WO1993007531A1

WO1993007531A1 - Optical focusing system

Info

Publication number: WO1993007531A1
Application number: PCT/US1992/008654
Authority: WO
Inventors: James Bovy Lakey
Original assignee: James Bovy Lakey
Priority date: 1991-10-09
Filing date: 1992-10-09
Publication date: 1993-04-15

Abstract

A method and apparatus for focusing an optical system, such as a single lens reflex camera, has a laser (25) to project a small beam of light through the optical system, including a focusing screen (15). When the system is out of focus, the light pattern will be broad, and when the system is in focus, the light pattern will be a single spot. The broad pattern is dependent on the particular focusing screen (15).

Description

OPTICAL FOCUSING SYSTEM

Field of the Invention

This invention relates generally to optically systems, and is more particularly concerned with a method and apparatus for accurately focusing an optical system on a given object. Background of the Invention

Optical systems either have fixed focus, wherein all lens elements are fixed in relation to the others, or they have variable focus wherein one or more lens elements are movable to change the distance at which the lens is focused. In the lens systems having variable focusing, there is a constant problem in achieving accurate focus.

The elementary focusing system for an optical system is simply to look through the optics and make adjustments until the object being sighted appears sharp and in focus. This system is not desirable when focus is critical because it depends entirely on the viewer's sight and judgement. There are also range finder systems wherein the ₍beam of light is split so the viewer looks through two lenses and receives a split image until the range finder system determines that the image is in focus. While the range finder system is accurate, in photographic cameras and the like the range finder is usually separate from the photographic lens, so it is possible to satisfy the range finder system and still have the photographic lens out of focus. Careful manufacture is required to prevent such discrepancies. A very popular focusing system, especially for reflex cameras, utilizes a focusing screen having a prismatic surface. The focusing screen is placed at a distance equal to the desired focusing point of the lens so that, when the lens is focused, the point of precise focus is the focusing screen. The viewer then looks through the focusing screen, generally by means of a prism, then through the lens, generally by means of a mirror. If the lens is properly focused, the focusing screen is precisely at the focal point and the image appears to be sharply focused. If the lens is not focused, the point of sharp focus is displaced fro the focusing screen so the prismatic surface of the focusing screen causes deviation of the light waves creating a highly noticeable effect. While the focusing screen has achieved great commercial success, there are some people who are unable to utilize the focusing screen with any accuracy. Furthermore, in low levels of light one cannot see the object well enough to determine whether or not the object is in focus, even with the focusing screen. Additionally, some cameras and the like that have automatic focusing means also utilize light reflected from the object to achieve accurate focusing. These cameras are unable to focus in extremely low levels of light.

Summary of the Invention

The present invention utilizes the conventional through the lens focusing system utilizing a prismatic screen. A very fine beam of light is directed against the object that is to be in focus, and the variable focus lens is manipulated until there is a single spot of light, which indicates that the lens if focused. In one form of the invention, the narrow beam of light is directed through the optical system so that the light pattern is provided on the object to be in focus. When the lens is out of focus, there will be a broad area of light; and, when the lens is in focus there will be one spot. Alternatively, the narrow light source can be directed directly towards the object to be in focus, and the viewer will look through the optical system. When the lens is out of focus, the viewer will see the broad light pattern, and when the lens is focused, there will be a single spot of light.

Brief Description of the Drawings

These and other features and advantages of the present invention will become apparent from consideration of the following specification when taken in conjunction with the accompanying drawings in which: Fig. 1 is a somewhat schematic illustration showing a conventional through the lens focusing system; Fig. 2 is a plan view showing a conventional prismatic focusing screen;

Fig. 3 is a side elevational view showing a reflex camera having the focusing system of the present invention mounted thereon; Fig. 4 is a top plan view of a conventional reflex camera showing a modified form of the invention mounted thereon;

Fig. 5 is an illustration to show the light pattern perceived where the lens of the optical system is not in focus;

Fig. 6 is a view similar to Fig. 5 but showing the light pattern when the lens is in focus; and,

Fig. 7 is a top plan view, on a reduced scale, showing a further modified form of the present invention.

