RT5FIAPIA: Film-Screen Acquisition, Processing and Image Analysis

RT5FIAPIA: Film-Screen Acquisition, Processing and Image Analysis Spectral Matching The most important consideration in selecting screen film is spectral absorption matching. For the screen to work at maximum efficiency, the light absorption characteristic of the film must match to the light...

RT5FIAPIA: Film-Screen Acquisition, Processing and Image Analysis Spectral Matching The most important consideration in selecting screen film is spectral absorption matching. For the screen to work at maximum efficiency, the light absorption characteristic of the film must match to the light from the screens Calcium Tungstate Screen – emit blue and blue violet light Rare-earth elements – ultraviolet, blue, green and red. NOTE: All silver halide film respond to violet and blue but not to green, yellow and red unless they are spectrally sensitized with dyes. Type of Films according to its sensitivity: Panchromatic film – Orthochromatic film sensitive to the – green sensitive film entire visible light spectrum In Safelight to Film: blue-sensitive film, an green-sensitive and amber filter is blue sensitive film, a used (550 nm red filter is used. wavelength) (600 nm wavelength) Film Humidity – 40-60% >60% - < 40% - increase the static fog artifacts MANUAL PROCESSING UNIT PROCESSING TANKS MASTER INSERT TANK TANKS MASTER TANK This tank serves as a water jacket to hold the insert tanks and is usually large enough to provide space between insert tanks for rinsing and washing of films. INSERT TANKS These are removable containers for the individual processing solutions (developer and fixer), and are spaced in the master tanks PROCESSING CHEMICALS DEVELOPER FIXER FILM PROCESSING The term applied to the chemical reactions that transform the latent image into a manifest image. Wetting Wetting agent - water During wetting, it penetrates the gelatin of the emulsion, causing it to swell. NOTE: In automatic processor, the wetting agent is in the developer. 1. Development The primary function of development is to convert the latent image into a visible image. A very short and critical stage where the latent image is converted to manifest image Principal action of the developer is to change the silver ions of exposed crystals into metallic silver. PROCESSING CHEMICALS FIXER DEVELOPER DEVELOPING FIXING DEVELOPER COMPONENTS: Component Chemical Function 1.Developing Phenidone / Metol Reducing agent; Agent (2) produces shades of gray rapidly Hydroquinone (1) Reducing agent; produces black tones slowly 2. Activator Sodium carbonate helps swell gelatin; produces alkalin ity; controls pH 3. Restrainer Potassium Bromide Antifog agent; protects unexposed crystals from chemical "attack". (also potassium iodide) DEVELOPER COMPONENTS: Component Chemical Function 4. Preservative Sodium Sulfite controls oxidation; maintains balance among developer components 5. Hardener Glutaraldehyde controls emulsion swelling and enhances archival quality. 6. Sequestering Chelates Removes metallic agent impurities ; stabilizes developin g agent DEVELOPER COMPONENTS: Component Chemical Function 7. Solvent Water Dissolves chemicals for use. The Developer contains alkali components or buffering agents: Sodium carbonate Sodium Hydroxide – aka lye, strongest alkali Purpose: enhance the action of the developing agent and controlling the concentration of hydrogen ions (pH)  DEVELOPING STAGE Reduction – neutralize positive ion EUR / OPE Oxidation – opposite of Electrons Oxidation reduction; reaction that Used Produces produces electron Reduction Electrons Redox reaction – reduction and oxidation work simultaneously. 2. FIXING When development is complete, the film must be treated so that the image will not fade. This stage of processing is fixing. The image is said to be fixed on the film, and this produces film of archival quality. FIXER COMPONENTS: Component Chemical Function 1. Activator Acetic Acid Neutralize developer and stop its action 2. Fixing Agent / Ammonium removes Clearing Agent / Thiosulfate undeveloped silver Hypo / Thiosulfate bromine from the emulsion. 3. Hardener Potassium Alum stiffens and shrinks emulsion. 4. Preservative Sodium Sulfite Maintains chemical balance FIXER COMPONENTS: Component Chemical Function 5. Buffer Acetate Maintains proper pH 6. Sequestering Boric Acids/salts Remove agent aluminum ions 7.Solvent Water Dissolves other components Hypo rentention - is the term used to describe the undesirable retention of the fixer in the emulsion Excess hypo slowly oxidizes and causes the image to discolor to brown over a long time. 3. WASHING This stage in processing is to wash away any residual chemicals remaining in the emulsion, particularly hypo that clings to the surface of the film. Note: Wash water should be maintained at approximately 3°C (5°F) below the developer temperature.  Inadequate washing leads to excessive hypo retention Wash bath also serves to and the production of an stabilize developer image that will fade, turn temperature. brown with time, and be of generally poor archival quality. 4. DRYING Final step of film processing Manual Processing – takes longer than 1 hour to be completed. Automatic Processing - the dry-to-drop time is 90 seconds