US2703281A - Auxiliary screening apparatus and method for multicolor photogravure - Google Patents

Description

AUXILIARY SCREENING APPARATUS AND METHOD FOR MULTICOLOR PHOTOGRAVURE Filed Oct. 16, 1952 2 Sheets-Sheet 1 March 1955 Y J G. CONSAUL ET AL 2,703,281

INVENTORS Jaw/v G. Cami/40 50w! VELT invert/5y March 1, 1955 J. G. CONSAUL ET AL 2,7

AUXILIARY SCREENING APPARATUS AND METHOD- FOR MULTICOLOR PHOTOGRAVURE Filed 001'. 16, 1952 2 Sheets-Sheet 2 IN VEN TORS (fa/11v 6'. Con/5,44 .awnv (/61 I5 United States Patent AUXILIARY SCREENING APPARATUS AND METHOD FOR MULTICOLOR PHGTO- GRAVURE John G. Consanl, Bayonne, and Edwin xVelten, Gladstone, N. J., assignors to Art Color Printing Company, New York, N. Y., a corporation of New York Application October 16, 1952, Serial No. 315,018

2 Claims. (Cl. 95- 5) v This invention relates to an auxiliary screening method device for use in making photographic positives in the practice of the multicolor rotogravure process.

In that process, color separation negatives are made, with the aid of color filters, of the colored transparencies or other colored art work to be reproduced. Usually four negatives are made, one in each' of the primary colors, and the fourth in black. The color separation negatives are retouched as required, and positives are then made photographically from them. In making the positives an ordinary square dot halftone screen is used, the screen being set at a different angle for each color, and black, the angular differences being usually in terms of 15.

In carrying out the method of this invention we provide an auxiliary screening device for use in conjunction with the ordinary square dot halftone screen in making positives from the color separation negatives. The auxiliary screening device is incorporated in the lens of the camera employed in making the positives, and is angularly adjustable in accord with the various settings of the halftone screen. The device includes guide means for facilitating its proper angular adjustments.

Provision of the auxiliary screening device effects the following results, among others:

It greatly improves the color values and contrasts of the positives made with its use.

It reduces the amount of retouching normally required, thereby decreasing the labor cost of making the finished positives.

It makes possible an increase in the tonal range of the positive plates, to an extent of about ten to fifteen percent, as compared with conventional gravure positive plates.

The dot formation produced by using the auxiliary screening device in association with an ordinary square dot halftone screen permits of more latitude in re-etching the printing cylinder then do the dot formations resulting from use of a standard gravure screen alone.

We are aware that in multicolor rotogravure photography, stops, such as Waterhouse stops, have heretofore at times been used. However, such stops necessitate that a different one be employed in making a positive from each color separation negative. Use of our adjustable auxiliary screening device obviates this.

The invention will appear more fully from the following description thereof, reference being had to the accompanying drawings, in which:

Figure 1 is a view in perspective of the lens of a camera for making gravure positive plates, the lens being equipped with the auxiliary screening device of this invention;

Fig. 2 is a view in elevation of the lens and screening device looking from the front;

Fig. 3 is a cross-sectional view, taken on the line 3-3 of Fig. 2, looking in the direction of the arrows;

Fig. 4 is a front plan view of the disk member of the screening device;

Fig. 5 is a diagrammatic view of the square dot formation of a conventional gravure screen; and,

Fig. 6 is a similar view of the dot formation resulting from use of an ordinary square dot halftone screen in association with the auxiliary screening device.

The lens, as well as the camera, are of the type commonly used in gravure photography and are illustrated in the drawing only to the extent necessary to describe the invention, the camera as a whole not being shown.

The lens structure comprises a barrel 10, a front lens 11 the mounting of which is threaded to the barrel at 12,

2,703,281 Patented Mar. 1, 1955 a diaphragm 13, and a rear lens 14. The lens is screwed at 15 to a plate 16 fixed to the front 17 of the camera.

The barrel has a slot '18 located in front of the diadisk 19 which may be made of metal or other suitable substance. The edge of the disk is wider than the width of the slot so as to preclude entry of light. The disk is adapted to turn angularly, in either direction, about its horizontal axis, and is provided with an arm or pointer 20 whereby it may be so turned. The arm is screwed or otherwise detachably secured to the disk at 21, and proj e cts through the slot 18.

The central portion 22 of disk 19 is preferably reduced in thickness, and a plurality of small circular apertures or openings 23 are drilled or otherwise formed therethrough. The apertures are arranged in two straight lines that cross each other at a right angle, as hestseen in Fig. 4. The center aperture is in line with the horizontal axes of the lenses 11 and 14. Each line preferably consists of seven apertures, the central one being common t both l nes A guide plate 24 has graduation markings 25 formed thereon, at intervals of fifteen degrees. Certain of the lines may be additionally marked with means to indicate the angular positions of the disk 19 required for photographing blue, red, yellow, and black separation negatives, respectively. The plate 24 is secured to plate 16, by set screws 26 or otherwise, directly behind and above the lens, in position to serve as a guide for the pointer or arm 20 of the disk 19.

To determine the preferred size and spacing of the apertures 23 the diaphragm 13 is set at F90. The size and spacing of the apertures will then be proportionate to the size of the diaphragm opening at that exposure index. The diameter of each aperture is /3 the diameter of the diaphragm opening, while the spacing of the apertures from center to center is /2, the diameter of said diaphragm opening. In other words, if the diaphragm opening is in diameter, then the diameter of each aperture will be A and the apertures will be spaced apart from center to center.

