JPH11281867A - Lens assembling body for camera, camera incorporating the same, and their manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent dust from accumulating on the outside surface of a lens without the danger of damaging the lens. SOLUTION: The lens assembling body 2 incorporates a frame 1 and an optical system formed of at least one front surface lens 3, the surface 3a of the front surface lens forms the front part surface of the body 2, the surface 3a forms a contact angle α of >=120 with the frame 1, and the lens 3 is formed of a transparent material having the hardness of equal to or more than that of tempered glass.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens assembly for photographing or photographing equipment such as a camera and a video camera.

[0002]

2. Description of the Related Art Such a lens assembly includes a frame and at least one lens, one of which is located on the surface of the lens.
One is the outer surface of the lens assembly. In currently used lens assemblies, special attention is paid to protecting the outer surface to prevent damage by hard objects.
Scratches on the lens surface will severely degrade the quality of the photo,
This caution is very important. The frame of such a lens assembly is generally cylindrical and extends outward beyond the outer surface of the lens. The angle formed by the coupling surface of the frame and the lens is generally close to 90 °. Thus, the lens is protected by the end of the frame.

In this type of structure, a groove is formed on the joint surface between the frame and the lens, and dust can accumulate there. To avoid this, the lens assembly is typically covered with a removable cap. Such attention can reduce the rate of accumulation of dust, but cannot completely prevent it. Furthermore, cleaning of the grooves is tricky and difficult to perform completely. The disadvantages are, for example,
It is particularly disadvantageous for small diameter lens assemblies to be incorporated into small cameras intended to be incorporated into watches. Such cameras are particularly exposed to debris. It has been observed that dirt accumulates in the cavities in a very short time during use.
Moreover, it is difficult to provide a removable cap that can be easily removed for this type of camera when taking a picture.

[0004]

SUMMARY OF THE INVENTION It is a primary object of the present invention to prevent the accumulation of debris on the exterior surface of a lens without risking damage to the lens. Another object of the present invention is to create a camera that is particularly robust and of high quality.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present invention provides
A lens assembly for a camera including a frame and at least one lens, wherein one of the surfaces of the lens forms an outer surface of the lens assembly, and the surface comprises
The present invention relates to a lens assembly having a connection angle of not less than ° and a lens formed of a transparent material having hardness equal to or higher than tempered glass.

[0006] As a result of these features, the lens assembly has no dents, so that accumulation of dust can be prevented and a clean state is maintained. Furthermore, the hardness of the material of the lens which is the outer surface of the lens assembly is equal to or higher than that of the tempered glass, so that it is practically scratch-resistant.

According to an advantageous feature of the invention, the lens assembly includes a first front lens, a second intermediate lens, and a third rear lens. The front lens and the rear lens are convergent lenses and are formed of a material having the highest possible refractive index and Abbe number. The intermediate lens is a diverging lens, which is formed of a material having the lowest possible Abbe number.
With such a structure, chromatic aberration can be corrected. Therefore, a lens assembly having a short length and excellent optical quality can be manufactured.

The present invention is a camera comprising a lens assembly including a case and fixedly attached to a wall of the case, at least a part of the case to which the lens assembly is attached and a lens assembly. It also relates to a camera characterized in that the front surface forms a substantially spherical surface. The present invention also relates to a method of manufacturing a camera capable of obtaining a completely continuous surface despite the addition of a lens assembly to the case. The present invention also relates to a camera comprising a lens assembly including a case and fixedly attached to a wall of the case, wherein a surface of the case to which the lens is attached is attached after the lens assembly is attached. ,
The present invention also relates to a method of manufacturing a camera characterized by polishing with particles having a hardness lower than the hardness of the material forming the front lens. Finally, the invention relates to a camera of very small dimensions, described in more detail below by way of example and referred to as a "watch camera" for convenience, the case being a watch case.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS Other advantages and features of the invention will become apparent on reading the following detailed description of embodiments, given by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which: FIG. There will be.

Throughout the description, the portion outside the camera and in front of the lens assembly is referred to as the "front" portion. Conversely, the "back" portion is located behind the lens assembly inside the camera. Further, the terms "radial" and "axial" are with respect to the optical axis of the lens assembly.

As can be seen from FIG. 1, a known lens assembly includes a cylindrical lens housing a set of lenses therein, including, for example, a converging front lens 3, a converging rear lens 4, and a diverging intermediate lens 5. Frame 1 is included. Front lens 3
Is the front surface of the lens assembly 2. This lens assembly 2 can focus the light beam 18 on the photosensitive surface 19. The interior of the frame 1 has a flat surface and a cylindrical surface. The cylindrical surfaces, labeled 6, 7, 8 respectively, ensure the radial positioning of the lenses 3, 4, 5. The flat surfaces labeled 9, 10, 11 serve as axial positioning surfaces for positioning the lenses 3, 4, 5 respectively. Lens 3, 4, 5
Is secured to the frame by means known, not shown, such as by bond bonding or by a threaded ring cooperating with a threaded hole formed in the frame.

