DE2151446A1 - Device for displaying the image of an original, in particular a slide - Google Patents

Description

PATENT LAWYERS 7 STUTTGART 1

DR-ING WOLFF H RARTELS long street 51

UK.-IIN ^. WULt-r, M. BAKItLi), TELEPHONE, d2 (0711) 29i310 _U? 72? 5

DR. BRANDES, DR.-ING. HELD telex.o / ^ w

DIPL.-PHYS. WOLFF

Device for imaging the image of an original, in particular a slide

The invention relates to a device for imaging the image of an original, in particular a slide, on a light-sensitive material with reduced contrast of the image, with a projection device and an im Projection beam path arranged, pictorial mask.

Towards the end of the 19th century, F. Reinitzer and O. Lehmann discovered independently of one another that certain substances, when transitioning from a solid crystalline state to an isotropic liquid state, change to a state that exists in a certain temperature range and in which the substance has similar flow properties shows those of liquids, but has optical properties comparable to those of the crystalline state. To identify these properties, Lehmann used the term "liquid crystal", which is still in use today. It is believed nowadays that substances exhibiting those properties are in a fourth physical state called the mesomorphic state or mesophase, since it is a state or phase that is intermediate between that of the anisotropic crystal and that of the isotropic Liquid lies. There are three different mesomorphic states or forms, namely the smectic, the nematic and the cholesteric mesophase. A nematic liquid crystal is essentially transparent and therefore allows light to pass through. But if you put them in a constant electric field, the molecules of some of these liquid crystals get into disorder, ε. ο that the material scatters light and has a milky white appearance. When the constant electric field is released, the molecules of the liquid crystal regain

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their original orientation, so that the liquid crystal is now transparent again. This phenomenon is for example in the Proceedings of the I.E.E.E., July 1968, pp 1162 to 1171, in an article by Heilmeier, Zanoni and Barton, who is entitled: "Dynamic Scattering: A New Electro-Optical Effect in Certain Classes of Nematic Liquid Crystals ".

The "optical memory" effect of a mixture of cholesteric and nematic liquid crystals is in an essay by Heilmeier and Goldmacher, the fc in the Applied Physics Letters of August 15, 1968, pp 132 and 133, entitled "A New Electric Field Controlled Reflective Optical Storage Effect in Mixed-Liquid Crystal Systems ". In this article the authors describe how a mixture of nematic and cholesteric mosomorphic materials as an optical memory in one constant electric field or an electric field that changes at a lower frequency, which originally translucent material into a milky white, light-diffusing material. The liquid crystal then also scatters still light when the electric field is broken down. The optical memory can be quickly erased or the Mixture can be placed in the state of transparency, that the liquid crystal with an alternating electric field exposed to a high frequency of more than 700 Hz.

A serious problem that occurs, for example, when the image of a slide on photographic paper Prints are to be made, is that the finished print has too high a contrast, because a slide one has a relatively large exposure latitude. It is therefore necessary to adjust the projected image of the slide mask so that the projected image has a reduced

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has trast, which is suitable for making prints. One method of doing this is to take an unexposed piece of film to be attached to the frame of the slide by means of a double-sided coated tape and it through the To expose slide positively. The film piece is then treated superficially by means of a viscous developer, so that a mask is created. Thereafter, the slide overlaid by the piece of film is placed in a position suitable for imaging brought, whereupon the mask is irradiated with light which is focused by a lens on photographic paper. The difficulties encountered with such a device are obvious. Appropriate resources must be available to attach and remove the piece of film from the slide mount. There are also significant difficulties with the covering of the film piece and Slide, because the mask expands during the development process. A viscous liquid developer must also be used must be available and replacements must be created for the masks that are used and useless for further use will. Such a process is cumbersome and time consuming, which increases the cost of making prints increase of slide images.

The invention is therefore based on the object. A device, in particular for such a purpose, to create with which, quickly, easily and cheaply lower contrast images of Have template images produced.

