JP2007328160A - Eyepiece optical system and viewfinder optical system having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eyepiece optical system capable of observing a large finder image with a simple lens configuration, maintaining a high optical performance while maintaining a high optical performance, and ensuring a sufficiently long eye relief, and a finder optical system having the eyepiece optical system To get.
An image inverting unit that reverses an image formed by an objective lens into an erect image and an eyepiece unit that enlarges and displays an image that has become an erect image by the image inverting unit. The eyepiece unit is an image inverting unit. The negative first lens, the positive second lens, and the observation side are concave and meniscus-shaped positive or negative third lens in order, and the second lens moves along the optical axis direction of the eyepiece lens portion for viewing. A diopter adjustment function for adjusting the degree of diopter, where 1.31 <| f1 / dp | <2.10 where the focal length of the first lens is f1 and the air conversion optical path length of the image inverting means is dp. Satisfy the following conditions.
[Selection] Figure 1

Description

  The present invention relates to an eyepiece optical system and a finder optical system having the eyepiece optical system, and is suitable for an imaging apparatus such as a digital single-lens reflex camera or a video camera.

  Conventionally, in a finder optical system of a single-lens reflex camera, a subject image by a photographing lens is formed on a focusing screen. The subject image formed on the focusing screen is converted into an erect image through an image inverting means such as a pentaprism, and then enlarged and displayed by an eyepiece so that the observer can observe it.

  An eyepiece used in such a finder optical system is required to have a high observation magnification and a sufficient eye relief, a diopter adjustment function, and high optical performance.

  In general, in such a finder optical system, the observation magnification is obtained by the ratio of the focal length of the objective lens and the eyepiece. For this reason, in order to increase the observation magnification, it is necessary to shorten the focal length of the eyepiece.

  However, in a finder optical system of a single-lens reflex camera, it is generally necessary to set the diopter near -1 diopter. Therefore, the substantial focal length of the eyepiece is determined by the distance from the focusing screen on which the object image is formed to the eyepiece (the optical path length to the main point position of the eyepiece).

  Therefore, in order to increase the observation magnification of the finder optical system most simply in a single-lens reflex camera, the optical path length of the pentaprism may be shortened, and the eyepiece may be disposed close to the pentaprism.

  However, with such a configuration, the observation unit (eye point) of the finder optical system moves to the object side from the rear surface of the camera, making it difficult for the observer to bring the pupil close to the eyepiece.

  Therefore, a finder optical system is known in which the observation magnification is increased by arranging the eyepiece lens close to the main point instead of arranging the eyepiece lens close to the pentaprism.

In this finder optical system, there is known a finder optical system in which an eyepiece is composed of a negative lens, a positive lens, and a meniscus negative lens having a concave eyepoint side in order from the focusing screen side where an object image is formed (Patent Document 1, 2).
JP 2001-324684 A JP 2000-98266 A

  In recent digital single-lens reflex cameras, an imaging means having a size similar to a so-called APS-C size having a smaller image circle than a so-called 35 mm silver salt film is used as a sensor.

  The viewfinder image observed by the viewfinder optical system is configured to be the same as or substantially the same as the object image formed on the imaging means surface. For this reason, the viewfinder image observed through the viewfinder optical system of the digital single-lens reflex camera becomes smaller than the viewfinder image observed with the conventional silver salt camera. By applying the above-described conventional finder optical system to a digital single-lens reflex camera similar to the APS-C size, the observation magnification (finder magnification) can be increased to about 0.9 times.

  However, the size of the viewfinder image observed with a digital single-lens reflex camera is not sufficient when the observation magnification is about 0.9.

  In order to increase the observation magnification, the method of increasing the number of constituent lenses of the eyepiece and shortening the focal length of the eyepiece is not good because the lens configuration becomes complicated.

  Further, in the finder optical system of a single-lens reflex camera, in order to make the eye relief sufficiently long, it is necessary to configure the pentaprism to be sufficiently large so as to minimize the scattering of light by the pentaprism.

  Here, the eye relief is the distance from the exit surface of the eyepiece to the observer's pupil (eye point).

  However, in that case, the optical path length from the focusing screen to the eyepiece lens is inevitably increased, and the focal length of the eyepiece lens is accordingly increased, and the observation magnification of the finder is decreased.

  Therefore, in order to make the eye relief sufficiently long while increasing the observation magnification of the finder, the position of the entrance pupil of the eyepiece is made as close as possible to the focusing screen, and the light beam is reduced without increasing the optical path length of the pentaprism. It becomes important to do.

  In the finder system of a single lens reflex camera, the observation magnification of the finder is determined appropriately by setting the optical path length of the pentaprism through which the light beam from the object image formed on the focusing screen passes and the configuration of the eyepiece that displays the object image. It is important to increase the size and obtain a long eye relief.

