Basic Photography Course

associated with the picture can be heard during
playback

Floppy disks used in electronic imaging can be

reused for endless times-the same as any other magnetic
recording medium. No chemicals or darkroom tech-
niques are required to produce these images. Once the
image is captured on the floppy disk, it can be
transmitted over the telephone lines, edited, and printed
using a video printer-all under normal room-lighting
conditions.

BLACK-AND-WHITE PRINTING PAPER

The performance and use of black-and-white

photographic printing paper, like black-and-white films,
depends on the characteristics of the paper material.
While the many types of photographic papers differ in
their characteristics, they all basically consist of the
emulsion on a paper support or base. Photographic
printing papers (both black and white and color) are
manufactured in both various cut sheet sizes, ranging

from 5x7 to 20x24 inches and rolls up to 1,000 feet long.

Photographic papers used in Navy imaging

facilities are either coated with polyethylene or are
resin-coated. These papers are coated on both sides of
the base. This clear coating is treated so the paper does
not stick to the surface of other prints during processing.
Polyethylene-coated papers (manufactured by Ilford)
can be marked on with pencils and pens. Coated papers
have water-resistant bases that provide short processing
times. Most black-and-white papers with these coatings
have developing agents incorporated in the emulsion.
The developing agents are activated when the paper is
exposed to an alkali solution. The characteristics of
resin-coated paper make it ideal for machine processing,
but they may also be tray-developed in a regular print
developer.

The image on black-and-white film is usually

negative or recorded in tones of gray in reverse of the
reflective brightness values of a scene. When the
negative image is projected onto black-and-white paper,
the resulting image is positive or recorded in tones of
gray relative to the reflective brightness values of the
original scene. A negative is usually used or viewed by
transmitted light. A paper print (or simply a print) is
usually viewed by reflected light and may be referred to
as a reflection print or reflection positive.

Emulsion Sensitivity

The emulsions used for printing paper are much

slower (less sensitive to light) than most film emulsions.

Figure 2-7.Cross section of variable-contrast black-and-white

paper.

A high sensitivity to light is not needed. Prints are often
manipulated by providing additional exposure or by

holding back exposure to selected areas of the print. If

the paper emulsions were fast, exposure times would be
extremely short and print manipulation would not be
possible.

The color or spectral sensitivity of a paper emulsion

indicates the response to specific colors of light or
radiation-the same as that for a film emulsion. The terms
colorblind, orthochromatic, and panchromatic are also
used to describe the spectral sensitivities of paper
emulsions. The response of a paper emulsion to

wavelengths other than ultraviolet radiation, violet, and
blue light is achieved by the addition of sensitizing dyes
to the emulsion during manufacturing.

The ranges of sensitivity for all paper emulsions

begin in the near-ultraviolet region of the invisible
portion of the electromagnetic spectrum. The color

sensitivity of undyed silver emulsions extend to blue and

blue-green. Panchromatic printing papers are sensitive
to ultraviolet radiation, violet, blue, green, and red light.
The color sensitivity of a black-and-white paper is NOT

a determining factor for selecting a paper to print a
specific black-and-white negative. Panchromatic

papers, however, are normally used to produce
black-and-white prints from color negatives. Color

sensitivity DOES determine whether or not a safelight
is required an, if so, what color of safelight can be used.

Variable Contrast Papers

Variable contrast papers are used almost exclusively

in Navy imaging facilities. The contrast of the print
image on variable contrast papers is controlled by the
specific color of the exposing light. Variable contrast
papers have two emulsion layers. The top layer is a
high-contrast emulsion and is sensitive to blue light. The
second emulsion layer is a low-contrast emulsion and is
sensitive to green light (fig. 2-7). When a normal
contrast negative is exposed through a variable contrast
filter with blue light, a harsh, contrasty print is produced.

2-9

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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 -> associated with the picture can be heard during playback Floppy disks used in electronic imaging can be reused for endless times-the same as any other magnetic recording medium. No chemicals or darkroom tech- niques are required to produce these images. Once the image is captured on the floppy disk, it can be transmitted over the telephone lines, edited, and printed using a video printer-all under normal room-lighting conditions. BLACK-AND-WHITE PRINTING PAPER The performance and use of black-and-white photographic printing paper, like black-and-white films, depends on the characteristics of the paper material. While the many types of photographic papers differ in their characteristics, they all basically consist of the emulsion on a paper support or base. Photographic printing papers (both black and white and color) are manufactured in both various cut sheet sizes, ranging from 5x7 to 20x24 inches and rolls up to 1,000 feet long. Photographic papers used in Navy imaging facilities are either coated with polyethylene or are resin-coated. These papers are coated on both sides of the base. This clear coating is treated so the paper does not stick to the surface of other prints during processing. Polyethylene-coated papers (manufactured by Ilford) can be marked on with pencils and pens. Coated papers have water-resistant bases that provide short processing times. Most black-and-white papers with these coatings have developing agents incorporated in the emulsion. The developing agents are activated when the paper is exposed to an alkali solution. The characteristics of resin-coated paper make it ideal for machine processing, but they may also be tray-developed in a regular print developer. The image on black-and-white film is usually negative or recorded in tones of gray in reverse of the reflective brightness values of a scene. When the negative image is projected onto black-and-white paper, the resulting image is positive or recorded in tones of gray relative to the reflective brightness values of the original scene. A negative is usually used or viewed by transmitted light. A paper print (or simply a print) is usually viewed by reflected light and may be referred to as a reflection print or reflection positive. Emulsion Sensitivity The emulsions used for printing paper are much slower (less sensitive to light) than most film emulsions. Figure 2-7.Cross section of variable-contrast black-and-white paper. A high sensitivity to light is not needed. Prints are often manipulated by providing additional exposure or by holding back exposure to selected areas of the print. If the paper emulsions were fast, exposure times would be extremely short and print manipulation would not be possible. The color or spectral sensitivity of a paper emulsion indicates the response to specific colors of light or radiation-the same as that for a film emulsion. The terms colorblind, orthochromatic, and panchromatic are also used to describe the spectral sensitivities of paper emulsions. The response of a paper emulsion to wavelengths other than ultraviolet radiation, violet, and blue light is achieved by the addition of sensitizing dyes to the emulsion during manufacturing. The ranges of sensitivity for all paper emulsions begin in the near-ultraviolet region of the invisible portion of the electromagnetic spectrum. The color sensitivity of undyed silver emulsions extend to blue and blue-green. Panchromatic printing papers are sensitive to ultraviolet radiation, violet, blue, green, and red light. The color sensitivity of a black-and-white paper is NOT a determining factor for selecting a paper to print a specific black-and-white negative. Panchromatic papers, however, are normally used to produce black-and-white prints from color negatives. Color sensitivity DOES determine whether or not a safelight is required an, if so, what color of safelight can be used. Variable Contrast Papers Variable contrast papers are used almost exclusively in Navy imaging facilities. The contrast of the print image on variable contrast papers is controlled by the specific color of the exposing light. Variable contrast papers have two emulsion layers. The top layer is a high-contrast emulsion and is sensitive to blue light. The second emulsion layer is a low-contrast emulsion and is sensitive to green light (fig. 2-7). When a normal contrast negative is exposed through a variable contrast filter with blue light, a harsh, contrasty print is produced. 2-9 contents Basic Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
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