| 摘要 |
PURPOSE:To make a projector lens compensable against a temperature change, by constituting the lens of prescribed lenses of 1st-5th groups and causing the focal lengths, radii of curvature, and powers of the lenses and the changing ratio of the refractive indexes of the lenses against temperature to satisfy specific conditions. CONSTITUTION:This projector lens is constituted from the screen side of a 1st group lens G1 of a positive lens, a 2nd group lens G2 of a negative lens, a 3rd group lens G3 of a positive lens, a 4th group lens G4 of a positive lens, and a 5th group lens G5 with its concave surface on the screen side and the lenses are caused to satisfy the conditions of Formulae (a)-(f). The f, r9, and psi1-psi4 of the formulae respectively represent the focal length of the whole system, radius of curvature of the 5th group lens on the screen side, and powers of the 1st-4th groups lenses. The (dN/dT)1 and (dN/dT)2 of the Formulae (f) respectively represent the changing ratios of the refractive indexes against temperature of the 1st and 2nd groups lenses. Therefore, even this projector lens has a large aperture ratio and large angle of field, it has an excellent image forming capability in which not only aberration correction but also compensations against variation of focussing positions are sufficiently performed.
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