WO2016124882A1

WO2016124882A1 - Apparatus for producing an optical illusion

Info

Publication number: WO2016124882A1
Application number: PCT/GB2016/000023
Authority: WO
Inventors: Nicholas Carl-Gustaf André WALLENBERG; John Theodore LINDQUIST
Original assignee: Metagram Ltd
Priority date: 2015-02-06
Filing date: 2016-02-02
Publication date: 2016-08-11
Also published as: GB201502075D0

Abstract

Apparatus (2) for producing an optical illusion, which apparatus (2) comprises: (i) image providing apparatus (4) for providing an image (6); (ii) a beam splitter (8) for causing the image (6) to be viewable remote from the image providing apparatus (4); and (iii) means (12) for providing relative movement between the image providing apparatus (4) and the beam splitter (8), and the apparatus (2) being such that: (iv) the relative movement between the image providing apparatus (4) and the beam splitter (8) causes the image (6) to become an image (6) which moves within a space, with the image movement being towards and away from a viewing position (10) and dependent upon the relative movement.

Description

APPARATUS FOR PRODUCING AN OPTICAL ILLUSION

This invention relates to apparatus for producing an optical illusion.

Apparatus for producing an optical illusion is well known. The optical illusion may be known under various terms including Pepper's Ghost or a volumetric display. The original known apparatus for producing a Pepper's Ghost comprised a beam splitter and a hidden room. Due to the use of the beam splitter, actors in the hidden room were able to appear ghost-like on a stage. More modern known apparatus is able to produce an image which seems to move through space. The image is bound to a fixed image display, and the content of the image can only move within the boundaries of the fixed image display.

It is an aim of the present invention to provide an improved apparatus.

Accordingly, in one non-limiting embodiment of the present invention there is provided apparatus for producing an optical illusion, which apparatus comprises:

(i) image providing apparatus for providing an image;

(ii) a beam splitter for causing the image to be viewable remote from the image providing apparatus; and

(iii) means for providing relative movement between the image providing apparatus and the beam splitter, and the apparatus being such that:

(iv) the relative movement between the image providing apparatus and the beam splitter causes the image to become an image which moves within a space, with the image movement being towards and away from a viewing position and dependent upon the relative movement.

The apparatus of the present invention is advantageous in that it is able to produce an image capable of multi-axis movement. The image may be a 3D image if the image provided by the image providing apparatus is a 3D image. The image may be a 2D image if the image provided by the image providing apparatus is 2D image. The image is able to travel through a space. With the apparatus of the present invention, the image may appear to be moving in a three dimensional manner throughout the space. The result is a vastly improved perception of reality as compared with the known apparatus with its two dimensional movement or X and Y axis movement. The image is not bound to a fixed position because the apparatus of the present invention does not require a fixed screen. If desired however, the apparatus of the present invention may use a fixed screen.

The image movement towards and away from the viewing position may be directly dependent upon the relative movement between the image providing apparatus and the beam splitter. Alternatively, the image movement may be an amplified movement which is a desired amplification of the actual movement caused by the relative movement between the image providing apparatus and the beam splitter. The amplification of the movement may be effected by amplifier means including optical amplifier means and electro- optical amplifier means. The optical amplifier means may include one or more lenses.

The apparatus of the present invention may be one in which the relative movement between the image providing apparatus and the beam splitter is in a direction which is at 90° to the direction of the image providing movement. If desired, the relative movement between the image providing apparatus and the beam splitter may be in a direction which is at an angle of more or less than 90° to the direction of the image movement.

Preferably, the apparatus is one in which the image providing apparatus is movable image providing apparatus, and in which the beam splitter is a fixed beam splitter, whereby the relative movement between the image providing apparatus and the beam splitter is caused by moving the image providing apparatus. The opoosite arrangement may however be employed in which case the image providing apparatus is a fixed image providing apparatus, and the beam splitter is a movable beam splitter. Still further, if desired, both the image providing apparatus and the beam splitter may be movable but relatively so, in order that there is the relative movement between the image providing apparatus and the beam splitter.

