Describe different types of Photographic Film. Give your recommendations for choice of film with adequate justification for the following.
(i) Vegetation mapping
(ii) Land Use Mapping/Soil Mapping of an Area
(iii) Mining Survey
(iv) Hydrological Survey/Mapping a Watershed Area.
A film is defined as, “A thin translucent strip or sheet of cellulose coated with a light-sensitive emulsion, used in a camera to take a still or moving pictures. ”
Photographic film is ordinarily composed of three distinct layers, namely: film base, emulsion and anti-halation backing.
The film base is a cellulose acetate base coated on one side with a light-sensitive layer known as emulsion and on the other side with an anti-halation backing which is an absorbing dye that prevents the formation of halos (ghost image) around bright images.
As shown below.
TYPES OF PHOTOGRAPHIC FILM:
A number of films are available, but the most commonly used are:
Black and White Films:
Black and white films are of two types:
The term panchromatic describes photographic films which are sensitive to all visible colours and some ultraviolet light.
Black and white panchromatic pictures appear “normal” to the human eye because it registers the entire visible spectrum, approximating the range of sensitivity of the human eye. Since it is a fast film (don’t change i.e. permanent) and is sensitive to a wide range of colors.
The quality of the pictures depends upon the time of exposure, the developer used, the time of development, the temperature of the developer and the photographic characteristics of the photographic emulsion.
Types of panchromatic films:
Standard Speed Super-XX and Double-X panchromatic films are superior to all other black and white films. They give best results to truly different colours but their lack of high sensitivity to green light makes separation of vegetation types (conifers and broadleaves) rather difficult.
These films are films which are sensitive to infra-red radiations. Where infra-red are the portion of the invisible electromagnetic spectrum consisting of radiation with a wavelength in the range 750 nm to 1mm, b/w light, and radio waves.
The green colouring matter of leaves has a very high reflectance in infra-red and therefore, the infra-red portion of the light spectrum is reflected by the leaf tissue instead of being absorbed. On account of this property, broadleaved vegetation is highly reflective, and therefore, photographed in light tones whereas conifers tend to absorb infra-red and consequently registers in darker tones.
The results gained by coloured photographs are much better than black and white photographs, however, the problem of cost, proper exposure, and development, haze and image sharpness have limited the actual application. A coloured film is shown as:
Like Black and white films, coloured films can also be of the panchromatic or infra-red type.
Examples of coloured films are: Eastman Kodak Company have developed the following films:
- Kodak Ektachrome aero film
- Super anscochrome
- Kodak aero ektacolour (negative) film
(i) For Vegetation mapping, an infrared film should be used as broadleaved vegetation is highly reflective, and therefore, photographed in light tones whereas conifers tend to absorb infra-red and consequently registers in darker tones and it is comparatively cheaper as compared to coloured films
(ii) For land use, mapping/ soil mapping of an area panchromatic film should be used.
(iii) For Mining survey, infrared films / coloured films should be used.
(iv) For Hydrological survey/ Mapping, a watershed area Black and white (panchromatic films) should be used as water registers dark tone on Black and white films.
For correction and improvements please use the comments section below.