JP2008052085A - Eyepiece lens, finder optical system and optical apparatus provided with the same - Google Patents

Abstract

Provided is an eyepiece that can adjust diopter and has a large pupil diameter, but can ensure a relatively high field of view observation magnification despite its very long overall length.
In an eyepiece lens EL used in a finder optical system VF for observing an image formed by an objective lens with an eyepiece lens, negative refractive powers arranged in order along the optical axis from the object side are provided. A first lens L1 having a positive birefringence, a second lens L2 having a positive refractive power, and a third lens L3 having a negative refractive power, and the second lens L2 is moved along the optical axis. The first lens L1 and the third lens L3 are each composed of a meniscus lens having a convex surface facing the object side, and the refractive index of the second lens L2 with respect to the d-line is n2. As a result, the condition of n2> 1.75 is satisfied.
[Selection] Figure 1

Description

  The present invention relates to an eyepiece, and more particularly to an eyepiece used in a single-lens reflex finder.

  The single-lens reflex finder is a real-image finder that observes the real image of the photographic lens with an eyepiece with positive refractive power. In general, the observation is performed by using an ocular positive lens that has been erased. In order to improve the photographer's ease of use, a single lens reflex finder is required to have a high observation magnification and diopter adjustment function. In consideration of use in dark places and when the photographer's eyes and the exit pupil of the eyepiece are misaligned, it is also desired to secure a wide pupil with good aberration correction at about φ10 mm at the eye point. ing.

  In order to increase the observation magnification, it is necessary to shorten the focal length of the eyepiece. However, since it is necessary to set the diopter in the vicinity of −1 [1 / m], the substantial focal length of the eyepiece is determined by the distance from the focusing screen to the eyepiece. Therefore, the simplest way to increase the viewfinder magnification is to shorten the optical path length of the pentaprism and place the eyepiece close to the pentaprism. On the other hand, if the distance (eye relief) from the apex of the eye point side lens surface of the eyepiece to the eye point is made sufficiently long, the pentaprism must be enlarged in order to reduce vignetting on the pentaprism exit surface. For this reason, the optical path length of the pentaprism is increased, and the observation magnification is reduced. That is, increasing the observation magnification and taking a sufficiently long eye relief are contradictory to each other.

An eyepiece for observing the image of the objective lens through an erecting system is used in a single-lens reflex camera. 2 lens group) and a negative lens group (third lens group), and appropriately set the refractive power of the second lens group and the third lens group and move the second lens group along the optical axis. Thus, there is known a type in which various aberrations are favorably corrected and the observation magnification is high and diopter adjustment is possible (for example, see Patent Document 1).
JP 2001-324684 A

  In recent years, with the digitalization of cameras, liquid crystal screens and various electronic components are mounted on the cameras, and the distance from the image sensor surface or film surface to the rear end surface of the camera has become significantly longer. In order to make it easier for the photographer to look into the viewfinder, the distance from the eye point to the rear end surface of the camera must be kept long enough.To do so, an eyepiece is placed near the rear end surface of the camera. It is necessary to ensure a sufficient eye relief of the eyepiece.

  However, if the eyepiece is disposed near the rear end surface of the camera, the distance from the focusing screen to the eyepiece becomes longer, and it is difficult to increase the observation magnification. In addition, as described above, when the eye relief of the eyepiece lens disposed near the rear end surface of the camera is sufficiently secured, the pentaprism must be enlarged, and the optical path length (glass path length) of the pentaprism is increased. The longer the distance from the focusing screen to the eyepiece, the more difficult it is to increase the observation magnification. Thus, with the digitalization of cameras, it has become very difficult to ensure a high field of view observation magnification.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an eyepiece that can adjust diopter and has a large pupil diameter, while ensuring a relatively high field of view observation magnification. And It is another object of the present invention to provide a finder optical system and an optical apparatus provided with such an eyepiece.

