This invention is concerned with improving the visibility of balls and other projectiles used in games,

The televising, filming, or watching of sports

> events _. is often unsatisfactory owing to the poor visibility of the ball, as happens in squash for example. As a result these games have not achieved the mass popularity that their intrinsic natures, or the superb skills of their leading exponents, deserve. . In some sports, such as golf, use is made of zoom lenses set at a long focal length, and while this improves the visibility of. the ball, it does so at the expense of losing the ball's relationship to its surroundings.

An object of one aspect of this invention is to provide a game projectile which enables the visibility of the projectile to be increased.

According to said one aspect of the invention there is provided a game projectile as least a portion of the outer surface- of which is retroreflective.

A retroreflective surface is hereby defined as being such that over a substantial range of angles relative to the normal to the surface, a substantial amount of light incident on the surf ce at that angle is reflected back in substantially the same direction as the incident light. Thus, retroreflection differs from the reflection provided by, say, a mirror where light is reflected from the surface on the opposite side of the normal to the incident light.

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When the projectile is televised, filmed, otherwise reproduced or viewed, using an optical system that includes a light source which is placed so that the angle between itself, the projectile, and the camera or eye, is small, the projectile can reflect increased amounts of light in relation to other objects in the field of view, or different light in terms of colour, intensity or variability.

According to a second aspect of the invention there is provided a system for enhancing a game projectile when viewing a game, which system employs a retroreflective game projectile according to said one aspect of the invention and further comprises means for projecting light from the viewing location or adjacent thereto towards the projectile, so that light from the projector means is reflected by the projectile back to the viewing location to enhance the projectile.

A cameramay be located at the viewing location to record the image.

Specific embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

Figures 1 to 3 are partial sectional views of three balls each according to the invention;

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Figures 4 and 5 are schematic diagrams each of a camera and light projector for use in a system according to the invention.

Figure 1 shows a portion of a squash ball 1 in cross-section. The rubber wall of the ball is formed with a plurality of recesses, each of which ^' --' accommodates a rigid container 2, whose floor contains an area of retroreflective material 3, such as 3M*s Scotchlite High Intensity Reflective Sheeting Type 7610. A lip 4 of -rubber covering the edge, and a little more, of the rigid container 2 ensures that the rubbery physical characteristics of the ball are maintained for play and that the containers 2 are held in position. Adhesives. may be used in addition. The retroreflective material is protected by the rigid containers 2. Rays 5 of light are shown striking the retroreflective material 3 and being returned in the direction of the source, which is the characteristic of this material. Discs of cube corner reflectors could be used instead of the rigid containers and 3M material. Alternatively, the retroreflective material may be glued directly to the ball without the use of the containers 2. Figure 2 shows a wall portion of another type of ball 1, in cross-section. The wall portion 6 is

transparent and the inner surface thereof is formed with an array of cube-corner reflectors. The cube-corner reflectors act together to provide a retroreflective surface. Balls made in this way might retain the aerodynamic qualities of the original.

Figure 3 shows a modification to the ball of _ Figure 2 _r in which the wall of the ball 1 has an outer layer 7 which is similar to the wall of the ball shown in Figure 2, and an inner layer 8 which is bonded to the inner retroreflective surface 2 of the outer layer 7 and which has a smooth inner surface. The purpose of providing the additional layer 8 is to reduce the stress concentrations between the cube corners when the ball is deformed, and thus increase the life of the ball. The relative refractive indexes of the materials from which the inner and outer layers are made must be chosen so as to cause substantial internal reflection at the cube-corner interface of the two layers, or alternatively a reflective coating may be bonded between the two layers.

If the outer retroreflective surface of the ball is non-planar (and unless the ballis faceted, it must be) then the corner cube elements, or retroreflective elements, must be as small as possible to ensure that the ray ^' of light reflected internally is not only reflected back in substantially the same direction,, internally, but also as near as possible in the same position, internally to ensure that it is refracted from the outer surface in substantially the same direction as it entered. This applies particularly to a golf ball having dimples 10 as shown in Figure 3. Small retroreflectors also have the further advantage that physical distortions.of the ball produce smaller angular distortions of the reflecting surfaces. As an alternative to using pieces of retroreflective sheet material on the surface of the game projectile or cube corner reflectors below the outer surface, other suitable means may be employed to render at least a ^" portion of the outer surface of the projectile retroreflective. For example, retroreflective beads may be embedded beneath the outer surface of the projectile.