  In order to observe the finder image well, it is necessary to adjust the diopter with an eyepiece. At this time, it is important that diopter adjustment can be easily performed when a part of the lenses in the eyepiece is moved.

  An object of the present invention is to provide an eyepiece optical system capable of observing a large finder image while maintaining high optical performance, having a large observation magnification, and ensuring a sufficiently long eye relief, and a finder optical system having the eyepiece optical system. .

The eyepiece optical system of the present invention is
In an eyepiece optical system having an image inverting means for inverting an image formed by an objective lens into an erect image, and an eyepiece lens section for enlarging and displaying an image that has become an erect image by the image inverting means.
The eyepiece unit includes, in order from the image inverting means, a first lens having a negative refractive power, a second lens having a positive refractive power, and a third lens having a meniscus positive or negative refractive power having a concave surface on the observation side. The second lens has a diopter adjustment function for adjusting diopter by moving along the optical axis direction of the eyepiece lens unit. The focal length of the first lens is f1, and the image inverting means When the air equivalent optical path length is dp,
1.33 <| f1 / dp | <2.10
It is characterized by satisfying the following conditions.

  According to the present invention, it is possible to obtain an eyepiece optical system that has a simple lens configuration, has a high observation magnification while maintaining a high optical performance, can observe a large finder image, and can secure an eye relief sufficiently long.

  FIG. 1 is a cross-sectional view of an essential part of Embodiment 1 when the eyepiece optical system of the present invention is applied to a finder optical system of a single-lens reflex camera (imaging device). 2 and 3 are an optical path diagram and an aberration diagram in which the optical path of the optical element of Numerical Example 1 of the eyepiece optical system of the present invention is developed. 4 and 5 are an optical path diagram and an aberration diagram in which the optical path of the optical element of Numerical Example 2 of the eyepiece optical system of the present invention is developed. 6 and 7 are an optical path diagram and an aberration diagram in which the optical path of the optical element of Numerical Example 3 of the eyepiece optical system of the present invention is developed. 8 and 9 are an optical path diagram and an aberration diagram in which the optical path of the optical element of Numerical Example 4 of the eyepiece optical system according to the present invention is developed. 10 and 11 are an optical path diagram and an aberration diagram in which the optical path of the optical element of Numerical Example 5 of the eyepiece optical system of the present invention is developed.

  In the optical path diagram and the aberration diagram, the viewfinder diopter is -1 diopter (standard diopter). In the optical path diagram, the left side where the image inverting means 5 is located is the object side (light incident side), and the right side of the eye point 7 side is the observation side (light emission side).

  In FIG. 1, reference numeral 1 denotes a lens system that can be fixed to or detached from a camera body (not shown). Reference numeral 2 denotes a quick return mirror which can be rotated around a rotation shaft 2a. Reference numeral 3 denotes a focusing screen (Fresnel lens). Reference numeral 4 denotes a focusing screen (matte surface) on which an object image is formed by the lens system 1. Reference numeral 5 denotes a pentaprism as an erect image forming member (image inverting means), and an object image formed on the focusing screen 4 is an erect image. Reference numeral 6 denotes an eyepiece lens unit constituting one element of the eyepiece optical system. Each member from the lens system 1 to the eyepiece 6 constitutes a finder optical system. Reference numeral 7 denotes the position of the eye point. IP is an image plane of the lens system 1 and corresponds to an imaging surface of a solid-state imaging device (imaging means) such as a CCD sensor or a CMOS sensor or a photosensitive surface such as a film (imaging means).

  EP is an eyepiece optical system, and has an image inverting means 5 and an eyepiece lens section 6.

  In the aberration diagrams, H is the height of the entrance pupil and Y is the maximum image height.

  When the optical system shown in FIG. 1 is handled as a finder optical system, the lens system 1 corresponds to an objective lens for forming an object image on the focusing screen 4 (hereinafter, when handled as a finder optical system, the lens system 1 is an objective lens). Referred to as lens 1).

  When handled as an imaging device, the lens system 1 corresponds to a photographing lens for forming an object image on the image plane IP (hereinafter, when handled as an imaging device, the lens system 1 is referred to as a photographing lens 1).

  When an image is formed on the image pickup means, the quick return mirror 2 is rotated as shown by an arrow so that the light beam from the photographing lens 1 enters the image plane IP. Then, an image corresponding to the object image formed on the focusing screen 4 (an image of a part or all of the object image or an image larger than the object image) is photoelectrically converted (received) by the imaging means arranged on the image plane IP. .

  In the finder optical system in this embodiment, the object image is reflected by the quick return mirror 2 by the objective lens 1 and formed on the focusing screen 4. The viewfinder image formed on the focusing screen 4 is observed as an erect image by the pentaprism 5 from the eye point 7 through the eyepiece 6.

