GB1598377A

GB1598377A - Device for optically inserting selected images of a plurality of symbols into an optical system

Info

Publication number: GB1598377A
Application number: GB8636/78A
Authority: GB
Original assignee: Bofors AB
Current assignee: Saab Bofors AB
Priority date: 1977-03-03
Filing date: 1978-03-03
Publication date: 1981-09-16
Also published as: DE2809067A1; DE2809067C2; SE7702365L; YU42778A; YU42277B; FR2382708B1; FR2382708A1; SE413056B

Description

(54) A DEVICE FOR OPTICALLY INSERTING SELECTED IMAGES OF A PLURALITY OF SYMBOLS INTO AN OPTICAL SYSTEM (71) We, AKTIEBOLAGET BOFORS of S-690 20 Bofors, Sweden, A Swedish joint-stock company acting under the laws of Sweden, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to an optical device.

Optical devices, particularly those incorporated in sights frequently use graticules or other reference symbols to indicate relative position of objects. In some cases it is desirable to use several different reference symbols in the same sight. Mechanical devices have been used to change the graticules. However, due to the high positional accuracy and functional reliability demanded in a sight such devices are complex and costly. It is desirable to have a device which uses few moving parts. Optical devices in which the different graticule images are projected onto a common viewing screen by different optical paths have been suggested as have systems in which the optical paths for differing graticules partly coincide but a different part of the optical spectrum is used for each graticule. Such devices, however, require a separate lens systems for each image. This requirement produces complicated adjustment problems and is also costly.

In accordance with this invention therefore we provide a device for optically inserting selected images of a plurality of symbols into a main optical system so that the or each selected symbol is superimposed on the image from the main optical system, comprising a plurality of symbols, a lens system for proJecting images of each of said symbols into said main optical system and a plurality of semi-transparent reflecting surfaces to transmit or reflect the image of each of said symbols to said lens system for projection thereby into said image plane, the symbols and said surfaces being arranged so that each symbol is located in the object plane of said lens system and the ray path from a symbol to said image plane is incident only once on the same semitransparent reflecting surface.

Figure 1 shows a sketch of the principle of an arrangement of reflecting surfaces in accordance with the invention, only the optical axis of the symbol-projecting arrangement then having been drawn. In an optical main system with the lens system 1 and the image surface 2 a plane parallel plate 3 is arranged, which lets through the radiation from the lens system 1 but the rear side of which has a reflecting surface 4. A second lens system 5 is arranged to reproduce symbols pl-p, on the image surface 2 via the reflecting surface 4. Semitransparent, reflecting surfaces s1sm are arranged in the path of the direction of the rays from the symbols to the lens system 5, and the symbols which are either transmitted through or reflected by the surfaces s1sm are arranged with equal optical wavelengths to the lens system 5. The path from the surface sl nearest the lens system 5 is common for the ray paths from all of the symbols p1-p.

Figure 2 shows a first embodiment, according to which the mirror/symbol arrangement is built up with the aid of the square ray-splitting prisms and compensation blocks. In this embodiment, two raysplitting prisms a1 and a2 are used, the reflecting diagonals of which are placed parallel to each other, and a compensation block c. Of the symbols p1-p3 two are arranged at two side surfaces at angles to each other on the second ray-splitting prism, and the third at one side surface of the compensation block. On the other side of each symbol p1, P2, p3 there is a plate bl, b2, b3, which for the purpose of obtaining light diffusion is preferably made of opal glass, but which in certain applications can also be entirely transparent. The symbols can either be arranged on their respective plates, or on their respective end surfaces of the prisms or compensation blocks. Behind each graticule, seen in the direction of the rays, a source of light is arranged, such as a lamp or a light diode, el-e3 which normally is not lit. A lamp ei is lit when the symbol pi in front of the lamp is to be projected. A plurality of lamps can, of course, be lit simultaneously, and a plurality of symbols can then be put together to form one symbol. The symbols can either consist of transparent sections in a coating which, for the rest, is not transparent, in which case the actual symbols are projected illuminated, or else they can consist of sections which are not transparent, in which case the symbols are projected dark against an illuminated background. In the latter case, the illuminating power of the sources of light ei must be kept so weak that the effect of their illumination has the least possible influence on the image projected through the optical main system. The symbol can, of course, in themselves consist of sources of light which are activated when the symbol in question is to be projected. In this connection, it is conceivable to allow each graticule bi to comprise a substrate with light diodes or the like applied in patterns.

