| 摘要 |
PURPOSE:To realize compact structure by providing the 1st and the 2nd groups of movable lenses which have negative and positive refracting power from an object side, and forming the 3rd fixed lens of one meniscus lens having a concave surface on the object side. CONSTITUTION:A movable lens as the 1st group having a negative refractive index and another movable lens as the 2nd group having a positive refractive index are arranged from the object side, and the 3rd fixed lens is formed of one meniscus lens having the concave surface on the object side at the back of the 1st and the 2nd groups. In this case, ¦f3¦/fw>10, where ¦f3¦ is the focal length of the 3rd lens and (fw) is the telephoto-side focal length of the whole zoom lens system. Then, ¦f3¦ is increased to reduce the influence of the eccentricity of the 3rd lens and variance of the thickness and air gaps before and behind the lens, facilitating the designing and assembling of a frame. Thus, a compact zoom lens is manufactured.
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