  In order to achieve such an object, in the present invention, in an eyepiece used in a finder optical system for observing an image formed by an objective lens with an eyepiece, negative refraction arranged in order from the object side along the optical axis. A first lens having a power, a biconvex second lens having a positive refractive power, and a third lens having a negative refractive power, and the first lens, the second lens, and the third lens. The diopter can be adjusted by moving at least one along the optical axis. The first lens and the third lens are each composed of a meniscus lens having a convex surface facing the object side. When the refractive index for the d-line of the lens is n2, the condition of n2> 1.75 is satisfied.

  In the above-described invention, it is preferable that at least one optical surface of the second lens is an aspherical surface.

Further, in the invention described above, the radius of curvature of the object side in the third lens and Ro _3, the radius of curvature of the surface of the eye point side in the third lens and _{Re 3, S3 = (Ro 3} + Re 3) / ( When the shape factor of the third lens defined by the conditional expression of Ro ₃ -Re ₃ ) is S3, it is preferable that the condition of S3> 2.4 is satisfied.

  In the above-described invention, it is preferable that the condition of 30> (ν1 + ν3) / 2 is satisfied where the Abbe number of the first lens is ν1 and the Abbe number of the third lens is ν3.

  Furthermore, in the above-described invention, it is preferable that diopter adjustment can be performed by moving the second lens among the first lens, the second lens, and the third lens along the optical axis.

  The finder optical system according to the present invention is a finder optical system for observing an image formed by an objective lens with an eyepiece, wherein the eyepiece is the eyepiece according to the present invention.

  Furthermore, an optical apparatus according to the present invention includes a finder optical system that observes an image formed by an objective lens with an eyepiece, and the finder optical system is the finder optical system according to the present invention.

  According to the present invention, it is possible to obtain an eyepiece that can adjust diopter and has a large pupil diameter, while ensuring a relatively high field of view observation magnification.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. A single lens reflex camera CAM provided with an eyepiece lens EL and a viewfinder optical system VF according to the present invention is shown in FIG. The single-lens reflex camera CAM includes an objective lens OL, a mirror M, an imaging device CCD for photographing, and a finder optical system VF. The finder optical system VF includes a focusing screen F, a condenser lens C, a pentaprism P, and an eyepiece lens EL arranged along the optical axis in order from the object side, and is formed by the objective lens OL. An image formed (formed) on the focusing screen F can be observed by the eyepiece lens EL. An eye point EP is provided behind the eyepiece lens EL.

  The objective lens OL forms a subject image on the image sensor CCD or the focusing screen F. The mirror M is inserted at an angle of 45 degrees with respect to the optical axis passing through the objective lens OL, and in a normal state (in a shooting standby state), light from a subject (not shown) passing through the objective lens OL is received. The light is reflected and imaged on the focusing screen F. When the shutter is released, the mirror is raised and jumps up, and light from a subject (not shown) passing through the objective lens OL forms an image on the image sensor CCD. ing. That is, the image sensor CCD and the focusing screen F are disposed at optically conjugate positions.

  The pentaprism P inverts the subject image (inverted image) on the focusing screen F formed by the objective lens OL into an upright image by inverting the image vertically. The pentaprism P allows the observer to observe the subject image as an erect image, and allows the finder optical system VF to be configured in a compact manner. A condenser lens C is provided between the focusing screen F and the pentaprism P, and the subject image on the focusing screen F is guided to the pentaprism P. The condenser lens C has a positive refractive power that suppresses the divergence of the light beam, and the spread of the light beam increases as the distance from the exit pupil of the objective lens OL increases. Therefore, the upright optical system and the eyepiece optical system increase in size. In order to prevent this, it is disposed near the imaging position of the subject image formed by the objective lens OL (for example, between the focusing screen F and the pentaprism P as in the present embodiment).