The frame 1 extends forward to extend the flange 12
To form The flange extends at least to the same position as the end of the lens 3 to protect the lens from body that may come into contact with the lens. The surface 3 'of the lens 3 and the flange 12 together form a groove 13 in which dirt deposits 14 tend to accumulate. This has the effect of reducing the effective diameter of the lens 3 or causing light diffusion which can affect the quality of the photograph. The smaller the angle α determined by the surface 3 ′ and the flange 12, the higher the risk of dust accumulation. As can be seen, this angle is typically less than 90 °.

The lens assembly according to the invention shown in FIG. 2 also comprises a frame 1 and an optical system formed by the same lens assembly. The frame 1 has the same positioning surfaces 6 to 11 for positioning the lenses 3, 4, 5. This differs from the lens assembly of FIG. 1 in that it does not include a flange. Conversely, the frame 1 has a flat front surface 15 adjacent to the surface of the lens 3a.

The surface of the lens and the front surface 15 together
An obtuse angle α close to 80 ° is formed. This is in any case greater than 120 °. It will be readily appreciated that in these situations it is virtually impossible for deposits to accumulate, which can affect the quality of the lens. Even if dust adheres to the surface of the lens 3a, it is fairly easy to clean it. When such a lens is attached to a camera that is fixed to the user's wrist, for example when the camera is integrated into a wristwatch, cleaning is almost automatic by rubbing clothes on the lens surface.

Obviously, the lens assembly shown in FIG. 2 is no longer protected against impacts and scratches. This problem is solved by using sapphire or tempered glass or another transparent material with a higher hardness than the lenses currently used in the manufacture of the front lens 3 so as not to scratch the lens. be able to. Apart from the hardness provided by sapphire, other optical properties of sapphire make it possible to create high quality lens assemblies with short lengths.

An interesting compromise can be achieved with three lenses. Front lens 3 both converging lenses
The rear lens 4 is made of a material having a high Abbe number (v). The intermediate lens 5 is a divergent lens and is made of a material having a low Abbe number. Furthermore, it is advantageous for the converging lenses 3 and 4 to have the highest possible refractive index and the diverging lens to have the lowest possible refractive index (n). In a particularly advantageous embodiment, the front lens 3 is made of sapphire (n =
1.768, v = 72.41) and the rear lens 4
With PMMA (polymethyl methacrylate) (n = 1.4
92, v = 57.43) and the intermediate lens 5 is SA
N (styrene acrylonitrile) (n = 1.59, v =
30). Although the refractive index of SAN is higher than PMMA, it is a completely satisfactory compromise from an optical point of view.
In addition, its mechanical properties provide a high level of safety, for example, against the risk of deformation due to temperature changes or impacts.

The following table shows, by way of example, the features of a compact, high optical quality lens assembly according to FIG. 2 made of the materials listed below.

Lens material R1 (mm) R2 (mm) φ (mm) e (mm) d (mm) 3 Sapphire 4.69 ∞ 6.1 2.00 0.38 4 PMMA 6.41 ∞ 4.7 1 .00 4.05 5 SAN-23.8-17.5 4.0 2.00 2.25

In this table, R1 is the radius of curvature of the front surface of the lens, R2 is the radius of curvature of the rear surface,
φ is its diameter, e is its thickness, and d is the distance along the optical axis from one lens to the next, or for lens 4 to the surface of the photoreceptor. The lens assembly made on this basis has a 20 ° aperture angle for a distance of 11.68 mm between the surface 3 'and the photoreceptor surface 19 where the image of the subject must appear. The focal length is 10.50mm
It is. Such a lens assembly is compatible with the dimensions of a watch.

Referring now to FIGS. 3 and 4, there is shown a wristwatch equipped with a camera according to the present invention. It includes a rectangular case 20 sealed at the top by a crystal glass 26 placed over a dial 27 with a display cell 28 mounted thereon. The lens assembly 22 is mounted on the wall of the case 20. It has the same features as the lens assembly described in FIG. This includes a front lens 23, a rear lens 24, and an intermediate lens 25.
Having. More precisely, the lens assembly 22 is mounted on a frame 21 having an axis substantially parallel to the front surface of the crystal glass 26 and fixed to the case 20, comparable to the frame 1 of FIG.

The lens assembly 22 includes the surface 2 of the lens 23.
3a and the surface 21 of the frame 21 adjacent to the lens 23
a having a front surface formed by An optoelectronic device 29 is arranged at the rear of the lens assembly 22. It converts light into electrical signals. These signals are shown schematically and processed by electronics 30 that controls both the wristwatch and the camera. The electronic circuit 30 is in particular connected to a display cell 28 which acts as a viewfinder. As can be seen in FIG. 4, the lens 23 projects slightly. Its surface 23a forms an obtuse angle α greater than 120 ° with the surface 21a of the frame 21.
As you can easily imagine, no trash can accumulate at this angle.

