Photosensitive Material – B & W. Photosensitive Material – B & W. The word photography means “ writing or drawing with light” a phrase that conveys both the creative & the chemical nature of the photographic process.
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The word photography means “ writing or drawing with light” a phrase that conveys both the creative & the chemical nature of the photographic process.
A camera is simply a device for bringing together a sharp image with the help of the light reflected from a scene & allowing it briefly to touch a film material so sensitive that the light leaves a trace which can be finalised into a finished picture.
To form an image on film requires a correct exposure which is a combination of aperture (Opening) & shutter speed (Time).
The modern camera uses a lens, a variable size opening or aperture & has a shutter that allows light in for the required amount of time, which the photographer can control.
Characteristics of Film
2. Colour Sensitivity
3. Film Speed
6. Exposure Latitude
1. An emulsion is a light sensitive material
coated on the surface of the film.
2. It is made of microscopic crystals of silver
halides. These include silver bromide in large
proportion, silver chloride & silver iodide in smaller
3. When the photographer opens the shutter, light
from the subject begins to act on the emulsion
coating on the film that contains these crystals of
4. These salts of silver are extremely light sensitive & darken instantaneously when exposed to light.
5. The light triggers a chemical change in the salts so that they start to form microscopic grains of black silver.
6. An image thus formed on film is called the latent image.
7. Latent image is defined as an invisible
image recorded on photographic
emulsions as a result of exposure to light.
8. The film is then treated with appropriate
chemicals to convert this latent image into
a visible one. This process is called
There are two types of films
Panchromatic film is a term used to describe
B & W photographic emulsions sensitive to
all colours of the visible spectrum & to a
certain amount of ultra-violet light. This film
requires to be processed in total darkness.
Orthochromatic film is a term used to describe B & W photographic emulsions sensitive to the blue & green regions of the spectrum but insensitive to red & orange light. Hence this film can be processed in red or orange safe light.
The degree of sensitivity of a film to light is known as film speed.
It is expressed numerically for the purpose of exposure calculations.
A film that is less sensitive to light & require
more light to expose is called slow film or
low speed film.
A film that is more sensitive to light & which
can be exposed in low light is called fast film
or high speed film.
Different units given by different photographic
companies in which film speed is measured :-
DIN – DEUTSCHE INDUSTRIE NORM
ASA – AMERICAN STANDARDS ASSOCIATION
ISO – INTERNATIONAL STANDARDS
DX – Coded Cassettes
DX coded films when loaded in the camera with
DX coded facility (sensors), the film speed I
automatically set on the camera.
DX – coded film cassettes have a chequer board
pattern of squares which the camera sensors read to
automatically set the film speed on the camera.
1. Granulartexture appearing to somedegree in all processed photographic materials is called grain.
3. In B & W photographs, the grains are minute particles of black metallic silver that constitutes the images.
4. The faster the film, the coarser the texture
of the grain.
5. The slower the film, the finer the texture of
6. Slower films are used to make big or life
Guidelines to achieve fine grain negative
1. Use slow speed film.
2. Do not over expose.
3. Do not over develop.
4. Use fine grain developer.
1. Gradation is described asthe range of
contrast or tonal variation in a
2. An image that has many different
intermediate tones between the darkest &
the lightest part is described as having a
3. An image that has very few variations
between the light & the dark parts is said
to have a hard gradation.
4. Gradation depends on the speed of the
film. Slow films produce hard gradations
& fast films produce soft gradation.
5. A film that gives the image in various tones of
grey resembling the light & shade of the subject
is called a normal contrast film. This is a
general purpose film.
6. A film that records images in total black & white,
without any middle tone, is called a high
contrast film. Such a film is used for graphics &
1. The degree by which the exposure can
be varied & still produce an acceptable
2. In other words, it is the tolerance of a film
emulsion to record satisfactorily & give
acceptable prints even if the exposure is
not exactly correct.
3. B & W films have more latitude than colour
4. Faster films tend to have a greater latitude
than slower films.