JPS6289920A - Lens holding mechanism - Google Patents

Abstract

PURPOSE:To extend a use temperature range and to eliminate the play of a lens by interposing members having the low coefficient of friction in plural positions between the outside edge part of the lens and a retaining ring and/or a lens barrel part. CONSTITUTION:The lens is held through friction washers 9 and 10. Consequently, the expansion and contraction of the lens based on the variance of temperature are absorbed by friction washers 9 and 10 though the temperature is varied during the use. That is, frictional resistances between the lens 7 and the rear friction washer 9 and between the lens 7 and the front friction washer 10 are reduced because the friction coefficients of friction washers are low. Further, the reduction of loose torque of a retaining ring 1 due to the stress relaxation of plastics is prevented by using the elasticity of front and rear friction washers 9 and 10, and the play due to the influence of the variance of temperature of the plastic lens is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lens holding mechanism for an optical device such as a camera lens, and particularly to a lens holding mechanism suitable for use with a plastic lens having relatively low temperature resistance.

Generally, a lens holding mechanism for an optical system such as a camera lens is constructed as shown in FIG. To briefly explain each part, reference numeral 4 denotes a lens frame mounting part, and a lens fitting part 5 is formed inside this lens frame mounting part 4. When assembling the parts, first, for example, a convex lens 7 is fitted into the fitting part 5,
Next, by screwing in a presser ring 1 which is screwed onto a threaded portion 3 formed on the inner wall of the lens frame 2, the inner diameter portion of the presser ring 1 is brought into contact with the peripheral edge of the lens 7, thereby holding the lens.

By the way, in such a lens holding mechanism, when parts assembled at room temperature are placed under high temperature or low temperature conditions, the following disadvantages arise due to differences in linear expansion coefficients of each part. That is, since the coefficient of linear expansion of the material forming the lens 7 is larger than that of the material forming the lens frame 2 and the presser ring 1, for example, under high temperature conditions, the volumetric expansion of the lens 7 causes the lens frame 2 and the presser ring 1 to expand. This will exceed the same increase in Ring 1. On the other hand, since the lens holding mechanism is originally constructed for the purpose of fixing the lens 7, it is already assembled to the design clearance under normal temperature conditions as described above, and as a result, under high temperature conditions, it is directly attached to the lens surface. This will give a shadow to the shape. In particular, this shadow is the lens 7 for the presser ring I.
It is most noticeable in the peripheral edge abutting part of the lens, and is also noticeable in plastic lenses where the hardness of the material forming the lens is relatively low. FIG. 2 shows a partially enlarged configuration diagram of the abutting portion (dotted chain line circle A section in FIG. 1). As is clear from the figure, stress is concentrated at the contact portion 8 between the lens 7 and the presser ring 1 due to the expansion of the lens 7, resulting in a dent in the surface of the lens 7.

To explain this state in more detail, the lens 7 tends to expand in the radial direction as it becomes hotter.
As described above, since the peripheral edge of the lens 7 is restricted by the presser ring 1, expansion in the radial direction is prevented. Also, due to this regulation, thermal stress is generated inside the lens, but the unregulated lens expands in the optical axis direction to cancel this thermal stress, and as a result, as shown in Figure 3. Although the spherical surface on the optical axis of the lens was at position IP under normal temperature conditions, it expanded to position P under high temperature conditions.
The radius of curvature of the lens changes from r=OP to r,=O,P, and the radius of curvature of the lens becomes smaller. In this case, the length of the arc, which is the spherical surface of the lens, is 1° at room temperature, and t'c from room temperature.
If β is the temperature when the temperature is high and α is the linear expansion coefficient of the lens, then X can be approximated as follows.

On the other hand, even under low temperature conditions, the situation is similar to that under high temperature conditions, but the phenomenon is opposite. In other words, the coefficient of linear expansion of the material forming the lens 7 is larger than that of the material forming the lens frame 2 and the presser ring 1, so as the temperature decreases, the lens shrinks more than the lens frame 2 and the presser ring 1. The lens 7 attempts to contract, but since the peripheral edge of the lens 7 is restricted by the presser ring 1, the lens 7 cannot be reduced further than the contraction of the presser ring 1. In this case, thermal stress is generated inside the lens 7, and the lens contracts in the optical axis direction to cancel this thermal stress.

