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IX-240 (Advanced Photo System).

The code for the film format of the Advanced Photo System. The IX stands for the exchange of magnetic, mechanical and optical information between the user and the lab. The camera's specification determines what form the IX takes.

Layer structure.

Colour 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. 18). The films for the Advanced Photo System also feature a magnetic layer on the film back. In the case of colour 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 (fast silver bromide emulsions always have high inherent sensitivity in the blue third of the spectral range irrespective of their specific sensitisation for a certain range 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 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 colour image.

Light.

Light is the electromagnetic radiation within the spectral range that can be perceived by the human eye. The visible range extends from approx. 380 to 750 nm ( nanometre). Photographic materials for taking pictures are sensitized for the range of visible light ( sensitisation).

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 × 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 × 10 = 100). Logarithms to the base 10 are generally abbreviated to lg or also log 10 . They form the basis of calculations in sensitometry.

Since sensitometric data frequently consist of geometrically increasing series of numbers, the advantages of calculating with logarithms quickly become clear when we look at the following list of logarithms with base 10:

A minus sign indicates that the respective figure is a decimal fraction (see Fig. 5 with logarithmic scaling).

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, and the gaps between the individual values on the exposure axis are the same because of their logarithmic division.

Lux

The unit of illumination or luminance 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 (abbreviated lx) is equivalent to a luminous flux of 1 lumen, which evenly illuminates an area of 1 m² . 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:

Illumination is measured with a luxmeter.

Lux-second.

The unit of measure for the intensity of an exposure is the lux-second (abbreviated lxs). In sensitometry, the lux-second is used as a measure for the exposure H = I x t. The exposure (H) can consist of a high exposure intensity (I) with a correspondingly short exposure time (t) (e. g. 10 lux × 1/ 1000 s), or of a low exposure intensity with a correspondingly longer exposure time, e. g. 1/ 1000 lux × 10 s ( reciprocity failure).

Magnetic layer (Advanced Photo System)

Transparent magnetic coating applied to the complete area of the back of the film. This coating is used for storing the film, shooting and processing data, and enables communication to take place between all the system components ( IX-240).

Main colour density.

The term is used to describe the colour density of a single layer in the spectral region in which the absorption maximum lies. The main colour density of the yellow dye lies in the blue spectral range, that of the magenta dye in the green and that of the cyan dye in the red spectral range ( masking, secondary colour density).

Masking.

In ideal circumstances (which are unattainable under practical conditions), a developed colour negative film should only form, in each individual colour-forming layer, the dye which has a spectral density in the blue, green or red spectral third of visible light. In other words, in theory only one particular dye should, through oxidative colour coupling, form without any secondary colour densities in any of the colour-forming layers.

However, the emulsion dyes have secondary absorptions in the other spectral thirds which can combine to make the colours greyer. For example, the emulsion dye of the developed magenta layer has its main colour density in the green spectral range, as well as additional undesirable secondary colour densities in the blue and red regions of the spectrum.

Colour negative films are nowadays masked to correct the saturation losses and colour impurities caused by these secondary absorptions. During colour development, colour positive masks are formed in addition to the emulsion dyes. Conventional colour negative films are provided with two colour masks, but most AGFACOLOR negative films have three. The colour of these masks corresponds to the particular undesirable absorptions of the image dyes. This means, for example, that the yellow secondary density of the magenta dye is compensated by a yellow dye image of low density that has the opposite gradation to the magenta image. Both yellow densities add up to generate a uniform yellow colour cast, which is then filtered out during the subsequent printing process. The colouring of the mask and the emulsion dyes jointly determine the film-specific colour rendition.

Controlling colour brilliance through triple masking.

Fig. 17: The extra third colour mask of the AGFACOLOR Professional films ensures cleaner reds and more brilliant yellows.

The secondary densities that are undesirable in photographic practice are:

With conventional colour negative films, only the yellow secondary density of the magenta and the magenta secondary density of the cyan are compensated. Modern AGFACOLOR films contain an extra third mask to correct the yellow secondary density of the cyan. Masking is carried out automatically during the processing (without any additional operation) by mask couplers incorporated in the emulsion layers. The colours of the mask couplers correspond to the colours of the secondary colour densities to be corrected. The mask couplers react with the oxidation product of the developer, and release their original colours. If we take the example of the yellow secondary density of the magenta image, this means that a yellow image of low density counteracts the magenta image. The yellow secondary density and the counteracting yellow secondary image add up to create a homogeneous colour haze, which can be filtered out during subsequent printing.

Micrometre (µm).

A physical unit of length equivalent to 10^-6 metres, i. e. one thousandth of a millimetre (1 µm = 10^-6 m). The average thickness of a human hair is 23 µm. The carrier material used for the Advanced Photo System has a thickness of only 90 µm (35 mm film has 125 µm).

Multiple layers.

The number of individual layers in modern colour films has risen appreciably compared with earlier colour films. Films with twelve or more layers are nowadays rather the rule than the exception. At the same time, the overall thickness of the emulsion has actually been reduced by the development of new coating techniques (e. g. cascade coating). It is nowadays normal to apply two of each of the three colour-forming emulsions, and in some cases even three of each. Yellow, magenta and cyan double layers consist of a faster top layer and a slower bottom one. This "bi-pack" system improves the grain in low and medium colour densities, a factor which benefits for example skin tones, because it produces a homogeneous surface effect. The light-sensitive emulsion layers of the several Agfa professional films comprise double and triple layers. The triple layers have a fast layer with a rather coarse grain at the top, a medium-fast layer in the middle, and a slow layer of particularly fine grain at the bottom. A number of black-and-white films also have double layers. The AGFAPAN APX 400, for example, is a double-layer film with a high-speed and a low-speed emulsion layer. The top, high-speed grainier layer is exposed at full intensity and thus ensures a high practical speed. The lower, slower layer, provides a fine grain in the low and medium densities which have a major influence on the picture.

Layer structure (schematic) : AGFACOLOR PORTRAIT XPS 160 PROFESSIONAL

Fig. 18: Layer structure of the AGFACOLOR PORTRAIT XPS 160 PROFESSIONAL with double and triple layers.

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