Polyester compositions and methods to prepare and use such compositions are provided. The polyester compositions include a polybutylene terephthalate resin (PBT) and at least one additive, and have a cyclic dimer content of less than 0.35 wt. % relative to the weight of the PBT. Molded parts prepared from such polyester compositions, and mirror optic systems such as headlights for motor vehicles or garden reflector lights which include the molded parts are also described.