Description of the Best Mode

Referring now more particularly to the drawings, and to those embodiments of the invention here presented by way of illustration, Fig. 1 is a schematic representation of a conventional system for a reflex camera. The variable focus lens is generally indicated at 10, and the focusing ring 11 will move one or more of the lens elements to change the focus of the lens

10. Behind the lens 10 is a mirror 12, and behind the mirror 12 is the film indicated at 14. Thus, when the mirror 12 is moved from the light path,, light passes through the lens 10 and is focused on the film 14. The mirror 12 is used during composition of the picture; and, with the mirror 12 in the position shown, light is reflected from the mirror 12, passes through the focusing screen 15, through the prism 16, then through the eyepiece 18 and to the viewer's eye 19. Those skilled in the art will realize that the focusing screen 15 is positioned so that, when the lens 10 is adjusted so the at the intended image is in focus on the film 14 when the mirror 12 is raised, the same image will be in focus on the focusing screen 15 when the mirror 12 is down.

A conventional focusing screen 15 is shown in Fig. 2 of the drawings. The center portion of the focusing screen 15 is designated at 20, and this area 20 has a prismatic surface. Concentric with the prismatic surface 20, there is a ground glass circle indicated at 21. It will be understood that different styles and designs of focusing screens are utilized by different cameras, but many conventional focusing systems utilize a prismatic area such as the area 20, and this feature is presented by way of an example of the present invention.

Looking now at Fig. 3 of the drawings, there is a conventional camera that might utilize the system shown in Fig. 1 of the drawings. Thus, the lens in Fig. 3 is designated at 10, and the focusing ring for the lens is designated at 11. The lens 10 is carried by a camera 22, and there is a housing 24 for the prism 16, the housing 24 having the eyepiece 18 at the rear thereof.

The camera 22 in Fig. 3 is shown as having a light source, such as a laser, 25 mounted to propagate light through the eyepiece 18. the light source 25 includes a flexible cord 26 having a switch 28 at the end thereof. With this-arrangement, it will be understood that light will pass through the eyepiece 18, through the prism 16, will be reflected from the mirror 12 and passed through the lens 10 to shine on some object. When the light source 25 is not to be used, the entire light source 25 can be pivoted about the hinge 29 so a person's eye can be placed adjacent to the eyepiece 18 for composing a picture.

Fig. 4 shows a slightly modified form of the invention illustrated in Fig. 3. In Fig. 4 the camera 22 is provided with a bracket 30 to hold the light source 25 at the side of the camera 22. The light is then propagated from the light source 25 directly to a subject to be photographed. As in Fig. 3, the device of Fig. 4 includes a cord 26 and a switch 28 for operation of the light source 25.

The light source 25 preferably has a very narrow beam. The preferred light source to achieve the best results is a laser because the laser has a very bright collimated beam of light. The importance of this will be understood from the following further description. Looking at Fig. 5 and 6 of the drawings, and considering the foregoing discussion, it will be understood that, when the light is propagated from the light source 25, the light will pass through the focusing screen 15, and particularly through the prismatic area 20 of the focusing screen 15. A focused beam of light can be thought of as a cone, with the tip of the cone at the point of focus, thus, if the focused beam of light has its tip at the focusing screen 15, there will be a single spot of light as shown in Fig. 6 of the drawings. However, if the tip of this cone is displaced front he focusing screen 15, there will be a broader area of light at the prismatic area 20 of the focusing screen 15, and the light will intercept more than one facet of the prismatic area 20. Since the facets are not in a single plane, the light will be refracted to provide a plurality of spots of light as illustrated in Fig. 5 of the drawings.

Utilizing the arrangement shown in Fig. 3 of the drawings, the light is propagated from the light source 25, through the camera, so that the spots of light will be on the subject to be photographed. On the other hand, utilizing the arrangement shown in Fig. 4, the photographer will view the subjects through the eyepiece of the camera, the light propagated from the light source 25 will shine directly on the subject to be photographed, and the light will then pass through the lens 10 of the camera 22 to be seen by the photographer. The operation of the device is substantially the same. In either case, the light must pass through the camera lens, and through the focusing screen 15.

