Printing Image Information Processing - Platemaking Photographic Technology (1)

Third section photographic process

With a plate making camera, the process of taking the image on the document onto the photosensitive material is called a plate making process. Monochrome lines and monotone continuation of the original, the general use of plate-making photographic process to make positive or negative picture negative, its low cost, simple process operation.

First, the camera equipment and equipment (a) plate making camera plate making camera is mainly composed of six major parts: plate making lens, lens frame, photo frame, manuscript frame, frame and light source. Compared with an ordinary camera, it has a relatively large external structure, and the object to be photographed is a flat original, which must be accompanied by an artificial light source (see FIG. 3-18).

Figure 3-18 Plate Camera

The plate making camera can be classified into horizontal, hanging, and vertical according to the position of the machine on the ground.

The horizontal camera has a simple structure and is easy to operate. It is often used to take pictures of the negatives below. Hanging camera, the operating range is easy to pass, easy to operate, often used to film, full-frame negative film. The vertical camera has a small footprint and is easy to operate. It is often used to photograph negative films that are less than four inches apart. If a vertical camera equipped with a prism is used, negative film negatives for letterpress plates can be directly taken.

(B) Platemaking camera auxiliary equipment

1. Plate-making lens A precision optical system for obtaining a clear image of a photosensitive material. Unlike ordinary photo lenses, it is necessary to eliminate various aberrations and chromatic aberrations. To eliminate achromatic lenses, mark them with "APO". There is an aperture in the lens to adjust the amount of light in the lens.

2. Color filters are optical devices that selectively absorb and transmit light of different wavelengths, and glass, or colloidal filters of four colors, red, green, blue, and yellow, are used for color separation.

3. The light source of the plate-making camera, which is commonly used in light sources, includes a halogen lamp, a metal halide lamp, and the like.

4. The automatic film processor automatically performs the processes of developing, fixing, washing, drying, and the like.

5. The copying machine attaches the photographed positive or negative film negatives to the photosensitive material and performs light exposure to make the original equipment for printing. After the original copy, the lines of the image are bright and clean, and dot density is high and uniform.

6. Densitometer Optical instruments for measuring the density of originals, negatives, positives, and prints. There are densitometers and transmission densitometers, as well as densitometers that can measure both reflection and transmission densities.

7. Locating the device used by the punch for the exact sleeve of each color separation film.

8. Screens use mainly touch screens.

(three) photosensitive materials

Any photochemical reaction that occurs upon exposure to light, followed by a series of rinsing and processing operations, the material that presents the actual or original image, collectively referred to as photographic material.

Photosensitive materials are classified into silver salt photosensitive materials and non-silver salt photosensitive materials. The plate-making photographic process mainly uses silver salt photosensitive material, and its composition is shown in Figure 3-19. The emulsion layer is the core part of the photosensitive material. The emulsion layer of silver salt photosensitive material consists of silver salt, animal glue, and pigment. Common silver salts include silver bromide (AgBr) and silver iodide (AgI). Animal glue can evenly disperse the photosensitive silver salt particles without sinking, so as to form a stable emulsion. The commonly used animal glue has gelatin. The pigment is used to increase the color-sensing properties of the emulsion, making it an emulsion that feels shade.

Figure 3-18 Schematic diagram of photosensitive material

Performance and use Type Name Sensitivity (DIN) Differential (r) Main use SO special hard color film 2 ≥ 6 Photo typesetting, screening copy, black and white lines to shoot the original OA rigid color film 10 3 to 4 shooting low contrast black and white manuscripts and copy. OB Neutral Positive Film 13 1.5 to 2 Shoots black and white originals and copies. The OC soft facets 17 1 to 1.4 capture high-contrast black-and-white originals. SP special full-color film 6 ≥ 5.5 Shoot color line originals, directly screen color separation. PA rigid full-color film 13 2.5 to 4.0 low-contrast color manuscript color separation. PB Neutral Panchromatic 17 1.5 to 2.0 Medium contrast color manuscript color separation. PC Soft Panchromatic 20 0.85~1.3 High-contrast color manuscript color separation.
Second, line original photographic process

The photographic process of line manuscripts is the basis for studying platemaking photography. Normally, silver salt photographic film is used for shooting. The main process flow is:

Loading Originals → Loading Photosensitive Films → Applying Light → Exposure → Developing → Fixing → Washing → Checking

The original is mounted on the center of the original holder.

The sensitized film is to mount the sensitized film, which is mounted on the center of the photographic plate, and the air pump is turned on so that it is attached to the photographic plate.

According to the lens formula 1/f=1/p+1/q, the distance between the manuscript (p-object distance) and the lithographic plate (q-pixel distance) is changed, and the correct size is obtained on the frosted glass of the photosensitive platen. The sharpest image.

Exposure is a photochemical reaction to light in the sensory light, creating a "latent image." The photochemical reaction is:

AgX+hν→Ag+X
(hν is a photon)

The development is in the developing machine, using the chemical action of the developer to reduce the latent image produced by the exposure to a visible image image.

Fixing is to convert the unsensitized silver halide on the photosensitive sheet into double salt, which is dissolved in water to prevent dark reaction from happening again, destroying the sharpness of the image.

After negative film negative film taken through the above process, the quality inspection must be corrected. You can use the camera to remake a positive negative when taking good negatives, or use a copy machine to make positive negatives for plate making.

The line document can also be shot with a wet film. The shooting process is as follows: First, the document is mounted on the document holder of the plate making camera, and it is in good condition. Then, the photosensitive liquid is coated on a clean glass plate, and the photosensitive liquid is generally called a dictionary glue, also called Luodian, and then the glass plate is immersed in a silver nitrate solution to generate iodination with sensitization performance. Mounted on the photographic plate of the camera and exposed, developed, fixed, and washed, negative film negatives for the dried copper-zinc plate were obtained. In order to increase the density of the negative image, thickening can be performed using copper sulfate and potassium bromide. If the density of a portion of the negative image is too large, thinning can be performed with a solution of red blood salt to dissolve the silver salt particles.