Patent ID: 8098365

Claim:
An illumination optical system which illuminates a plane to be illuminated using light from a light source, the system comprising: a first integrator and a second integrator disposed in order from the light source; a diaphragm having an aperture of constant area and disposed closer to the first integrator than to the second integrator; and an irradiation range adjustment unit including a zoom optical system disposed closer to the light source than the first integrator and configured to adjust an irradiation range of the light from the zoom optical system on a plane where the diaphragm is disposed, the irradiation range including the aperture of the constant area, wherein the irradiation range adjustment unit adjusts the irradiation range by a zooming operation of the zoom optical system, and wherein a shape of an effective light source on a pupil plane of the illumination optical system is not changed by adjusting the irradiation range.