This paper examines the use of customized spacers to compensate for symmetric errors in lens systems. Examples of errors amenable to this type of compensation include radius, thickness and index of refraction of lenses and lens-to-lens spacing in lens barrels. Spacers used to separate consecutive lenses are selected after the optics have been fabricated and measured. A method is described for specification of spacer thickness as a function of the errors to be compensated by the spacer. The use of binning to enhance the efficiency of spacer selection is briefly explored.