JP2005148487A - Finder adapter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a finder adapter which has a continuous diopter adjusting function, which is small in size and which has good optical performance. <P>SOLUTION: A finder adapter Ga is to be mounted at the back of an eyepiece optical system Gf in a finder optical system and comprises a first lens group G1 having negative refractive power and a second lens group G2 having positive refractive power in the successive order from an object side. The finder diopter is continuously corrected by moving the first lens group in the optical axis direction and the following conditional equations (1), (2) and (3) are satisfied, i.e., (1) 2.5<f1+f2<5.0 (2) 150<¾f1xf2¾<600 and (3) ¾f1/f2¾>0.8 where f1 is the focal distance of the first lens group and f2 is the focal distance of the second lens group. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a novel finder adapter. More specifically, the present invention relates to a small finder adapter that can be attached to the back of an eyepiece optical system in a viewfinder of various cameras to add a continuous diopter adjustment function.

2. Description of the Related Art Conventionally, a finder adapter has been proposed for mounting on a finder eyepiece of a camera and adjusting the finder diopter. Among them, a method of performing diopter correction by attaching a lens group for diopter correction inside or behind the eyepiece optical system of the finder is well known. In Patent Literature 1 and Patent Literature 2, a diopter correcting lens group is configured to be attachable to and detachable from a Galileo type finder optical system, thereby realizing a finder adapter having both a diopter correcting function and an image magnifying function.

  Also, a finder adapter having both a continuous diopter correction function and an image enlargement function by moving an internal lens group constituting the finder adapter has been put into practical use.

JP 11-337847 A

JP 2002-328301 A

  By the way, in recent years, there is a high demand for downsizing and thinning of digital cameras, and a small and thin finder system is also demanded. Therefore, a viewfinder mounted on a small and thin digital camera has been proposed that omits the diopter adjustment function and has only a fixed reference diopter. However, when the observer's eye condition is nearsightedness or farsightedness, the finder does not have a diopter adjustment function, so that a good visual field image cannot be obtained.

  On the other hand, as shown in Patent Document 1 and Patent Document 2 described above, in a finder adapter that performs diopter correction by inserting a lens group for diopter correction, a plurality of observers with different eye states can be obtained. When used, it is necessary to attach / detach or replace the correction lens group each time, which is very inconvenient.

  In addition, in a finder adapter having both a continuous diopter correction function and an image enlargement function, the adapter itself to be attached is increased in size, which is not suitable for downsizing and thinning of the camera body. Furthermore, since the vignetting of the peripheral image occurs by enlarging the image, the composition cannot be determined by checking the entire field of view.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a finder adapter that has a continuous diopter adjustment function, is small, and has good optical performance.

In order to solve the above-described problem, the finder adapter of the present invention is attached to the rear of the eyepiece optical system in the finder optical system, and has a first lens group having a negative refractive power and a positive refractive power in order from the object side. The second lens group is configured to continuously correct the finder diopter by moving the first lens group in the optical axis direction, and f1 is the focal length of the first lens group, and f2 is the second lens. As the focal length of the group, the following conditional expressions (1), (2) and (3) are satisfied.
(1) 2.5 <f1 + f2 <5.0
(2) 150 <| f1 · f2 | <600
(3) | f1 / f2 |> 0.8

Further, another finder adapter of the present invention is attached to the rear of the eyepiece optical system in the finder optical system in order to solve the above-described problem, and in order from the object side, the first lens group having a negative refractive power is positive with the first lens group. A second lens group having refractive power, and continuously correcting the finder diopter by moving the second lens group in the optical axis direction, and f1 is a focal length of the first lens group, f2 The following conditional expressions (1), (2), and (3) are satisfied, where is the focal length of the second lens group.
(1) 2.5 <f1 + f2 <5.0
(2) 150 <| f1 · f2 | <600
(3) | f1 / f2 |> 0.8

  Therefore, the finder adapter of the present invention is reduced in size and thickness, has good optical performance, and is easy to see.

The finder adapter according to the present invention is a finder adapter that is attached to the rear of the eyepiece optical system in the finder optical system, and in order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power. The finder diopter is continuously corrected by moving the first lens group in the optical axis direction, and the following conditional expressions (1), (2) and (3) are satisfied: Features.
(1) 2.5 <f1 + f2 <5.0
(2) 150 <| f1 · f2 | <600
(3) | f1 / f2 |> 0.8
However,
f1: The focal length of the first lens group f2: The focal length of the second lens group.

