Basic Photography Course

light-colored object records as a heavy-density (dark)
area, and a dark-colored object records as a low-density
(thin) area; therefore, a negative image is reversed

compared to the original scene. This reversal is
produced by a bright object in the scene reflecting more
light than a darker object. The greater amount of
reflected light from the brighter object affects more
silver halides in the emulsion.

The portions of the negative where the most silver

halides have been affected are referred to as
HIGHLIGHTS. The portions that are least affected are
referred to as SHADOW AREAS. The light reflections
from objects other than the brightest and darkest are
referred to as MIDTONES.

The amount of metallic silver deposit in any portion

of a negative is referred to as density. The amount of
light that a negative transmits in a given period of time
is controlled by the density of the metallic silver
deposits. Therefore, density is used to describe the
light-stopping ability of a negative.

The difference in densities between areas in a

negative is known as contrast. The total contrast
(density range) of a negative is defined as the difference
in density between the least-dense shadow area and the
most-dense highlight area in a negative.

Emulsion Latitude

The inherent ability of a black-and-white film to

record a range of scene brightness differences as
differences in density is termed emulsion latitude
Normal- and low-contrast emulsions can record a wide
range of scene brightness values and are considered to
have a wide emulsion latitude or long scale.
High-contrast emulsions record a short range of scene
brightness values and are considered to have a narrow
emulsion latitude or short scale.

Exposure Latitude

The amount the exposure can be varied (increased

or decreased) from the ideal exposure and still provide
an acceptable negative is termed exposure latitude.

The least amount of exposure that records sufficient

shadow detail generally provides the best quality
negative and is considered the ideal exposure. The use

of a determined exposure index leads to the ideal
exposure for a particular film and process combination.
Generally, the use of the assigned ISO speed provides

acceptable results.

Emulsion Definition

Several factors, including graininess, resolving

power (resolution), and acutance, affect the definition
or capability of an emulsion to produce a clear, sharp
image.

GRAININESS.

The negative image consists of

nearly an infinite number of density deposits of metallic
silver. To the naked eye, these grains of silver appear as
a smooth, continuous deposit; however, when the image
is magnified significantly, a speckled, granular, or
mottledeffect becomes apparent. This appearance of the
enlarged image is called graininess.

The graininess of a negative depends upon the size

of the silver halides in the emulsion, the exposure the
emulsion received, and the clumping action of the

metallic silver grains during development. Although

each emulsion has an inherent grain size, the graininess
effect in a negative can be minimized by giving the film
correct exposure and proper development. As a general
rule, slower speed emulsions have a finer grain

(a smaller grain size) than faster speed emulsions.

The Eastman Kodak Company uses modem tabular,

or T-grain, technology in some of their emulsions. In
doing so, flat, tabular crystals are used which are very
efficient in absorbing light. In T-grain emulsions, fewer
silver halide crystals are needed, because the crystals
have a relatively large surface area for light to strike, but
are thin and contain a small amount of silver halides.
These properties provide higher resolution and lower
graininess compared to other films with the same
relative film speed.

Not all black-and-white films form the final image

in black metallic silver; for example, Ilford's XP-1
black-and-white film produces a dye image. The
advantage of this technology is the film can be processed
in color-processing chemicals along with color film and
then printed on black-and-white paper.

RESOLVING POWER.

This is a term used to

define the ability of an emulsion to record fine detail.
The resolving power, or resolution, of an emulsion is
expressed as line pairs per millimeter. Resolving power
is determined by photographing a lined test chart at a
greatly reduced size then counting the lines present in
one millimeter of film.

ACUTANCE.

This is the ability of an emulsion to

produce sharp edges between image density differences.
Do not confuse this with the ability of an emulsion to
produce sharp images controlled by lens focus.
Although an image is in focus, the line between

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Basic Photography Course

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DOFMaster for Windows On-line Depth of Field Calculator DOFMaster for Mobile Devices On-line Depth of Field Table Hyperfocal Distance Chart Articles FAQ Recommended Books Support Contact Links Home As an Amazon Associate I earn from qualifying purchases.	contents <- previous page next page -> light-colored object records as a heavy-density (dark) area, and a dark-colored object records as a low-density (thin) area; therefore, a negative image is reversed compared to the original scene. This reversal is produced by a bright object in the scene reflecting more light than a darker object. The greater amount of reflected light from the brighter object affects more silver halides in the emulsion. The portions of the negative where the most silver halides have been affected are referred to as HIGHLIGHTS. The portions that are least affected are referred to as SHADOW AREAS. The light reflections from objects other than the brightest and darkest are referred to as MIDTONES. The amount of metallic silver deposit in any portion of a negative is referred to as density. The amount of light that a negative transmits in a given period of time is controlled by the density of the metallic silver deposits. Therefore, density is used to describe the light-stopping ability of a negative. The difference in densities between areas in a negative is known as contrast. The total contrast (density range) of a negative is defined as the difference in density between the least-dense shadow area and the most-dense highlight area in a negative. Emulsion Latitude The inherent ability of a black-and-white film to record a range of scene brightness differences as differences in density is termed emulsion latitude Normal- and low-contrast emulsions can record a wide range of scene brightness values and are considered to have a wide emulsion latitude or long scale. High-contrast emulsions record a short range of scene brightness values and are considered to have a narrow emulsion latitude or short scale. Exposure Latitude The amount the exposure can be varied (increased or decreased) from the ideal exposure and still provide an acceptable negative is termed exposure latitude. The least amount of exposure that records sufficient shadow detail generally provides the best quality negative and is considered the ideal exposure. The use of a determined exposure index leads to the ideal exposure for a particular film and process combination. Generally, the use of the assigned ISO speed provides acceptable results. Emulsion Definition Several factors, including graininess, resolving power (resolution), and acutance, affect the definition or capability of an emulsion to produce a clear, sharp image. GRAININESS. The negative image consists of nearly an infinite number of density deposits of metallic silver. To the naked eye, these grains of silver appear as a smooth, continuous deposit; however, when the image is magnified significantly, a speckled, granular, or mottledeffect becomes apparent. This appearance of the enlarged image is called graininess. The graininess of a negative depends upon the size of the silver halides in the emulsion, the exposure the emulsion received, and the clumping action of the metallic silver grains during development. Although each emulsion has an inherent grain size, the graininess effect in a negative can be minimized by giving the film correct exposure and proper development. As a general rule, slower speed emulsions have a finer grain (a smaller grain size) than faster speed emulsions. The Eastman Kodak Company uses modem tabular, or T-grain, technology in some of their emulsions. In doing so, flat, tabular crystals are used which are very efficient in absorbing light. In T-grain emulsions, fewer silver halide crystals are needed, because the crystals have a relatively large surface area for light to strike, but are thin and contain a small amount of silver halides. These properties provide higher resolution and lower graininess compared to other films with the same relative film speed. Not all black-and-white films form the final image in black metallic silver; for example, Ilford's XP-1 black-and-white film produces a dye image. The advantage of this technology is the film can be processed in color-processing chemicals along with color film and then printed on black-and-white paper. RESOLVING POWER. This is a term used to define the ability of an emulsion to record fine detail. The resolving power, or resolution, of an emulsion is expressed as line pairs per millimeter. Resolving power is determined by photographing a lined test chart at a greatly reduced size then counting the lines present in one millimeter of film. ACUTANCE. This is the ability of an emulsion to produce sharp edges between image density differences. Do not confuse this with the ability of an emulsion to produce sharp images controlled by lens focus. Although an image is in focus, the line between a 2-4 contents Basic Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
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