  The eyepiece 6 according to the present invention includes, in order from the object side to the observation side, a first lens 6a having a negative refractive power, a second lens 6b having a positive refractive power, a concave on the eyepoint side, and a meniscus positive or negative refraction. It consists of a third lens 6c of force. Then, the diopter adjustment is performed by moving the second lens 6b along the optical axis La of the eyepiece 6 by the diopter adjusting mechanism 8.

  An optical member such as a lens or a filter may be provided on at least one of the object side of the first lens 6a or the observation side of the third lens 6c.

  As an image inverting means applicable in this embodiment, any optical member capable of inverting an image, such as a Porro prism or roof prism, may be used.

In each embodiment, the focal lengths of the first lens 6a and the second lens 6b are f1 and f2, respectively, the Abbe number of the material of the first lens 6a is νd, the air conversion optical path length of the image inverting means 5 is dp, and the eyepiece 6 When the focal length of the entire system is f
1.33 <| f1 / dp | <2.10 (1)
20 <νd <32 (2)
0.5 <f2 / f <0.6 (3)
Is satisfied.

Here, when the air-converted optical path length dp is Nd as the refractive index of the material and L is the length when the optical path is expanded,
dp = L / Nd
It is represented by

  Conditional expression (1) specifies the ratio between the focal length of the first lens 6 a having negative refractive power and the air-converted optical path length dp of the image inverting means (penta prism) 5. This makes it possible to maintain a sufficiently long eye relief and high optical performance while realizing a high observation magnification (finder magnification) to enlarge the viewfinder image.

  In order to increase the observation magnification of the finder optical system, the focal length of the eyepiece unit 6 is shortened, that is, the distance from the focusing screen 4 to the eyepiece unit 6 (the optical path length to the principal point position of the eyepiece unit 6). ) Must be shortened. When the distance from the focusing screen 4 to the eyepiece unit 6 is shortened, it is necessary to shorten the focal length of the eyepiece unit 6 in order to set the diopter near −1 diopter.

  When the eyepiece 6 is composed of a first lens 6a having a negative refractive power, a second lens 6b having a positive refractive power, and a third lens 6c having a negative or positive refractive power, the positive lens of the second lens 6b is used. By increasing the refractive power, the focal length of the eyepiece lens unit 6 can be shortened.

  However, the second lens 6b already has a strong positive refractive power for adjusting the diopter, and if the positive refractive power is further increased, it is difficult to satisfactorily correct aberrations such as spherical aberration and field curvature. become. Therefore, in order to shorten the focal length of the eyepiece 6, it is desirable to shorten the focal length of the entire eyepiece 6 by reducing the negative refractive power of the first lens 6 a.

  Conditional expression (1) is a condition set in order to sufficiently secure the eye relief while shortening the focal length of the eyepiece lens unit 6 and realizing a high observation magnification.

  If the lower limit of conditional expression (1) is exceeded, the negative refractive power of the first lens 6a becomes too strong, so it becomes difficult to shorten the focal length of the eyepiece 6 and it is difficult to achieve a high observation magnification. become. Further, when trying to shorten the focal length of the entire system of the eyepiece 6 beyond the lower limit, the negative refractive power of the first lens 6a becomes too strong, so that various aberrations such as spherical aberration and field curvature are corrected well. It becomes difficult.

  If the upper limit of the conditional expression (1) is exceeded, the negative refractive power of the first lens 6a becomes too weak, so that the entrance pupil position of the eyepiece 6 becomes too far (goes to the observation side) and the pentaprism 5 There is a lot of vignetting of light and eye relief becomes too short.

  Conditional expression (2) specifies the Abbe number of the material of the first lens 6a having a negative refractive power, mainly corrects the lateral chromatic aberration favorably, and maintains high optical performance while enlarging the finder image. is there.

  By satisfying the conditional expression (1) described above, it is possible to ensure a high observation magnification and a sufficient eye relief. However, since the negative refractive power of the first lens 6a becomes weak, the correction of the lateral chromatic aberration may be insufficient. Conditional expression (2) is a conditional expression set in order to achieve a high optical performance while ensuring a sufficient eye relief and satisfactorily correcting lateral chromatic aberration while realizing a high observation magnification.

  If the lower limit of conditional expression (2) is exceeded, the number of materials that can be selected becomes extremely small, which is not good. When the upper limit of conditional expression (2) is exceeded, correction of lateral chromatic aberration by the first lens 6a having negative refractive power becomes insufficient, and it becomes difficult to obtain high optical performance.

  Conditional expression (3) relates to the refractive power of the second lens 6b having a positive refractive power so as to widen the diopter adjustment range while maintaining the optical performance.