  The eyepiece lens EL includes a first lens L1 having a negative refractive power, a biconvex second lens L2 having a positive refractive power, and a negative refractive power, arranged in order from the object side along the optical axis. The second lens L2 is moved along the optical axis so that diopter adjustment can be performed. The first lens L1 and the third lens L3 are meniscus lenses having negative refractive power with a convex surface facing the object side.

  When the refractive index of the second lens L2 with respect to the d-line is n2, the second lens L2 satisfies the condition expressed by the following conditional expression (1).

  n2> 1.75 (1)

  Since the distance from the focusing screen F to the eyepiece lens EL is large, it is very difficult to secure a high observation magnification in the visual field range. However, the first lens L1 is made to be a meniscus lens while increasing the refractive index of the second lens L2. Thus, distortion and coma can be corrected, and by making the third lens L3 a meniscus lens, it is possible to ensure a predetermined observation magnification while taking sufficient eye relief.

  The light greatly bounced up by the first lens L1 is largely bent by the second lens L2, but if the radius of curvature on the object side of the second lens L2 is too small, the spherical aberration cannot be corrected. By selecting a glass with a high refractive index so as to satisfy the condition of conditional expression (1), the radius of curvature can be increased while giving the second lens L2 a large refractive power. Occurrence can be suppressed and good aberration correction can be achieved as a whole. Further, if the radius of curvature is small, the lens thickness must be increased in order to ensure the outer diameter, but the second lens L2 can be made thinner than before by using high refractive index glass. By thinning the lens, the distance between the exit surface of the pentaprism P and the eye point EP can be shortened, which leads to securing a high observation magnification.

  At this time, spherical aberration can be corrected more satisfactorily by making the optical surface of the second lens L2 an aspherical surface. In particular, since the aspherical surface can be used effectively by making the object side surface of the second lens L2 an aspherical surface, the spherical aberration and coma aberration at each diopter at the time of diopter adjustment are improved. It becomes possible to correct, and aberration variation during diopter adjustment can be suppressed. In addition, by adjusting the diopter by moving the second lens L2 along the optical axis, the second lens L2 has a high refractive index. , Aberration variation of spherical aberration) can be reduced.

  Furthermore, the third lens L3 preferably satisfies the condition represented by the following conditional expression (2) in order to increase the observation magnification while ensuring sufficient eye relief.

  S3> 2.4 (2)

Here, S3 is a shape factor of the third lens L3, and is defined by a conditional expression of S3 = (Ro ₃ + Re ₃ ) / (Ro ₃ −Re ₃ ). Ro ₃ is the radius of curvature of the object side surface of the third lens L3, and Re ₃ is the radius of curvature of the surface of the third lens L3 on the eye point EP side.

  Conditional expression (2) defines the shape of the third lens L3. Originally, the stronger the negative refractive index of the third lens L3, the more advantageous is to increase the observation magnification. However, in order to adjust the diopter, the negative refractive power of the first lens L1 must be strong. Therefore, the third lens L3 has a shape that satisfies the conditional expression (2) while increasing the lens thickness while reducing the negative refractive power, so that the object side surface of the third lens L3 is land light. The eye point EP side surface acts negatively to make the principal point the eye point EP side, widen the principal point interval, and increase the observation magnification. The land light is a light beam that is farthest from the optical axis among light beams whose image height reaches zero.

  Further, the shape of conditional expression (2) facilitates securing of eye relief. Further, by setting the lower limit value of conditional expression (2) to 3.4 or more, when considering the locus of light from the eye point EP side, the third lens L3 increases light from the eye point EP with respect to the oblique light flux. By connecting to the second lens L2 without being refracted, and thereby preventing the vignetting by suppressing the height of the light beam on the exit surface of the pentaprism P, the enlargement of the pentaprism P can be avoided.

  In order to correct chromatic aberration satisfactorily, it is preferable that the condition expressed by the following conditional expression (3) is satisfied.