The apparatus of the present invention may be one in which the means for providing relative movement between the image providing apparatus and the beam splitter is mechanical drive apparatus. The mechanical drive apparatus may be a linear drive apparatus that provides linear movement. Other types of mechanical drive apparatus may however be employed so that, for example, the mechanical drive apparatus may be a rotary drive apparatus, a robot arm, or a multi-access system comprising a plurality of linear actuators. The mechanical drive apparatus may be a mechanical, hydraulic, pneumatic, piezoelectric, electro-mechanical, telescoping or magnetic drive apparatus.

The apparatus of the present invention may alternatively be one in which the means for providing relative movement between the imaging providing apparatus and the beam splitter is an electronic apparatus. The electronic apparatus may comprise a sandwich of transparent screens. Other types of electronic apparatus may be employed for electronically providing the required relative movement.

The apparatus of the present invention may include computer control means for controlling the relative movement between the image providing apparatus and the beam splitter. Alternatively, if desired, the relative movement between the image providing apparatus and the beam splitter may be effected by other means.

Where computer control means is employed, then the computer control means may be a central processing unit (CPU). Other types of computer control means may be employed. The computer control means may employ synchronising software for ensuring that the relative movement between the image providing apparatus and the beam splitter is synchronised to other operational parts of the apparatus of the present invention. The apparatus of the present invention may include a sound system for providing sound to accompany the image. Any suitable and appropriate sound system may be employed.

The apparatus of the present invention may be one in which the drive apparatus moves the image providing apparatus and/or the beam splitter to and fro. The drive apparatus may also move the image providing apparatus and/or the beam splitter from side to side. Thus the drive apparatus may cause movement in two planes.

The image providing apparatus may provide a real-time image or a video image. The image may be an electronic image. The image is able to move with multi-axis movement.

The beam splitter may be a 50 : 50 beam splitter. Other ratios of beam splitting may be employed.

The beam splitter may be a mirror, a plate, a cube, or a wedge. Other types of beam splitters may be employed including single optical devices or combination arrangements employing two or more optical devices. The beam splitter may be made of any suitable and appropriate materials including glass or plastics film materials.

The apparatus of the present invention may include a housing. The housing may form a blackout chamber. The blackout chamber may be for providing a space in which the image providing apparatus is located and can move. By ensuring that everything is in darkness, the only thing an audience can see is light from the image. The image providing apparatus may be a monitor/TV type of display apparatus, a projector apparatus, or a volumetric display apparatus. The monitor/TV type of apparatus may be a monitor, a television, a plasma screen, a OLED, a LED, a 3D TV, a curved TV, a transparent display apparatus, or an OLED translucent apparatus. Any suitable and appropriate projector providing apparatus may be employed. The volumetric display may also be known as a light field display.

The apparatus may comprise one, two or more of the image providing apparatus; one, two or more of the beam splitters; and one, two or more of the drive apparatus, and the apparatus being such that it provides a plurality of the images. The multiple image providing apparatus, the beam splitters and the drive apparatus may all be so positioned relative to each other as to provide the plurality of the images as layers which are behind each other when the layers are viewed from one side of the apparatus. The apparatus may be one in which the multiple image providing apparatus are positioned behind each other and offset, and in which the beam splitters are positioned behind each other and offset.

Alternatively, the apparatus may be one in which the multiple image providing apparatus, the beam splitters and the drive apparatus are all positioned relative to each other so as to provide the plurality of the images such that at least one of the images is viewable from a first viewpoint and at least one of the images is viewable from a second viewpoint. One image could, for example, show the front side of an object and the other image could then show the rear side of the object. The apparatus may be one in which the multiple image providing apparatus are positioned behind each other, and in which the beam splitter splits the beam in at least two directions. The beam splitters may split the beam in at least two directions which are in a straight line.

Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings in which:

Figure 1 shows first apparatus for producing an optical illusion;

Figure 2 show second apparatus for producing an optical illusion;

Figure 3 shows third apparatus for producing an optical illusion;

Figure 4 shows fourth apparatus for producing an optical illusion;

Figure 5 illustrates different movement axes for the apparatus shown in Figure 4;

Figure 6 shows how the apparatus of Figure 4 may take the form of a black box;

Figure 7 shows fifth apparatus for producing an optical illusion;

Figure 8 shows sixth apparatus for producing an optical illusion;

Figure 9 shows seventh apparatus for producing an optical illusion;

Figure 10 - 16 show different types of apparatus for producing an optical illusion, with the apparatus being operable to enable a viewer to look into corners or confined spaced;

