JPS61149922A - Optical system - Google Patents

Abstract

PURPOSE:To maintain optical conjugation between the exit pupil of the 1st optical system and the exit pupil of the 2nd optical system by providing a field lens formed by using an optical system which includes a variable refracting power element and adjusting the refracting power of the variable refracting power element. CONSTITUTION:The pressure ring 14 of the field lens 3 is screwed in a lens barrel 9 to press the 1st elastic body 11 through the 2nd elastic material layer 12, and consequently the center part of the 2nd elastic material layer is projected upward. The 2nd elastic material layer 12 functions to hold the surface of the center part of the 1st elastic body 11 almost spherically by its tension. Thus, the refracting power of the 1st elastic body 11 is varied. This refracting power is set to a desired value by adjusting the extent of the threadable engagement of the pressure ring 14. Consequently, the exit pupil B1 of the 1st optical system 1 and the exit pupil A2 of the 2nd optical system 2 become optical conjugate to each other and an image which does not get dark at its peripheral part is obtained on the image formation surface C2 of the whole optical system.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an optical system using a field lens.

[Conventional technology]

A field lens is used to effectively cause the light flux that has passed through the first optical system to enter the second optical system. That is, the field lens is arranged near the image formation plane of the first optical system, and the exit pupil of the first optical system and the entrance pupil of the second optical system are made optically conjugate. It has the function of making the light flux emitted from the second optical system enter the entrance pupil of the second optical system, and a lens or a reflecting mirror is used. Thus, the field lens has the effect of simply changing the direction of the light beam, and has little effect on the imaging relationship of the entire optical system.

An optical system using such a field lens can achieve a desired level of I
It is used in many optical devices because it is possible to arrange an fK imaging plane. However, in recent years, in optical systems using field lenses, it has become possible to zoom by replacing the first or second optical system with another optical system, or by moving the first or second optical system or a part thereof. Lens systems are becoming more and more frequently used.

[Problem that the invention seeks to solve]

However, when the first or second optical system has different characteristics as described above, the exit pupil position or entrance pupil position generally changes, so the exit pupil of the first optical system and the second optical system are different. The conjugate relationship with the entrance pupil of the optical system is lost, and a part of the light flux that has passed through the first optical system cannot pass through the second optical system, and is shadowed around the image plane by the entire optical system. occurs.

In order to prevent such problems from occurring, it is recommended to configure the entire interchangeable lens system or zoom lens system so that the exit pupil position of the first optical system and the entrance pupil position of the second optical system are always in the same position. Although this is conceivable, when using a lens system over a wide focal length range such as an optical system for a camera, this becomes a significant design constraint and makes it difficult to obtain good imaging performance.

[Means for solving problems]

According to the present invention, in order to solve the problems of the prior art as described above, there is provided an optical system characterized by using an optical system including a variable refractive power element as a field lens.

[Effect]

In the optical system of the present invention, it is possible to maintain optical conjugation between the exit pupil of the first optical system and the entrance pupil of the second optical system by adjusting the refractive power of the variable refractive power element of the field lens. can.

〔Example〕

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

FIGS. 1(1-) and 1) are schematic optical diagrams for explaining the principle of the optical system of the present invention.

In FIG. 1 (-), 1 is the first optical system, and AI
+81 is divided by the entrance pupil and exit pupil, respectively.

2 is a second optical system, and A2+82 are its entrance pupil and exit pupil, respectively. Reference numeral 3 denotes a field lens arranged in the vicinity of the imaging plane (ie, the primary imaging plane) C1 of the first optical system 1. The first optical system 1, the second optical system 2, and the field lens 3 are arranged coaxially. C2 is the imaging plane of the second optical system 2 (that is, the imaging plane of the entire optical system). The field lens 3 consists of a variable refractive power element, and in FIG. 1 (&), the exit @ B t of the first optical system
The second optical system 20 is placed at a distance a from the entrance pupil A, and a distance b from the entrance pupil A of the second optical system 20. In this case,
The refractive power ψ of the field lens 3 is adjusted to satisfy the relationship ψ=-11b. In this way, the exit tii B 1 of the first optical system and the entrance pupil A2 of the second optical system 2 become optically conjugate, and all the light beams exiting the first optical system enter the second optical system 2. The light enters the entrance pupil A2, and a good image with no peripheral shadows can be obtained on the imaging plane C of the entire optical system.

FIG. 1(b) shows the first optical system 1 in FIG. 1(&).
FIG. 3 is a diagram showing a case where Ike's first optical system 1' is used instead. In FIG. 1(b), AI'tB4' are the entrance pupil and exit pupil of the first optical system 1', respectively. Figure 1(b)
In this case, the field lens 3 is placed at a distance a/ from the exit pupil B,/ of the first optical system 1'. Therefore, in this case, the refractive power ψ of the field lens 3 is adjusted so as to satisfy the relationship ψ=+;. Thus, in this case as well, all the light beams emitted from the first optical system 1' enter the entrance pupil A2 of the second optical system 2, and the image forming plane C of the entire optical system is
2, a good image with no peripheral shadows can be obtained.

