Basic Photography Course

or print. The color sensitivity determines how the film
is classed. There are four general classes of
black-and-white film emulsions. The four classes are as
follows: colorblind (monochromatic), orthochromatic,
panchromatic, and infrared. Some of these emulsions
respond to a wide range of wavelengths of light. Others

respond to only a narrow band of wavelengths.
Light-sensitive emulsions are sensitive to all
wavelengths of ultraviolet radiation. For all practical
purposes, the general classes of emulsions are

considered insensitive to the shorter wavelengths of
ultraviolet (UV) radiation. This is because glass lenses
and the gelatin in most film emulsions completely

absorb the shorter wavelengths of ultraviolet radiation.
When UV is to be used for photography, a special film
with a thin emulsion is required.

Color-blind Emulsions.

Black-and-white color-

blind emulsions are sensitive only to UV radiation,
violet, and blue light. Green and red objects record only

as clear areas in the black-and-white negative and

reproduce as dark areas in the print. Color-blind films
are used primarily for copying and graphic arts
photography and may be assigned three or more ISO

values; for example, ISO/50 for daylight, ISO/8 for
tungsten light, ISO/20 for white-flame arcs, and ISO/12

for pulsed xenon.

Orthochromatic Emulsions.

Orthochromatic

emulsions are sensitive to ultraviolet radiation, violet,
blue, and green light. The sensitivity to green light is

gained by the addition of a sensitizing dye to the
color-blind silver halides. The emulsions provide an
approximate correct reproduction of blue and green
objects as corresponding tones of gray in a print;
however, red objects record as clear areas in the negative
and black areas in the print. since the emulsion is not
sensitive to red. Various orthochromatic films with
different degrees of contrast, color sensitivity, and
emulsion speed are available. Their trade names usually
contain the word ortho. Orthochromatic emulsions are
used primarily for copying and graphic arts
photography.

Orthochromatic emulsions that may be used in

either daylight or tungsten light are assigned two
separate ISO film speeds. This is because these
emulsions are highly sensitive to the predominantly blue
colored daylight and less sensitive to the tungsten light
that has a higher content of red light.

Panchromatic Emulsions.

Panchromatic emulsions

are sensitive to UV radiation, violet, blue, green, and
red. The emulsion spectral sensitivity to green and red
light is gained by adding sensitizing dyes to the

color-blind silver halides. Panchromatic film of varying
degrees of contrast, color sensitivity, and emulsion
speed is available. Panchromatic emulsions are used for
copying, portraiture, and general black-and-white
photography.

Panchromatic emulsions are assigned only one IS0

film speed. This is because panchromatic emulsions are
sensitive to red light and have an almost equal response
to predominately blue-colored daylight and
predominately red-colored tungsten light.

Infrared Emulsions.

Infrared (IR) emulsions are

sensitive to UV radiation, violet, and blue light, with

little or no sensitivity to yellow-green light but with

additional sensitivity to red and IR radiation. The
sensitivity to infrared radiation is gained by adding a
sensitizing dye to the color-blind silver halides. Infrared
emulsions are commonly used for aerial and medical
photography as well as forensic photography
(photography used for evidence). For best results a
black-and-white UV film should be exposed only with
IR radiation. To prevent any IR radiation or visible light
from affecting the infrared emulsion during exposure,

you must use a dark, red filter over the camera lens.

Since infrared radiation does not focus at the same

point as visible light, a lens focus adjustment is
necessary for critical focusing. Most lenses have a
calibrated infrared focusing position on the focusing

scale. This position is usually marked by a small, red dot
or the letter R in red.

Determining a useful exposure index becomes a

problem with infrared film, because exposure meters are
calibrated for visible light and similar light sources can
emit different amounts of infrared radiation. When using
infrared film, you should make trial exposures for each
particular film and photographic situation.

