All Figures

Figure 1: The CCM parameterisation of the Milky Way extinction curve (solid black line) for four different RV (0.5, 2, 3.1 and 4) where the highest values of RV correspond to the flattest curves. We also show the Fitzpatrick parameterisation (dotted blue) with RV=3.1, the Prévot law for SMC-like extinction (dashed green) with RV=3.1 and the starburst extinction law (dashed dotted yellow) with the preferred value for starburst galaxies RV=4.05 (Calzetti et al. 2000). is the extinction at wavelength and AV is the visual extinction.

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In the text

	Figure 2: A histogram over rest-frame B-V for the quasars in SDSS DR3 (solid line), and for the quasar images in our sample (dashed line).
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In the text

	Figure 3: Uncertainties in the template colours for u-g, u-r, u-i, u-z, g-r, g-i, g-z, r-i, r-z, i-z (from black to light grey) as a function of redshift z.
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In the text

	Figure 4: Confidence levels for some of the quasar images that could be fitted by dust extinction in the intervening galaxy using the Fitzpatrick extinction law. The levels correspond to 1 for one parameter (black line) and 68% (dark blue region) and 90% (pale blue) for two parameters.
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In the text

Figure 5: Comparison of the measured magnitudes (black signs) with the fitted magnitudes (light blue solid line) for the images that could be fitted using the dust laws. The dark blue dotted line shows the expected magnitudes without dust. Note that sometimes only one line is visible when the best fit is with little or no extinction. The ground-based measurements are marked with plus signs while the HST observations are marked with triangles. All magnitudes are normalised so that the magnitude at the longest wavelength is zero.

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In the text

Figure 6: Comparison of the measured magnitudes (black signs) with the fitted magnitudes (light blue solid line) for the images that were badly fitted using the dust laws. The dark blue dotted line shows the expected magnitudes for no extinction. Note that sometimes only one line is visible when the best fit is with little or no extinction. The ground-based measurements are marked with plus signs while the HST observations are marked with triangles. All magnitudes are normalised so that the magnitude at the longest wavelength is zero.

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In the text

Figure 7: The co-added probability distributions for the fits with intervening dust following the Fitzpatrick extinction law, weighted by the probability of the fit. The dotted line shows the added probability when using the well fitted quasar images in Table 3 and the solid line when also the objects in Table 4 are included. The added probabilities for the subset of early-type galaxies (dashed line), late-type galaxies (dash-dot) and starburst/star-forming galaxies (dash-dot-dot-dot) are also included in the figure.

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In the text

Figure 8: The fitted values of RV with the 1 errorbars for all images that could be fitted using the Fitzpatrick parameterisation of dust in an intervening galaxy. The first panel shows RV as a function of dust redshift and the second as a function of colour excess. In the first panel, the results from the different images of the same quasar will be plotted on top of each other since they all have the same redshift. In the second panel, the results of different images will be plotted in different places along the x axis since E(B-V) differs at least slightly between the images. The fitted values which have a larger probability than 10% (see Table 3) are plotted with stars and dark blue solid errorbars while the less reliable ones, with a smaller probability than 10%, are plotted with plus signs and dotted light blue errorbars. The most probable value of RV found when co-adding the probability distributions for the fits (see Fig. 7) is indicated with a dotted line at RV = 2.4.

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In the text

	Figure 9: The values for different E(B-V) in the host galaxy (first panel) and RV in the intervening galaxy (second panel) for MG0414+0534 .
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In the text