Another finder adapter according to the present invention is a finder adapter that is attached to the rear of the eyepiece optical system in the finder optical system, and has a first lens group having a negative refractive power and a positive refractive power in order from the object side. The second lens group is configured to continuously correct the finder diopter by moving the second lens group in the optical axis direction, and the following conditional expressions (1), (2), and (3) It is characterized by satisfaction.
(1) 2.5 <f1 + f2 <5.0
(2) 150 <| f1 · f2 | <600
(3) | f1 / f2 |> 0.8
However,
f1: The focal length of the first lens group f2: The focal length of the second lens group.

  Therefore, the finder adapter of the present invention can be reduced in size and thickness, can adjust diopter in a practically sufficient range, and can obtain sufficient optical performance. it can.

In the invention described in claim 2 and claim 4, each of the first lens group and the second lens group is constituted by one lens, and R11 is a lens constituting the first lens group. The radius of curvature of the surface on the incident side, n is the refractive index at the d-line of the lens constituting the first lens group of the finder adapter, and L is the most viewed by the first lens group of the finder adapter from the exit surface of the final lens of the finder As an air conversion distance on the optical axis to the entrance surface of the lens (or the lens constituting the first lens group of the finder adapter) constituting the first lens group when positioned on the side, the following conditional expression (4 ) | R11 | · L / n <55
Therefore, the size and thickness of the viewfinder can be further reduced, the pupil diameter of the finder can be increased, and the configuration can be reduced at a low cost.

  In the invention described in claims 5 to 8, since the eye cup is provided, the visibility of the finder is further improved.

  The best mode for carrying out the finder adapter of the present invention will be described below with reference to the accompanying drawings.

  1 to 4 show a first embodiment (numerical example 1) of the finder adapter of the present invention, and FIGS. 5 to 8 show a second embodiment (numerical example 2) of the finder adapter of the present invention. 9 to 12 show a third embodiment (numerical example 3) of the finder adapter of the present invention, and FIGS. 13 to 16 show a fourth embodiment (numerical example 4) of the finder adapter of the present invention. It is.

  As shown in FIGS. 1, 5, 9, and 13, the finder adapters Ga1, Ga2, Ga3, and Ga4 according to the present invention are finder adapters that are attached to the rear of the eyepiece optical system Gf of the finder optical system. In order from the side, the lens unit includes a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power. 1, 5, 9, and 13, the upper row shows the state when the diopter is −4 Dpt, and the lower row shows the state when the diopter is +2 Dpt.

  The finder adapters Ga1 and Ga2 according to the first and second embodiments continuously correct the finder diopter by moving the first lens group G1 having negative refractive power on the optical axis. (See FIGS. 1 and 5). At this time, the second lens group G2 having a positive refractive power is fixed.

  The finder adapters Ga3 and Ga4 according to the third and fourth embodiments continuously move the second lens group G2 having a positive refractive power on the optical axis to continuously adjust the finder diopter. It correct | amends (refer FIG.9 and FIG.13). At this time, the first lens group having negative refractive power is fixed.

By setting f1 as the focal length of the first lens group G1 and f2 as the focal length of the second lens group G2, the following conditional expressions (1), (2), and (3) are satisfied: A small finder adapter with good optical performance has been realized.
(1) 2.5 <f1 + f2 <5.0
(2) 150 <| f1 · f2 | <600
(3) | f1 / f2 |> 0.8

  Conditional expression (1) sets the total length of the finder adapter at the reference diopter of the finder. If the upper limit is exceeded, the total length becomes long, and the size and thickness cannot be reduced. On the other hand, if the lower limit is exceeded, the diopter adjustment range becomes narrow or the magnification becomes small, and the desired optical performance cannot be sufficiently obtained.

  The above conditional expression (2) is a diopter correction lens that is a movable group of the finder adapter (the first lens group G1 in the first and second embodiments Ga1 and Ga2, and the third and fourth lenses). In Embodiments Ga3 and Ga4, the second lens group G2) is set. If the upper limit is exceeded, the amount of movement of the diopter correction lens increases, and it is impossible to reduce the size and thickness. On the other hand, if the lower limit is not reached, the magnification becomes small and the viewfinder becomes difficult to see.

  Conditional expression (3) sets the lower limit value of the magnification of the finder adapter, and if it falls outside this lower limit value, it becomes difficult to see.

Further, each of the two lens groups G1 and G2 is composed of one lens, R11 is a radius of curvature of an incident side surface of the lens constituting the first lens group G1, and n is a first lens group G1 of the finder adapter. In the first and second embodiments Ga1 and Ga2, the first lens group of the finder adapter is positioned closest to the observer side from the exit surface of the final lens of the finder. In the third and fourth embodiments Ga3 and Ga4, L is changed from the exit surface of the final lens of the finder to the finder in the third and fourth embodiments Ga3 and Ga4. It is desirable to set the air equivalent distance on the optical axis to the entrance surface of the lens constituting the first lens group of the adapter so as to satisfy the conditional expression (4).
(4) | R11 | · L / n <55

  By configuring each of the two lens groups G1 and G2 with a single lens, not only can the size and thickness be reduced, but also the cost can be reduced. In addition, by satisfying conditional expression (4), the pupil diameter of the finder can be made sufficiently large, and good optical performance can be obtained.