A light source on the same optical path as a camera is often obtained, in general photographic work, by using partially reflecting mirrors or beam splitters. This has the disadvantage that light is lost on both the outward and inward journeys. Experiments with a squash ball incorporating 3M Sheeting Type 7610 show that good optical results can be obtained with a light source slightly to one side of the camera lens, without using a beam splitter. However, heat generated by the lamp and the physical bulk of the lamp are disadvantages. Figure 4 shows an arrangement whereby these disadvantages can be minimized. Figure 4 shows an optical arrangement effectively providing a light source in the region of the camera lens, that is not bulky and does not generate much heat in the region of the camera 20. The real light source 22 is shaped and directed by reflector 24, through a heat filter 26, onto a stationery convex fully-reflecting mirror 28, which reshapes and redirects the light. The camera 20 is pointed through a hole 30 in the mirror 28 and can pan and tilt on a suitable mount that takes account of the hole in the mirror.

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The system shown in Figure 4 is of particular use for filming or televising a game at close quarters, for example squash. The light source 22 and mirrors are arranged to illuminate at least a large part of the squash court. The game of squash is played with a retroreflective squash ball, which reflects light from the source back to the camera 20 to enhance the ball in relation to the remainder of the picture. Referring now to Figure 5, there is shown a light source and camera arranged particularly for viewing a game from a distance, for example golf, driving. The light source 22, mirror.24 and heat filter 26 are similar to those shown in Figure 4. The mirror 28, however, of the Figure 5 embodiment has two main differences. Firstly, it has a larger radius of curvature than the mirror 28 in Figure 4, so that the field of projection is small. The half-angle of the cone of projected light may be, for example, 3h° . Secondly, the mirror is mounted for universal pivotal movement, that is in an up and down direction and from side to side and a combination of these movements. Furthermore, the arrangement includes a telescopic sight which is also mounted for universal pivotal movement and a half-speed drive mechanism

34 which moves the mirror 28 in response to movement

of the sight 32. Pivoting movement of the sight 32 by a particular angle about the horizontal axis 36 aligned with light beam from the mirror 24 (i.e. up-and-down movement of the sight) causes the drive mechanism 34 to pivot the mirror 28 by half that angular amount about the horizontal axis 38 lying in the general plane of the mirror. Furthermore, pivoting of the sight 32 by a particular angle about the vertical axis 4θ causes the drive mechanism 34 to pivot the mirror 28 by half that amount about the vertical axis 42 passing through the centre of the mirror 28. Thus, once the drive mechanism has been initially set-up so that the light beam is projected by the mirror in the same direction as that in which the sight is pointing, when the sight is moved, the light beam will follow the direction in which the sight points. The drive mechanism may utilise gears, or pulleys and cables, to provide the necessary gearing, or alternatively the mirror 28 may be driven by motors, the orientation of the sight 32 being detected by potentiαraeters and which provide signals which are used by a control unit to operate the motors.

In use, the camera 20 is set up with a wide angle lens so that it sees the whole of a game scene, for example a golf hole from tee to green.. The

telescopic sight 32 has cross wires which are sighted on a retroreflective golf ball and an operator follows the ball with the sight, when it is ..driven from the tee. The beam of light from the mirror 28 therefore tracks the ball, and the light reflected by the ball back to the camera therefore enhances the image of the ball in relation to its surroundings.

The mirrors 28 may also perform other functions such as smoothing out slightly varying intensities of light. The mirrors 28 may also be constructed in a number of sections, each with its own light source, arranged so that each sectionreflects approximately into the same field of view, and different lights may be used, singly, additively or successively.

In practice, it is not necessary for the mirror 28 to project light from a point on the centre-line of the camera; the mirrors 28 may be mounted slightly to one side of the camera.