WO2000019251A1

WO2000019251A1 - A colour filter device

Info

Publication number: WO2000019251A1
Application number: PCT/SE1999/001327
Authority: WO
Inventors: Richard Ryan Magnusson
Original assignee: Richard Ryan Magnusson
Priority date: 1998-09-30
Filing date: 1999-07-30
Publication date: 2000-04-06
Also published as: AU5661999A; SE9803323L; SE9803323D0; SE511560C2; WO2000019251A9

Abstract

The invention concerns a colour filter device (10) comprising at least a first (12), a second (14), and a third (16) element. Each of the first (12) and the second (14) elements comprises a polarizer. The first (12) and the second (14) elements are arranged such that an optical path (24) is formed between them. The third element (16) comprises a birefringent means positioned on the optical path (24) between the polarizers (12, 14) and is arranged to transmit electromagnetic radiation. The third element (16) and at least one of the first (12) and the second (14) elements are controllably arranged in such a manner that, concerning the first (12) and the second (14) elements, the direction of polarization of the element is variable and concerning the third (16) element, the birefringent means is rotatable. By said control of the elements (12, 14, 16), the transmitted spectral range may be changed.

Description

A colour filter device

BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention concerns a colour filter device for transmission of a variable spectral range. Colour filter devices have applications in many different situations. For example, in connection with a photographic equipment, such as a camera or a projector, it is often interesting to use a filter which transmits a desired wave length interval, i.e. a desired colour. In such contexts, it is common to have a number of different colour filters and to select one filter with a desired transmission for a specific application, and to apply this filter to the photographic equipment. Also in connection with illumination devices, it is known to arrange a colour filter in the path of the emitted light. At theatre, sport, and similar public events, large spotlights are often used. In order to achieve a desired effect, it is thereby often desirable that the light emitted from the spotlight has a certain colour. Therefore, a large colour filter, which is positioned in front of the spotlight, is often used. If it is desired to change the colour of the emitted light, it is necessary to change the relatively large colour filter, which is attached to the spotlight.

There also exist spotlights, for example in discos, exhibition halls, or in other public contexts, where it is desirable to be able to vary the colour of the emitted light. It thereby happens, that a so-called filter wheel is used in front of the spotlight (or in front of another illumination device). Such a filter wheel comprises a number of colour filters of different colours distributed around the filter wheel. The filter wheel is positioned relative to the illumination device such that a selected filter is located in the path of the light emitted from the illumination device. Since the filter wheel may be rotated about an axis, which usually is located to the side of the light-beam from the illumination device, another filter may be positioned in the path of the emitted light by a rotation of the filter wheel. Such a filter wheel requires a relatively large space and is relatively complicated to arrange at the illumination device. Furthermore, the number of possible selectable spectral ranges is limited to the number of filters in the filter wheel.

SPIE Volume 103, Systems Integration and Optical Design II, 1977, pp. 99-101 , describes a colour filter device. The colour filter device comprises polyvinyl alcohol membranes and plastic polarizers. It is not exactly clear how the polyvinyl alcohol membranes are arranged relative to the polarizers. It appears, however, from page 100 as if a large number of polyvinyl alcohol membranes are laminated between glass plates. The adjustment of the filter is done in that the polarizers are rotated by means of a single knob (see page 99, the first paragraph).

Prior known non-controllable colour filters are often produced by a coloured glass or consist of a dielectric multi-layer filter.

The above described filters are either relatively complicated to produce or do not allow for the possibility to vary the transmitted spectral range.

SUMMARY OF THE INVENTION

The purpose of the present invention is to achieve a colour filter device for the transmission of a variable spectral range, which colour filter device is relatively inexpensive and simple to produce and to apply at the same time as the transmitted spectral range may be varied in a simple manner.