Figure 17 is a perspective view of a part of the apparatus of the present invention, the part being means for providing relative movement between image providing apparatus and a beam splitter, and the means being in the form of mechanical drive apparatus; Figure 18 is an end view of the mechanical drive apparatus shown in Figure 17;

Figures 19 - 22 show different types of mechanical drive means in the form of different types of linear actuators;

Figure 23 shows mechanical drive apparatus;

Figure 24 shows a plate beam splitter;

Figure 25 shows a cube beam splitter;

Figure 26 shows a foil beam splitter;

Figures 27 - 30 show four different types of image providing apparatus; and

Figure 31 shows a part of the apparatus of the invention, the part being means for providing relative movement between image providing apparatus and a beam splitter, and the means being in the form of an electronic apparatus.

Referring to Figure 1, there is shown apparatus 2 for producing an optical illusion. The apparatus 2 comprises image providing apparatus 4 for providing an image 6. The apparatus 2 further comprises a beam splitter 8 for causing the image 6 to be viewable at a position 10 remote from the image providing apparatus 4. The apparatus 2 further comprises drive apparatus 12 for providing relative movement between the image providing apparatus 4 and the beam splitter 8.

The relative movement between the image providing apparatus 4 and the beam splitter 8 causes the image 6 display to become an image 6 which moves within a space, with image movement being towards and away from a viewing position and dependent upon the relative movement. The image movement is able to be a multi-axis movement. The image movement is indicated by arrow 14. The viewing position which is indicated an eye 16 which may in fact be an eye of one or more actual viewers. The image movement may be directly dependent upon the relative movement, whereby the image movement is equal to the amount of the relative movement between the image providing apparatus 4 and the beam splitter 8. Alternatively, the image movement may be an amplification of the relative movement between the image providing apparatus 4 and the beam splitter 8.

As can be seen from Figure 1 , the relative movement between the image providing apparatus 4 and the beam splitter 8 is in a direction which is at 90° to the direction of the image movement. The image movement is vertical as shown in Figure 1 and is caused by movement of the image providing apparatus 4 vertically, as shown somewhat schematically as being controlled by vertical guides 18 forming part of the drive apparatus 12. The image movement is thus horizontal as shown in Figure 1. The image 6 may be any suitable and appropriate desired image, and it may be regarded as being in the form of a volumetric display.

The image providing apparatus 4 is movable image providing apparatus 4. The beam splitter 8 is a fixed beam splitter 8. Thus the relative movement between the image providing apparatus 4 and the beam splitter 8 is caused by moving the image providing apparatus 4. The movement of the image providing apparatus 4 is up and down the guides 18 as indicated by the arrow 20. The arrow 20 thus indicates the movement axis of the image providing apparatus 4. In an alternative embodiment of the invention, the beam splitter 8 could be a movable beam splitter 8, with the image providing apparatus 4 then being a fixed image providing apparatus 4. Alternatively, both the image providing apparatus 4 and the beam splitter 8 could be movable providing they were also able to be moved relative to each other to provide the relative movement between the image providing apparatus 4 and the beam splitter 8.

The drive apparatus 12 is a linear drive apparatus 12 that provides linear movement. The linear drive apparatus 12 includes an actuator 22.

The apparatus 2 includes computer control means 24 for controlling the relative movement between the image providing apparatus 4 and the beam splitter 8. The computer control means 24 is a central processing unit (CPU). The CPU may include synchronizing software for synchronising the operation of the apparatus 2. As shown, the apparatus 2 includes a sound system 26 for providing sound for accompanying the image 6. The sound system 26 feeds via a sound feed 28 to the computer control means 24. The computer control means 24 then provides motion control via a motion control feed 30 to the actuator 22. The computer control means 24 also provides image data to the image providing apparatus 4 via a video feed 31.

The image providing apparatus 4, the image 6 and the guides 18 may be enclosed in a blackout chamber 32 as shown. By ensuring that everything is in darkness, the only thing an audience can see is light from the image 6.

The drive apparatus 12 moves the image providing apparatus 4 up and down as shown. This causes the image 6 at the position 10 to appear to move towards and away from the eye 16. The overall effect is that the image 6 as viewed at the position 10 appears to be moving in depth with multi-axis movement, rather than simple constrained two dimensional movement or X and Y axis movement that would be the case with only the beam splitter 8. The beam splitter 8 is a 50 : 50 beam splitter 8. The beam splitter 8 is shown as a mirror beam splitter 8 but other types of beam splitter may be employed.