In accordance with the figure, in this embodiment the two ray-splitting prisms a1 and a2 are arranged beside each other in a straight line with the optical axis of the common lens system 5. At the end turned away from the lens system 5 of the farther ray-splitting prism a2 the first graticule bl with the symbol p1 is arranged. When the lamp el behind this graticule is lit, the radiation from the object p1 is transmitted through the semitransparent, reflecting surfaces of the two prisms a2 and al.

The second graticule b2 with the symbol P2 is arranged at one of the sides of the prism a2 opposite the side with the graticule bl and so that it is reflected by the reflecting surface of the prism. When the lamp e2 arranged behind this graticule is lit the radiation from the object P2 is reflected by the reflecting surface of the prism a2 and is transmitted through the reflecting surface of the prism al. The radiation from the two objects p1 and p2 thus have the same path from the reflecting surface of the prism a2 and thus the same path length to the lens system 5.

The third graticule b3 with the symbol p3 is placed so that it is reflected by the reflecting surface of the prism al i.e. so that when the lamp arranged behind this graticule is lit the radiation from the object p3 iS incident on one of the side of the prism a1 which is parallel to the optical axis through the lens system 5. In order that the optical path length for the symbol p3 shall be of the same length as for the symbols p1 and P2 a compensation block c is placed between the graticule b3 and the prism al. This compensation block should appropriately consist of the same material as the prism, or of a material with the same refractive index for the light used from the lamp, in which case the compensation block has the same dimensions as the prisms a1 and a2, but can also consist of a different material, but when determining optical path length, consideration must be given to this, and the compensation block will not have the same dimensions as the prisms.

As approx. 50% of the light is lost at each passage through or reflection by an oblique, reflecting semi-transparent surface, the lamps e1 and e2 for the symbols p1 and P2 which are to pass two oblique surfaces, must have a greater illuminating power than the lamp e3 for the symbol p3 which is only to pass one oblique surface, in order that the same luminous intensity may be obtained in the projected image of each symbol.

The advantage of using ray-splitting prisms and compensation blocks and graticules and/or resolution plates which elements are cemented together to form one unit is that the mechanical construction will.

be extremely stable. The adjustment of the symbols in relation to the lends system 5 and the image surface 2 need only be mde for one of the symbols, and is then applicable to all of them.

Figure 3 shows another embodiment with square ray-splitting prisms and compensation blocks. In this embodiment, not all of the diagonals in the ray-splitting prisms are directed parallel to each other, but certain prisms have the diagonals directed across the others. As will be noted from the figures, the prisms A2 and A3 form a system of the same type as the prisms a1 and a2 in Figure 2. The prism A3, as in the case of a2 is provided with graticules B1 and B2 with the symbols B1 and B2 and behind these there are arranged lamps or light diodes or other sources of light E1 and E2, respectively. The graticules should appropriately be made of opal glass, and the sources of light are provided with reflectors or condenser optics so that an essentially collimated pencil of rays from the sources of light is obtained and so that illumination of equal strength will be obtained for each symbol to the extent possible. In this embodiment there is also a narrow spacing plate F1-F6 between each graticule B1-B6 with its symbol facing inwards, and the nearest prism surface. The purpose of these spacing plates is to ensure that at the assembly, i.e. at the cementing together of all the parts comprised in the ray-splitting block, all of the symbols will be set in the correct positions, so that consequently, the optical path length from each symbol to the lens system 8 will actually be of equal length. In practice, the individual dimensions of the ray-splitting prisms can differ in each individual case, and in order to compensate for this the plates F1-F, are inserted, and their thicknesses are thus to be adapted individually to each symbol, in order that equal path lengths will be obtained. In this embodiment, instead of the compensation block c, a prism A4 of the same type has also been arranged against the underside of the prism A2 in the figure.