This purpose is achieved by a colour filter device for the transmission of a variable spectral range, comprising at a least first, a second and a third element, wherein each of the first and the second elements comprises a polarizer, wherein the first and the second elements are arranged such that an optical path is formed between them, and the third element comprises a birefringent means positioned on the optical path between the polarizers and arranged to transmit electromagnetic radiation, wherein the third element and at least one of the first and the second elements are controllably arranged in such a manner that, concerning the first and the second element, the direction of polarization of the element is variable and concerning the third element, the birefringent means is rotatable, wherein through said control of the elements the transmitted spectral range is changed.

According to an embodiment of the invention, the colour filter device comprises a fourth element in the form of a birefringent means positioned on the optical path between the first and the second element and arranged to transmit electromagnetic radiation. With a further birefringent means, it has been shown that the transmitted spectral range may be varied to a larger extent (i.e. more colours may be selected).

According to a further embodiment of the invention, the colour filter device comprises a fifth element in the form of a birefringent means positioned along the optical path between the first and the second element and arranged to transmit electromagnetic radiation, wherein at least three of the elements are controllable. By this embodiment, the selected transmitted spectral range may be further varied, such that more distinct transmitted primary colours may be obtained.

According to another embodiment of the invention, at least four of the elements are controllable. By this embodiment, it has appeared that many different shades of colour may be obtained in the transmitted light.

According to another embodiment of the invention, the colour filter device comprises a holding member, which holds the elements in position relative to each other and which allows for a rotation of at least the controllable elements about a common axis of rotation, which extends through all the elements, wherein the control of the controllable elements is done by a rotation of the respective element about said axis of rotation. This embodiment has appeared to be advantageous in that the different elements are held in position in a safe manner and in that a controlled control of the transmitted spectral range may be performed in that the controllable elements rotate about a common axis of rotation.

According to another embodiment of the invention, the polarizers and the birefringent means consist of plastic materials. By producing the different elements in plastic materials, it has been shown that an inexpensive and useful colour filter device may be obtained.

According to a further embodiment of the invention, the birefringent means consist of cellophane or polypropylene. These materials have been shown to function well as birefringent means and may, furthermore, be obtained at a low price.

According to a further embodiment of the invention, the colour filter device comprises drive units for driving the controllable elements and a control unit comprising a storage means for storing information concerning the setting of the controllable elements for obtaining transmission of different spectral ranges of electromagnetic radiation which is transmitted through the device, wherein the control unit, in response to an input of an operator of a desired transmitted spectral range, controls the drive units such that the controllable elements are automatically set such that the desired transmission is obtained. This embodiment of the invention has the advantage that it is possible to store information in advance about different transmitted spectral ranges such that the controllable elements, by the input from an operator, are automatically set such that a desired transmission is obtained.

According to a further embodiment of the invention, the colour filter device comprises a maintaining member suited to be connected to a photographic equipment such that the colour filter device may be held at the photographic equipment such that the electromagnetic radiation, which is received by or emitted from the photographic equipment, passes through the colour filter device. By this embodiment of the invention, a colour filter device which can easily be applied to different photographic equipments is obtained.

The invention also concerns a photographic equipment comprising a colour filter device according to any of the embodiments which has been described above.

The invention also concerns an illumination device comprising means for receiving a light-producing member and a filter device for filtering the light from the light-producing member when this member is in operation in the illumination device, wherein the filter device comprises a colour filter device according to any of the embodiments which have been described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be explained with the help of embodiments given as examples and with reference to the appended drawings, on which

