A programmable illuminator for a photolithography system includes a light source, a first optical system having a light uniformizing element, a programmable micro-mirror device, and a second optical system that forms an illumination field that illuminates a reticle. The programmable micro-mirror device can be configured to perform shutter and edge-exposure-blocking functions that have previously required relatively large mechanical devices. Methods of improving illumination field uniformity using the programmable illuminator are also disclosed.