WO1999035528A1

WO1999035528A1 - Optical apparatus

Info

Publication number: WO1999035528A1
Application number: PCT/GB1999/000003
Authority: WO
Inventors: Gordon Frank Hazelrigg Lloyd
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1998-01-07
Filing date: 1999-01-06
Publication date: 1999-07-15
Anticipated expiration: 2000-07-07
Also published as: ZA99108B; AU2063599A; GB9800332D0

Abstract

Optical apparatus (3) to provide a visual image to an observer including at least one objective (4) located in fixed relation to the observer's head (2) and additionally comprising at least one mirror (9) arranged in relation to the objective (4) so as to form a virtual objective (10) at a position which is closer to one of the observer's eye than the real objective (4). The invention may be utilised in binocular systems wherein two objectives are located in fixed relation to the observer's head and away from the observer's field of view, and additionally comprising a mirror for each objective.

Description

OPTICAL APPARATUS

The invention relates to optical apparatus which is mounted in fixed relation to the head of an observer (e.g. attached to a helmet) and used to augment observer vision. It particularly applies to optical apparatus which provides enhanced or additional visual images or information either to the wearer of the apparatus or to other observers. The invention has application in head mounted optical systems for aircrew, military personnel, rescue services as well as having application in the leisure and entertainment field. The invention has particular but not exclusive application to optical apparatus providing display information which supplements normal observer vision.

Over recent years there has been an increasing number of visual aids which have been made available to enhance pilot operation performance; these supply the pilot with additional visual information to augment normal pilot vision of views outside and inside the cockpit. Examples of such visual aids are weapon aiming systems, thermal imaging systems and image intensifiers such as night vision apparatus.

Such supplementary visual information is usually displayed just outside the central field of view or on display means such as a panel which can be moved into position in the central field of view. Alternatively a particularly useful facility is to superimpose the display image over the pilot's central field of view. UK patent application GB 2283833 describes the use of an inclined planar combiner located in front of the pilot's eye to mix images provided by a supplementary optical system with the pilots normal view. The system uses miniature display means mounted on the helmet. It is advantageous for the objectives of such optical systems to be mounted on the helmet; in this way they can be more easily arranged always to point in the same direction as the wearer's head, thus ensuring that the images displayed to the pilot are viewed from the correct perspective.

Because the observer's field of view is to be unobstructed, it is a requirement that the bulk of the optical system (which provides the pilot with augmented visual information) is located away from the pilot's field of view so as not to interfere with or obstruct it. The usual location for mounting optical system components, such as miniature cameras, is outside the rim of the face aperture of the helmet. It is therefore not possible to physically position the objectives at the eyes, and in many instances the objective lens can be located some distance from the viewer's eyes.

A problem arises is that with a camera mounted on the helmet, the viewpoints will have different forward line of sight than the eyes which causes viewpoint problems; for example the cockpit structure such as the canopy or arch may obstruct the camera view outside the cockpit.

In most cases these optical systems are binocular ones comprising two separate optical sub-systems for each eye and located symmetrically about the plane of the wearer's nose. ,ln the case of cameras which are mounted normally on the sides of the helmet, the objectives thereof have a separation which is significantly greater that between the pilot's eyes. When the images produced by the two optical systems are presented to the respective eyes of the observer, a phenomenon called hyperstereopsis arises, which causes a further problem. The effect of this to the viewer is as if his eyes are widely spaced as if on stalks. This results in double vision of close objects such as cockpit structure and instrumentation and, for helicopters and VSTOL (Vertical / Short Take-Off & Landing) aircraft, close objects outside the cockpit. It results in exaggerated and therefore unfamiliar depth perception for objects from about 5 metres to about 300 metres away. Moreover the effects of enhanced depth perception is upsetting and uncomfortable. Therefore further problems arise with binocular systems.

It is an objective of the invention to provide a supplementary optical system which augments normal observer vision and provides images to an observer which overcomes the above problems and ensures that the effective position of the objectives is as close as possible to observer's eyes. It is a further object of the invention to eliminate hyperstereopsis and provide comfortable image presentation as well as to overcome the problem of double vision for close objects such as cockpit structure and instrumentation.

According to a first aspect of the present invention, optical apparatus to provide a visual image to an observer includes at least one objective located in fixed relation to the observers head and additionally comprising at least one mirror arranged in relation to the objective so as to form an a virtual objective at a position which is closer to one of the observers eye than the real objective. The invention makes use of the fact that optically virtual position of the objective can be made different to the real location of the objectives by using mirrors.

According to a second aspect of the present invention, optical apparatus to provide binocular visual images to an observer includes two objectives located in fixed relation to the observers head, and additionally comprising a mirror for each objective and arranged in relation thereto, so as to form virtual objective at a position which is closer to one of the observers eye than the real objective.

Preferably, said objectives and mirrors are mounted on a helmet to be worn by the observer.

In a preferred embodiment, the optical apparatus further comprises video means adapted to receive a signal corresponding to the real objective and visually reproduce said signal in the field of view of the observer.

The video means may comprise a camera adapted to receive the signal corresponding to the real objective. Ideally, the video means comprises a combiner adapted to visually reproduce the signal in the field of view of the observer.

The invention will now be described by way of example with reference to the schematic drawings of which:

Figures 1a and b show front and side views respectively of a helmet incorporating a binocular optical system arranged according to known techniques.

Figures 2a and b show front and side views respectively of one embodiment a helmet mounted optical system according to the invention.

Figure 2c shows alternative arrangements of objectives based on the embodiment of figures 2a and b. Figures 3a and b show front and side elevations respectively of an image enhancement system such as a night vision system, incorporating the invention.

