This paper is an effort to quantify such variables as penetration depth, intensity, and defect contrast in reflection X-ray topographs. The analysis includes an appropriate combination of geometrical, polarization, absorption, and scattering factors. Quantitative measurements have been made for a variety of diffracting planes and wavelengths on Si and Ge. The calculations also fit qualitatively (fluorescent screen intensity} with observations on Zn, ZnO, CdS, GaAs, GaP. Topographs from some or all of these materials will be shown to illustrate how these calculations can predict useful diffraction conditions.