| 摘要 |
PROBLEM TO BE SOLVED: To obtain satisfactory image-forming characteristics, even if the distribution of energy lines incident onto a projecting optical system is changed, by adjusting fluctuations in magnification and focus in accordance with changes in the state of distribution of the luminous flux of illumination on the pupil surface of the projecting optical system. SOLUTION: Illuminating light emitted from a light source 10 has the divergence of its luminous flux adjusted appropriately, when passing through an illuminating aperture stop 18, in accordance with theσvalue of the stop 18 or with the number of apertures. Thus, a time constant corresponding to the set number of apertures of the stop 18 is stored in a memory 42 in advance, and the amount of fluctuation of a magnification is obtained by a controller 28 based on the time constant selected by a selector 40. Based on the amount of fluctuation and a pressure within a sealed lens chamber 24F detected by a pressure sensor 38, a control signal is outputted from the controller 28 to a pressure regulator 32. In response thereto, the regulator 32 controls the pressure within the chamber 24F utilizing a pressurization system 34 and an exhaust system 36. As a result, the magnification of a projecting lens 24 is controlled so as to be set at a predetermined value.
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