Fig. 1 shows schematically a cross-sectional view of a colour filter device according to the invention, Fig. 2 shows schematically a photographic equipment comprising a colour filter device, and Fig. 3 shows schematically an illumination device comprising a colour filter device.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Fig. 1 shows schematically an embodiment of the invention. The colour filter according to this embodiment is generally designated by 10. The colour filter comprises a holding member 22. The holding member may suitably be tubular. In fig. 1 , a cross-sectional view seen from the side of the holding member 22 is thus shown. In the holding member, a first element 12 and a second element 14 are arranged. The first element 12 comprises a polarizer. Also the second element 14 comprises a polarizer. The polarizers 12, 14 are suitably, but not necessarily, thin plastic polarizers which may be obtained relatively inexpensively (for example from Polaroid Corporation). The direction of polarization may with such an element easily be changed by rotating the element. Even though suitably plastic polarizers are used, it is also within the frame of the invention to use other kinds of polarizers 12, 14. It is thus possible that the polarizers 12, 14 consist of a liquid crystal material, such that the direction of polarization is not changed by rotating the element, but is done through electrical control. Also other kinds of polarizers, where the polarizing properties are caused and/or changed in an electro-optic manner, may be used. It is also possible to use polarizers, where the polarization or the direction of polarization may be locally controlled. The polarizer may thus be controlled such that the different parts of the polarizers have different polarizing properties. Thereby, also the wave length range transmitted through the colour filter may be locally controlled.

Between the polarizers 12, 14, a third element 16, a fourth element 18, and a fifth element 20 are positioned. These elements comprise a birefringent means. Different birefringent plastic materials have been shown to function well. Such materials may be obtained at a low price. For example, polypropylene or cellophane may be used. Also other birefringent plastic materials (which, for example, are produced with built-in tensions or other structural order) may be used. Cellophane has been shown to function particularly well. Also a so-called bi-axial pp (polypropylene) has appeared to function very well. The different elements 12-20 are suitably round such that they may be rotated in the holding member 22. In order to hold the elements 12-20 in position in a stretched-out state, periphery holders 36 are suitably used. The periphery holder 36 may thus consist of a kind of frame which is attached around the periphery of the elements 12-20. It is also possible to arrange a birefringent means in the form of a thin plastic film with built-in tensions on a rigid transparent plastic plate, for example of an epoxy plastic material. In order to hold the elements 12-20 in a plane state, it is also possible to arrange the elements 12-20 between protecting transparent layers (not shown in the figure). These layers may, for example, consist of an optical glass or of other suitable rigid optical plastic materials. These protective layers are suitably formed as plane-parallel plates. Each of the elements 12 to 20 may thus be arranged between a pair of such plates. In certain applications, when the colour filter 10 is exposed to high temperatures (for example when it is used in connection with an illumination device), the elements 12-20 may also be provided with a protective layer against heat radiation. The elements 12-20 may also be provided with a particular layer for the protection against scratches or other wear. Such protective layers may, for example, be provided on the outside of the plane-parallel plates between which the respective element 12-20 is arranged.

In order to set the colour filter 10 such that a desired transmission is achieved, the birefringent means 16, 18, 20 are rotatably arranged. The elements 16, 18, 20 are suitably arranged in recesses 37 in the holding member 22 such that they may be turned or rotated around an axis of rotation 24, which is located centrally in the holding member 22. Furthermore, the polarizers 12, 14 are arranged such that the direction of polarization may be changed. As has already been noted above, this can also be achieved in that the polarizers 12, 14 are rotatably arranged. The holding member 22 is suitably opaque in order to prevent light from reaching the inner of the filter device 10 from the side.

It should be noted that the polarizers 12, 14 or the birefringent means 16, 18, 20 do not necessarily have to cover the whole cross- sectional area of the tubular holding member 22. It certain applications (for example in the use of the colour filter device 10 in connection with a camera), it may be desirable that only a part of the electromagnetic radiation, which is transmitted through the device, is filtered. This may be achieved, for example, in that one of the polarizers 12, 14 only covers a part of the cross-sectional area of the holding member 22. By rotating such a "partial" polarizer, the part of the transmitted radiation which is filtered may be changed. In case, for example, a polarizer of a liquid crystal material is used, it may suitably through electric control be selected which part of the cross-sectional area the polarizer should cover.