  30> (ν1 + ν3) / 2 (3)

  Here, ν1 is the Abbe number of the first lens L1, and ν3 is the Abbe number of the third lens L3.

  When the second lens L2 satisfies the condition represented by the conditional expression (1), the chromatic aberration increases in the second lens L2, and therefore the first lens L1 and the third lens L3 are represented by the conditional expression (3). Satisfying the conditions makes it possible to sufficiently correct chromatic aberration. When the first lens L1 and the third lens L3 are in a condition that exceeds the upper limit value of the conditional expression (3), the lateral chromatic aberration cannot be corrected. Furthermore, after the first lens L1 and the third lens L3 satisfy the condition represented by the conditional expression (3), the Abbe number ν2 of the second lens L2 is a condition represented by the following conditional expression (4). Is preferably satisfied.

  ν2> 40 (4)

  In the single-lens reflex camera CAM having such a configuration, light from a subject (not shown) passes through the objective lens OL, is reflected by the mirror M toward the focusing screen F, and a subject image is formed on the focusing screen F. The In the finder optical system VF, the light beam from the subject image on the focusing screen F passes through the condenser lens C, the pentaprism P, and the eyepiece EL, and is guided to the eye point EP. Can observe a real image of a subject (not shown). At the time of shutter release, light from a subject (not shown) that has passed through the objective lens OL is imaged on the image sensor CCD because the mirror M is in a mirror-up state.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. Table 1, Table 2, and Table 3 are shown below. These are tables of specifications of the lenses in the first, second, and third examples of the eyepiece according to the present invention. In either table, the leftmost item is the number of each optical surface (hereinafter referred to as surface number) with the focal plane formed on the focusing screen F as 1, r is the radius of curvature of each optical surface, and d is each optical surface. The distance on the optical axis from the surface to the next optical surface (hereinafter referred to as the surface interval), n (d) represents the refractive index with respect to the d-line (wavelength 587.6 nm), and νd represents the Abbe number.

In each table, an aspherical surface marked with * indicates the height from the tangential plane at the apex of the aspherical surface to the position on the aspherical surface at the height h (incident height) in the direction perpendicular to the optical axis. when the distance along the axis (aspherical amount) x, the reference spherical curvature radius (paraxial curvature radius) r, a conic constant kappa, the n-th order aspherical coefficient was C _n, the following conditional expression ( 5).

x = (h ² / r) / {1+ (1−Κ · h ² / r ² ) ^1/2 }
+ C ₄ h ⁴ + C ₆ h ⁶ + C ₈ h ⁸ + C ₁₀ h ¹⁰ (5)

  In the table, the focal length f, the radius of curvature r, the surface interval d, and other units of length are “mm”. However, even if the optical system is proportionally enlarged or reduced, the optical performance equivalent to that of the present invention can be obtained.

  The unit of diopter in the table is [1 / m]. For example, the diopter X [1 / m] indicates a state in which an image by the eyepiece lens can be located at a position of 1 / X [m (meter)] on the optical axis from the eye point. At this time, the sign is negative when the image is closer to the object side than the eye point.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a lens configuration diagram of an eyepiece according to a first example (when the diopter is −1 [1 / m]). In FIG. 1 (the same applies to FIGS. 5 and 9), the pentaprism P is shown in a state of being developed on a thick parallel surface plate, and only the focal plane I formed on the focal plate F is shown for the focal plate F. Has been. Table 1 shows the specifications of each lens in the first example. Surface numbers 1 to 11 in Table 1 correspond to surfaces 1 to 11 in FIG.