FIG. 2 is an optical diagram showing an embodiment in which the optical system of the present invention is applied to a finder optical system of a single-lens reflex camera.

In FIG. 2, 4 is a photographing lens system, and the lens system 4
Is it a camera? It can be attached to and detached from the device (not shown). 5
is a quick return mirror, which moves to the position indicated by the dotted line only when shooting. C4 is the image forming surface of the photographing lens system 4, 6 is a field lens arranged near the image forming surface C4, 7 is an R tag, and 8 is an eyepiece lens system.

As explained with reference to FIG. 1, the field lens 6 is for making the exit pupil of the photographic lens system 4 and the entrance pupil of the eyepiece lens system 8 conjugate, and by replacing the photographic lens system 4, the photographic lens system can be changed. Even when the position of the exit pupil of the eyepiece system 8 changes, the refractive power can be adjusted to always maintain the exit pupil conjugate with the entrance pupil of the eyepiece system 8.

FIG. 3 is a schematic cross-sectional view showing the specific structure of the field lens 6. As shown in FIG.

In FIG. 3, 9 is a lens barrel, and 10 is a glass convex lens fixed to the lens barrel 9. In FIG. Reference numeral 11 denotes a first elastic body constituting the variable refractive power element, and is made of, for example, glue-shaped silicone rubber. Reference numeral 12 denotes a second elastic layer constituting the variable refractive power element.

The elastic layer 12 has a higher elastic modulus than the first elastic body 11 and is made of, for example, dull silicone rubber or a polyester film with a higher crosslink density than the elastic body 11. 1
Reference numeral 3 designates an aperture plate having a circular opening and is movable in the vertical direction along the lens barrel 9 without contacting the periphery of the second elastic layer 12; 14 is formed on the outer peripheral surface of the lens barrel 9; It is a holding ring which is fitted from above to the lens barrel 9, and has a female thread corresponding to a male thread in the holding ring 14, and the aperture plate 13 is pressed from above by the lower end of the inner part of the lens barrel 9 of the holding ring 14. It is now possible to do so.

Thus, as shown in FIG. 3(b), by screwing the presser ring 14 into the lens barrel 9, pressure is applied to the first elastic body 11 via the second elastic body layer 12, and thereby the second elastic body 11 is pressed. The central portion of the elastic layer (i.e., the portion not in contact with the aperture plate 13)
to protrude upward. The second elastic body layer 12 has a function of keeping the surface of the central portion of the first elastic body 11 in a shape close to a spherical surface due to its tension. Thus, the first elastic body 1
The refractive power of 1 can be changed. The refractive power of the first elastic body 11 can be set to a desired value by adjusting the screwing amount of the presser ring 14.

In this embodiment, each time the camera user replaces the photographic lens 4, the camera user observes the image in the finder and adjusts the screwing amount of the presser ring 14 until no shading occurs at the periphery of the image. The objective is achieved by changing the refractive power of the lens.

Normally, in the finder optical system of an eye reflex camera, a diffuser plate is placed as a focusing plate at the position of the imaging plane C4 of the photographic lens 4, so even if the photographic lens system 4 is replaced, the periphery of the field of view of the eyepiece lens 8 is obscured. does not occur often. However, using a diffuser plate reduces the overall light intensity, so when photographing at low illuminance, it is necessary to use a diffuser plate with low diffusivity or a transparent focusing plate, and in this case, shadows around the periphery of the field of view become a problem. Therefore, by adopting the configuration as in the above-described embodiment of the present invention, it is possible to significantly reduce the shadowing at the periphery of the viewfinder field of view when changing the photographing lens.

FIG. 4 is an optical diagram showing an embodiment in which the optical system of the present invention is applied to an optical system of a focus detection device.

In FIG. 4, Cs is the expected imaging plane of the photographing lens system, which is not shown. Reference numeral 15 denotes a field lens with variable refractive power arranged near the imaging surface CS. The field lens 15 and a photographic lens (not shown) are arranged coaxially. Two imaging lenses 16 and 16' are arranged vertically symmetrically across the optical axis X. The optical axes of the imaging lenses 16 and 16' are both parallel to the optical axis X of the field lens 15. 17,
Reference numeral 17' denotes a light receiving means consisting of a plurality of light receiving elements arranged in a line in the vertical direction on the image forming plane of the imaging lenses 16 and 16', respectively.

The principle of focus detection using such an optical system is described in Japanese Patent Application Laid-Open No. 58-8
This has already been disclosed in Japanese Patent Application No. 8709, and to briefly explain it here, when the image formed by the photographing lens system is on the planned imaging plane CII, the same output is obtained from the corresponding light receiving elements in the light receiving means 17 and 17'. If the light receiving means 17 and 17' are arranged symmetrically with respect to the optical axis At the position 10,000, the position shifts upward, while at the other position it shifts downward, so the light receiving means 17 and 17' cannot obtain the same output from the corresponding light receiving elements, and by comparing their outputs, The amount of shift is determined, and from this the focus of the photographic lens system is detected.

