| 摘要 |
PURPOSE:To compensate aberrations over the entire zoom area with small-sized constitution by forming a zoom lens of five-group, five-element constitution consisting of a front group which has positive refracting power on the whole and a rear group which consist of a negative meniscus lens having a large-curvature concave surface on the image side and a biconvex lens and has positive refracting power on the whole, and satisfying specific conditions. CONSTITUTION:This zoom lens consists of the front group which has the positive refracting power on the whole and the rear group which consists of the negative meniscus lens having the large-curvature concave surface on the image side and biconvex lens and has the positive refracting power on the whole, and meets requirements shown by inequalities. In the inequalities, ni is the refractive index on a line (d) of an (i)th lens, nui the Abbe number of the (i)th lens, fF the composite focal length of the front group of a 5th lens element, fR the composite focal length of the front group of the 5th lens element, (d) the air gap between the front group and rear group of the 5th lens element, and f5 the composite focal length of the whole of the 5th lens element. Consequently, the zoom lens has an about 6X zoom ratio and an about F1.4 large diameter over the entire focal length range except nearby the telephoto range, a zoom system and an image formation system are both compact and small in front lens diameter, and the aberrations are compensated excellently.
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