We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
known and variable values. If a strip of a photographic plate be exposed in such a way that successive areas receive exposures increasing by consecutive powers of two, it will be found upon development that a series of spots of increasing opacity are obtained. By measuring the density of each of these spots, plotting the value obtained against the logarithm of the exposures given, a curve is obtained which is known as the "characteristic curve" of the plate. The curves shown in Figure 6 were obtained in this manner. The curve designated by the letters AB was obtained from a strip that was developed for three minutes in a standard developer, while that designated by the letters A' B' was obtained by a six minute development. It is customary to express the blackness or opacity of a photographic deposit in terms of its "density," D.
It will be noted with reference to Figure 6 that the portion of the curve between the points A and B is a straight line. This line extended cuts the log exposure axis at O and the value of expos
/
M
y
J
4
/
X
/
y
/
^'f
y^^
/
b
y
s
/
/
y
/
y
fi
y
/
r^
y
a
—
—
i—
LOG eXPOSURC
Fig. 6 — Characteristic Curves of Photographic Materials.
ure at the point O is termed the "inertia" of the plate. It will be noted further that the straight line portion of both curves shown in Figure 6 cuts the log E axis at the same point, thus showing that "inertia" is independent of the time of development. This is true only under certain conditions which depend upon the constitution of the developing solution. It should be pointed out that inertia is expressed in exposure units and that exposure E is equal to the product of the time exposure (t) by the illumination (N) incident on the plate during exposure. Illumination is usually expressed in meter candles and time in seconds exposure. Consequently, inertia is in meter candle seconds. Since the candle is the unit of intensity based upon the visibility of radiation values, it is a visual unit. Pho
84