This prism A4 has its semi-transparent reflecting diagonal facing the direction opposite that of the diagonals of the prism A2 and A3 as a graticule arranged facing the side of the prism should not be arranged so that it is illuminated by the same lamp as the granticule B2. The graticule B4 has consequently been arranged opposite the surface of the prism A4 facing the lamp E2. The prism A1 facing nearest to the common lens system 8 also has its semi-transparent reflecting surface turned in the same direction as the prism A4, as no extra optical element such as a prism or a compensation block can be applied against the underside of the prism A1 in the figure because of the graticule B4 and the lamp E4.

Against the upper side of the prism A1 a compensation block C is cemented and on the opposite side of this, a further prism A5.

In this case, the diagonal of the prism can be facing any one of the four possible directions, i.e. in the two directions shown in the figure for the prisms A1-A4 and in addition thereto upwards and downwards from the plane of the paper, and in the figure they have been turned so that the graticule B5 is on the left side of the prism in the figure, i.e.

turned away from the optical main system.

In the figure it is also shown that the sides of the prisms and the compensation block through which there should not be any radiation have a light-absorbing coating, in order to reduce undesirable reflections to a minimum. They can, for instance, be painted black. As will be noted from the figure, the prism Al has the coating D1 on its lower surface, the prisms A2 and A3 have the coatings D2 and D3, respectively, on their upper surfaces, the prism A4 has the coating D4 on its left surface, and the prism A5 has the coating D5 on its right surface, and the compensation block C has the coatings D6 and D7 on its side surfaces.

These coatings also reduce the risk for stray light in the system.

In Figure 3 it is also shown that the plane parallel plate 6 in the main system, which can also consist of a ray-splitting prism corresponding to the plate 3 in Figures 1 and 2, need not be inclined at a 45" angle to the optical axis of the main system. As will be noted from the figure, however, the raysplitting block with its lens system must then be given a corresponding inclination, as with an inclination other than 45" the optical axis of the lens system 8 of the compensation system will of course obtain an angle other than 90" towards the optical axis of the main system. The inclination of the plate 6 can be chosen entirely in accordance with practical reasons. It should, of course, be obvious that instead of having a plate 6 or instead of the single ray-splitting prism used instead of this, also prisms of a more complex nature can be used.

Many different modifications are possible within the scope of the invention.

WHAT WE CLAIM IS: 1. A device for optically inserting selected images of a plurality of symbols into a main optical system so that the or each selected symbol is superimposed on the image from the main optical system, comprising a plurality of symbols, a lens system for projecting images of each of said symbols into said main optical system and a plurality of semi-transparent reflecting surfaces to transmit or reflect the image of each of said symbols to said lens system for projecting thereby into said image plane, the symbols and said surfaces being arranged so that each symbol is located in the object plane of said lens system and the ray path from a symbol to said image plane is incident only once on the same semitransparent reflecting surface.

2. A device according to Claim 1, wherein each reflecting surface is provided in a beam-splitting prism.

3. A device according to Claim 2, wherein the prisms are assembled to form a single unit.

4. A device according to Claim 2 or Claim 3, wherein each beam-splitting prism is a square prism having the reflecting surface at an angle of 45" to the side surfaces thereof.

5. A device according to Claim 3 or Claim 4, wherein at the places in the unit of beam-splitting prisms where only a straight ray path is required through a beamsplitting prism, this prism is replaced by a compensation block made of material through which the light used can pass and preferably of the same material as the beam-splitting prisms.

6. A device according to any one of Claims 2 to 5, wherein each symbol is arranged on a side surface of one of said prisms.