The entire apparatus 2 can easily and inexpensively be constructed. The sound system 26 can include speakers and is able to give realistic sound to accompany the movement of the image display 6 as seen by the eye 16. The apparatus 2 thus enables the viewing of holograms that travel in depth, in addition to travelling in a two dimensional plane.

In Figures 2 - 32, similar parts as in Figure 1 have been given the same reference numerals for ease of comparison and understanding.

In Figure 2, there is shown apparatus 34 which uses the actuator 22 and also a second actuator 36 to enable movement of the image providing apparatus 4 in the direction shown by the arrow 38. As can be seen from a comparison of the arrows 20 - 38, the two actuators 22, 36 enable the image providing apparatus 4 and therefore the image 6 to be moved along two different axes which are at 90° to each other as shown in Figure 2. As the image 6 passes through the beam splitter 8, the movement afforded by the actuators 22, 36 may be seen as movement in the direction of arrows 14 and 40. Thus the apparatus 34 enables, by the use of the two actuators 22, 36, movement of the image 6 along two axes. Figure 3 shows apparatus 42 which uses the actuators 22 and 36, and which also uses a third actuator 44. The use of the three actuators 22, 36, 44 enables three axes of movement as shown by arrows 14 and 46.

Figure 4 shows part of apparatus 48 which uses drive means in the form of a robot arm 50. The robot arm 50 is able to produce movement along 4, 5, 6 or more axes as can be appreciated from the arrows shown at position 10 in Figure 4.

Figure 5 shows apparatus 52 which is like the apparatus shown in Figure 4 but which includes drive apparatus 12 including a guide 18. The drive apparatus 12 is a linear drive apparatus 12. The linear drive apparatus 12 and the robot arm 50 combine together to provide dexterity of movement of the image 6 as well as easy travel of the image 6 to and fro in a vertical direction.

Figure 6 shows how the apparatus shown in previous Figures is able to have a blackout chamber 32 formed by a housing 52. The housing 52 has a viewing window 54 which is variable in size by a slidable shutter 56.

Referring now to Figure 7, there is shown apparatus 58 of the present invention. The apparatus 58 has a blackout chamber 32 provided with two units each comprising the image providing apparatus 4, the beam splitter 8, and the drive apparatus 12. In the right hand unit, the drive apparatus comprises the actuator 22 to give an image 6 in the form of a triangle. In the left hand unit, the drive apparatus 12 includes the actuator 36 which gives an image 60 which has been shown as a square for ease of identification. The two images 6, 60 pass through their respective beam splitters 8 as shown, and are then seen as two layers which are imposed upon each other and which are viewable from the eye 16, which sees the images 6, 60 in front of one another as shown schematically as image 62.

Figure 8 shows apparatus 64 which uses two blackout chambers 32. The right hand blackout chamber 32 uses the beam splitter 8 in the configuration shown in previous drawings. This produces the triangular image 6 viewable from the eye 16 as shown. The left hand beam splitter 8 is inclined in the opposite direction to the right hand beam splitter 8. This enables a second viewing point, illustrated by eye 66, to see the square image 60 as shown in Figure 8. The right hand unit shown in Figure 8 is provided with a video feed. The left hand unit is provided with a video feed 68 in the same manner as in Figure 7. In the apparatus 64, two sound systems 26 are employed as shown. Both sound systems 26 are controlled by the computer control means 24. In an alternative embodiment, the two blackout chambers 32 may be joined to form a single blackout chamber.

Figure 9 shows apparatus 70 which contains two units 72, 74. The units 74 is like the unit shown in the blackout chamber 32 in Figure 7. The unit 74 is the same as the unit 72 except that it is being used to produce two different image displays 76, 78. The image display 76 is a circle. The image display 78 is a five-sided shape as shewn.

Figure 10 shows apparatus 80 for producing an optical illusion. The apparatus 80 comprises two units 82, 84, with each unit 82, 84 comprising image providing apparatus 4, a beam splitter 8 and drive apparatus 12 comprising the guides 18. Each unit 82, 84 has a blackout chamber 32. The unit 82 produces a triangular image display 6. The unit 84 produces a circular image display 86. The units 82, 84 are placed at an angle to each other as shown in Figure 10 whereby the images 6, 86 are at right angles to each other. The illustrated images 6,86 are shown solely to illustrate which displays are creating which images, and the images may be any desired images including, for example, real-time images, video images, and volumetric display images.

