| 摘要 |
PURPOSE:To compensate deterioration in optical characteristics due to temperature variation by selecting properly the refractive index, temperature variation coefficient, and focal length of the material of a plastic lens at room temperature. CONSTITUTION:A front group consists of a 1st positive meniscus lens which has convex surfaces r1 and r2 on an object side, a 2nd negative meniscus lens which has convex surfaces r3 and r4 on the object side, and a 3rd positive meniscus lens which has convex surfaces r5 and r6 on the object side. A rear group is formed of 4th, 5th, and 6th lenses which have convex surfaces r7-r12 arranged symmetrically about a diaphragm arranged behind the 3rd lens. The 1st and 6th lenses made of plastic materials with positive power decrease in refractive index and decrease in radius of curvature as the temperature rises, so they operate to increase the focal length of the whole lens system. Further, the 2nd and 5th lenses having negative power decrease in refractive index and increase in radius of curvature to shorten the focal length of the whole system.
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