Composition and operation of light painted field
First, terminology
Resolution: the number of dots that can be emitted by an inch length. The unit is PDI.
Optical density: it refers to the amount of silver particles in the emulsion film, which is the blocking ability of light. The unit is "D", and the formula is D=lg (incident light energy / transmission light energy).
Contrast coefficient: the contrast coefficient refers to the degree of change in the optical density of the negative film after being washed by standard washing process under different intensity and light.
Two, light painted film (silver film) structure
Three. The composition and effect of light painted field
1 surface:
Play a role to prevent scratching, protect the silver halide emulsion layer is destroyed!
2, film (silver halide emulsion layer)
The main ingredients of the emulsion are silver bromide, silver chloride, silver iodide and other silver salt photosensitive substances, and gelatin and pigment can restore the silver nucleus under the action of light. But silver salt is not soluble in water. Therefore, gelatin is used to suspend it and coat it on the substrate. The pigment in emulsion is sensitizing.
3, adhesive layer
The emulsion layer is attached to the substrate. In order to improve the binding force between the emulsion and the substrate, the water solution of gelatin and chrome alum is used as a binding layer to make it firmly combined.
4, polyester base
The carrier film, film base generally used nitrocellulose, cellulose acetate or polyester film. The first two flexible base, polyester chip size is stable
5, anti halo / electrostatic layer
To prevent halo and static electricity, under normal circumstances, the bottom of photographic negatives will reflect light and make the emulsion layer photosensitive again, resulting in halo. Halo to prevent the use of gelatin and Fuchsine water solution coated on the base surface to absorb light. It is called a halo proof layer.
Four, the operation process of light painted field
1. light drawing
In fact, the light painting is a light process. After the film is exposed, the silver salt is restored to the silver center, but at this time the film can not be seen on the film, which is called the latent image. The common optical machines are flat type laser drawing machine, inner barrel type laser drawing machine, roll barrel type laser plotter, etc.
2, development
The silver salt after illumination is reduced to black silver particles. The temperature of developer has a great influence on the developing speed. The higher the temperature, the faster the developing speed. It is more suitable for developing temperature from 18 to 25. The main components of shadow solution consist of developer, protective agent, accelerator and inhibitor.
1, developer: the role of the developer is to reduce the silver salt of the photosensitive into silver, so the developer is also a reducing agent, and the chemicals commonly used as reducing agents are hydroquinone and methylene phenol sulfate, etc.
2, protectant: the role of protectant prevents the oxidation of developer. Sodium sulfite is usually used as a protective agent.
3, accelerant: accelerant is an alkaline substance, the effect is to accelerate the development, often used as accelerant of sodium carbonate, borax, sodium hydroxide and so on, of which sodium hydroxide is a strong accelerator.
4, inhibitors: the effect of inhibitors is to inhibit the inhibition of no? The silver salt of light is reduced to silver, which prevents the part of the light from producing fog when it is developed. Potassium bromide is a good inhibitor. It inhibits the strong photosensitive place and inhibits the weak spots.
3, fixing
The removal of no reduction of silver halide using ammonia thiosulfate, or it will destroy the original silver exposure image.
Five, the process parameters of each process and the solution of the common problems
1, development
Attention should be paid to the control of several parameters:
A concentration: the concentration is generally based on the parameters provided by the material supplier. The concentration of the new drug may be high, but the concentration of the old liquid is low. It is necessary to control the developing time and avoid the lack of display and development.
The temperature of B potion is too high. It will cause excessive visibility and edge halo.
The development time of C: the control of developing time has a direct effect on the effect of photographic negatives. Developing time
In short, the optical density is not enough; the developing time is lengthened, the fog aggravated.
2, fixing
The fixing time must be controlled over 60 seconds. The fixing time is not enough, then the production master color is not transparent, when the liquid concentration is reduced, should be extended to fixing time. When the potion is too old, silver precipitation will increase the fog
3, water washing
Such as washing time, variable production master huang.
3, other matters of attention
A, not long time exposure in photographic safety light, it will aggravate the fog.
B, a photographic film should be kept dry, wet photographic fog aggravated.
C and fixing water should not be dripped into the developer's water.
D, such as washing time, variable production master huang.
Six, evaluation of the effect of the photographic film
1, the light density of the negatives:
Can be detected by optical density measuring instrument, generally the light shielding area is greater than that of 4.0D; the photic zone should be less than 0.15D.
2, contrast contrast
In order to make a better contrast, you can make a better negative film, otherwise the light density will be difficult to achieve. Even if you lengthen the development time, the light density is required, but it will bring you more fog.
3, line edge gradient
That is to say if no confusion, whether sharp edge line!
4, there is no blisters
Some negative if light intensity adjustment is not good, it is easy to produce sand.