In order for the invention to function, it is necessary that there are two polarizers 12, 14 and at least one birefringent means, for example 16, arranged between the polarizers 12, 14. A better variation of the transmitted spectral range is obtained if there are two or preferably three birefringent means 16, 18, 20 between the polarizers 12, 14. With three birefringent means 16, 18, 20, such as is shown in fig. 1 , a very good variation of the transmitted spectral range is obtained. With three birefringent means 16, 18, 20, the elements may thus be set such that the filter functions as a distinct blue, yellow, magenta, or green filter. It is also not necessary that all the elements 12-20 are controllably arranged in the holding member 22. In order to obtain a good variation of the transmitted spectral range, it is, however, advantageous if at least four of the elements 12-20 are controllably arranged. The control of the elements 12-20 is done as has been said above, suitably through a rotation of the respective element. This rotation may be performed manually. This may be done, for example, in that a pin (not shown) is arranged at the periphery holder 36 of the element, which pin suitably extends out in a radial direction through a slot (not shown) in the holding member 22 such that the pin may be reached from the outside of the holding member 22. An operator may thereby manually adjust the degree of rotation of the respective element 12- 20 by moving the pin along the slot in the holding member 22.

In the embodiment shown in fig. 1 , the control of the elements 12- 20 is however done by electric control. The elements 12-20 are therefore provided with drive units 26. These drive units 26 may consist of micro-motors, which as such are known. The drive units 26 are suitably arranged in connection to the holding member 22. The drive units 26 are thus connected to the elements 12-20 (or to the periphery holder 36 of the elements) via a drive-connection 38. The drive-connection 38 may, for example, consist of a cog gear or a friction gear. The drive units 26 (for example the micro-motors) are suitably controlled by a control unit 28. The drive units 26 are connected to the control unit 28 via a connecting means 34. The control unit 28 comprises suitably a storage means 30. The control unit 28 is also suitably connected to an input unit 32. The control unit 28, the storage means 30, the input unit 32 and the connecting means 34 are in fig. 1 only schematically drawn. The control unit 28 and the input unit 32 may, for example, be arranged in connection to the holding member 22 or also be arranged at a distance from the holding member 22, i.e. at a position from which the colour filter 10 is to be controlled. The control units 28 may suitably comprise a micro-processor with the help of which the elements 12 to 20 may be controlled. The control may suitably be done such that an operator, via the input unit 32, sets the different elements 12 to 20 by a rotation relative to the axis of rotation 24 until a desired transmission (a desired colour) is obtained. Thereafter, the angles of rotation of the set elements 12-20 are stored in the storage means 30. Such an adjustment may be done for many different transmitted spectral ranges (i.e. different colours). The settings of the different elements 12 to 20 in order to obtain the different transmitted spectral ranges may thus be stored in the storage means 30. When such an adjustment is done, an operator may later by an input via the input unit 32 indicate a desired transmitted spectral range, whereafter the control unit 28 with the help of the storage means 30 via the drive units 26 automatically sets the elements 12 to 20 in such a manner that the desired spectral range is obtained.

The colour filter 10 may also be provided with a maintaining member 40 suited to be connected to a photographic equipment 42. This maintaining member 40 may, for example, consist of a thread. In this manner, the colour filter 10 may be connected for example to a camera 42 in that it is screwed to the thread which is often provided on a camera objective. The photographic equipment 42 which is shown in fig. 1 may thus constitute a camera. The photographic equipment 42 may also, for example, constitute a projector or other photographic equipment. The colour filter 10 may, of course, also be arranged to be provided on other equipment than a photographic equipment 42. The colour filter 10 is thus useful in all contexts where it is desired to transmit a certain spectral range, for example in connection with illuminations and in connection with optical instruments of different kinds. It should again be noted that the figure only shows a schematic cross-sectional view of the holding member 22 and the elements 12 to 20. Since the elements 12 to 20 constitute very thin plastic materials, they may be positioned very close to each other in the holding member 22. The . device 10 may thus be made very compact, and the length of the whole device may be only some centimetre.

