| 摘要 |
PURPOSE:To reduce brightness loss and to improve chromatic aberration by applying a filter which is made of a transmission wavelength selective material with desired transmissivity to wavelength to an expansion lens and increasing the density of the wavelength selective material toward the outer periphery of the lens gradually. CONSTITUTION:A projection lens consists of the 1st lens 1, the 2nd lens 2, and the 3rd lens 3, and the 2nd filter 2 is provided with the filter 4. Then the transmissivity of the filter 4 is varied in a radial direction of the lens in the direction of the external diameter (as the diameter increases) as shown in a graph. In the graph, (f) is a radial position, 0 the center of the lens, 1.0 the outer diameter part of the lens, and alpha and beta optional constant.
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