| 摘要 |
An afocal zoom lens system is provided that has particular utility for use in aircraft navigation systems where a unitary (1.0x) magnification power is desirable. Two embodiments are disclosed, the first providing an 8:1 magnification ratio with the second embodiment providing a 12:1 ratio. Both embodiments employ four lens groups including a front fixed objective lens (A,E), a second lens group including a negative zooming element (B,F), a third fixed group (C,G) and a fourth rear negative zooming element (D,H). In the highest magnification position, the lenses are arranged so that the front zooming element is positioned adjacent the positive lens of the the third group to form a weak negative doublet. In the minimum magnification position, the front zoom element is widely separated from the third group to create an inverse telephoto Galilean form. The rear zoom element and aperture stop move together to maintain collimation of the output beam and to hold the diameter of the on-axis exit beam to a constant value.
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