Agfa Library: Technical Terms - L





















 




L

Layer structure

Color materials of the AGFACOLOR type are made up of a base with three
differently sensitized emulsion layers (which in turn can consist of
several part-layers) plus a number of auxiliary layers, such as
protective layers, active interlayers, adhesive layers, anti-halation
layers, filter layers and antistatic layers (see Fig. 19).

In the case of color materials, the top blue-sensitive emulsion layer
has a yellow coupler, the middle, green-sensitive layer a magenta
coupler and the bottom red-sensitive layer a cyan coupler. Also very
important are the yellow filter and anti-halation layers. The yellow
filter layer is always below the blue-sensitive emulsion, since it has
to prevent the exposure of the middle and lower layers in the region of
their own sensitivity (highly sensitive silver bromide emulsions always
have a high inherent sensitivity in the blue third of the spectral
range irrespective of their specific sensitization for a certain area
of the visible light). The anti-halation undercoat makes a major
contribution to the sharpness of the image (anti-halation).

Since the general speed of printing materials is very much lower than
that of photographic materials, it is usual to dispense with the yellow
filter layer here. Green and red-sensitized silver chloride emulsions
with only a slight inherent sensitivity in the blue third of the
spectral region are used for the rendition of magenta and cyan
respectively.

The order of the dye-forming emulsion layers may also be different in
printing materials. Basically, the top layer can produce either the
yellow, the magenta or the cyan color image (principle of layers in
different order).

 

Light  

The term used to describe the electromagnetic radiation within the
spectral range that can be perceived by the human eye. The visible
range extends from approx. 380 to 760 nm (nanometer). Photographic materials for
taking pictures are sensitized for the range of visible light (sensitization).

 

Logarithms  

The logarithm of a number to a given base is the power to which the
base must be raised to produce the number. For example, the logarithm
of 64 to the base 8 is 2 (8² = 8 x 8 = 64).

In sensitometry, use is generally made of logarithms to the base 10.
The logarithm of 100 to the base 10, for example, is also 2 (10² =
10 x 10 = 100).

Logarithms to the base 10 can be recognized from the generally written
shortened form, lg or also log 10 . They form the basis of calculations
in sensitometry.

Since sensitometric data frequently consist of geometrically increasing
series of numbers (e.g. the scaling of x-axis and y-axis, see Fig. 23), the advantages
of calculating with logarithms quickly become understandable when we
look at the following list of logarithms with base 10:


lg 0,001 = -3 (10¯³ = 0,001)
 

lg 0,01 = -2 (10¯² = 0,01)
 

lg 0,1 = -1 (10¯¹ = 0,1)
 

lg 1 = 0 (10° =1)
 

lg 10 = 1 (10¹ = 10)
 

lg 100 = 2 (10² = 100)
 

lg 1000 = 3 (10³ = 1000)


A minus sign indicates that the respective figure is a decimal
fraction.

In the Technical Data Sheets there are many examples to illustrate the
advantages of giving sensitometric data in the form of logarithms. The
logarithmic figures on the exposure axis of the density curve of e.g. +1,
0, -1, -2 mean, for instance, an exposure intensity of 10, 1, 0.1, 0.01 lux-seconds, whereby the gaps between the
individual values on the exposure axis are the same because of their
logarithmic division.

 

Lux  

The unit of illumination or illuminance is E = 1 lux. In terms of order
of magnitude, 1 lux represents the illumination provided by a household
candle at a distance of 1 m.

An illumination of E = 1 lux ( Abbr.: lx) is equivalent to a luminous
flux of 1 lumen, which evenly illuminates an area of 1 m 2 . The
illumination falls (at constant luminous flux) with the square of the
distance from the light source of the illuminated area.

Examples of the illumination of some natural light sources:


80,000lx: summer sunlight
 

5,000 lx: diffuse daylight
 

0.25 lx: full moon
 

0.10 lx: clear starlight


Illumination is measured with a luxmeter.

 

Lux-second  

The unit of measure for the intensity of an exposure is the lux-second
( Abbr.: lxs). In sensitometry,
the lux-second is used as a measure for giving the exposure H = l x t.
The product of the exposure (H) can be formed from a high exposure
intensity (l) at a correspondingly short exposure time (t) (e.g. 10 lux
x 1/1000 s), or from a low exposure intensity at a correspondingly
longer exposure time, e.g. 1/1000 lux x 10 s (reciprocity failure).



 



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