This task is based on a device of the aforementioned Type solved according to the invention in that the mask at least temporarily by an optionally selectively scattering Unit is formed, which in the given order a transparent first electrode, a photoconductive layer, has a layer of a liquid crystal and a transparent second electrode to which one of the potential of the

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first electrode different potential can be laid. For example, it could be a DC voltage to the first and second electrode are applied. The sandwich-like unit is arranged in the beam path of the projection device, an image of the image of the original, for example a slide, on a light-sensitive material generated. The arrangement of a slide as a template is basically made so that the outside of the first electrode facing the slide. Lies during the projection of the original image onto the surface the photoconductive layer at the electrodes has an equal voltage, the more brightly illuminated areas of the photoconductive layer are more conductive than the less exposed Areas and therefore cause them in the adjacent areas of the liquid crystal corresponding to them a stronger scattering of the light than in those areas of the liquid crystal, which the adjacent, correspond to less illuminated areas of the photoconductive layer. Hence the brightness of the illuminated areas of the resulting image projected onto the light-sensitive material is less than in the original image of the previous. position so that the image has a lower contrast than the original image.

In a first embodiment of the device according to the invention a liquid crystal of the nematic type is used so that the image in the crystal can be removed by that the DC voltage applied to the electrodes is reduced. builds. The sandwich-like unit then exists for exposure of the image of another template is available.

In a second embodiment of the device according to the Invention, a mixture of nematic and cholesteric materials is used as the liquid crystal, which the

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saves generated image (hence the term "optical memory") , even if the DC voltage has been reduced. In this embodiment it is provided that a slide as a template, the unit and the slide are irradiated by means of the projection device that the unit on the side facing away from the photosensitive material of the slide is arranged and that a second projection device is provided which the image of the slide projected onto the photoconductive layer of the unit. First, with the help of the second projection device the photoconductive layer of the unit creates a photo of the slide, so that a in the liquid crystal masking image is created. Then, with the help of the first projection device, the unit is still in front of the slide shines through, with some light being scattered from the layer of the liquid crystal, in particular in those areas corresponding to the brightly lit areas of the slide. That in the nematic-cholesteric liquid crystal Stored image can be deleted by applying an alternating voltage of sufficiently high frequency to the electrodes of the unit whereupon the unit for exposing the image another slide is available again.

When masking the projected image, for example of a slide, a liquid crystal of the nematic or nematic-cholesteric type according to the invention is used no adjustment problems occur, nor does the otherwise physically trained mask have to be thrown away after use because the liquid crystal of the unit can always be used.

Int the following is the invention on the basis of two by the drawing illustrated embodiments of the device according to the invention explained in detail.

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Show it:

Pig. 1 is a schematically illustrated perspective

View of the essential parts of a first embodiment,
Fig. 2 shows a cross section along the line II - II in Fig. 1 through the unit of the embodiment,

Fig. 3 is a schematic, partially broken off and sectioned illustrated plan view of the essential parts of a second embodiment and FIG. 4 shows a cross section along the line IV - IV in FIG. 3 through the unit of the second embodiment.

It is known that liquid crystals, particularly those of the nematic type or those which are a combination of nematic and cholesteric materials, are normally transparent, but can be caused thereby. To scatter light so that they are brought into an electric field. If, according to the invention, a unit of two electrodes, a photoconductive layer and a layer of a liquid crystal is arranged in the path of the rays used to project the image of a slide, the liquid crystal can serve to partially illuminate the light to scatter light rays associated with the illuminated area ^{e of this} image, so that ~ ^ ä ^

borrowed material on which an image of the original image of the slide is to be produced. Accordingly, the can be used to make a print from the image of a slide or another high-contrast original can achieve the desired reduced contrast without the need to use a To make the mask physically and to make it coincide with the slide, as explained.