As a result, as shown in FIG. 4, the spherical surface on the optical axis of lens 7, which was at position P under normal temperature conditions, shifts to position P2 under low temperature conditions, and the radius of curvature of lens 7 is r- From 100 books, r2=○zpz, and a phenomenon that occurs is completely opposite to that under the high temperature condition. In this case, the arc length of the lens is at room temperature! . , than at room temperature.
c When the temperature is low! 2. If the coefficient of linear expansion of the lens is α, then I! 2#β.・It can be approximated by (l+αt).

In such conventional lens holding mechanisms, the radius of curvature of the lens changes due to temperature changes, and even if the parts are assembled accurately at room temperature, the focal position of the lens may shift significantly depending on the temperature at which it is used. This was a cause of worsening various aberrations. This problem is particularly severe in plastic lenses that have relatively low temperature resistance.

The present invention eliminates such disadvantages, and constitutes a lens holding mechanism with strong temperature resistance that is unaffected by temperature changes even for plastic lenses with relatively low temperature resistance, thereby expanding the operating temperature range of plastic lenses. The purpose is to Another object of the present invention is to prevent the retaining ring 1 from loosening, which occurs due to stress relaxation in the plastic lens, and to eliminate the occurrence of wobbling of the lens.

That is, the present invention provides a lens holding mechanism for holding a lens on a lens frame with a holding ring, in which the lens is provided with an outer edge, and a friction coefficient is provided at multiple locations between the outer edge and the holding ring and/or the lens frame barrel. The present invention is characterized in that a small member, such as a sheet member, is interposed to correct the effect of temperature change on the radius of curvature of the lens.

Hereinafter, various embodiments applicable to the present invention will be described with reference to the drawings.

FIG. 5 shows a lens holding mechanism according to a first embodiment of the present invention, and FIG. 5A shows a side sectional view including the optical axis, and FIG.

In the figure, the lens barrel mounting part 4, the lens frame 2, the screw part 3, the fitting part 5, the holding ring 1, and the lens 7 are formed exactly the same as in the conventional system explained in FIG. There is. This means that the lens holding mechanism according to the present invention can be applied as is to conventional general systems, and is particularly noteworthy from the viewpoints of mass production, low cost, and work efficiency. It is.

First, the rear friction washer 9 is fitted into the fitting part 5.

The shape of the rear friction washer 9 is such that it can be fitted into the fitting portion 5, and the abutting portion of the lens frame attachment portion and the lens 7 is formed in the shape of a flat sheet. Further, the material is a member having a small coefficient of friction, such as a Teflon (trade name) material, and the coefficient of friction is about μ=O, OS~0.15.

Although other materials may be freely used, synthetic resins with a friction coefficient in the range of μ above and moderate elasticity,
It is desirable to use other equally effective materials. Next, the plastic lens 7 is fitted from the plane side into the lens frame adjustment section 4 and brought into contact with the rear friction washer 9. Then, the front friction washer 10 is further inserted into the lens frame, brought into contact with the spherical side of the lens 70, and the retaining ring 1 is screwed into the threaded portion 3 formed on the inner wall of the lens frame 2, while being screwed into the lens 70. Front and rear friction washers 9 and 10 are interposed on both front and rear sides of the lens 7 to hold the lens 7. An exploded perspective view of each part in the above assembly is shown in Figure 5. However, in the lens holding mechanism assembled in this way, the lens is held with the friction washers 9 and 10 interposed, so even if there is a temperature change during use, the lens will not expand or expand due to the temperature change. The shrinkage will be absorbed by the friction washers 9 and 10. This is because the coefficient of friction of the friction washer is small as mentioned above.
This is because the frictional resistance between the lens 7 and the rear friction washer 9 and between the lens 7 and the front friction washer 10 is reduced.

Therefore, it is possible to correct changes in the radius of curvature of the lens due to temperature changes, and it is also possible to prevent focus shifts and aberrations from worsening due to temperature changes, and it is possible to expand the operating temperature range of the plastic lens.

