JPS61270714A - Lens system having temperature compensating function - Google Patents

Abstract

PURPOSE:To compensate optical displacement due to temperature change precisely by combining two materials having different coefficients of thermal expansion and moving a lens holding position in accordance with the temperature change. CONSTITUTION:A lens 1 is held between a pair of rings 3, 4 and 3', 4' so as to be moved. Since the focal distance of the lens 1 is changed at the change of temperature, the lens position is moved front and back so that a focus is controlled so as to be formed correctly on an image formation surface 8 and tapers 5, 6, 5', 6' are fitted to the rings 3, 3', 3, 3'. At the increase of the temperature, the inner diameters of the rings 4, 4' consisting of a material having a large coefficient of expansion are expanded by the thermal expansion, the ring 4 pushes the ring 3, lens 1, and ring 3' along the tapers 5, 6 and the ring 4' accepts the forward movement of the ring 3' along the tapers 5', 6' in accordance with the expansion of the diameter. Thus, the position of the lens system is moved forward to compensate the shear of the image formation surface.

Description

[Detailed description of the invention] (Technical field) The present invention relates to a temperature compensation lens system.

(Background Art) In the past, lenses have been increasingly made of plastic from the viewpoint of improving productivity and reducing the weight of lenses.

This movement is beginning to be applied not only to eyeglass lenses but also to optical lenses.

(Problem to be solved by the invention) However, plastic has an expansion coefficient more than 10 times larger than that of glass, and its refractive index is also temperature dependent, so changes in focal length etc. due to changes in temperature are , which cannot be ignored compared to the case of glass. In particular, in a lens assembly system in which the focal lengths of individual lenses are related, the influence on resolution is significant. Therefore, in order to correct the optical displacement caused by temperature changes and perform the function correctly,
It is necessary to adjust the position of the optical elements in accordance with temperature changes.

For example, lenses made of polymethyl methacrylate (PMMA) increase in focal length as the temperature increases. The amount of change in focal length is specifically described as follows. That is, lens diameter D = 3Q mm yi, thickness d = 10
Radius of curvature of the plate and lens surface R, = R, = 39111m
, + biconvex lens. The focal length f is generally (1)
It is expressed by the formula.

The refractive index of PMMA has temperature dependence as expressed by equation (2). (Nikkan Kogyo Shimbun Series Plastic Materials Course 1z Acrylic Resin) Chi=1.4933-1.1x10-'t-2.1xlO
-'t'' (2) (1=temperature °C) Also, the PMMAO thermal expansion coefficient is approximately 7 x 10-'/d
eg, the amount of change caused by the temperature-dependent change in refractive index and the change in d%R,,R, due to thermal expansion and contraction is 0°C if the temperature changes from 0°C to 50°C.
Focal length f0 = 28J32 an is f at 50°C. = 4 - 27 ÷ because it reaches Q, it reaches 457 mm.

This situation is schematically shown in FIG. At low temperatures, the image is correctly formed on the imaging plane 8 as shown by the solid line in part A of Figure 2, but as the temperature rises, the focal length changes as shown by the two-dot chain line in part B of Figure 2. If it is too long, the image will not be formed correctly on the imaging plane 8.

As described above, unless correction is made for temperature changes, accurate imaging will not be possible. However, as shown by the solid line in part B of Figure 2, if you adjust the distance between the lens and the imaging plane by a distance corresponding to the amount of change in focal length, regardless of changes in the usage environment,
It becomes possible to obtain correct imaging.

The present invention aims to provide a lens system that easily and accurately compensates for optical displacements caused by expansion and contraction of lens materials due to temperature changes and changes in refractive index as described above.

(Structure of the Invention) The present invention is a temperature compensating lens system in which a lens holding position can be moved in response to temperature changes by combining two materials with different coefficients of thermal expansion. That is, in a set of rings 3.4 made of two materials with different coefficients of thermal expansion, a taper 5.6 is provided on the surface where the rings 3.4 contact,
At least one set of rings 3.4 in which the outer diameter of the ring 4 made of a material with a large coefficient of thermal expansion is smaller than the outer diameter of the ring 3 made of a material with a small coefficient of thermal expansion, and a taper with a similar configuration. This is a temperature compensating lens system in which a lens 1 is held between at least one pair of lenses 3', 4' or a spring 90 in opposite directions so as to be movable in response to temperature changes.

Next, the present invention will be explained based on the drawings.

FIG. 1 is a cross-sectional view showing one embodiment of the present invention.

1 is a lens, 2 is a lens barrel, 3.3' is a ring made of a material with a small coefficient of thermal expansion, 44' is made of a material with a large coefficient of thermal expansion, and ring 3.3' also has a small outer diameter. It is a ring with a diameter.

Therefore, a space 7 is formed between 4.4' and the lens barrel 2, which can accommodate changes in diameter due to expansion and contraction of 4.4'. As shown in the figure, the rings 3.3', 4.4' have tapers 5.6.5', 6' formed on their mutually contacting surfaces.

The lens 1 is movably held between a pair of rings 3.4, 3' and 4'. When the temperature changes, the focal length of the lens 1 changes, so it is necessary to move the lens position back and forth to adjust the focus so that it is properly focused on the image plane 8. In the present invention, the rings 3.3' and 4.4' are tapered by 5.6 to accommodate this movement.
．． 5' and 6' are provided. For example, when the temperature rises, the inner diameter of the ring 4.4' made of a material with a large coefficient of expansion expands due to thermal expansion, as shown in parts A and B in FIG. In this way, ring 4 pushes ring 3, lens 1 and ring 3' forward according to the taper 5.6, while ring 4' is forced forward by the taper 5', 6' due to the enlargement of its diameter.
Accordingly, the ring 3' acts to accommodate the forward movement of the ring 3'. In this way, the lens system position is moved forward by the change in focal length to compensate for the shift in the imaging plane. still,
The diagram indicated by the two-dot chain line in part B of FIG. 2 shows the shift in the focal point position when the above-described correction is not performed.