The first disclosed embodiment of FIGS. 1 and 2 is provided with a projection device ~ P, a light source

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for example the lamp 2, and a condenser lens 4 / with the help of which a slide 6 can be x-rayed, which is fastened in a replaceable holder 8. The image of the slide 6 serving as a template is projected onto a sandwich-like unit S, whereupon the projected Image is imaged by a field lens 10 and an objective lens 12 on a photosensitive material 14, which is strip-shaped and is held and transported by two interacting rollers 16 and 18, respectively. As best shown in FIG. 2, the unit S has two transparent electrodes 20 arranged at a distance from one another

via one and 22, for example made of electrically conductive glass, which / Switches 26 are connected to a DC voltage source 24. Next to the first electrode 20 is located, with this in contact, a photoconductive layer 28. Between the second electrode 22 and the photoconductive Finally, layer 28 is a layer 30 of liquid crystal of the natal type. of course is the photoconductive layer 28 also transparent, so that the image of the slide 6 through the unit S on the photosensitive material 14 can be projected. Since a slide has a relatively large exposure latitude is the contrast between the lighter and darker ones Areas of the image larger than is permitted for making prints, for example on photographic paper, if Good quality prints are expected. In Fig. 2 the one through one of the lighter areas of the slide 6 is urgent Light beam indicated symbolically by a long arrow 32, while the one going through a darker area Projection beam is indicated by a short arrow 34. If only a little or on the photoconductive layer 28 if there is no light at all, it behaves partially or fully

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the

constantly like an isolator. The DC voltage prevailing between electrodes 20 and 22 then falls for the most part on the photoconductive layer 28, while on the layer 30 of the liquid crystal only a small voltage drop he follows. Under these circumstances, the liquid crystal of the layer 30 is transparent, so that the projection light is the Unit S penetrates unhindered. With increasing illuminance on the surface of the photoconductive layer 28, however, their conductivity also increases, so that now

P on the layer 30 of the liquid crystal is a larger one Voltage drop occurs, leading to a partial scattering of the incident light by the nematic liquid Crystal leads. The photoconductive layer 28 is made selectively conductive by the fact that the image of the slide 6 is exposed and projected through. In areas of great brightness, such as the area 36 lying in front of the arrow 32 the photoconductive layer 28, this becomes electrically conductive due to the high illuminance while it continues isolated in areas with little or no light. Such an area "is for example in front of the Arrow 34. It follows, therefore, that the layer from the

fc liquid crystal scatters light in areas that are illuminated Corresponds to areas of the adjacent photoconductive layer, but remains transparent in other areas. Therefore, the bright light beam represented by the long arrow 32 is scattered to some extent, so that the Luminous flux penetrating through the layer 30 of the liquid crystal, which acts on the photosensitive material 14, has a lower "strength" J ~, which is due to the somewhat shorter arrow 38 is symbolized, and therefore also causes a lower illuminance on the material 14. Some of the light is scattered, as the arrows 40 indicate, and therefore does not strike the objective lens 12

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and consequently does not expose the photosensitive Material 14. The lower brightness light represented by arrow 34 penetrates the liquid crystal almost not weakened, such as the approximately equal lengths of the arrow 34 and that reproducing the emerging projection beam Arrow 42 clarify. Of course, the brightness of the beam indicated by the arrow 38 is still greater than that of the projection beam represented by arrow 42. The in the different length of the However, the difference in brightness expressed by arrows 38 and 42 is smaller than that which is greater Indicate the difference in length with arrows. 32 and 34. Therefore, the impingement on the photosensitive material 14 generates Light an image that has a lower contrast than the image of the original, namely the slide 6.

A suitable material for the liquid crystal is a nematic mesophase of N- (p-methoxybenzyliben) -p-buthylaniline, which is in the mesar "phase between 17 ° C. and 44 ° C. The photoconductive material is 4,4'- Diethylamino-2,2 ^f dimethyltriphenol methane and a polycarbonate resin together with a pyrylium dye, prepared according to Example 1 given in British Patent 1,153,506.

