The focal plane power distribution due to a bright source is analyzed for an infrared imaging optical system. Irradiance from the bright source is spread throughout the focal plane according to the characteristics of the system. This effect is attributed to diffraction, reflection and scattering in the optical train. Expected focal plane power distributions due to diffraction and multiple reflections between dielectric surfaces are calculated and compared to measured data. The difference is attributed to scatter characteristics of the optical elements. A brief overview of the major sources of scatter lays groundwork for a further analysis of scattering characteristics in the optical system.