Referring to the second embodiment shown in FIGS. 5 and 6, this camera differs from FIGS. 3 and 4 in that the surface 23a of the front lens 23 is basically completely incorporated into the surface of the case 20. It can be seen that this is different from that shown in FIG. Therefore, the outer peripheral surface 20a of the case 20 corresponding to the middle part of the wristwatch has a spherical surface 31 indicated by a dotted line in FIG.
to go into. The radius R of this spherical surface is substantially equal to the spherical surface constituting the front surface 23a of the front lens 23. Accordingly, the case 20 and the lens 23 are provided with a groove which is likely to cause accumulation of dust in the portion of the case 20 on which the lens 23 is mounted,
Form a continuous surface without holes or protrusions.

The characteristics of the lens assembly satisfying these conditions as shown in FIG. 4 are defined in the following table.

Lens Material R1 (mm) R2 (mm) φ (mm) e (mm) d (mm) 23 Sapphire 17.5-143 4.8 1.26 0.124 PMMA 13.1 445 6.0 2.0 3.1 25 SAN 2.64 2.15 3.5 1.74 3.3

In order to obtain the most even surface possible, it can be envisaged to perform a finishing machining operation on the outer surface of the case after the lens assembly 22 has been mounted on the case. The material forming the case 20 and the frame 21 has a lower hardness than the material of the lens 23.
By properly selecting the abrasive, the height difference between the case 20, the frame 21, and the front lens 23 can be reduced.
It is possible to remove it without changing its surface condition.

In this configuration, the lens 23 can be made of tempered glass, but is more advantageously made of sapphire. Thus, the hardness of the lens 23 is sufficient to avoid damage during both the finish machining operation and normal use. It should be noted that it would be possible to create a lens assembly where the window was formed of flat sapphire and the lens was placed behind such a window. Tests performed have shown that the price is substantially the same, but the optical quality is low and the length of the lens assembly is long.

If the material used is sapphire, it is evident that the lens is machined from the crystal according to an orientation that guarantees a constant index of refraction, regardless of the incident ray angle. In other words, the optical axis of sapphire is the same as the axis of the lens assembly. Thus, the camera described herein has an advantageous structure with respect to both optical and mechanical features. Therefore, it can be used even in particularly severe conditions without thereby affecting its performance.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens assembly according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a lens assembly according to an embodiment of the present invention.

FIG. 3 is a perspective view of the timepiece camera according to the embodiment of the present invention.

FIG. 4 is a plane IV- which is parallel to the timepiece and crosses the optical axis.
FIG. 4 is a cross-sectional view of the lens assembly of FIG. 3 along IV.

FIG. 5 is a perspective view of a second alternative embodiment of the timepiece camera according to the present invention.

FIG. 6 shows a plane VI- which is parallel to the timepiece and crosses the optical axis.
FIG. 6 is a cross-sectional view of the lens assembly of FIG. 5 along VI.

[Explanation of symbols]

 Reference Signs List 1 frame 2 lens assembly 3 front lens 4 rear lens 5 intermediate lens 12 flange 13 groove 14 dust deposit 21 frame 22 lens assembly 23 front lens 24 rear lens 25 intermediate lens

Claims (8)

[Claims] 1. A lens assembly for a camera comprising an optical system having a frame (1, 21) and at least one front lens (3, 23), wherein the front lens surface (3 ′,
23a) forms the front surface of the lens assembly and the full lens surface (3 ', 23a) is the frame (1, 2).
A lens having a bond angle (α) having a value of 120 ° or more with respect to 1) and wherein the front lens (3, 23) is formed of a transparent material having a hardness equal to or higher than that of tempered glass. Assembly. 2. The lens assembly according to claim 1, wherein the front lens is a convergent lens. 3. The front surface (3 ′, 3 ′) of the lens (3, 23).
Lens assembly according to claim 1 or 2, characterized in that 23a) and the frame (1, 21) form a continuous surface. 4. The lens assembly according to claim 1, wherein the transparent material is selected from sapphire and tempered glass. 5. The optical system of the lens assembly further includes a converging rear lens (4, 24) and an intermediate lens (5, 25),
These lenses are aligned with the first lens (3,23), the intermediate lens (5,25) is a divergent lens and has a lower Abbe number than the material forming the converging lens (3,4; 23,24). The lens assembly according to claim 2, wherein the lens assembly is formed of a material having the following. 6. A camera comprising a case (20) and comprising a lens assembly (22) according to any one of claims 1 to 5, fixed to a wall of the case (20). And at least a part of the case to which the lens assembly (22) is attached, and a front surface (2) of the front lens (23).
3a) is substantially spherical. 7. A camera according to claim 6, wherein the case (20) is a watch case. 8. Abrading at least the surface of the case (20) to which the lens assembly is attached with particles having a lower hardness than the material forming the front lens (3, 23) after attaching the lens assembly thereto. The method for manufacturing a camera according to claim 6, wherein: