam and H _ { 0 } = 64 \pm 4 km/sec/Mpc for a filled beam .
We also discuss the future prospects for distinguishing quintessence from a cosmological constant with time delays .