| 摘要 |
PROBLEM TO BE SOLVED: To obtain a variable power optical system for projecting a picture on a display element which is miniaturized and advanced in terms of high pixel formation, and having slight transverse chromatic aberration by constituting a negative lens in a second group, the negative lens in a third group and a positive lens in a fourth group of lens material satisfying a specified condition. SOLUTION: This system is constituted of a first group Gr1 to the fourth group Gr4. At the time of variable power, at least the second group Gr2 and the third group Gr3 are moved in the direction of an optical axis. The negative lens in the second group Gr2, the negative lens in the third group Gr3 and the positive lens in the fourth group Gr4 are constituted of the lens material satisfying the condition of 0.015<Θ-(0.644-0.00168.νd)<0.06, 65<νd<100. In expressions,Θ=(ng-nF)/(nF-nC),νd=(nd-1)/(nF-nC), (ng), nF, nC and (nd) respectively mean refracting power to a g-line (wavelength 435.84nm), an F-line (wavelength 486.13nm), a c-line (wavelength 656.28nm) and a d-line (wavelength 587.56nm).
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