JPS6289919A - Lens holding mechanism - Google Patents

Abstract

PURPOSE:To absorb expansion and contraction of a lens due to the variation of temperature to prevent the change of the radius of curvature of the lens by holding the lens in the surface part of an outside edge part, which is provided around the lens and has parallel faces, with a member having a low frictional resistance between them. CONSTITUTION:The lens is held through friction washers 9 and 10. Consequently, expansion and contraction of the lens based on the variation 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 coefficients of friction of friction washers are low. Thus, the change of the radius of curvature of the lens due to the variation of temperature is compensated and movement of the focus or degradation in aberrations due to the variation of temperature is prevented, and the use temperature range of the plastic lens is extended.

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, 4 is a lens camera body attachment part, and a lens fitting part 5 is formed inside this lens frame body attachment part 4 . When assembling the parts, first, for example, the convex lens 7 is fitted into the fitting part 5, and then the presser ring 1, which is screwed into the threaded part 3 formed on the inner wall of the lens frame 2, is screwed into the inner diameter part of the presser ring 1. is brought into contact with the peripheral edge of the lens 7 to hold 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 used to form the lens 7 is greater than that of the materials used to form the lens frame 2 and the presser ring 1, the volumetric expansion of the lens 7 is greater than that of the materials used to form the lens frame 2 and the holding ring 1. This exceeds the same increase in presser 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 cannot be directly attached to the lens surface. This will affect the shape. In particular, this effect is most noticeable at the peripheral edge contact portion of the lens 7 with the presser ring 1, and is also significant in plastic lenses where the hardness of the material forming the lens is relatively low. A partially enlarged configuration diagram of the abutting part (dotted chain line circle A section in Figure 1 of Base) is shown in Figure 2 of Base. 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 on the surface of the lens 70.

To explain this state in more detail, the lens 7 tends to expand in the radial direction as it becomes hotter.
As described above, the peripheral edge of the lens 7 is restricted by the retainer ring l, so that expansion in the radial direction is prevented. Also, due to this regulation, thermal stress is generated inside the lens, but in order to cancel this thermal stress, the unregulated lens expands in the optical axis direction, and as a result, the lens Although the spherical surface on the optical axis is at position P under normal temperature conditions, it expands to position P under high temperature conditions,
The radius of curvature of the lens changes from r=0 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 β at room temperature. , t' from room temperature
c When the temperature is high, ll and the coefficient of linear expansion of the lens are α, then β1#β.・It can be approximated by (1+αt).

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 of 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 changed from r-OP. r
z = Oz P z, which is the opposite of the case under the above-mentioned high-temperature condition, and the phenomenon becomes larger. In this case, the arc length of the lens is β at room temperature. , when the t'c temperature is lower than the room temperature, 12 and the coefficient of linear expansion of the lens is α, it can be approximated by 12≧10·(1−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, which have relatively weak body temperature characteristics.

Japanese Patent Application Laid-Open No. 49-64445 was invented in an attempt to solve the above-mentioned problems of the conventional system. In this invention, a member made of fluororesin and having a small coefficient of friction is interposed between the tapered surface formed on the inner diameter of the lens frame and the tapered surface formed on the outer diameter of the lens.

However, the above-mentioned fluororesin has a small coefficient of friction but is elastic, so it cannot hold the lens securely, and it must be formed into a conical shape to be interposed between the tapered surfaces, which increases costs. There was a problem.

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 in a lens frame with a holding ring, in which a member with a small coefficient of friction is provided on at least one surface of an outer edge portion having parallel surfaces integrally provided around the lens. This feature is characterized in that the influence of the radius of curvature of the lens due to temperature change is corrected by interposition.

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, which is noteworthy from the viewpoints of mass production, cost reduction, and work efficiency. .

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 portion that contacts the lens frame leg portion 4 and the lens 7 is formed into a flat sheet shape. 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 0.08 to 0.15.

Although other materials may be freely used, constituent 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 leg attachment part 4 and brought into contact with the rear friction washer 9. Then, the front friction ring 10 is further inserted into the lens frame, brought into contact with the spherical side of the lens 7, and the presser ring 1 is screwed into the threaded portion 3 formed on the inner wall of the lens frame 2. 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 contract due to the change. will be absorbed by the friction washers 9 and 10. This is because the friction coefficient of the friction washer is small as described above, so that 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, the front and rear friction washers 9,
This can be prevented by utilizing the elasticity of the plastic lens 7, and it is also possible to prevent the plastic lens 7 from wobbling due to the influence of temperature changes.

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 an outer edge portion 11 having a parallel surface is provided around the lens 7, and as is clear from FIG. 6, this parallel surface is perpendicular to the optical axis. is formed. Other than the shape of 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 are held in contact with each other so as to sandwich the parallel surfaces of the outer edge 11 formed on the lens 7, as shown in FIG. become.

