An inspection system includes a projection system including a radiation source configured to transmit an illumination beam along an illumination path and an aperture stop configured to select a portion of the illumination beam. The inspection system also includes an aperture stop that selects a portion of the illumination beam and an optical system that transmits the selected portion of the illumination beam towards an object and transmit a signal beam scattered from the object. The inspection system also includes a detector that detects the signal beam.