Experimental results on mild lead telluride (PbTe) material and vacuum-deposited multilayers are reported. Optical absorption of mild lead telluride is determined by envelope methods and found to be different from that of stoichiometric lead telluride on cooling. Generally, the performance of multilayer coatings which are composed of mild PbTe/ZnSe is deteriorated in middle infrared band when temperature decreases. The wavelength shift of a multilayer filter is essentially a linear function of filter temperature.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.