(Table 1)
Surface number r d νd n (d)
1 ∞ 2.4 1.0000
2 ∞ 4.7 56.05 1.5688
3 −65.0349 2.8 1.0000
4 ∞ 111.498 56.05 1.5688
5 ∞ 0.1 1.0000
6 399.9059 1.1 23.78 1.8467
7 42.7155 (d1) 1.0000
8 * 27.409 4.4 45.21 1.7911
9 −89.4324 (d2) 1.0000
10 34.2149 5.2 25.42 1.8052
11 20.9939 (d3) 1.0000
(Aspheric coefficient)
Surface number Κ C ₄ C ₆ C ₈ C ₁₀
8 -0.3400 0.00000 0.00000 0.00000 0.00000
(Variable interval)
Diopter -1 -3 +1
Focal length 73.1 70.2 76.9
d1 2.8 0.7 5.4
d2 3.4 5.5 0.8
d3 23.7 20.7 27.7
(Conditional value)
Conditional expression (1) n2 = 1.7911
Conditional expression (2) S3 = 4.18
Conditional expression (3) (ν1 + ν3) /2=24.5
Conditional expression (4) ν2 = 45

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (4) are satisfied.

  2, 3 and 4 are graphs showing various aberrations when the diopter is -1 [1 / m] and various aberrations when the diopter is -3 [1 / m] in the first embodiment. FIG. 6 is a diagram illustrating various aberrations when the diopter is +1 [1 / m]. Each aberration diagram shows the results for d-line (λ = 587.6 nm), g-line (λ = 435.8 nm), C-line (λ = 656.3 nm), and F-line (λ = 486.1 nm). Α represents a half angle of view, and D represents diopter (a unit of diopter and is synonymous with [1 / m]). In the spherical aberration diagram, the value of Y2 corresponding to the maximum aperture (incident height at which the light beam from the on-axis object is incident on the surface (second surface) next to the focal plane (first surface)) is shown. The distortion diagram shows the maximum half field angle, and the coma diagram shows the half field value.

  In the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. The description of the aberration diagrams is the same in the other examples. As shown in each aberration diagram, it can be seen that the various aberrations of the optical system at each diopter are well corrected despite the long optical path length of the finder optical system VF and diopter adjustment. Each aberration diagram shows the aberration when the pupil diameter of the eye point EP is set to φ10 mm. The coma aberration, the spherical aberration, and the distortion aberration are corrected well at such a large pupil diameter. I understand.

  As a result, according to the eyepiece lens EL according to the first example, in the finder optical system VF of the single-lens reflex camera CAM using the pentaprism P, the distance from the focusing screen F to the eyepiece lens EL is very long. Therefore, it is possible to obtain an eyepiece that can adjust the diopter and has a large pupil diameter while ensuring a relatively high field of view observation magnification. Further, according to the finder optical system VF and the single-lens reflex camera CAM provided with such an eyepiece lens EL, the diopter can be adjusted even though the distance from the focusing screen F to the eyepiece lens EL is very long. While having a pupil diameter, a relatively high field of view observation magnification can be ensured.

(Second embodiment)
A second embodiment of the present invention will be described below with reference to FIGS. FIG. 5 is a lens configuration diagram of the eyepiece lens according to the second example (when the diopter is −1 [1 / m]). The eyepiece of the second example has the same configuration as the eyepiece of the first example, and the same reference numerals as those of the first example are given to the respective parts.

  Table 2 below shows the specifications of each lens in the second example. The surface numbers 1 to 11 in Table 2 correspond to the surfaces 1 to 11 in FIG. In Table 2, an aspherical lens surface is marked with an asterisk (*) to the right of the surface number.

(Table 2)
Surface number r d νd n (d)
1 ∞ 2.4 1.0000
2 ∞ 4.7 56.05 1.5688
3 −65.0349 2.8 1.0000
4 ∞ 111.498 56.05 1.5688
5 ∞ 0.1 1.0000
6 500.0000 1.1 23.78 1.8467
7 42.8065 (d1) 1.0000
8 * 26.7871 5 45.46 1.8014
9 −88.4767 (d2) 1.0000
10 37.666 5.2 27.79 1.7408
11 21 (d3) 1.0000
(Aspheric coefficient)
Surface number Κ C ₄ C ₆ C ₈ C ₁₀
8 -0.3859 0.00000 0.00000 0.00000 0.00000
(Variable interval)
Diopter -1 -3 +1
Focal length 73.6 70.5 78
d1 2.9 0.8 5.6
d2 3.5 5.6 0.8
d3 23.7 20.7 27.7
(Conditional value)
Conditional expression (1) n2 = 1.8014
Conditional expression (2) S3 = 3.52
Conditional expression (3) (ν1 + ν3) / 2 = 26
Conditional expression (4) ν2 = 46

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (4) are satisfied.