7. A device according to any one of Claim 2 to 6 in which each symbol is incorporated in a transparent plate.

8. A device according to Claim 7,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. ray-splitting block, all of the symbols will be set in the correct positions, so that consequently, the optical path length from each symbol to the lens system 8 will actually be of equal length. In practice, the individual dimensions of the ray-splitting prisms can differ in each individual case, and in order to compensate for this the plates F1-F, are inserted, and their thicknesses are thus to be adapted individually to each symbol, in order that equal path lengths will be obtained. In this embodiment, instead of the compensation block c, a prism A4 of the same type has also been arranged against the underside of the prism A2 in the figure. This prism A4 has its semi-transparent reflecting diagonal facing the direction opposite that of the diagonals of the prism A2 and A3 as a graticule arranged facing the side of the prism should not be arranged so that it is illuminated by the same lamp as the granticule B2. The graticule B4 has consequently been arranged opposite the surface of the prism A4 facing the lamp E2. The prism A1 facing nearest to the common lens system 8 also has its semi-transparent reflecting surface turned in the same direction as the prism A4, as no extra optical element such as a prism or a compensation block can be applied against the underside of the prism A1 in the figure because of the graticule B4 and the lamp E4. Against the upper side of the prism A1 a compensation block C is cemented and on the opposite side of this, a further prism A5. In this case, the diagonal of the prism can be facing any one of the four possible directions, i.e. in the two directions shown in the figure for the prisms A1-A4 and in addition thereto upwards and downwards from the plane of the paper, and in the figure they have been turned so that the graticule B5 is on the left side of the prism in the figure, i.e. turned away from the optical main system. In the figure it is also shown that the sides of the prisms and the compensation block through which there should not be any radiation have a light-absorbing coating, in order to reduce undesirable reflections to a minimum. They can, for instance, be painted black. As will be noted from the figure, the prism Al has the coating D1 on its lower surface, the prisms A2 and A3 have the coatings D2 and D3, respectively, on their upper surfaces, the prism A4 has the coating D4 on its left surface, and the prism A5 has the coating D5 on its right surface, and the compensation block C has the coatings D6 and D7 on its side surfaces. These coatings also reduce the risk for stray light in the system. In Figure 3 it is also shown that the plane parallel plate 6 in the main system, which can also consist of a ray-splitting prism corresponding to the plate 3 in Figures 1 and 2, need not be inclined at a 45" angle to the optical axis of the main system. As will be noted from the figure, however, the raysplitting block with its lens system must then be given a corresponding inclination, as with an inclination other than 45" the optical axis of the lens system 8 of the compensation system will of course obtain an angle other than 90" towards the optical axis of the main system. The inclination of the plate 6 can be chosen entirely in accordance with practical reasons. It should, of course, be obvious that instead of having a plate 6 or instead of the single ray-splitting prism used instead of this, also prisms of a more complex nature can be used. Many different modifications are possible within the scope of the invention. WHAT WE CLAIM IS:

1. A device for optically inserting selected images of a plurality of symbols into a main optical system so that the or each selected symbol is superimposed on the image from the main optical system, comprising a plurality of symbols, a lens system for projecting images of each of said symbols into said main optical system and a plurality of semi-transparent reflecting surfaces to transmit or reflect the image of each of said symbols to said lens system for projecting thereby into said image plane, the symbols and said surfaces being arranged so that each symbol is located in the object plane of said lens system and the ray path from a symbol to said image plane is incident only once on the same semitransparent reflecting surface.

8. A device according to Claim 7,

wherein said plate comprises opal glass.

9. A device according to any preceding claim in which each symbol may be selectively illuminated.

10. A device according to Claim 9, wherein each symbol is illuminated by a light emitting diode.

11. A device according to any one of Claims 2 to 10, wherein a transparent plate is arranged between at least one symbol and a prism.

12. A device substantially as hereinbefore described with reference to and as illustrated in Figures 2 or 3 of the accompanying drawings.