JPH0332044B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a plastic lens holding device, and more particularly to a plastic lens holding device that absorbs deformation of the lens due to changes in ambient temperature using an elastic member made of a material slightly softer than the hardness of the lens. It is. First, a method of holding a conventional general lens using a barrel portion formed on a lens holding cylinder and a holding ring for holding the lens will be described. FIG. 1A is a longitudinal sectional view showing an example of a conventional method of holding a lens in a holding tube. The method of holding the lens 2 in the holding tube 1 is to abut the lens 2 against the corner part 3a of the barreled part 3 that is integrally machined with the holding tube, and then insert a retaining ring 4 with a thread turned around the circumference, also on the inside side. A partially threaded portion 5 is screwed into a turned holding cylinder 1 and held by being pressed against a corner portion 3a. The holding ring 4 is screwed together with the holding cylinder 1 through a threaded portion 5, and is held in the holding cylinder 1 while being press-fitted to the lens 2. In addition, the body part 3
is provided with a fitting part 6, the inner diameter of which is made slightly larger than the outer diameter of the lens 2. However, the difference between the inner diameter of this fitting part 6 and the outer diameter of the lens 2 is
The amount of rattling is extremely small so that this rattling does not affect the lens performance since it causes rattling when it is assembled into the barreled portion 3 of the holding tube 1. Now, if the material of this lens 2 is glass, even if the lens system shown in FIG. Since the coefficient is small, the inner diameter of the holding tube 1 is larger than the outer diameter of the lens 2, and a phenomenon in which the holding tube 1 tightens the lens 2 does not occur. However, if the material forming the lens 2 is plastic, the expansion of the lens 2 is much larger than the expansion of the holding tube 1, so if the lens system shown in Figure 1A is held in a high temperature state, the lens The outer diameter of the holding cylinder 1 is larger than the inner diameter of the barreled part 3 of the holding cylinder 1.