Furthermore, both the front and rear friction washers 9 were used to reduce the loosening torque of the retainer ring 1, which was caused by stress relaxation in the plastic.
This can be prevented by utilizing the elasticity of No. 10, and it is also possible to prevent wobbling due to the influence of temperature changes of the plastic lens.

6 and 7 show a second embodiment of the present invention, and both are side sectional views including the optical axis of the lens holding mechanism. The difference from the first embodiment described above is that the lens 70 is provided with an outer edge 11 having a parallel surface, and as is clear from FIG. 6, this parallel surface is perpendicular to the optical axis. It is formed. Other than the shape of the lens 7, the first
In FIGS. 6 and 7, the same parts as those in FIG. 5 are given the same numbers, and detailed explanations thereof will be omitted since the embodiment can be implemented in exactly the same manner as in the embodiment. In the second embodiment, the rear friction washer 9 and the front friction washer 10 hold the lens 7 by abutting on the parallel surfaces of the outer edge 11 formed on the lens 7, respectively, as shown in FIG. Become.

By the way, in the second embodiment, by providing an "outer edge part 11" on the lens 7, it is possible to control the spherical surface of the lens as in the conventional method described above (see Fig. 1), or in the first embodiment (see Fig. 5a). ) is eliminated, so that the front friction washer 10 is interposed only between the lens 7 and the presser foot N1 as shown in FIG. 7, and even if the rear friction washer 9 is removed, the result as shown in FIG. 6 is eliminated. Approximately the same effect can be obtained using both washers shown in . This is clear from the experimental data described below. In addition, in FIG. 7, the front friction washer 10
Although the case where only the rear friction washer 9 is used is shown as an example, the result is exactly the same even if only the rear friction washer 9 interposed between the lens 7 and the lens barrel mounting portion 4 is used. In this way, in the second example, better results than in the first example could be obtained.

In order to clarify the effects of the present invention, actual measurement data of the radius of curvature of the lens in the second example will be listed below.

In order to clarify the effects of the present invention, experimental data on the radius of curvature of the lens in the second example is shown below.

Table 1 Table 2 Table 3 Note) The friction washer is made of Teflon (trade name) material and has a friction coefficient of μ=0.08 to 0.15 (common to Tables 1 to 3).

Table 4 (Conventional method...Figure 1) Unit: m7m
As described above, in the second example, the radius of curvature of the lens hardly changes under any of the temperature conditions of room temperature, high temperature, and low temperature, and this is clear from Tables 1 to 3. Also, even if both the rear friction washer 9 and the front friction washer IO are used as shown in Figure 6 (Table 1), or if only one friction washer is used as shown in Figure 7 (Table 1), (Table 2 or Table 3), there is almost no difference in the results. Table 4 also lists actual measurements under the same conditions for the conventional method described above (see FIG. 1). As described above, although in the conventional method, the radius of curvature of the lens changes significantly under high or low temperature conditions, in the case of the second embodiment, there is almost no change at all, and the effect of the present invention is achieved. You can understand how big it is.

The invention is further not limited to the above embodiments. Next, examples will be shown in which various shapes are used in place of the friction washer described above. FIG. 8 shows a third embodiment of the present invention, in which a member with a small friction coefficient is used as a fragment member in place of the friction washer. Although the lens 7a is different in type from the lens 7 described above, the periphery of the lens is similar to that of the second embodiment (
An outer edge portion 11 similar to that shown in FIG. 6) is formed.

In the third embodiment, the material of the friction washers 9 and 10 is exactly the same, and only the shape is different.
They can be attached at equal intervals on a plane that includes the lens and does not block the light beam of the lens (see FIG. 8C), or strip-shaped fragment members 13 can be attached at equal intervals on the outer edge 12. Good (see Figure 8C).

It should be noted that these are just examples that can be implemented without impairing the effects of the present invention even if the shapes are different, and various other shapes may be freely used. Although FIG. 8 shows only a single lens, assembly into the lens frame can be performed in exactly the same manner as in the second embodiment (FIG. 6).

Further, FIG. 9 shows a fourth embodiment according to the present invention.