A suitable thickness for the liquid crystal layer 30 is 12 µm while the photoconductive layer 28 is 10 µm thick. The two layers 28 and 30 are expediently separated by a layer of cellulose nitrate with a thickness of at most 1 μm . This layer prevents adverse chemical reactions between the liquid crystal and the photoconductive material. A voltage of 250 to 400 volts on electrodes 20 and 22 is sufficient. An illuminance of 10 764 Ix

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(1,000 lm / sq.ft.) Is suitable, although this value differs from the photographic properties of the light-sensitive material 14 depends.

If another slide is to be projected, the layer 30 made of the liquid crystal can thereby be completely restored be made transparent that the switch 26 is momentarily opened, so that the layer 30 lying on Stress is relieved. For the subsequent projection of another image, the slide 6 can be replaced by a second slide be replaced, its image by the sandwich-like Unit S is projected as long as switch 26 is closed. ,

The second embodiment according to FIGS. 3 and 4 is provided with a first projection device P ¹ corresponding to the projection device P of the first embodiment, which has a light source, for example a lamp 102, which sends part of its light through a lens. The light emerging from the lens 104 is reflected by a mirror 106. The projection beam then passes through a sandwich-like unit S ¹ , which will be explained in more detail below, and through a slide 110 which is exchangeably fastened in a holder 112. The image of the slide is projected with the aid of an objective lens through a half-silvered mirror 116 onto a photosensitive material 118, for example a photographic film, which lies against a film carrier 120 and is covered by a mask 122, which results in sharp edges of the print to be produced.

A masking image is generated on a layer 130 of the unit S ¹ made of liquid crystal by means of a second projection device before the slide image is projected onto the light-sensitive material 118. The second pro

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The projection device has a lamp 124 , the light of which penetrates through an associated lens 126 and is reflected by the semi-silvered mirror 116 into the main beam ^{path, so that the objective lens 114 common to the two projection devices and the slide 110 project their image onto the unit S 1} . The unit S ¹ is similar to the unit S of the first embodiment with the exception that the liquid crystal forming the layer 130 consists of the mixture of a nematic mesophase and a cholesteric mesophase, which contains the nematic and the cholesteric mesophase in a weight ratio of 10: 1 . N- (p-methoxybenzyliben) -p-butylaniline is suitable as the nematic material, while cholesteryl oleyl carbonate is suitable as the cholesteric mesophase. Depending on the switching state of a switch, the electrodes 128 and 129 can be connected to a direct voltage source 134 or an alternating voltage source 135.

In order to create a masking image in the layer 130 of the liquid crystal, the switch 136 is toggled so that that the DC voltage supplied by the source 134 is applied to the electrodes 128 and 129. In addition, the Lamp 124 switched on, the light of which projects the image of the slide HO onto the photoconductive layer 132. The illuminance used for masking is approximately 10 764 Ix. Leave the lighter areas of the slide more light through, as indicated by the longer arrow 138, while the darker areas of the slide let through less light, as the shorter arrow 140 indicates. Therefore, those areas become the photoconductive Layer 132, which includes, for example, the area 142, which is exposed to a considerable luminous flux be electrically conductive, so that the adjacent area

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a voltage drop occurs in the layer 130 of the liquid crystal which is sufficient to cause a molecular reorientation and to diffuse the incident light. Those areas of the photoconductive layer 132 which are denoted by " Little or no light at all is applied, including the area in front of arrow 140, for example counts, remain essentially insulating and change the properties of the corresponding areas of the liquid Not crystal in terms of light transmission.

