| 摘要 |
PURPOSE:To perform accurate measuring by providing a fixed diaphragm between a front and a rear group of lenses, forming its aperture in a circular shape, and providing a variable diaphragm before the front group or behind the rear group of lenses. CONSTITUTION:A lens unit 20 is provided with the front group 25 and the rear group 26 of lenses. Between them, a first color filter plate 27, the fixed diaphragm 28, and a second color filter plate 29 are arranged in this order. Behind the rear group 26, the variable diaphragm 30 consisting of a pair of diaphragm plates 30a and 30b is provided. These diaphragm plates 30a and 30b can be moved closer or apart in the vertical direction of exposure light. Since the aperture 28a of the fixed diaphragm part 28 has the circular shape, there is no decrease in the quantity of light with an open diaphragm. As a result, the three-color component of the exposure light can be measured accurately by a measuring means 33. The accurate measurement of the three-color component of the exposure light is thereby surely performed. |
