Advanced Photography Course

formula by the capital letter 0 and is the reciprocal of
the transmission (T). The formula for opacity is given
as follows:

= Amount of incident light

Amount of transmitted light

You can see that opacity is the transmission

formula inverted. Again, when a material has 10 mc
of light falling on it and 5 mc is being transmitted,
you can determine the opacity by the formula O =

10/5, or 2. Putting it a different way, opacity is the

reciprocal of transmission, or O = 1/0.50 = 2. Or,
when 2 mc is being transmitted, the formula is O =

1/0.20, or O = 10/2; in either case, the opacity is 5.

DENSITY

Density is indicated by the capital letter D and is

another way of expressing opacity or the

light-stopping ability of a medium. Density is nothing

more than the common logarithm of opacity. For
example, when opacity is 2.0, the density is log 2 =
0.30.

In sensitometry, density is the term with which

you are most concerned. However, density cannot be
disassociated from transmission and opacity, because

they all are dependent and directly related to each
other. When the value of any one of these factors is

known, you can calculate the others. When you know
the transmission of a film, you can easily determine
the density. Or conversely, you can measure the
density and then determine the amount of
transmission. While charts are available to provide
some conversions directly, you should be capable of
determining any of those figures.

SENSITOMETERS

Sensitometric-densitometric testing requires a

method of providing the exact same exposure to
different emulsions, or the same emulsion type that is
processed differently, and then comparing the resulting
densities.

Sensitometers make controlled exposures that are

suitable for sensitometric-densitometric testing
procedures. Densitometers measure density.

For sensitometric testing purposes, you must

provide a way of exposing sensitized material with a
known quantity and quality of light.

One of the first requirements for sensitometric

control is to have a sample of the light-sensitive
material that has been exposed properly under
measurable and reproducible conditions. For
sensitometric test purposes, it is common practice to
expose a strip of film, so a number of varying
exposures are made on the same strip. This series of
controlled exposures is made with a sensitometer
through a series of neutral-density filters.

Ideally, a sensitometer should be designed so you

can do the following:

Predetermine the total amount of exposure.

Determine the difference in exposures given

to various areas.

Control the color quality of the light.

Reproduce or duplicate the exposure
consistently.

Obtain a wide enough range of exposures to
produce densities ranging from very light to
dark.

Scenes that might be photographed include a wide

range of brightness values that are represented on a

negative as areas of varying amounts of density;
however, these different densities are scattered
throughout the picture area and are difficult to
measure. For the sake of simplicity, uniformity, and
reproduceability in the application of sensitometry, the
exposures produced by a sensitometer are arranged in
a series of gradually increasing steps. These steps
correspond to the relative brightness values of a
normal scene. The exposures are made on a length of
film or paper of the same type that you are
processing. This sample is called a sensitometric

strip.

"Photographic exposure" is defined as the product

of illumination and time. The two important parts of
a sensitometer are the light source and the device for
controlling the amount of light transmitted to the
emulsion. Since total exposure is the result of the
intensity of illumination and the length of time it is

2-5

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Advanced 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 -> formula by the capital letter 0 and is the reciprocal of the transmission (T). The formula for opacity is given as follows: O = Amount of incident light Amount of transmitted light You can see that opacity is the transmission formula inverted. Again, when a material has 10 mc of light falling on it and 5 mc is being transmitted, you can determine the opacity by the formula O = 10/5, or 2. Putting it a different way, opacity is the reciprocal of transmission, or O = 1/0.50 = 2. Or, when 2 mc is being transmitted, the formula is O = 1/0.20, or O = 10/2; in either case, the opacity is 5. DENSITY Density is indicated by the capital letter D and is another way of expressing opacity or the light-stopping ability of a medium. Density is nothing more than the common logarithm of opacity. For example, when opacity is 2.0, the density is log 2 = 0.30. In sensitometry, density is the term with which you are most concerned. However, density cannot be disassociated from transmission and opacity, because they all are dependent and directly related to each other. When the value of any one of these factors is known, you can calculate the others. When you know the transmission of a film, you can easily determine the density. Or conversely, you can measure the density and then determine the amount of transmission. While charts are available to provide some conversions directly, you should be capable of determining any of those figures. SENSITOMETERS Sensitometric-densitometric testing requires a method of providing the exact same exposure to different emulsions, or the same emulsion type that is processed differently, and then comparing the resulting densities. Sensitometers make controlled exposures that are suitable for sensitometric-densitometric testing procedures. Densitometers measure density. For sensitometric testing purposes, you must provide a way of exposing sensitized material with a known quantity and quality of light. One of the first requirements for sensitometric control is to have a sample of the light-sensitive material that has been exposed properly under measurable and reproducible conditions. For sensitometric test purposes, it is common practice to expose a strip of film, so a number of varying exposures are made on the same strip. This series of controlled exposures is made with a sensitometer through a series of neutral-density filters. Ideally, a sensitometer should be designed so you can do the following: Predetermine the total amount of exposure. Determine the difference in exposures given to various areas. Control the color quality of the light. Reproduce or duplicate the exposure consistently. Obtain a wide enough range of exposures to produce densities ranging from very light to dark. Scenes that might be photographed include a wide range of brightness values that are represented on a negative as areas of varying amounts of density; however, these different densities are scattered throughout the picture area and are difficult to measure. For the sake of simplicity, uniformity, and reproduceability in the application of sensitometry, the exposures produced by a sensitometer are arranged in a series of gradually increasing steps. These steps correspond to the relative brightness values of a normal scene. The exposures are made on a length of film or paper of the same type that you are processing. This sample is called a sensitometric strip. "Photographic exposure" is defined as the product of illumination and time. The two important parts of a sensitometer are the light source and the device for controlling the amount of light transmitted to the emulsion. Since total exposure is the result of the intensity of illumination and the length of time it is 2-5 contents Advanced Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
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