  FIGS. 6, 7 and 8 are graphs showing various aberrations when the diopter is −1 [1 / m] and various aberrations when the diopter is −3 [1 / m] in the second embodiment. FIG. 6 is a diagram illustrating various aberrations when the diopter is +1 [1 / m]. As shown in each aberration diagram, it can be seen that the various aberrations of the optical system at each diopter are well corrected despite the long optical path length of the finder optical system VF and diopter adjustment. It can also be seen that coma, spherical aberration, and distortion are well corrected at a large pupil diameter (φ10 mm), as in the first embodiment.

  As a result, according to the eyepiece lens EL according to the second example, the same effect as in the first example can be obtained. Further, according to the finder optical system VF and the single-lens reflex camera CAM provided with such an eyepiece lens EL, the same effects as those in the first embodiment can be obtained.

(Third embodiment)
Hereinafter, a third embodiment of the present invention will be described with reference to FIGS. 9 to 12 and Table 3. FIG. FIG. 9 is a lens configuration diagram of an eyepiece lens according to a third example (when the diopter is −1 [1 / m]). The eyepiece of the third example has the same configuration as the eyepiece of the first example, and the same reference numerals as those in the first example are given to the respective parts.

  Table 3 below shows the specifications of each lens in the third example. The surface numbers 1 to 11 in Table 3 correspond to the surfaces 1 to 11 in FIG. In Table 3, a lens surface formed in an aspherical shape is marked with * on the right side of the surface number.

(Table 3)
Surface number r d νd n (d)
1 ∞ 2.4 1.0000
2 ∞ 4.7 56.05 1.5688
3 −65.0349 2.8 1.0000
4 ∞ 111.498 56.05 1.5688
5 ∞ 0.1 1.0000
6 400.0000 1.1 22.76 1.8081
7 41.8967 (d1) 1.0000
8 * 29.9677 4.5 40.76 1.8830
9 -130.4499 (d2) 1.0000
10 31.0801 4.7 18.9 1.9229
11 21 (d3) 1.0000
(Aspheric coefficient)
Surface number Κ C ₄ C ₆ C ₈ C ₁₀
8 -0.1190 0.00000 0.00000 0.00000 0.00000
(Variable interval)
Diopter -1 -3 +1
Focal length 73.6 70.7 77.4
d1 2.9 0.7 5.6
d2 3.5 5.7 0.8
d3 24.2 21.2 28.2
(Conditional value)
Conditional expression (1) n2 = 1.883
Conditional expression (2) S3 = 5.17
Conditional expression (3) (ν1 + ν3) / 2 = 21
Conditional expression (4) ν2 = 41

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (4) are satisfied.

  FIGS. 10, 11 and 12 are graphs showing various aberrations when the diopter is -1 [1 / m] and various aberrations when the diopter is -3 [1 / m] in the third embodiment. FIG. 6 is a diagram illustrating various aberrations when the diopter is +1 [1 / m]. As shown in each aberration diagram, it can be seen that the various aberrations of the optical system at each diopter are well corrected despite the long optical path length of the finder optical system VF and diopter adjustment. It can also be seen that coma, spherical aberration, and distortion are well corrected at a large pupil diameter (φ10 mm), as in the first embodiment.

