| 摘要 |
An optical zoom includes three, respectively negative, positive and positive lens groups. A first lens group (G 1 ) includes a negative lens (L 1 ) and a positive lens (L 2 ) The second lens group (G 2 ) includes a positive lens, a negative lens and an aspherical plastic lens. The third lens group (G 3 ) includes a positive lens. During zooming, the first and second lens groups are independently moved from each other.
The first lens group of the optical zoom satisfies the following inequalities:
|fg2/f1g| > 1.8 and
Xp < 73
where fg2 denotes the focal length of the second lens L 2 , f1g denotes the focal length of the first lens group (G 1 ) and Xp = Np2 2 x Vp2 where Np2 und Vp2 respectiely denote the refractive index and Abbe number of the second lens L 2 , which is made of plastic.
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