  Furthermore, the visibility of the finder can be improved by attaching an eye cup to the finder adapter.

  FIG. 17 shows a specific application example of the finder adapter according to the present invention.

  The viewfinder adapter 10 is configured to be detachably attached to the rear side of the viewfinder 30 of the digital camera 20.

  The finder adapter 10 has a frame-shaped main housing 11 that opens forward and backward, and the first lens group G1 and the second lens group G2 (only the second lens group G2 in FIG. 17 are visible). ) Is supported. The main casing 11 is provided with a diopter adjustment dial 12, and a part of the diopter adjustment dial 12 protrudes from the side surface of the main casing 11. By operating the portion of the diopter adjustment dial 12 that protrudes from the side surface of the main housing 11, the diopter adjustment dial 12 is rotated to adjust the diopter correction lens (first and second embodiments Ga1 and Ga2). The first lens group G1 and the second lens group G2 in the third and fourth embodiments Ga3 and Ga4) are moved on the optical axis to adjust the finder diopter. It is like that.

  An eye cup 13 is integrally formed at the rear end of the main housing 11 so as to protrude toward the rear.

  The digital camera 20 includes a retractable variable focal length type photographing lens 21, and converts a subject image captured by the photographing lens 21 into an electric signal by a solid-state imaging device provided in the housing 22, and converts the electric signal into a desired signal. It is configured to be able to record on a recording medium.

  The finder 30 provided in the digital camera 20 is an electrical view finder, and an image of the subject imaged on the solid-state image sensor is displayed on the finder liquid crystal display panel 31 disposed in the housing 22. An observer views an image displayed on the liquid crystal display panel 31 through the eyepiece optical system Gf. A plane mirror 32 for bending the optical path inclined at approximately 45 ° is inserted between the first lens L1 and the second lens L2 of the eyepiece optical system Gf, and the thickness of the digital camera 20 is measured by the finder lens system. Care is taken so that there is no increase. The observer observes the image displayed on the liquid crystal display panel 31 through the eyepiece optical system Gf from the eyepiece frame 23 protruding from the back surface of the housing 22.

  The viewfinder adapter 10 is detachably attached to the eyepiece frame 23 of the digital camera 20. Engagement grooves 23a and 23a opened on the upper end surface are formed on both side surfaces of the eyepiece frame 23. Correspondingly, the front end portion of the housing 11 of the finder adapter 10 is opened forward and downward (not shown). A recess is formed, and engagement protrusions (not shown) are formed on both inner side surfaces of the recess. Therefore, the lower end of the engaging ridge of the finder adapter 10 is aligned with the upper ends of the engaging grooves 23a, 23a of the eyepiece frame 23 from above, and the finder adapter 10 is moved downward as it is, so that the engaging grooves 23a, The engaging protrusion of the finder adapter 10 is engaged with 23a. Accordingly, the finder adapter 10 is attached to the eyepiece frame 23 so as to wrap the eyepiece frame 23 in the recess at the front end portion of the finder adapter 10, and the engagement grooves 23a and 23a are engaged with the engagement protrusions. This prevents the viewfinder adapter 10 from falling off the eyepiece frame 23. In this way, the finder adapter 10 is mounted behind the eyepiece optical system Gf of the finder 30 of the digital camera 20.

  Then, the diopter of the finder 30 of the digital camera 20 is set to, for example, -1 Dpt, and this is set as a reference diopter, and the diopter adjustment dial 12 is rotated to adjust the diopter correction lens (the first lens group G1 or the second lens). By moving the group G2) on the optical axis, the diopter can be continuously corrected, for example, in the range of −4 Dpt to +2 Dpt.

  In the above example, the finder adapter 10 is described as being attached to the rear of the electric viewfinder. However, the scope of application of the finder adapter according to the present invention is not limited to the electric viewfinder, and liquid crystal is not used. Instead of the display panel 31, an object image is formed by an objective optical system, an inverted image obtained thereby is converted into an erect image by an inversion optical system, and the optical viewfinder is used to observe the erect image through an eyepiece optical system. Of course, it is applicable.