Fig. 2 shows an example of a photographic equipment 42 (in this case a camera). The photographic equipment 42 has an objective 44. The objective 44 defines an optical axis. The photographic equipment 42 comprises here a colour filter device 10 of the kind that has been described above.

Fig. 3 shows schematically an example of an illumination device 46 according to the invention. The illumination device 46 comprises a housing 48 and a support 56 which hold the illumination device 46. The illumination device 46 comprises a means 50 for receiving a light-producing member 52. The light-producing member 52 may, for example, constitute a lamp. Furthermore, the illumination device 46 may comprise a reflector 54 in order to direct the radiation emitted from the light-producing member 52. The radiation may thus be directed in a direction which may constitute the optical axis 45 of the illumination device 46. The illumination device 46 comprises a filter device 10 for filtering the light from the light-producing member 52 when this member is in operation in the illumination device 46.

With the present invention, a relatively simple, inexpensive, and well-functioning, controllable colour filter 10 is thus obtained, which may be used in may applications. The colour filter 10 may be produced in different sizes. For example, in order to cover a large spotlight or for covering a smaller pencil of rays in an optical instrument or the like. The filter 10 may be used in many different illumination contexts, for example for theatre illumination, studio illumination, or studio flashes, common home illumination such as table lamps or light-tubes, and in offices or in the industry. The colour filter device 10 may also be used in different contexts where a colour filter is desired in different optical apparatuses. If only one birefringent means 16 is used, certain spectral ranges may be transmitted; for example a blue or a yellow spectral range may be selected with the help of the control of the controllable elements 12, 14, 16. With the help of two birefringent means 16, 18, more shades of colour may be obtained in the transmitted light. If the device comprises three birefringent means 16, 18, 20, it has been shown that very clear colours of the transmitted light may be obtained. Such a filter with three birefringent means 16, 18, 20 may thus produce clear blue, yellow, magenta, and green transmitted light. Of course, more than three birefringent means 16, 18, 20 may be used in the colour filter device 10. In order to obtain clear nuances of the transmitted light it is (in the case that three birefringent means 16, 18, 20 are used) desirable that at least four of the elements 12 to 20 are controllable. By control of the elements 12 to 20 is in the present application meant the following:

Concerning the polarizers 12 and 14 that the direction of polarization may be changed. This may be done, when for example plastic polarizers 12, 14 are used, in that these polarizers are rotated around the axis of rotation 24. Concerning the birefringent means 16, 18, 20 is by control meant that these elements are rotated relative to the axis of rotation 24, such that the orientation of the birefringent means relative to the direction of polarization of the incident polarized light may be varied. Depending on which desired spectral range is to be transmitted through the colour filter device 10, one or more of the elements 12 to 20 must be controlled. Exactly how much and which elements 12-20 that have to be rotated in order to obtain a desired transmitted spectral range, the person skilled in the art may easily find out by trying different settings of the elements 12-20. In the embodiment shown in fig. 1 , it may thus be programmed in the control unit 28 how the different elements 12-20 should be set in order to obtain a desired transmission. The different elements 12-20 may, as has been mentioned above, be produced to be very thin. For example, a cellophane membrane which is used for the birefringent means 16 to 20 may have a thickness of only 10 to 20 μm. The drive units 26 may, as has been mentioned above, constitute micro-motors or piezo-motors. In applications where the compactness of the colour filter device 10 is not so important, also larger electrical motors 26 may be used. The controllable elements 12 to 20 should, of course, be controllable independently of each other in such a manner that the different elements 12 to 20 may be set by being rotated different amounts about the axis of rotation 24. Since the different elements 12-20 may be made quite large, a colour filter device 10 may be designed to have a large aperture. Furthermore, since the colour filter device may be made compact, the device may have a large field of view. According to the invention, a well-functioning, compact, inexpensive, and controllable colour filter device 10 can thus be obtained. The colour filter device gives the possibility to, in a simple manner, select many different transmitted spectral ranges.

