| 摘要 |
A zoom objective for a photographic printer has a housing which accommodates two groups of lenses. One group is fixed and the other group is shiftable along the optical axis of the objective to change the magnification. The housing is externally threaded and meshes with an internally threaded magnification ring which surrounds the housing and serves to move the shiftable lens group. A clamping ring circumscribes the housing on either side of the magnification ring, and the clamping rings constitute abutments for the magnification ring. The clamping rings are adjustable along the optical axis of the objective. The housing is further surrounded by an internally threaded focusing ring which is in mesh with the housing and is provided with mounting elements for mounting the objective in a printer. The position of the housing in the printer can be varied by rotating the housing and the focusing ring relative to one another. This allows the objective to be focused following a change in magnification. Two additional clamping rings circumscribe the housing with one of the additional clamping rings being disposed on either side of the focusing ring. The additional clamping rings, which are again adjustable along the optical axis of the objective, function as abutments for the focusing ring.
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