Some Thoughts on the Optics of Wet Printing

Joseph W. Schmit

Reversal dupe negatives and other dupes are, by necessity, often printed on optical printers having specular illuminating systems. With this type of illumination, scratches and similar blemishes on the original will show on the dupe print. The defects of the original can be rendered invisible or nearly invisible by either coating the original with a liquid during exposure or by total immersion in a suitable liquid. The principal methods of wet and liquid-gate printing are briefly described. Open-face or wet printing with a liquid coating on both sides of the original has been in prolonged use because this method does not require extensive modifications of the printing equipment. In the open-face method, irregularities in the liquid coating or unevenness of the liquid surface may cause visible defects in the printed dupe. The inter-relation between the prismatic effect of the liquid coating, the geometry of the relay illumination optics and the aperture of the copy lens has been explored and a method of minimizing defects due to the prismatic effect is described. The method is also applicable to wet open-face reduction printing. An alternative method of avoiding the prismatic-effect markings on the print for small copy-lens apertures is mentioned. A comparison is made between the open-face wet printing and the total immersion liquid-gate method.

Print ISSN
Published
1977-08
Content type
Original Research
DOI
10.5594/J17866