The present invention is not limited to the shown embodiments but may be varied and modified within the scope of the following claims.

Claims

1. A colour filter device (10) for the transmission of a variable spectral range, comprising at least a first (12), a second (14) and a third (16) element, wherein each of the first (12) and the second (14) elements comprises a polarizer, wherein the first (12) and the second (14) elements are arranged such that an optical path (24) is formed between them, and the third element (16) comprises a birefringent means positioned on the optical path (24) between the polarizers (12, 14) and arranged to transmit electromagnetic radiation, wherein the third element (16) and at least one of the first (12) and the second (14) elements are controllably arranged in such a manner that, concerning the first (12) and the second (14) element, the direction of polarization of the element is variable and concerning the third (16) element, the birefringent means is rotatable, wherein through said control of the elements (12, 14, 16) the transmitted spectral range is changed.

2. A colour filter device (10) according to claim 1 , comprising a fourth (18) element in the form of a birefringent means positioned on the optical path (24) between the first (12) and the second (14) element and arranged to transmit electromagnetic radiation.

3. A colour filter device (10) according to claim 2, comprising a fifth (20) element in the form of a birefringent means positioned on the optical path (24) between the first (12) and the second (14) element and arranged to transmit electromagnetic radiation, wherein at least three of the elements (12-20) are controllable.

4. A colour filter device (10) according to claim 3, wherein at least four of the elements (12-20) are controllable.

5. A colour filter device (10) according to any of the preceding claims, comprising a holding member (22) which holds the elements (12-20) in position relative to each other and which allows for a rotation of at least the controllable elements (12-20) about a common axis of rotation (24) which extends through all the

5. Fargfilteranordning (10) enligt nagot av fόregaende krav, innefattande ett hallarorgan (22) som haller elementen (12-20) pa plats relativt varandra och som tillater vridning av atminstone de reglerbara elementen (12-20) omkring en gemensam rota- tionsaxel (24) som stracker sig genom alia elementen (12-20), varvid regleringen av de reglerbara elementen (12-20) gόrs genom en vridning av respektive element (12-20) omkring namnda rotationsaxel (24).

6. Fargfilteranordning (10) enligt nagot av fόregaende krav, varvid polarisatorerna (12, 14) och de dubbelbrytande medlen (16, 18, 20) bestar av plastmaterial.

7. Fargfilteranordning (10) enligt nagot av fόregaende krav, varvid de dubbelbrytande medlen (16, 18, 20) bestar av cellofan eller polypropylen.

8. Fargfilteranordning (10) enligt nagot av fόregaende krav, innefattande drivenheter (26) for att driva de reglerbara ele- menten (12-20) och en kontrollenhet (28) innefattande ett lag- ringmedel (30) for att lagra information om de reglerbara ele- mentens (12-20) installing for att uppna transmission av olika spektralomraden hos elektromagnetisk straining som transmitte- ras genom anordningen (10), varvid kontrollenheten (28), som svar pa en operators inmatning av όnskat transmitterat spektral- omrade, styr drivenheterna (26) sa att de reglerbara elementen (12-20) installes automatiskt sa att den όnskade transmissionen erhalles.

9. Fargfilteranordning 10 enligt nagot av fόregaende krav, innefattande ett fasthallarorgan (40) anpassat att anslutas till en fotografisk utrustning (42) sa att fargfilteranordningen (10) kan fasthallas vid den fotografiska utrustningen (42) pa sa satt att den elektromagnetiska stralningen som mottas av eller utsandes fran den fotografiska utrustningen (42) passerar genom fargfilteranordningen. filtering the light from the light producing member (52) when this member is in operation in the illumination device (46), wherein the filter device (10) comprises a colour filter device (10) according to any of the claims 1 -9.