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We propose ultraviolet (UV) imaging to construct spectral energy distributions (SEDs) for a sample of active galactic nuclei (AGN) at redshifts from virgul0.3 to virgul1.0 that have reverberation mapping (RM) measurements of the broad line region. We will use UV--optical SEDs to examine the origin of deviations of sources from the local radius-luminosity (R-L) relation that is used to estimate black hole masses in AGN at high redshift. Because the R-L relation depends on the amount of ionizing radiation reaching the line-emitting gas comma we expect that the R-L relation will depend on the SED of the sources. Our proposed observations will quantify any dependence of the R-L relation on the SED of the AGN and will allow us to apply the R-L relationship to estimate black hole masses in sources spanning a wide range of redshifts and accretion properties. All black hole mass estimates in AGN across the observable universe rely on the calibration and application of the R-L relation it is thus imperative that we understand its limitations and possible dependencies on various AGN properties. This work will be fundamental for studies of the formation and evolution of galaxies and their supermassive black holes.