  As a result, according to the eyepiece lens EL according to the third example, the same effect as in the first example can be obtained. Further, according to the finder optical system VF and the single-lens reflex camera CAM provided with such an eyepiece lens EL, the same effects as those in the first embodiment can be obtained.

  The eyepiece according to the present embodiment is not limited to the eyepiece used in the finder optical system of a single-lens reflex camera, and can be widely used as an eyepiece for a finder of a real image optical system. Further, the above-described embodiment is merely an example, and is not limited to the above-described configuration and shape, and can be appropriately modified and changed within the scope of the present invention.

  Further, in the above-described embodiment, the diopter adjustment can be performed by moving the second lens L2 along the optical axis, but is not limited thereto. For example, the diopter adjustment may be performed by moving the first lens L1, or by moving both the first lens L1 and the second lens L2, and the first lens L1 and the second lens L2. The third lens L3 may be configured so that diopter adjustment can be performed by moving at least one of the third lenses L3 along the optical axis.

It is a lens block diagram of the eyepiece which concerns on 1st Example. FIG. 6 is various aberration diagrams when the diopter is −1 [1 / m] in the first example. FIG. 6 is various aberration diagrams when the diopter is −3 [1 / m] in the first example. It is an aberration diagram when the diopter in the first example is +1 [1 / m]. It is a lens block diagram of the eyepiece which concerns on 2nd Example. It is an aberration diagram when the diopter in the second example is -1 [1 / m]. It is an aberration diagram when the diopter in the second example is −3 [1 / m]. FIG. 6 is various aberration diagrams when the diopter is +1 [1 / m] in the second embodiment. It is a lens block diagram of the eyepiece which concerns on 3rd Example. It is an aberration diagram when the diopter in the third example is -1 [1 / m]. It is an aberration diagram when the diopter in the third example is −3 [1 / m]. It is an aberration diagram when the diopter in the third example is +1 [1 / m]. It is a schematic block diagram of the single-lens reflex camera provided with the eyepiece and finder optical system which concern on this invention.

Explanation of symbols

CAM single-lens reflex camera (optical equipment) VF finder optical system OL objective lens EL eyepiece L1 first lens L2 second lens L3 third lens

Claims (7)

In an eyepiece used in a viewfinder optical system for observing an image formed by an objective lens with an eyepiece,
A first lens having negative refractive power, arranged in order from the object side along the optical axis, a biconvex second lens having positive refractive power, and a third lens having negative refractive power The diopter adjustment can be performed by moving at least one of the first lens, the second lens, and the third lens along the optical axis,
The first lens and the third lens are each composed of a meniscus lens having a convex surface facing the object side,
When the refractive index of the second lens with respect to the d-line is n2, the following formula n2> 1.75
An eyepiece characterized by satisfying the above conditions.   The eyepiece according to claim 1, wherein at least one optical surface of the second lens is an aspherical surface. The radius of curvature of the object side in the third lens and Ro _3, the radius of curvature of the eye point side in the third lens and _{Re 3, S3 = (Ro 3} + Re 3) / (Ro 3 -Re 3 ) Where S3 is the shape factor of the third lens defined by the conditional expression S3> 2.4
The eyepiece according to claim 1 or 2, wherein the following condition is satisfied. When the Abbe number of the first lens is ν1 and the Abbe number of the third lens is ν3, the following expression 30> (ν1 + ν3) / 2
The eyepiece according to any one of claims 1 to 3, wherein the following condition is satisfied.   The diopter adjustment is possible by moving the second lens among the first lens, the second lens, and the third lens along an optical axis. The eyepiece according to any one of claims 1 to 4. In the viewfinder optical system that observes the image formed by the objective lens with the eyepiece,
A finder optical system, wherein the eyepiece lens is the eyepiece lens according to any one of claims 1 to 5. With a viewfinder optical system that observes the image formed by the objective lens with an eyepiece,
An optical apparatus, wherein the finder optical system is the finder optical system according to claim 6.

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