| 摘要 |
A projection diaphragm assembly for achieving halftone negatives with conventional cameras capturing the range and contrast of reproduction materials to be copied, retarding the lighter gray from the white in black and white halftone negatives and separating the gray-white contrast relation for printing purposes is provided. The projection diaphragm is to be utilized in conjunction with a halftone screen of conventional form and may be utilized in front of the associated camera lens assembly or between the front and rear elements of the associated camera lens assembly. The diaphragm assembly includes a frame supported from the associated camera for angular displacement about the center axis of the camera lens assembly and a pair of aperture defining superposed plates are supported from the frame for simultaneous inverse rectilinear shifting diametrically of the associated camera lens axis. The plates are disposed normal to the associated lens axis and include variably registrable openings formed therethrough. When the openings are partially or fully registered with each other, they define an aperture centered on the center axis of the associated lens assembly and the cross-sectional shape of the aperture formed may be square, rectangular or generally elliptical, according to the cross-sectional shapes of the partially or fully registered plate openings defining the aperture. Of course, inasmuch as the frame supporting the plates is rotatable about the center axis of the associated lens assembly, a square or rectangular aperture may be rotated to define a diamond-shaped aperture and elliptical aperture may also be similarly rotated.
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