Chapter 4- Image Capture Mediums- Film and CCD/CMOS Sensors Flashcards
Monochrome film- Describe the physical structure of the film.
The light-sensitive layer of photographic emulsion (silver halide suspended in gelatin medium) is coated onto a clear substrate material (e.g cellulose triacetate, PET or PEN).
Monochrome film- Prior to the following stages of manufacture, untreated silver halide crystals are only sensitive to the blue and ultra violet region of the spectrum, resulting in blue subjects looking white and other colours looking much darker. What 5 stages are now used to treat the silver halide crystals to make a photographic emulsion?
Emulsification First ripening Emulsion washing Second ripening Dye sensitisation
Monochrome film- What is the resulting emulsion described as (in reference to colour sensitivity)?
Panchromatic (sensitive to all colours of the visible spectrum)
Monochrome film- What is Orthochromatic film?
Graphic art film designed for copying that is insensitive to red light
There is also film emulsions available that are sensitive to the infra-red region of the spectrum
Monochromatic film-What is Latent Image Formation?
The process by which minor specks of atomic silver is generated after silver halide grains/crystals are exposed to light
Monochromatic film-What is a ‘Latent Image’ and what technique is it detected by?
A latent image is an invisible image formed from the silver formation however it is not visible to the human eye. It must be detected through a technique called Electron Spin Resonance (ESP)
Monochromatic film-The film development process is essentially a reduction and amplification process. Explain how.
During the chemical development, the silver halide struck by light during exposure are reduced to metallic silver. The individual specks formed on the crystals expand until each crystal has turned black. In addition, in well-exposed regions, individual crystals stick together. This is why it can be considered an amplification process; as the development increases minor levels of silver present by a million times
Monochromatic film-The final stage of the development is fixation to make the image permanent. What does this involve?
Removal of any unexposed silver halide crystals, which would darken the overall image if present. These are removed by transforming into soluble compounds and washed away. The film is then dried and the result is a negative
Monochromatic film-Who are the main manufacturers of monochrome reversal film?
Ilford, Kodak, Fujifilm
Monochromatic film-Why is there an ‘anti-halation backing’ on monochromatic negative film?
Light used to bounce off the back and cause a halo shape/effect so this layer counteracts it
Monochromatic film-What do more advanced types of monochromatic film have?
Mixtures of different crystal layers (e.g tabular grains and dimensional grains)
Colour NEGATIVE film-Colour negative film is coated with a number of emulsion layers, in which order are they?
The uppermost emulsion layer is sensitive to blue light and ultraviolet radiation.
Layer two is a yellow filter layer (a non light-sensitive yellow dye) which is to block the blue from penetrating to the two lower layers.
The next emulsion layer is sensitive to green light.
Layer four is a red/pink dye filter layer.
The final layer is sensitive to red light
Colour NEGATIVE film- As with monochrome film, exposure to light forms a latent image. What is the difference though with colour film?
A latent image is formed in all three emulsion layers. Blue areas of the image will only form in the blue emulsion layer etc.
Any orange areas will register in both the green and red as it is a mixture
Colour NEGATIVE film-The development process is very similar to that in monochrome film. It is the colour development stage that imparts them. How does colour dye form?
The presence of colour couplers between emulsion layers react with the oxidation products of the colour development stage to produce coloured dyes within the individual emulsion layers (the strength of colour proportional to amount of light exposure)
Colour NEGATIVE film-
Where is yellow dye formed?
Where is magenta dye formed?
Where is cyan dye formed?
Yellow dye is formed in the blue-sensitive emulsion layer
Magenta dye is formed in the green-sensitive emulsion layer
Cyan dye is formed in the red-sensitive emulsion layer
Colour NEGATIVE film-The final bleach-fix stage removes which parts of the film?
All (exposed or not) silver halides, yellow and red filter layers and anti-halation backing- leaving just the layered dye images