Screen printing plate making process (2)

There are also some small tools in the dark room: 1 stainless steel 60 cm or 30 cm scale; 22 m tape measure; 3 protractor; 4 slide ruler. Dark indoor and outdoor need to have 20 times magnifying glass, film cutting knife, punching machine (Figure 2-67), density meter and so on.

Dark walls and dark walls are to be decorated with a matte gray, while others are painted dark in the dark room, but as long as the safety light is sufficient and outdoor light cannot leak. If the reflection of security light can make the room brighter, this is good for both work and psychological. When performing color separation and using full-color film, it is necessary to work in a dark room, and bright walls will make people feel happy when the job is finished.

3 photography work. In the case of a darkroom camera equipped with a vacuum suction plate, the actual shooting operation is described as follows:

a. Place the original. Load the original on the original holder. Originals are classified into reflective originals and transmissive originals. Strong pictures that reflect light, photographs, etc. are reflective originals, and natural originals, negatives, and photo plates, which can transmit light, are transmission originals. The original should be placed in the original holder. The simplest original holder is to hold the original in two pieces of glass. Such as oil paintings and other uneven surface manuscripts, without glass clips, clips directly on the holder with the original clip can be up and down. In recent years, the document holders used in the camera have mostly been detachable document holders. When loading the original, place the original holder horizontally, open the front glass cover, place the original on the rear panel, close the cover glass, and then take the original holder for photography. The back panel for reflecting originals is a panel of woolen wood. Reflectors and transparencies can use glass platen.

Reflecting originals require two illumination sources, symmetrically placed at a 45° angle from the original, and placed approximately one meter from the center of the original. Transmit the original, add a piece of frosted glass 20 centimeters behind the original, and arrange 1 to 2 equidistant light sources behind it to make the light evenly transmitted, as shown in Figure 2-68.

After fixing the original on the original holder, turn on the light source, open the shutter, adjust the aperture to the maximum, and observe the image on the frosted glass. Then rotate the handle to adjust the size and focus. An image with the same size as the size of the original document is referred to as an original large size photograph, a larger scale photograph than the original document, and a smaller scale photograph than the original document. The ratio to the original is called the magnification, which can be expressed as a percentage. The original large photograph is 100%, the enlarged photograph is more than 100%, and the reduced photograph is less than 100%.

The area of ​​the image and the range of magnification vary depending on the type of camera and the lens focal length used. For example, a camera with a focal length of 30 centimeters is currently used, and the maximum photographing area is 27 x 27 centimeters; the focal length of 45 centimeters is 39 x 39 centimeters; and the focal length of 60 centimeters is 50 x 50 centimeters. Magnification is generally magnified by 3 to 4 times. Reduced to 1/3 to 1/5 In order to save space, compact cameras with magnifications of 2 to 3 or 1/2 to 1/3 are now used.

b. For light. The light is to find the clearest image on the frosted glass at a specified magnification, also called "focus." Although the front and rear positions of the document holder and the lens holder are controlled by the two jog handles, the focusing is still not easy.

First, the object distance between the lens and the original and the image distance between the lens and the frosted glass should be calculated based on the relationship between the original size (the length of one side of the length and width), the magnification, and the distance between the lens and the focal point. Then move the original and the lens frame, and finally achieve accurate focusing, then use a magnifying glass to look at the subtle levels and determine the magnification. For convenience, 100%, 50%, 200%, etc., should be marked on the platform of the original plus or the lens holder for easy use. On the side of the frosted glass where it is easy to see, the magnification is indicated by a tape through the rotation of the handle, and a dial is attached to the camera and the handle of the lens holder. Through the scale, the magnification can be known. See Figure 2-69.

After determining the approximate focus point, use a magnifying glass to make fine adjustments from the center to the periphery.

Since the aperture is open when observing the image on the frosted glass, the aperture should be reduced to 16 to 22F when the light is on. Note that it should not be excessively reduced.

Second, you should adjust the position of the light source again. Close the shutter after the hazard, adjust the timer to the proper exposure time, and adsorb the film on the adsorption board. When the film is loaded so as not to cause creases, the end should be absorbed first, then slowly put it down in other directions. The complete adsorption, the suction of the suction plate should be adjusted according to the size of the soft palate. The suction plate is replaced with a frosted glass frame and then closed in the direction of the lens. When opening the light source, close the shutter first. It is most convenient for the shutter and the light switch to be connected together. Adjust the aperture and lighting distance when the exposure time exceeds 10 seconds. The exposure error is less than 10 seconds, except for using the flash.

c. Developer Fix. After the exposure is completed, the shutter is closed, the vacuum pump is turned off, the suction plate is opened, the film is taken out, and the emulsion film is immersed in the developer solution with the face down. As shown in Figure 2-70, shake the film or developer disk quickly. Prevent uneven development or blistering. After several seconds of repetition, the emulsion film is faced upward again, and the developing plate is uniformly shaken and developed for a predetermined period of time. Or, the left hand lifts one end of the developing plate, the right hand takes out the film, the film is immersed in the developing solution, and then the left hand drops the developing plate, so that the developer flows, and the film is completely immersed in the developing solution, as in the previous method. Shake the plate. The developer should be developed using the developer defined by the film. If it is a Fujifilm film, use a Fuji developer solution. If you use a small film, you should use the Xixiliushi developer. The amount of developer placed in the developer tray should not be too high. If too much, it will spill or stir unevenly. If the amount of the developer is too small, the development is uneven and spots easily occur. The standard depth of developer in the pan is approximately 1.5 cm. If the disc is too large, the developer can be more. The development time should be fixed, but the exposure time should be slightly shorter, and the development time should be slightly longer, so that a negative contrast can be made.