This invention relates to optical apparatus for creating an image against a background, which is particularly suitable for use as a training aid for a golfer.
It is desirable in various situations to have an image which is superimposed against a background view. For example a golfer, addressing a ball, can be assisted in his stroke if an image, which is visible only to the golfer, is superimposed on his normal field of vision. This type of situation is described for example in the specification of international application No. PCT/IB02/00953.
This international application describes a system wherein light is concentrated by a collector element and then passed through a reticle (a light grid) which directs an image onto a reflector which is in the nature of a beam splitter and which reflects light from the reticle towards an eye while at the same passing light in a direction from a normal field of vision. Normally the fabrication of a beam splitter, in the type of application referred to, requires the application of a light reflective coating to what may be referred to as an internal surface of a lens ie. a surface which faces an eye. The application of this type of light coating can be expensive and, if the coating is not of a satisfactory material, the coating can be easily damaged by scratching, abrasion or the like. A further factor with this type of lens is that the user's second eye, which does not receive the image from the reticle, is directly exposed to the general field of view. In other words one eye, which receives the image, views the general field of vision through a lens while no lens is positioned between the other eye and the general field of view. To some extent this imbalance is compensated for by an external lens or visor which covers both eyes but the overall appearance of the end product can be unacceptable to certain users. Also, the different light intensities on the eyes of a user can be disturbing and affect the user's vision and balance.
U.S. Pat. No. 3,498,293 describes a system which is used to orientate a person. Use is made of a lens which is mirrored or a beam splitter which is wavelength dependent ie. selectively reflective, and a gravity dependent device.
The problems encountered in orientating a user are quite different from those encountered in addressing a golf ball. In the specification of this patent reference is made to golf but there is no disclosure however of how a ball is to be targeted. The lenses in one embodiment are semi-transparent but there is no disclosure as to the further nature of the lenses.
It is known that semi-transparent lenses can generate ghost or secondary images but the problem associated therewith is not identified in the aforementioned American specification nor addressed.
U.S. Pat. No. 4,806,011 discloses a system wherein a small secondary lens, which is partly reflective, is used to project an image onto an eye of a user. The position of the secondary lens and its size can be problematic and can present a source of physical danger to a user.
In providing an optical apparatus which can be used as a golf training aid it is desirable to have a system which, as far as is possible, has the appearance of a normal pair of spectacles or sunglasses, which is not unreasonably bulky and which is relatively easy and inexpensive to manufacture.