[Table] FIG. 1B is a diagram showing the relative displacement of the inner and outer diameters of the holding cylinder 1 and the lens 2 depending on the above-mentioned temperatures. 1st
In FIG. B, the solid line shows the normal temperature state, the dashed line shows the free expansion state of the lens 2 and the holding cylinder 1, and the dotted line shows the balanced expansion state of the lens 2 and the holding cylinder 1. That is, looking at Figure 1B, the outer diameter of the lens at room temperature is
D ₁ and the barreled inner diameter D _K become as the temperature increases.
If there are no restrictions, lens 2 will expand to its outer diameter.
D′ _L , and the inner diameter of the barreled portion 3 is D′ _K. However, in reality, even if the lens 2 in Fig. 1A tries to expand, it is held down by the barreled portion 3, and as shown in Fig. 1B, the outer diameter D _L of the lens 2 is the outer diameter D' _L of the free expansion lens. The lens 2 on the inside tries _to expand even if the barreled part 3 expands in FIG. As shown in Figure B, the inner diameter D _K of the barreled part 3
has an inner diameter D'' _K that is even larger than the inner diameter D' _K. Therefore, if the lens 2 and holding tube 1 shown in Fig. 1A are placed in a high temperature state, compressive stress will be applied to the lens and to the holding cylinder as shown in Fig. 1B. A tensile stress is generated, and the mutual tension is balanced, resulting in the lens outer diameter D″ _L and the holding cylinder outer diameter D″ _K.And ,
This stress causes the thinnest part of the plastic lens, that is, the outer periphery of the positive lens 2, to
If it is a negative lens, surface distortion such as fine wrinkles or undulations will occur on the lens surface in the center, and the radius of curvature will change significantly, resulting in large changes in aberration characteristics and changes in imaging characteristics. . Lenses are generally designed to provide the best overall optical performance, so if surface distortion occurs or the radius of curvature changes as described above, the overall optical performance of the lens usually deteriorates. In particular, spherical aberration and coma aberration often worsen. When both ends are fixed, if compressive stress is generated, buckling may occur in a negative lens with a thin center thickness. In addition, these influences may cause the optical axis of the lens system to deviate from the central axis of the holding cylinder, decenter or tilt the lens, or change the distance between the lenses, leading to a risk of deterioration of lens performance. These things have been one of the major drawbacks of using plastic lenses. The present invention eliminates the above-mentioned drawbacks and eliminates the optical disturbance caused by the difference in coefficient of linear expansion between the lens and the holding tube made of different materials, especially the deformation that occurs in the lens at high temperatures, when using a plastic lens.
An elastic member is provided between the plastic lens and the holding member to absorb dimensional changes due to temperature changes between the lens and the barrel, which removes the material and prevents deformation of the lens surface, which greatly affects lens performance. It is an object of the present invention to provide a holding device that can suppress as much as possible. The present invention provides a plastic lens having a lens surface that has different effects on the optical performance of the lens system due to changes in surface distortion and curvature when deformed due to temperature changes. In a holding device that holds a plastic lens with a holding cylinder made of a material with a high expansion coefficient, it is formed protruding from the inner wall surface of the lens holding cylinder that holds a plastic lens, and when deformed, the lens system is affected by surface distortion and changes in curvature. A barreled part having a corner part that comes into contact with the lens surface that has a large effect on the optical performance of the lens, a holding member that holds the lens, and a change in surface distortion and curvature when the holding member is deformed. and a ring-shaped elastic member formed of a material slightly softer than the hardness of the lens, interposed between the lens surface and the lens surface that has a small effect on the optical performance of the lens system, and the inner edge of the elastic member This feature is characterized in that the deformation of the lens due to expansion or contraction of the lens is absorbed and held by pressing the lens. Hereinafter, the present invention will be explained in detail with reference to the drawings. FIG. 2 is a longitudinal sectional view showing the structure of an embodiment of the holding device according to the present invention. The lens holding cylinder 11 projects from its inner wall surface to integrally form a barreled part 12, and one lens surface _r2 of a biconvex plastic lens 13 is brought into contact with a corner part 23 of this barreled part. The other lens surface r ₁ of the plastic lens 13
In this case, the inner edge of a ring-shaped elastic member 24, which is slightly softer than the hardness of the plastic lens, is brought into contact with the inner edge of the elastic member 24, and a presser ring 15 is placed on the outside of this elastic member. A threaded portion is formed on the outer circumferential surface of this presser ring 15 and screwed into a threaded portion 16 formed on the inner circumferential surface of the holding cylinder 11. Therefore, by screwing in the presser ring 15, the plastic lens 13 can be held in pressure contact with the corner portion 23 of the barreled portion 12 via the elastic member 24. At this time, since each of the lens surfaces of the plastic lens 13 is convex, the corner portion 23 of the barreled portion 12 and the inner edge of the annular elastic member 24 that are in contact with the lens surface act as a so-called bellchuck, that is, a lens holding cylinder. It acts in the direction of aligning the optical axis of the lens with the central axis of lens 11. In particular, since the elastic member 24 performs the above-mentioned function rather than the rigid retaining ring 15, the contact surface with the lens surface can be large, which is convenient. In a lens system having a plastic lens 13, even if the surface distortion and curvature of the lens surface _r1 of the lens 13 change due to deformation, this will have little effect on the optical performance of the lens system, but the lens surface _r2 will have a small effect on the optical performance of the lens system. Assuming that changes in bending distortion and curvature due to deformation have a strong influence on the optical performance of the lens system, the lens surface _r1 , which has a small influence on the lens system, allows some deformation and improves the optical performance of the lens system. Lens surface r ₂ has a strong influence on
Try not to deform it as much as possible. For this purpose, the lens surface _r2 of the plastic lens 13, which has a large influence on the optical performance due to changes in distortion and curvature due to deformation, is pressed against the corner portion 23 of the barreled portion 12, thereby reducing surface distortion and curvature due to deformation. Elastic member ₂
4 with a presser ring 15. In general, a lens surface with a small radius of curvature has a larger change in refractive power between the vicinity of the central axis and the periphery of the lens, and also has a larger rate of change in the radius of curvature when deformed, resulting in spherical aberration and coma aberration. This surface is pressed against the corner portion 23 because it is likely to be affected. With this structure, when the plastic lens 13 is deformed, the elastic member 24 first absorbs the deformation of the plastic lens, thereby preventing large stress from acting on the plastic lens. Furthermore, if the plastic lens 13 deforms significantly, the elastic member 24 cannot sufficiently absorb this deformation, and the plastic lens receives stress, but the lens surface _r1 , which has a small effect on lens performance, deforms. , the deformation of the lens surface _r2 , which greatly affects lens performance, is prevented. Therefore, overall deterioration of lens performance can be suppressed as much as possible. Further, since the position of the lens surface _r2 is regulated by the corner portion 23 of the barreled portion 12 and does not change in the optical axis direction, there is also the effect that an air distance between adjacent lenses can be ensured. Note that the present invention is not limited to the above-described embodiments, and various changes can be made within the scope of the claims. As described above in the examples, the effects of the present invention can be summarized as follows. (b) By providing an elastic member that is made of a highly elastic material and absorbs deformation between the lens and the holding member, deformation occurs in the vicinity of the minimum thickness of the lens, which is different from that before deformation. The lens used to have 2 to 3 Newton rings, but as a result of deformation, there were 10 or more Newton rings, or it deformed to the extent that it did not form a ring shape, whereas according to the present invention, before deformation I was able to keep two or three of the Newton rings on the lens. In particular, the Newton ring on the lens surface that comes into contact with the barreled part was able to be maintained at the same level as before deformation. (b) The lens surface, which has a large effect on the optical performance of the lens system due to changes in surface distortion and curvature caused by deformation, is brought into contact with the barreled part, and the lens surface, which is less affected by changes in surface distortion and curvature caused by deformation, is brought into contact with the barreled part. Because it is configured to be pressed by a presser member through an elastic member,
Even if the lens surface, which has a small effect on optical performance when deformed, deforms, the deformation of the lens surface, which has a large effect on optical performance when deformed, can be suppressed as much as possible, reducing the overall deterioration of optical performance. be able to. (c) Since the position of the lens surface, which has a large effect on optical performance, is regulated by the barreled part, fluctuations in the air distance between adjacent lenses can be suppressed.
Deterioration of the optical performance of the lens system as a whole can be suppressed.

