I. terminology
Light painting resolution: refers to how many points can be placed in one inch length; unit: PDI
Optical density: refers to the amount of silver particles reduced in the emulsion film, that is, the ability to block light, the unit is “D”, the formula: D=lg (incident light energy/transmitted light energy)
Gamma: Gamma refers to the degree to which the optical density of the negative film changes after being subjected to different intensities of light?
II. The composition and function of light painting film
1 surface layer:
It plays a role in preventing scratches and protects the silver salt emulsion layer from being damaged!
2.Drug film (silver salt emulsion layer)
In the image layer, the main components of the emulsion are silver bromide, silver chloride, silver iodide and other silver salt photosensitive substances, as well as gelatin and pigments that can restore the silver core center under the action of light. But the silver salt is insoluble in water, so gelatin is used to make it into a suspended state and coated on the film base. The pigment in the emulsion plays a sensitizing effect.
3. Adhesive layer
Promote the adhesion of the emulsion layer to the film base. In order to improve the bonding force between the emulsion and the film base, an aqueous solution of gelatin and chrome alum is used as the bonding layer to make it firmly bonded.
4. Polyester base layer
Carrier film base and negative film base generally use nitrocellulose, acetate or polyester film base. The first two kinds of film bases have great flexibility, and the size of polyester film base is relatively stable
5. Anti-halo/static layer
Anti-halo and static electricity. Under normal circumstances, the bottom surface of the photographic film base will reflect light, making the emulsion layer sensitized again to produce halo. To prevent halo, an aqueous solution of gelatin plus basic fuchsin is used to coat the back of the film base to absorb light. It is called the anti-halation layer.
III, the operation process of light painting film
1. Light painting
Light painting is actually a light process. After the film is exposed, the silver salt restores the silver center, but at this time, no graphics can be seen on the film, which is called a latent image. Commonly used light machines are: flat-panel laser light drawing machines , Inner barrel type laser light plotter, outer barrel type laser light plotter, etc.
2. developing
The silver salt after illumination is reduced to black silver particles. The temperature of the developer has a great influence on the development speed. The higher the temperature, the faster the development speed. The suitable developing temperature is 18℃～25℃. The main components of the shadow fluid are composed of developer, protectant, accelerator and inhibitor. Its functions are as follows:
1).Developer: The function of the developer is to reduce the photosensitive silver salt to silver.Therefore, the developer is also a reducing agent. The chemicals commonly used as reducing agents include hydroquinone and p-cresol sulfate.
2). Protective agent: The protective agent prevents the developer from oxidizing, and sodium sulfite is often used as a protective agent.
3).Accelerator: Accelerator is an alkaline substance whose function is to accelerate the development. Commonly used accelerators are sodium carbonate, borax, sodium hydroxide, etc., of which sodium hydroxide is a strong accelerator.
4). Inhibitor: The role of inhibitor is to inhibit the reduction of light silver salt to silver, which can prevent the unlighted part from generating fog during development. Potassium bromide is a good inhibitor, and it has a strong photosensitive Places are weakly inhibited, and places with weak light sensitivity are strong.
IV. Fixing
Use ammonium thiosulfate to remove the silver salt that has not been reduced to silver, otherwise this part of the silver salt will be exposed again, destroying the original image.