The fourth embodiment shows a case where the lens is a rectangular lens 7c, and in this case, the friction washers 9 and 1 used in the second embodiment are
0 can be implemented with a rectangular deformed friction washer 16 by matching the shape of the rectangular lens 7c. Furthermore, FIG. 10 shows a fifth embodiment showing the most extreme case, and the shape of the low-friction member interposed in the lens contact portion according to the present invention can be formed completely independently of the shape of the lens. This means that even such a thing can enjoy the effects of the present invention.

The third to fifth embodiments described above are representative examples of the shape deformation of the friction washer used in the first embodiment or the second embodiment, and do not affect the assembly of the lens holding mechanism. Alternatively, various shapes can be used as long as there are no problems such as not blocking the light beam of the lens system.

On the other hand, the sixth embodiment of the present invention is not limited to the embodiments described above, and instead of the sheet member such as the friction washer described above, a lens contacting portion may be provided with a predetermined wall thickness. This method involves applying a friction damping agent. Even in this case, the effects of the present invention can be enjoyed,
Further, when molding a lens, the present invention can be widely applied, such as double molding or inserting a friction damping portion, that is, a contact portion of the lens.

Thus, according to the lens holding mechanism according to the present invention, since the lens is held by interposing members with low frictional resistance at multiple locations on the outer edge of the lens, expansion and contraction of the lens due to temperature changes can be absorbed. In addition, the radius of curvature of the lens can be prevented from changing, and even a plastic lens with relatively low temperature resistance can be used in an expanded temperature range.

Furthermore, in the present invention, by utilizing the elasticity of the member with low frictional resistance, the reduction in the loosening torque of the presser ring, which conventionally occurs due to stress relaxation due to temperature changes, vibrations, etc. of plastic, can be prevented, and the lens is held in place. It is also possible to eliminate rattling of the lens in the mechanism.

Furthermore, the present invention has the advantage that it can be directly applied to conventional lens holding mechanisms, and therefore brings many benefits from the viewpoints of mass production, cost reduction, and work efficiency. The technical effects of the invention are extremely large.

[Brief explanation of drawings]

FIG. 1 is a side sectional view including the optical axis showing an example of a conventional lens holding mechanism. FIG. 2 is a partially enlarged view of part A of the dashed-dotted line in FIG. FIG. 3 is an explanatory diagram showing the adverse effects of the conventional lens holding mechanism at high temperatures. FIG. 4 is an explanatory diagram showing the adverse effects of the conventional lens holding mechanism at low temperatures. FIG. 5a is a side sectional view including the optical axis of a lens holding mechanism showing a first embodiment of the present invention. FIG. 5 is an exploded perspective view of FIG. 5a. 6 and 7 are side sectional views including the optical axis of a lens holding mechanism showing a second embodiment of the present invention. FIG. 8 shows a lens in the case where the third embodiment of the present invention is applied, and FIG. 8a is a front view, and FIG.
Figure C is a back view. FIG. 9 is a perspective view of a lens to which the fourth embodiment of the present invention is applied. FIG. 10 shows perspective views of lenses when the fifth embodiment of the present invention is applied. 1... Holding ring 2... Lens frame 4... Lens barrel attachment part 5... Fitting part 7.7a, 7b, 7C---L/:/z 9... Rear friction Washer 10...Rear friction washer 11.12...Outer edge portion 13 of the lens with parallel surfaces
... (rectangular sheet-like) fragment member 14 ... (circular sheet-like) fragment member 15 ... fragment member 16 ... deformed friction washer Fig. 1 @ Fig. 2 Fig. 3 Fig. 4 @ 5 Fig. 6 1. , l , l ;2 Figure 7 tMS diagram

Claims (1)

[Claims] (1) In a lens holding mechanism that holds a lens in a lens frame with a holding ring, an outer edge portion having a parallel surface is provided on the outer periphery of the lens, and the outer edge of the lens and the holding ring and/or the lens frame barrel are provided. A lens holding mechanism characterized in that members having a small coefficient of friction are interposed at a plurality of locations between the attachment parts to correct the influence of the radius of curvature of the lens due to temperature changes.