Abstract: Methods and apparatus for controlling illumination uniformity by altering the size of a slit are disclosed. According to one aspect of the present invention, an apparatus includes a light source, an exposure surface, and an illumination unit. The light source generates a beam that is projected onto the exposure surface. The illumination arrangement includes a first support surface and a first removable plate that is configured to be coupled to the first support surface. A first edge of the first removable plate and a second edge cooperate to at least partially define a slit through which the beam is projected.