Figures 11 - 16 show six further different types of apparatus of the present invention. The different types of apparatus 88, 90, 92, 94 and 98 is able to have one or more beam splitters 8 positioned as shown to enable a person 100 to see an image 6 as a hologram at different positions, with the different positions being all at an angle to the original image providing apparatus 4. The viewer 100 views, as appropriate, light rays that have either passed through the beam splitter 8 or that have been reflected by the beam splitter 8. Figure 16 shows how the apparatus 98 is able to be configured so that it is able to be watched by the person 100 and also another person 102.

Figures 17 and 18 show drive apparatus 104 for use in the present invention. The drive apparatus 104 is linear drive apparatus 104. The drive apparatus 104 comprises a frame 106, a stage 108, a motor 110 and a transmission 112. The drive apparatus 104 also comprises an upper linear drive mechanism 114, a linear guide counter-weight rail 116, a linear guide major rail 118, a screen mount and linear runner 120, and a linear drive tensioner 122. A counter-weight 124 is employed as shown. The apparatus 104 also comprises an upper linear drive mechanism 126. The drive apparatus 104 may be employed in various different embodiments of the invention as shown in previous Figures.

Figure 19 shows drive apparatus 128 comprises a robot arm 130.

Figure 20 shows drive apparatus 132 comprising a robot arm 134 mounted on a moving mechanism 136 which is able to slide to and fro along a rail 138.

Figure 21 shows three moving rails 140, 142, 144, all mounted in different directions. Figure 22 shows two moving rails, 146, 148 moving in two different directions.

Figure 23 shows drive apparatus in the form of a magnetic drive apparatus 150 having a magnetic shaft 152, a coil 154 and a forcer 156. Electrical energization of the coil 154 causes the magnetic shaft 152 to be drawn into the coil 154 or forced out of the coil 154 due to the positioning of the positioning of the magnetic north and sole poles as shown in Figure 23.

Figure 24 shows a plate beam splitter 158 with a coating 160. A beam 162 is also shown.

Figure 25 shows a cube beam splitter 164 able to operate with an incident light beam 166, a transmitted light beam 168 and a reflected light beam 170.

Figure 26 shows a foil beam splitter 172 having a foil 174 and being viewed by persons 176.

Figures 27 - 30 show four different types of image providing apparatus. More specifically, Figure 27 shows image providing apparatus 178 in the form of a TV monitor. The TV monitor 178 may alternatively be a television. The monitor/television 178 may be a plasma device, an LED device, a OLED device, a 3D device, or a curved device.

Figure 28 shows image providing apparatus 180 in the form of a projector. The projector 180 may be a digital projector or a film projector.

Figure 29 shows alternative image providing apparatus 182 which is another form of projector.

Figure 30 shows image providing apparatus 184 giving a 360° light field volumetric display. The image providing apparatus 184 can operate in a linear or rotary drive manner as desired.

Figure 31 shows part of the apparatus of the present invention, the part being means for providing relative movement between the image providing apparatus and a beam splitter, and the means being in the form of an electronic apparatus 186. The electronic apparatus 186 comprises a sandwich 188 of transparent screens. An image 190 is able to move as shown across the sandwich 188 of transparent screens. Also shown in Figure 31 is a beam splitter 192, a viewer's eye 194 and a projected image 196. The use of the electronic apparatus 186 is an alternative to the use of the mechanical drive apparatus shown in Figures 19 - 23.

The apparatus of the present invention may be used in a cinema, or in a shop. For use in a shop, the apparatus may be used in a shop window and may show, for example, animation of people in the shop. Thus, for example, the animation may be of a model walking through fashion clothing, or a person driving cars. The image may be any appropriate image display, and it is able to be shown with physical movement due to the use of the one or more units of drive apparatus. The image display, including background scenery, may be provided by a computer program. The computer program may be purchased by a buyer of the apparatus of the present invention or, alternatively, the buyer may generate their own computer program.

