Light homogenizing elements with corrective features

A method of correcting an illumination system comprising:

• producing a light field at an image plane of an illumination system, the illumination system comprising a light source producing light at an operating wavelength, the light source operatively coupled to a first lens array, the first lens array comprising a plurality of lenslets, the plurality of lenslets including a first lenslet and a second lenslet, the first lenslet having a first aperture and the second lenslet having a second aperture;
• determining a uniformity of the light field at the image plane by measuring the irradiance of the light field at a plurality of locations in the image plane;
• and
• improving the uniformity of the light field, the improving including modifying the first lenslet to include a first corrective feature, the first corrective feature defining a first corrected portion of the first aperture and reducing a transmittance of the operating wavelength through the first lenslet.