| 摘要 |
An infra-red objective zoom lens has a fixed front positive singlet, a movable negative component, a movable positive singlet and a fixed rear component. The zoom lens can be relatively short and can be used with an "eye-piece" lens to form an infra-red afocal telescope. The system can be further shortened by using a rear group of telephoto form. The fixed front positive singlet is shaped so that at high magnification it gives undercorrected third and fifth order spherical aberration, and the moveable negative component has at least one lens element shaped so that at high magnification the negative component gives compensating overcorrected third and fifth order spherical aberration.
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