Contrast

In the development process, the silver halide grains

in a black-and-white film exposed to light remain in the
film. These grains form the image of the original scene.
The colors of the scene are recorded in the negative as
densities of gray instead of appearing as their original
colors. These densities of gray can range from very
dense to very thin. This depends upon the brightness of
the objects in the scene, their color, and the color

sensitivity of the film. The ratio of the maximum to the
minimum brightness of objects in a scene is referred to
as the scene brightness range. Most long scale
black-and-white films are capable of recording scene
brightness ranges up to 128:1. In a negative, a

2-3

contents

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 -> or print. The color sensitivity determines how the film is classed. There are four general classes of black-and-white film emulsions. The four classes are as follows: colorblind (monochromatic), orthochromatic, panchromatic, and infrared. Some of these emulsions respond to a wide range of wavelengths of light. Others respond to only a narrow band of wavelengths. Light-sensitive emulsions are sensitive to all wavelengths of ultraviolet radiation. For all practical purposes, the general classes of emulsions are considered insensitive to the shorter wavelengths of ultraviolet (UV) radiation. This is because glass lenses and the gelatin in most film emulsions completely absorb the shorter wavelengths of ultraviolet radiation. When UV is to be used for photography, a special film with a thin emulsion is required. Color-blind Emulsions. Black-and-white color- blind emulsions are sensitive only to UV radiation, violet, and blue light. Green and red objects record only as clear areas in the black-and-white negative and reproduce as dark areas in the print. Color-blind films are used primarily for copying and graphic arts photography and may be assigned three or more ISO values; for example, ISO/50 for daylight, ISO/8 for tungsten light, ISO/20 for white-flame arcs, and ISO/12 for pulsed xenon. Orthochromatic Emulsions. Orthochromatic emulsions are sensitive to ultraviolet radiation, violet, blue, and green light. The sensitivity to green light is gained by the addition of a sensitizing dye to the color-blind silver halides. The emulsions provide an approximate correct reproduction of blue and green objects as corresponding tones of gray in a print; however, red objects record as clear areas in the negative and black areas in the print. since the emulsion is not sensitive to red. Various orthochromatic films with different degrees of contrast, color sensitivity, and emulsion speed are available. Their trade names usually contain the word ortho. Orthochromatic emulsions are used primarily for copying and graphic arts photography. Orthochromatic emulsions that may be used in either daylight or tungsten light are assigned two separate ISO film speeds. This is because these emulsions are highly sensitive to the predominantly blue colored daylight and less sensitive to the tungsten light that has a higher content of red light. Panchromatic Emulsions. Panchromatic emulsions are sensitive to UV radiation, violet, blue, green, and red. The emulsion spectral sensitivity to green and red light is gained by adding sensitizing dyes to the color-blind silver halides. Panchromatic film of varying degrees of contrast, color sensitivity, and emulsion speed is available. Panchromatic emulsions are used for copying, portraiture, and general black-and-white photography. Panchromatic emulsions are assigned only one IS0 film speed. This is because panchromatic emulsions are sensitive to red light and have an almost equal response to predominately blue-colored daylight and predominately red-colored tungsten light. Infrared Emulsions. Infrared (IR) emulsions are sensitive to UV radiation, violet, and blue light, with little or no sensitivity to yellow-green light but with additional sensitivity to red and IR radiation. The sensitivity to infrared radiation is gained by adding a sensitizing dye to the color-blind silver halides. Infrared emulsions are commonly used for aerial and medical photography as well as forensic photography (photography used for evidence). For best results a black-and-white UV film should be exposed only with IR radiation. To prevent any IR radiation or visible light from affecting the infrared emulsion during exposure, you must use a dark, red filter over the camera lens. Since infrared radiation does not focus at the same point as visible light, a lens focus adjustment is necessary for critical focusing. Most lenses have a calibrated infrared focusing position on the focusing scale. This position is usually marked by a small, red dot or the letter R in red. Determining a useful exposure index becomes a problem with infrared film, because exposure meters are calibrated for visible light and similar light sources can emit different amounts of infrared radiation. When using infrared film, you should make trial exposures for each particular film and photographic situation. Contrast In the development process, the silver halide grains in a black-and-white film exposed to light remain in the film. These grains form the image of the original scene. The colors of the scene are recorded in the negative as densities of gray instead of appearing as their original colors. These densities of gray can range from very dense to very thin. This depends upon the brightness of the objects in the scene, their color, and the color sensitivity of the film. The ratio of the maximum to the minimum brightness of objects in a scene is referred to as the scene brightness range. Most long scale black-and-white films are capable of recording scene brightness ranges up to 128:1. In a negative, a 2-3 contents Basic Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
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