We demonstrate the method of diffraction at shallow angles of incidence, using the intrinsically highly collimated x-ray beam generated by a synchrotron source, through the study of diamond thin films in their as-deposited (i.e., on substrate) state. As the incident angle is decreased, scattering from the diamond film can be isolated as contributions from the substrate are reduced. Diamond films deposited onto both silicon and steel substrates have been examined, evidence of an interfacial region between the film and silicon wafer has been observed, and conventional transmission x-ray diffraction has been used as a complement to the shallow angle results from the films deposited on steel.