In this focus detection device, when the photographing lens system is replaced, the exit pupil position generally shifts, so if the refractive power of the field lens 15 remains unchanged, the imaging lens 16,
The light beam incident on the light receiving section 16' is eclipsed, and the output of the light receiving means 17 or the light receiving element in the peripheral portion of the light receiving means 17' is greatly reduced, making it impossible to accurately detect the focus.

In this implementation device, the field lens 15 has variable refractive power, so when the taking lens system is replaced, the exit pupil of the taking lens system and the entrance pupil of the imaging lens 16, 16' become conjugate. The refractive power of the field lens 15 can be adjusted to
' There is no vignetting of the light beam incident on the lens, and accurate focus detection becomes possible.

FIG. 5 is a schematic diagram showing a specific structure of the field lens 15 and its refractive power adjusting means.

In FIG. 5, 9 is a lens barrel, 10 is a glass lens, 11 is a first elastic body, and 12 is a second elastic layer. These are the same members as in the field lens shown in FIG. Reference numeral 13' designates an aperture plate whose one end is in contact with the periphery of the second elastic layer 120, and the other end is formed with a flange-shaped portion projecting outward.

- In addition, the lens barrel 9 is also formed with a flange-like portion that projects outward. Both ends of the piezoelectric bimorph element 180 are fixed between these two flange-like parts.

In FIG. 5, R is a resistance provided within the lens barrel of the photographic lens system. This resistor R has a shape corresponding to the exit pupil position of the photographic lens system. Further, 19 is a power supply that generates a reference voltage, 20 is an operational amplifier, and 'R1
w R snow is resistance. Further, 21 and 21' are electrical contacts that are connected when mechanically connecting the lens barrel of the photographing lens system and the main body of the apparatus.

22 is a high voltage generation circuit.

Thus, by applying a control voltage corresponding to the value of the resistor R17) to the high voltage generating circuit 22, a high voltage directly corresponding to the resistor R can be applied to the piezoelectric bimorph element 18. By controlling the degree of expansion and contraction of the aperture plate 13' and moving the aperture plate 13', the refractive power of the field lens 15 can be set to a predetermined value in the same manner as in FIG.

In the optical system of this embodiment, the pupil position information for setting the refractive power of the variable refractive power element of the field lens 15 is held in the photographic lens system as a resistance R within the lens barrel of the photographic lens system. By attaching the photographing lens system to the main body of the apparatus, the refractive power of the variable refractive power element is automatically adjusted.

In the above embodiments, the variable refractive power element of the field 9 lens was exemplified using deformation due to pressure of an elastic body, but the variable refractive power element in the optical system of the present invention is not limited to this. , for example, the special public service of 1983
An appropriate element can be used, such as the one disclosed in Japanese Patent No. 19324, that is, the one that utilizes a change in the refractive index of liquid crystal.

〔Effect of the invention〕

According to the optical system of the present invention as described above, it is possible to realize a field lens with variable refractive power using a relatively thin lens system, thereby changing the characteristics of the first optical system and/or the second optical system. Even in this case, the exit pupil of the first optical system can be maintained conjugate with the entrance pupil of the second optical system without affecting the imaging performance of the entire optical system. Further, the variable refractive power element of the field lens used in the optical system of the present invention can be configured in a curved manner and does not move in the optical axis direction, so it has the advantage that high precision is not required.

[Brief explanation of drawings]

FIGS. 10 and 1(b) are optical diagrams showing the principle of the optical system of the present invention. FIG. 2 and FIG. 4 are both optical diagrams showing an embodiment of the optical system of the present invention. FIGS. 3(a) and 3(b) are cross-sectional views of the field lens. FIG. 5 is a block diagram of a field lens and its refractive power adjusting means. 1.2 Two optical systems, 3, 6, 15: Field lens, 4
: photography lens system, s: i-eye lens system, 10: is 2-lens lens, 11: elastic body, 12: elastic body/L16: imaging lens, 18: pymorph element. Agent Patent Attorney Seki Yamashita Children Figure 1 (0) Figure 1 (b) Figure 3 Figure 4 16゛ Figure 5 F? 1

Claims (2)

[Claims] (1) An optical system having a configuration of a first optical system, a field lens, and a second optical system from the light flux incident side, characterized in that an optical system including a variable refractive power element is used as the field lens, Optical system. (2) Exit pupil position information of the first optical system and/or
Based on the entrance pupil position information of the optical system, the refractive power of the variable refractive power element of the field lens is adjusted so that the exit pupil of the first optical system is imaged near the entrance pupil of the second optical system. The optical system according to claim 1, having means for.