By the way, in the second embodiment, by providing the outer edge part 12 on the lens 7, it is possible to control the spherical surface of the lens as in the conventional method (see FIG. 1), or as in the first embodiment (see FIG. 5a). Since there is no contact part of the lens against the spherical surface, the front friction washer 10 is interposed only between the lens 7 and the holding ring l as shown in FIG. Approximately the same effect can be obtained using both washers shown in FIG. This is clear from the experimental data described below. In addition, in Fig. 7, the front friction washer 1
0 is used as an example, but conversely, the rear friction washer 9 interposed between the lens 7 and the lens frame adjustment section 4
The results are exactly the same even if only . 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, experimental data on the radius of curvature of the lens in the second example will be listed below.

Table 1 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 As described above, in the second example, the radius of curvature of the lens hardly changes under any of the temperature conditions: room temperature, high temperature, and low temperature, and this is clear from Tables 1 to 3. be. Furthermore, even if both the rear friction washer 9 and the front friction washer 10 are used as shown in Fig. 6 (Table 1), or when either one of the friction washers is used as shown in Fig. 7 (the second Table 3) shows almost no difference in the results. Table 4 also lists actual measurements of the conventional method (see FIG. 1) described above under the same conditions. 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 according to the present invention, in which a member with a small friction coefficient used instead of the friction washer is used as a fragment member. Although the type is different, the periphery of the lens is An outer edge portion 12 similar to that of the embodiment (see FIG. 6) is formed.

In a third embodiment, the friction washer 9
and 10, the material is exactly the same and only the shape is different, - As an example, a circular sheet-like fragment member 14 is shown in a plan view including the outer edge 12 of the lens 7a, and at equal intervals in the part that does not block the light beam of the lens. It can also be pasted on (No. 8
(See FIG. 8C), or strip-shaped fragment members 13 may be attached to the outer edge 12 at equal intervals (see FIG. 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 carried out 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. In this case, the shapes of the friction washers 9 and 10 used in the second embodiment are changed to the shape of the rectangular lens 7C, and a rectangular deformed friction washer 16 is used. Show what you can do. Furthermore, FIG. 10 shows a fifth embodiment showing the most extreme case, and according to the present invention, the shape of the low-friction member interposed in the lens contact portion can be formed completely independent of the shape of the lens. It means that it is possible, and indicates 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, it is not limited to the above-described embodiments,
A sixth embodiment of the present invention, although not shown, is a method in which a friction damping agent is applied to a lens contacting portion to a predetermined thickness instead of using a sheet member such as the friction washer. Even in this case, the effects of the present invention can be enjoyed, and the present invention can be widely used, such as by double molding or inserting the friction damping part, that is, the contact part of the lens when forming the lens. (This is applicable.

Thus, according to the lens holding mechanism according to the present invention, since the lens is held by interposing a member with low frictional resistance on at least one surface portion of the outer edge portion having parallel surfaces provided around the lens, A member capable of absorbing expansion and contraction of the lens due to temperature changes and preventing changes in the radius of curvature of the lens, and having low frictional resistance at the outer edge formed by a plane parallel to the periphery of the lens. This has the advantage of relatively low cost. As mentioned above, it is possible to prevent the focus position from shifting due to changes in the radius of curvature of the lens, or from worsening various aberrations, and as a result, even for plastic lenses with relatively low temperature resistance, the temperature range in which they can be used is expanded. can be achieved.

[Brief explanation of drawings]

Fig. 1 is a side cross-sectional view including the optical axis showing an example of a conventional lens holding mechanism, Fig. 2 is a partial enlarged view of the dashed-dotted line circle A in Fig. 1, and Fig. 3 is a lens holding mechanism according to the conventional method. FIG. 4 is an explanatory diagram showing the disadvantages of the mechanism at high temperatures; FIG. 4 is an explanatory diagram showing the disadvantages 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. FIG. 8 is a side sectional view including the optical axis of a lens holding mechanism showing a second embodiment according to the present invention, and FIG. is a side sectional view including the optical axis,
9 is a perspective view of the lens when the fourth embodiment of the present invention is applied, and FIG. 10 is a perspective view of the lens when the fifth embodiment of the present invention is applied. are shown respectively. 1... Holding ring 2... Lens frame 4... Lens frame barrel attaching part 5... Fitting parts 7.7a, 7b, 1c... Lens 9... Rear friction washer 10...・Front friction washer 11.12... Outer edge portion 13 of the lens having parallel surfaces.
... (rectangular sheet-like) fragment member 14 ... (circular sheet-like) fragment member 15 ... fragment member 16 ... deformed friction washer @ 1 Figure 2 Figure 3 Figure 4 Figure 5 tXs diagram aX1 Figure 118

Claims (1)

[Claims] (1) In a lens holding mechanism that holds a lens in a lens frame with a presser ring, a barrel part formed on the inner diameter part of the lens frame, an outer edge part with a parallel surface integrally provided around the lens, and the above-mentioned A lens holder consisting of an outer edge, a presser ring that presses the outer edge against the barrel, and a friction washer with a small friction coefficient provided between the barrel and the outer edge and/or between the presser ring and the outer edge. mechanism.