Conversely, when the temperature decreases, as shown in the change from B to K in FIG. 2, the inner diameter of the ring 4.4' decreases due to contraction. Due to this force, the ring 4' pushes back the rings 1 and 3, while the ring 4, like 4', reduces its diameter and acts to receive the pushed back ring 3.

Here, the rings 4, 3, 4' and 3' do not necessarily have to be arranged in the current arrangement, and it goes without saying that the same effect can be obtained even if their positional relationship is reversed.

Alternatively, as shown in FIG. 3, the lens 1 may be held between a pair of rings 3' and 4' by a spring 9.

The present invention is based on the movement principle as described above, and easily and precisely compensates for optical displacement in response to temperature changes.

The distance to move the lens system is taper 5.6.5',
It can be set in advance by changing the slope θ of 6'. Further, as shown in FIG. 4, the rings 3.3' and 4.4' can be arbitrarily adjusted by using two or more pairs of rings with different coefficients of thermal expansion as shown in FIG. The structure is similar to that shown in FIG.
and a ring 4.4' made of a material with a large coefficient of thermal expansion, with tapers 11, 12, 11' and 12' provided therebetween. By doing this, the moving distance of the cylinder lens 1 can be made larger than that shown in Fig. 1.
It can be used in environments with severe temperature changes or when lens materials with large temperature changes are used. If it is desired to further increase the moving distance of the lens 1, a pair of rings having different coefficients of thermal expansion may be further attached to the outside of the rings 10 and 10'.

Materials with different coefficients of thermal expansion used in the present invention can be selected from a wide range of commercially available materials. Examples of materials with a small coefficient of thermal expansion include ordinary metals, glass, ceramics, etc. In particular, the same material as that of the two lens barrels may be used. On the other hand, examples of materials having a large coefficient of thermal expansion include aftershocks, plastics, and the like. These are determined by considering workability, hardness, strength, durability, stability, weight, distance to be moved, etc.

(Example) A biconvex lens made of PMMA, lens diameter D = 3Q mm
yl, the thickness d = 10 mm, and the radius of curvature of the lens surface R, = n, = 30 mm, as described in the section (Problems to be solved by the invention), the temperature from 0 °C to 50 °C The focal length for the change is Q, 457 m
It becomes m longer. In order to correct this change in focal length, the lens system may be configured as follows.

Steel is a material with a small coefficient of thermal expansion (coefficient of linear expansion α=
1.3 x 10') Also, high-density polyethylene (linear expansion coefficient α = 12 x 10') is used as a material with a large thermal expansion coefficient.
-I') is used. Standard diameter at 0°C: If all 29 rings prepared identically are heated to 50°C, the standard diameter of the ring made of steel is 29.019 mm1 The standard diameter of the ring made of high-density polyethylene is 29.174 mm.
The relative movement in the radial direction in the taper is 0.07
It will be 8mm. As shown in Fig. 5, if we use a mechanism with six tapers so that the amount of movement is redundant, by setting the slope θ of the taper to 45°32', the taper 1
Therefore, a movement of 60.076 mm is possible, and an overall correction amount of Q is 455 mm. As a result, optical displacement due to temperature change can be corrected and more accurate imaging can be obtained.

(Effects of the Invention) As described above, the present invention has a simple structure, can reliably and precisely compensate for optical displacement due to temperature changes, and can be used without considering temperature changes occurring in the climate, region, or facility. This made it possible.

Specific applications of the temperature compensation lens system of the present invention include:
An example is a relay lens system for a zoom lens in a video camera. In such a lens assembly system as in this case, the positions of individual lenses cannot be adjusted manually, and it is impossible to correct optical displacement caused by temperature changes.

On the other hand, by using the temperature-compensating lens system of the present invention, this problem can be easily solved without using any mechanical mechanism, and as a result, the weight reduction and productivity improvement due to the use of plastic lenses has been made. This will greatly contribute to the

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, and FIG. 2 is a cross-sectional view for explaining the effects associated with temperature changes. 3, 4, and 5 are cross-sectional views showing other embodiments. 1 Lens 2 Lens barrel 3.3' Ring 4 made of material with a small coefficient of thermal expansion
．． 4' Ring made of material with a large coefficient of thermal expansion 5.
5' Taper 6.6' formed on a ring made of a material with a small coefficient of thermal expansion Taper 7 formed on a ring made of a material with a large coefficient of thermal expansion Space 8 Image plane 9 Spring 10.10' Added at both ends Ring 11.11' made of a material with a small coefficient of thermal expansion Ring 4.4' Ring 10.10'
Taper 12.12' formed on the surface in contact with Ring 10.10' Taper θ Taper slope Z3

Claims (1)

[Claims] 1. A temperature-compensating lens system in which a lens holding position can be moved in response to temperature changes by combining two materials with different coefficients of thermal expansion. 2. In a set of rings 3, 4 made of two materials with different coefficients of thermal expansion, tapers 5, 6 are provided on the surfaces where the rings 3, 4 contact, so that the outside of the ring 4 made of a material with a large coefficient of thermal expansion is at least one set of rings 3, 4 whose diameter is smaller than the outer diameter of the ring 3 made of a material with a small coefficient of thermal expansion; at least one set of rings 3' having a similar configuration but tapered in opposite directions; A temperature compensating lens system in which a lens 1 is held between 4' so that it can be moved according to temperature changes. 3. The temperature compensation lens system according to claim 2, wherein the lens 1 is sandwiched between at least one set of rings 3, 4 made of two materials having different coefficients of thermal expansion and a spring 9.