[Brief explanation of drawings]

Figure 1A is a vertical cross-sectional view showing a conventional method of holding a lens in a holding tube, and Figure 1B is a diagram showing the relative displacement of the inner and outer diameters of the holding tube and lens due to temperature in Figure 1A. , FIG. 2 is a longitudinal sectional view of an embodiment of the holding device of the present invention. 11... Lens holding tube, 12... Trunked part, 1
3... Biconvex plastic lens, 15... Presser ring, 16... Threaded portion, 24... Annular elastic member,
r ₁ , r ₂ ... lens surface.

Claims (1)

[Claims] 1 A plastic lens has a lens surface that has different effects on the optical performance of the lens system due to changes in surface distortion and curvature when deformed due to temperature changes.
In a holding device that holds a plastic lens with a holding cylinder made of a material whose coefficient of linear expansion is smaller than that of the lens, a surface formed protruding from the inner wall surface of the lens holding cylinder that holds the plastic lens, and which is formed when the plastic lens is deformed. A barreled part having a corner part that comes into contact with a lens surface that has a large effect on the optical performance of the lens system due to changes in distortion and curvature, a holding member that holds down the lens, and a case where the holding member is deformed. and a ring-shaped elastic member formed of a material slightly softer than the hardness of the lens, interposed between the lens surface and the lens surface whose surface distortion and curvature changes have little effect on the optical performance of the lens system. A holding device for a plastic lens, characterized in that the inner edge of the elastic member presses the lens to absorb and hold the lens deformation due to expansion or contraction of the lens.