In using the arrangement illustrated in Fig. 3, one would point the camera at the intended subject, energize the light source 25, and view the spots of light on the subject. If there is a plurality of spots as illustrated in Fig. 5, the focusing ring 11 will be rotated until the plurality of spots merge into a single spot as shown in Fig. 6. At this point, the subject has been placed into focus, and the light source 25 can be pivoted or otherwise removed form the eyepiece 18, and the photographer can take the picture as usual. In utilizing the arrangement shown in Fig. 4, the photographer will have his eye at the eyepiece 18 and will energize the light source 25. The photographer might then see a plurality of spots on the subject to be photographed. Again, the focusing ring 11 will be rotated until the plurality of spots merge into a single spot as shown in Fig. 6, and the picture can be taken. One additional technique for utilizing the arrangement of the present invention is shown in Fig. 7 of the drawings. In this arrangement, there is a beam splitter 31 fixed to the lens 10 of the camera 22. With this arrangement, the light source 25 can be positioned against the eyepiece 18 as in Fig. 3; and, when light is propagated from the light source 25 and through the lens 10, the photographer can view the light pattern through the beam splitter at 32. As before, the focusing ring 11 will be manipulated until there is a single spot of light indicating that the lens is focused.

The above discussion relates to the use of prismatic focusing screen so that the prismatic surface creates the plurality of spots as shown in Fig. 5. However, the focusing system can equally well be used with other focusing screens. For example, with a focusing screen that produces a split image for focusing, the pattern created when the lens is out of focus will be an elongated bar. when the lens is in focus, there will be a single spot as in Fig. 6. thus, any focusing screen will serve, but the specific pattern displayed when the lens is out of focus will be different for each different focusing screen.

Further, though the preferred embodiment of the invention utilizes a small, collimated beam of light to produce a single spot when the lens is in focus, a broader beam of light can also be used. The broad beam of light will illuminate substantially the entire focusing screen, so the "in focus" clue is that the focusing screen is clearly in focus, rather than being a smear of light.

It will therefore be understood by those skilled in the art that the particular embodiments of the invention here presented are by way of illustration only, and are meant to be in no way restrictive; therefore, numerous changes and modifications may be made, and the full use of equivalents resorted to, without departing from the spirit or scope of the invention as outlined in the appended claims.

Claims

1. A method for focusing an optical system, wherein said optical system includes a variable focus lens (10), a focusing screen (15) interposable in the path of light, and an eyepiece (18) for viewing through said lens (10), said method including the steps of propagating a beam of light through said lens (10), and adjusting said variable focus lens until said beam of light produces indications that said variable focus lens is in focus.

2. A method as claimed in claim 1, wherein said beam of light is propagated through said eyepiece (18), so that said indications are on the subject to be in focus.

3. A method as claimed in claim 1, wherein said beam of light is shone directly on the subject to be in focus, and the said step of adjusting said variable focus lens (10) comprises the step of adjusting said variable focus lens (10) until said indications are observed through said eye piece (18).

4. A method as claimed in claim 1, wherein the said step of propagating a beam of light through said lens comprises the step of propagating a narrow, collimated beam of light through said lens.

5. A method as claimed in claim 4, wherein said focusing screen (15) includes a prismatic surface (20), and including the step of propagating said light through said prismatic surface (20), said step of adjusting said variable focus lens comprising the step of adjusting said lens until said light produces a single spot of light as said indication that said variable focus lens is in focus.

6. A method as claimed in claim 5, wherein said step of propagating a beam of light comprises propagating a beam of laser light.

7. Focusing apparatus, for an optical system including a variable focus lens (10), a focusing screen (15) interposable in the path of light through said optical system, and an eyepiece (18) for viewing through said lens (10), said apparatus comprising a light source (25) for projecting a narrow beam of light onto the object to be in focus, and means (18) for observing said narrow beam of light through said focusing screen (15) .

8. Focusing apparatus as claimed in claim 7, and further including means for disposing said light source (25) adjacent to said eyepiece (18) so that said beam of light passes through said optical system and onto said object to be in focus.

9. Focusing apparatus as claimed in claim 7, and further including beam splitting means (31) for viewing said object to be in focus while said light source (25) is adjacent to said eyepiece (18).

10. Focusing apparatus as claimed in claim 7, and including means (30) for supporting said light source (25) adjacent to said optical system for projecting said narrow beam of light directly onto said object to be in focus, so that said beam of light can be observed through said optical system, including said focusing screen (15) .

11. Focusing apparatus as claimed in claim 7, wherein said light source (25) comprises a source of collimated light.

12. Focusing apparatus as claimed in claim 7, wherein said light source comprises a laser.