Blades pivotally attached together linked to push rods and inserted into an illumination energy or flux. The blades extend longitudinally along the length of a rectangular illumination field or slit used to image a reticle onto a photosensitive substrate. The push rods are coupled to a flexure or link pivotally connected to each end of a substantially rectangular blade. The corners of the rectangular blades have a radius providing a smooth transition between blades. A frame holds the push rods in place as the blades are moved into and out of the illumination energy or flux. The push rods may be adjusted by a screw or other equivalent devices or methods. The lateral or sideways forces resulting from the movement of the blades is compensated for by the flexures or links resulting in less stress being placed on the blades. Slots placed at pivot points in the blades may also be used to facilitate movement of the blades. The illumination energy of the rectangular illumination field or slot is adjusted to provide a uniform illumination energy. Also included is a method of adjusting the device to provide a predetermined exposure dose along the length of the illumination field as a function of line width. Different feature types may be imaged separately to optimize control over line width variation.This is particularly advantageous in a scanning lithography system used in the manufacture of semiconductors.