While we have found that the best results are obtained by use of an auxiliary screening disk having seven apertures in each line of the cross, which apertures are of the size, and spaced, as described in the foregoing paragraph, it is to be understood that it may be possible to vary the number, size, and spacing of the apertures, or to set the diaphragm at a different exposure index.

The graduations 25 of the guide plate 24 are so disposed in relation to the angular positions of the ordinary square dot halftone screen that when that screen is turned to the angle required for any color of the multicolor or four color printing, and the pointer 20 is directed to the corresponding color on the guide plate, the lines of apertures 23 will appear to pass diagonally through the square dots of the halftone screen, as viewed on the ground glass plate at the back of the camera, with the round apertures centered in the square dots. In Fig. 5 of the drawings we have indicated the square dot markings 27 of the conventional screen, and in Fig. 6 the result obtained with use of the auxiliary screening device in association with the ordinary square dot halftone screen is shown schematically. In the latter case circular markings 28 are formed within the square markings 27, thus increasing somewhat the thickness of the combined markings.

Carbon tissues prepared from the positives are applied to the surface of the printing cylinder, and the cylinder is then etched. The markings 27 caused by the conventional screen, or the combined markings 27 and 28 caused by use of the auxiliary screening device in addition to the ordinary square dot halftone screen, as applied by the carbon tissue to the surface of the cylinder, serve as a resist to prevent etching of those markings, and thus for-m walls between the square wells etched into the cylinder. Since the combined square and circular markings 2728, resulting from use of the auxiliary screening device, are thicker than the square markings 27 alone, a somewhat greater surface area of the cylinder will remain unetched in the former than in the latter case. This gives the cylinder increased wearing surface and consequently allows for longer runs in the printing.

While the auxiliary screening device is intended primarily for making positive plates it may also be used in making color separation negatives where the latter are to be formed wi h halftone dots. In either case the halftone screen is placed at a different angle for each color and the black, and the auxiliary screening device is adjusted angularly to accord therewith.

In the claims the term lens is used to indicate the entire lens rather than the optical lenses themselves.

What we claim is:

1. An auxiliary screening method for multicolor photogravure which consists in making photographically a series of positives each of a different color separation negative through a conventional square ruled half-tone screen together with an auxiliary screen having only two series of a like number of circular openings all of the same size arranged in two rows, each consisting of seven openings, that cross each other at a right-angle at the common center opening of both rows, turning the auxiliary screen angularly about the axis of the common center opening, in steps of 15 and multiples thereof, to correspond to the setting of the half-tone screen for the color of the particular color separation negative to be photographed so that the circular openings of the auxiliary screen will appear to pass diagonally through and be centered in the square dots of the half-tone screen.

2. In multicolor photogravure the combination with a half-tone square ruled screen and a photogravure lens, of an auxiliary screening disk fitting in the lens to turn axially about its axis, said auxiliary screen having only two series of a like number of circular openings all of the same size arranged in two rows, each consisting of seven openings, that cross each other at a right angle at the common center opening of both rows, an arm secured to the disk for turning it angularly, said arm projecting outwardly of the lens through a slot, the disk being disposed in the plane of the slot and being wider than the slot to close it against entry of light, and a guide plate mounted at and above the back of the lens and across which the arm is movable, said plate having graduations that indicate various angular adjustment positions of the disk.

References Cited in the file of this patent UNITED STATES PATENTS 1,513,379 Douthitt Oct. 28, 1924 1,664,137 Stewart et a1. Mar. 27, 1928 2,182,559 Henderson Dec. 5, 1939 2,376,596 Huggins May 22, 1945 OTHER REFERENCES Mertle, Half-Tone Stops, The American Photoengraver, vol. 21, No. 10, September 1929, pp. 937-951.

Claims (1)

1. AN AUXIALLIARY SCREENING METHOD FOR MULTICOLOR PHOTOGRAVURE WHICH CONSISTS IN MAKING PHOTOGRAPHICALLY A SERIES OF POSITIVES EACH OF A DIFFERENT COLOR SEPARATION NEGATIVE THROUGH A CONVENTIONAL SQUARE RULED HALF-TONE SCREEN TOGETHER WITH A AUXILIARY SCREEN HAVING ONLY TWO SERIES OF A LIKE NUMBER OF CIRCULAR OPENING ALL OF THE SAME SIZE ARRANGED IN TWO ROWS, EACH CONSISTING OF SEVEN OPENINGS, THAT CROSS EACH OTHER AT A RIGHT-ANGLE AT THE COMMON CENTER OPENING OF BOTH ROS, TURNING THE AUXILIARY SCREEN ANGULARLY ABOUT THE AXIS OF THE COMMON CENTER OPENING IN STEPS OF 15* AND MULTIPLES THEREOF, TO CORRESPOND TO THE SETTING OF THE HALF-TONE SCREEN FOR THE COLOR OF THE PARTICULAR COLOR SEPARATION NEGATIVE TO BE PHOTOGRAPHED SO THAT THE CIRCULAR OPENINGS OF THE AUXILIARY SCREEN WILL APPEAR TO PASS DIAGONALLY THROUGH AND BE CENTERED IN THE SQUARE DOTS OF THE HALF-TONE SCREEN.

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