Thus, the layer 130 in the liquid crystal shows a masking one Image that is intended and suitable for disintegrating

scatter that falls into those areas that correspond to the lighter areas of the slide 110 and allow light to pass through, that falls into those areas that correspond to the darker areas of the slide. When the lamp 124 switched off and the DC voltage applied to electrodes 128 and 129 is reduced, the image remains fluid Crystal obtained thanks to its storage properties *. The timespan, which is required to create the masking image in the liquid crystal can either be controlled thereby that the lighting duration of the lamp 124 is controlled,

ψ or in that the duration of the application of the DC voltage supplied by the source 134 is controlled. The latter has proven to be more advantageous, since sharply defined DC voltage pulses can be generated. A voltage of 400 volts applied for half a second is sufficient. Thereafter, the lamp 102 is turned on to project the image of the slide onto the photosensitive material 118. The illumination of the layer 130 is essentially uniform, as indicated by the solid arrows 144 and 146 of the same length. The light bundle identified by the arrow 144 hits the layer 130, "the liquid crystal of which is part of the incident light

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scatters, as indicated by the arrows 148, and allows a weaker luminous flux, denoted by a shorter arrow 150, to pass through to the slide. On the other hand, the light bundle indicated by the arrow 146 is transmitted essentially unattenuated by the liquid crystal of the layer 130 and the remaining parts of the unit S ¹ , which is why the arrow 152 is not shortened. The light represented by arrow 152 therefore has the same brightness as the incident light represented by arrow 146. Thus, an illumination of the slide 110 through the unit S * has the consequence that it is illuminated more intensely in its dark areas and less intensely in its light areas in comparison to direct illumination by the lamp 102. This reduces the contrast of the generated image that is projected onto the photosensitive material 118. The intensity and duration of the lamp 102 are determined by the properties of the photosensitive material 118 to be exposed. After this material has been exposed, the lamp 102 can be switched off and the alternating voltage of the source 135 can be applied to the electrodes 128 and 129 with the aid of the switch 136, so that the liquid crystal of the layer 130 assumes its "dormant" or transparent state again Another mask is ready for the next slide to be projected. An alternating voltage of 600 volts with a frequency of 1,000 Hz, which is applied for one to two seconds, is sufficient.

The description shows that devices designed according to the invention make it unnecessary to bring the slide with the mask to the pack and / or to make the mask one Use developer solution.

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Claims (7)

215HA6- PATENT CLAIMS Vl)) Device for imaging the image of an original, in particular a slide, on a light-sensitive material with reduced contrast of the image, with a projection device and a pictorial mask arranged in the projection beam path, characterized in that the mask is at least temporarily replaced by an optionally selectively scattering Unit (S; S ¹ ) is formed which, in the order given, comprises a transparent first electrode (20; 128), a photoconductive layer (28; 132), a layer (30; 130) made of a liquid crystal and a transparent second electrode (22; 129) to which a potential different from the potential of the first electrode (20; 127) can be applied. 2) Device according to claim 1, characterized in that in a slide (6) as a template this is irradiated and that the unit (S) is arranged between the slide (6) and the photosensitive material (14) and the first and second electrodes (20 or 22) are facing the slide (6) or the material (14). 3) Device according to claim 1, characterized in that with a slide (110) as a template, the unit (S ') and the slide (110) are irradiated by means of the projection device (1O2, · 104, 106, 114) that the unit (S ^f ) is arranged on the side of the slide (110) facing away from the photosensitive material (118) and that a second projection device (124, 126, 116, 114) is provided which the image of the slide (110) onto the photoconductive layer (132) of the unit (S ¹ ) is projected. 209817/1334 215H46 4) Apparatus according to claim 3, characterized in that the Projection devices for an advance activity of the second projection device (124, 126, 116, 114) independently are operable from each other. 5) Apparatus according to claim 3 or 4, characterized in that the second projection device (124, 126, 116, 114) has a has, in the projection beam path, semi-silver-plated mirror (116). 6) Device according to one of claims 3 to 5, characterized in that the two electrodes (128, 129) of the unit (S ¹ ) can be optionally connected to a direct voltage and an alternating voltage source (134 or 135) by means of a changeover switch (136) are. 7) Device according to one of claims 1 to 6, characterized in that the unit (S, S ¹ ) comprises a separating layer arranged between the photoconductive layer (28; 132) and the layer (30; 130) made of a liquid crystal, preferably made of Cellulose nitrate. 209817/1334