Figures 1a and b show front and side views respectively of a conventional binocular optical system mounted on a helmet 1 and used to supplement normal pilot vision by displaying additional visual information to a pilot 2. The system comprises two low light miniature TV cameras 3 each including an objective 4 and a charged coupled device (CCD) 5 symmetrically arranged on each side of the helmet as shown. These miniature cameras are generally located in any of positions A to B to C. Each camera is connected to a video system which is installed in the aircraft and not shown for clarity. Essentially the video system produces an image to be displayed on two miniature cathode ray tubes 6 also symmetrically arranged in the forehead area of the helmet and oriented towards a concave collimator 7. This collimates and reflects display light from the CRTs towards an inclined combiner 8 and to the wearer's eyes. The inclined combiner is semi-transparent and allows light from in front of it to pass through freely so as not to obscure normal vision, but at the same time reflects light from the concave collimator towards the eyes.

The above mentioned system allows images from the optical system (such as one used in aiming and weapon systems) to be superposed on the pilots normal view.

As mentioned, common positions of the cameras and therefore objectives tend to vary between positions A and C as shown. At position A the objectives are far apart horizontally in comparison with human eye separation. When the image is supplied to the eyes from each respective objective the view to the wearer is such that his eyes are effectively in the positions of the objectives; it is as if the wearer has eyes which are widely spaced. This leads to the aforementioned problems of hyperstereopsis and double vision.

At location C the objectives are close together at about the same spacing as human eyes. This eliminates the problem described above but the pilots viewpoint is much higher than it should be. In many aircraft this higher viewpoint is obstructed by cockpit structure above the windscreen.

Figure 2a and 2b side and front elevations respectively of an embodiment of the invention showing a helmet 1 worn by a pilot 2 . Located on the outside of the helmet is a binocular optical system comprising two low light television cameras 3 each connected to video system in a similar fashion as described above . The video system has outputs into two CRT tubes 6 which present respective images to each eye by means of a collimator 7 and an inclined combiner 8. Mounted on the helmet are two mirrors 9, one for each camera. The cameras and mirrors are so located and arranged that the camera objectives 4 are oriented towards the mirror. Each mirror serves to reflect incoming from a generally horizontal axis to the respective objective of the camera. Due to this positioning a virtual objective 10 is formed in the position as shown. The image formed on the objectives and eventually displayed to the pilot is from the viewpoint of the virtual objectives, in other words it is as if observers eyes are located at the position of the respective virtual objectives. As seen in figure 2b, the mirrors and objectives of are located directly above the location of the helmets wearer's eyes. This ensures that the distance between the virtual objectives is roughly equal to the distance between the eyes of the wearer and that the optical system provides binocular vision which is similar to human binocular viewing.

The "virtual objectives" position can be close to the eyes as shown. However the virtual objectives can be formed closer to the eyes or even at the eyes by suitable positioning of the camera and mirror.

Figure 2c shows camera positioning in which three alternative arrangements are shown, each camera being located such that their optical axes are not interfering with those of the CRT display optics. Although three cameras 11 ,12, and 13 and their respective mirrors 14, 15 and 16 are shown one or two of them are dispensed of and the figure is only to indicate the following arrangements: cameras 11 and 12 or cameras 12 and 13 can be used in combination to provide a binocular system or single central camera 12 may be utilised. The spacing between the cameras 11 and 12, (and 12 and 13) is preferably the same as the distance between human eyes; this endure that hyperstereopsis and hypostereopsis is prevented.

Figures 3 a and b show side and front elevations of an embodiment of the invention which can be incorporated onto an image enhancement system such as night vision image intensifier. Attached to the observer's head is an image display panel 17. Also in fixed location to the head is located a binocular system 18 comprising two image intensifier tubes 19 which are connected to the display. In front of the display screen and in front of each eye are located two mirrors 20, each mirror orientated so as to reflect incoming horizontal light towards the objective of the image intensified tube. As shown, for each eye, virtual objectives are created as shown which are each in the proximity of the respective eye. A further advantage of such a system is that it allows image intensifier tubes to be located vertically, such that their centres of mass are close to the head. With conventional systems it was necessary for the tubes to be located horizontally in front of the face which resulted from heavy helmet.

Claims

1. Optical apparatus (3) to provide a visual image to an observer (2) including at least one objective (4) located in fixed relation to the observers head (2) and additionally comprising at least one mirror (9) arranged in relation to the objective (4) so as to form an a virtual objective (10) at a position which is closer to one of the observers eye than the real objective (4).

2. Optical apparatus (3) to provide binocular visual images to an observer including two objectives (11 , 12, 13) located in fixed relation to the observers head and additionally comprising a mirror (14, 15, 16) for each objective and arranged in relation thereto, so as to form virtual objective at a position which is closer to one of the observers eye than the real objective.

3. Optical apparatus as claimed in any preceding claim wherein said objectives and mirrors are mounted on a helmet (1 ) to be worn by the observer (2).

4. Optical apparatus as claimed in any preceding claim wherein the apparatus further comprises video means adapted to receive a signal corresponding to the real objective and visually reproduce said signal in the field of view of the observer.

5. Optical apparatus as claimed in claim 4 wherein the video means comprises a camera adapted to receive the signal corresponding to the real objective.

6. Optical apparatus as claimed in claim 4 wherein the video means comprises a combiner adapted to visually reproduce the signal in the field of view of the observer.

7. Optical apparatus as herein before described with reference to figures 2a to 2c, 3a and 3b.