  Satisfying the above-described conditional expression (1) makes it possible to ensure a high observation magnification and a sufficient eye relief, but the negative refractive power of the first lens 6a becomes weak. For this reason, if the positive refractive power of the second lens 6b becomes too strong exceeding the lower limit of the conditional expression (3), it becomes difficult to satisfactorily correct various aberrations such as spherical aberration and curvature of field. If the positive refractive power of the second lens 6b becomes too weak beyond the upper limit, it becomes difficult to take a sufficient adjustment range for diopter adjustment.

  In each embodiment, the numerical ranges of conditional expressions (1) to (3) are more preferably set as follows.

1.35 <| f1 / dp | <2.05 (1a)
21 <νd <31 (2a)
0.51 <f2 / f <0.58 (3a)
As described above, according to each embodiment, by appropriately setting each element of the eyepiece optical system, it is possible to ensure high optical performance, a high observation magnification, and a sufficiently long eye relief.

  Next, numerical data of each numerical example will be shown. In each numerical example, the order from the object side (focus plate side) to the observation side (eye point side) is shown.

  In each numerical example, i indicates the order of the surfaces from the object side, Ri is the radius of curvature of the lens surface, Di is the distance between the i-th surface and the (i + 1) -th surface, and Ni and νi are d-glands, respectively. Indicates the refractive index and Abbe number of the material. Two surfaces on the most object side are flat surfaces and are image inverting means.

  In each numerical example, an asterisk represents an aspherical surface, and the aspherical shape has an X axis in the optical axis direction, a Y axis in the direction perpendicular to the optical axis, and the light traveling direction is positive, and R is a paraxial curvature. Assuming radius, K, B, C, D, E,

Is defined by The display of “e-0X” means “10 ^−X ”.

  Moreover, the calculation result of the rough viewfinder magnification and eye relief when realizing the finder optical system of each numerical example is shown. The viewfinder magnification can be expressed as an afocal angular magnification when an objective lens (photographing lens) having a focal length of 50 mm is used. Here, it is approximately represented by the ratio of the focal length of the objective lens to the focal length of the eyepiece optical system.

  Table 1 shows the relationship between the conditional expression at the time of −1 diopter and the numerical values in the numerical examples.

Sectional drawing of the principal part of the imaging device using the finder optical system of this invention Sectional drawing when the optical path of Numerical Example 1 of the present invention is developed Aberration diagram of Numerical Example 1 of the present invention Sectional drawing when the optical path of Numerical Example 2 of the present invention is developed Aberration diagram of Numerical Example 2 of the present invention Sectional drawing when developing the optical path of Numerical Example 3 of the present invention Aberration diagram of Numerical Example 3 of the present invention Sectional drawing when developing the optical path of Numerical Example 4 of the present invention Aberration diagram of Numerical Example 4 of the present invention Sectional drawing when developing the optical path of Numerical Example 5 of the present invention Aberration diagram of Numerical Example 5 of the present invention

Explanation of symbols

1: Lens system 2: Quick return mirror 3: Focus plate (Fresnel lens)
4: Focus plate (matte surface)
5: Penta prism 6a: Negative first lens constituting the eyepiece lens portion 6b: Positive second lens constituting the eyepiece lens portion 6c: Third lens constituting the eyepiece lens portion 7: Eye point 8: Diopter adjustment Mechanism EP: Eyepiece optical system La: Optical axis

Claims (5)

In an eyepiece optical system having an image inverting means for inverting an image formed by an objective lens into an erect image, and an eyepiece lens section for enlarging and displaying an image that has become an erect image by the image inverting means.
The eyepiece unit includes, in order from the image inverting means, a first lens having a negative refractive power, a second lens having a positive refractive power, and a third lens having a meniscus positive or negative refractive power having a concave surface on the observation side. The second lens has a diopter adjustment function for adjusting diopter by moving along the optical axis direction of the eyepiece lens unit. The focal length of the first lens is f1, and the image inverting means When the air equivalent optical path length is dp,
1.33 <| f1 / dp | <2.10
An eyepiece optical system characterized by satisfying the following conditions. When the Abbe number of the material of the first lens is νd,
20 <νd <32
The eyepiece optical system according to claim 1, wherein the following condition is satisfied. When the focal length of the second lens is f2, and the focal length of the whole eyepiece lens unit is f,
0.5 <f2 / f <0.6
The eyepiece optical system according to claim 1, wherein the following condition is satisfied.   A viewfinder optical system comprising the eyepiece optical system according to any one of claims 1 to 3 and the objective lens.   An imaging apparatus comprising: the finder optical system according to claim 4; and an imaging unit that receives an image corresponding to an object image displayed by the finder optical system.

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