The apparatus may form an interactive apparatus for use in plays and theatres and halls, giving an interactive experience. The apparatus may then be installed in theatres and halls as appropriate. With the use of a volumetric image, the apparatus of the present invention may give the illusion of a person or object moving around another moving person or object. The apparatus of the present invention is able to give movement to image displays. By increasing the number of beam splitters used in the apparatus of the present invention, it is possible to give a visual impression of going increasing further away from a viewer. A later beam splitter will not normally cause the image of that beam splitter to appear before the or each other beam splitter. This is due to it not normally being possible to have an image in front of the beam splitter. The image is only normally seen once it has gone through the beam splitter.

It is to be appreciated that the embodiments of the invention described above with reference to the accompanying drawings have been given by way of example only and that modifications may be effected. Thus, for example, the illustrated apparatus may take various physical shapes and may be sold as a box-tape container for being looked into, or may be sold as stage apparatus for operating on a stage and viewed by a film or theatre audience. Individual components shown in the drawings are not limited to use in their drawings and they may be used in other drawings and in all aspects of the invention.

Claims

1. Apparatus for producing an optical illusion, which apparatus comprises:

(i) image providing apparatus for providing an image;

2. Apparatus according to claim 1 in which the relative movement between the image providing apparatus and the beam splitter is in a direction which is at 90° to the direction of the image movement.

3. Apparatus according to claim 1 cr claim 2 in which the image providing apparatus is movable image providing apparatus, and in which the beam splitter is a fixed beam splitter, whereby the relative movement between the image providing apparatus and the beam splitter is caused by moving the image providing apparatus.

4. Apparatus according to any one of the preceding claims in which the means for providing relative movement between the image providing apparatus and the beam splitter is mechanical drive apparatus.

5. Apparatus according to claim 4 in which the mechanical drive apparatus is a linear drive apparatus for providing linear movement.

6. Apparatus according to claim 4 or claim 5 in which the mechanical drive apparatus is a mechanical, hydraulic, pneumatic, piezoelectric, electromechanical, telescoping or magnetic drive apparatus.

7. Apparatus according to any one of claims 1 - 3 in which the means for providing relative movement between the image providing apparatus and the beam splitter is an electronic apparatus.

8. Apparatus according to claim 7 in which the electronic apparatus comprises a sandwich of transparent screens.

9. Apparatus according to any one of the preceding claims and including computer control means for controlling the relative movement between the image providing apparatus and the beam splitter.

10. Apparatus according to claim 9 in which the computer control means is a central processing unit.

11. Apparatus according to any one of the preceding claims and including a sound system for providing sound to accompany the image.

12. Apparatus according to any one of the preceding claims in which the drive apparatus moves the image providing apparatus and/or the beam splitter to and fro.

13. Apparatus according to claim 12 in which the drive apparatus also moves the image providing apparatus and/or the beam splitter from side to side.

14. Apparatus according to any one of the preceding claims in which the image providing apparatus provides a real-time image or a video image.

15. Apparatus according to any one of the preceding claims in which the beam splitter is a mirror, a plate, a cube, or a wedge.

16. Apparatus according to any one of the preceding claims and including a housing forming a blackout chamber.

17. Apparatus according to claim 16 in which the blackout chamber is for at least a display screen forming part of the image providing apparatus, and the beam splitter,

18. Apparatus according to any one of the preceding claims in which the image providing apparatus is a monitor/TV, a projector, or a volumetric display apparatus.

19. Apparatus according to any one of the preceding claims and comprising two or more of the image providing apparatus, two or more of the beam splitters, and two or more of the drive apparatus, and the apparatus being such that it provides a plurality of the images.

20. Apparatus according to claim 19 in which the image providing apparatus, the beam splitters and the drive apparatus are all so positioned relative to each other as to provide the plurality of the images as layers which are behind each other when the layers are viewed from one side of the apparatus.

21. Apparatus according to claim 20 in which the image providing apparatus are positioned behind each other and offset, and in which the beam splitters are positioned behind each other and offset.

22. Apparatus according to claim 19 in which the image providing apparatus, the beam splitters and the drive apparatus are all positioned relative to each other so as to provide the plurality of the images such that at least one of the images is viewable from a first viewpoint and at least one of the images is viewable from a second viewpoint.

23. Apparatus according to claim 22 in which the image providing apparatus are positioned behind each other, and in which the beam splitters split the beam in at least two directions.