エレクトロファックス用の複写レンズ

抄録

Apochromatic “Process” lenses have been higher to utilized as the copying lens for the electrofax process of the “Photostat” type, being accompanied by such shortcomings that, in the case of non-sensitized white electrofax papers in combination with fluorescent chemical lamps as the illuminating light source for the original, the visual best focus differ appreciably from the best focus for the actinic ray—near ultraviolet ray with a maximum effect at about 370 mµ in wavelength—, and furthermore that, the slow speed of these lenses, F/9 or so at full aperture but are to be stopped down to ca. F/22 for better results, hinder the practicability of the electrofax copying Process.
A special apochromatic lens of F/5.6 relative aperture and of 180 mm focal length was designed and manufactured, whose chromatic aberration was so corrected that the image plane for λ 370 mµ coincide with that for visual d-line (λ 588 mµ), with the result that no altering of focus from the visual best focus be necessary, either in case of white electrofax papers combined with chemical lamps or dye-sensitized electrofax papers combined with tungsten lamps. Further, the designing principle of the lens was to attain satisfactory performance at unit magnification (natural size copying) and at full aperture, being same in the former respect with, but differen in the latter respect from, the designing principle of “Process” lenses.
The new lens is of the “Orthometar” type, but is perfectly symmetric with respect to the central diaphragm. It covers sharply, at unit magnification, the angular field of 530°, or the object of 368 mm diameter.