Next, each numerical example in each embodiment Ga1, Ga2, Ga3, and Ga4 of the finder adapter of the present invention will be shown. The meanings of symbols used in each numerical example are as follows. In each numerical example, each numerical value from the object plane Op (imaging plane) to the eye point Ep (observation position) is shown.
Si: i-th surface counted from the object side Ri: radius of curvature of the surface Si di: surface distance between the i-th surface and the (i + 1) -th surface from the object side ni: d-line of the i-th lens ( Refractive index νi at a wavelength of 587.6 nm): Abbe number of i-th lens *: surface using an aspherical surface

  In each numerical example, some surfaces are constituted by aspheric surfaces. Here, the aspherical shape is defined by Equation 1 where X is the depth of the aspherical surface and H is the height from the optical axis. A, B, C, and D are fourth-order, sixth-order, eighth-order, and tenth-order aspheric coefficients, respectively.

  Table 1 shows specific numerical values of the optical system in the first embodiment shown in FIG.

  In Numerical Example 1, the third surface (the surface on the observer side of the first lens L1 of the eyepiece optical system Gf of the finder), the fifth surface (the surface on the observer side of the second lens L2 of the eyepiece optical system Gf), The sixth surface (the object side surface of the first lens group G1 of the finder adapter Ga) and the ninth surface (the surface on the observer side of the second lens group G2 of the finder adapter Ga1) are formed as aspherical surfaces. Table 2 shows the aspheric coefficients of these surfaces.

  In the finder adapter Ga1 according to the first embodiment, the first lens group G1 moves on the optical axis to correct the finder diopter. Accordingly, the surface intervals d5 (D1) and d7 (D2) are variable. Accordingly, in addition to the reference diopter (-1 Dpt) in Numerical Example 1, the numerical values of the surface intervals d5 and d7 when the diopter is -4Dpt and the diopter + 2Dpt are shown in Table 3.

  FIG. 2 shows a spherical aberration diagram, an astigmatism diagram, and a distortion diagram at a reference diopter (−1 Dpt), FIG. 3 at a diopter −4 Dpt, and FIG. 4 at a diopter +2 Dpt. In the spherical aberration diagram, the solid line indicates the value on the d line, the broken line indicates the value on the C line, and the alternate long and short dash line indicates the value on the F line. In the astigmatism diagram, the solid line indicates the value on the sagittal image plane and the broken line indicates the value on the tangential image plane. Is shown.

  Table 4 shows specific numerical values of the optical system in the second embodiment shown in FIG.

  In Numerical Example 2, the third surface (the surface on the observer side of the first lens L1 of the eyepiece optical system Gf of the finder), the fifth surface (the surface on the observer side of the second lens L2 of the eyepiece optical system Gf), The sixth surface (the object side surface of the first lens group G1 of the finder adapter Ga2) and the ninth surface (the surface on the observer side of the second lens group G2 of the finder adapter Ga2) are formed as aspherical surfaces. Table 5 shows the aspheric coefficients of these surfaces.

  In the finder adapter Ga2 according to the second embodiment, the first lens group G1 moves on the optical axis to correct the finder diopter. Accordingly, the surface intervals d5 (D1) and d7 (D2) are variable. Therefore, in addition to the reference diopter (−1 Dpt) in Numerical Example 2, the numerical values of the surface intervals d5 and d7 when the diopter is −4Dpt and the diopter + 2Dpt are shown in Table 6.

FIG. 6 shows a spherical aberration diagram, an astigmatism diagram, and a distortion diagram at a reference diopter (−1 Dpt), FIG. 7 at a diopter −4 Dpt, and FIG. 8 at a diopter +2 Dpt. In the spherical aberration diagram, the solid line indicates the value on the d line, the broken line indicates the value on the C line, and the alternate long and short dash line indicates the value on the F line. In the astigmatism diagram, the solid line indicates the value on the sagittal image plane and the broken line indicates the value on the tangential image plane. Is shown.

  Table 7 shows each numerical value of the optical system in the third embodiment shown in FIG.

  In Numerical Example 3, the third surface (the surface on the observer side of the first lens L1 of the eyepiece optical system Gf of the finder), the fifth surface (the surface on the observer side of the second lens L2 of the eyepiece optical system Gf), The sixth surface (the object side surface of the first lens group G1 of the finder adapter Ga3) and the ninth surface (the surface on the observer side of the second lens group G2 of the finder adapter Ga3) are formed as aspherical surfaces. Table 8 shows the aspheric coefficients of these surfaces.

  In the finder adapter Ga3 according to the third embodiment, the second lens group G2 moves on the optical axis to correct the finder diopter. Accordingly, the surface distances d7 (D2) and d9 (D3) are variable. Therefore, in addition to the reference diopter (−1 Dpt) in Numerical Example 3, the numerical values of the surface distances d7 and d9 when the diopter is −4Dpt and the diopter + 2Dpt are shown in Table 9.

  FIG. 10 shows a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram at a reference diopter (−1 Dpt), FIG. 11 at a diopter −4 Dpt, and FIG. 12 at a diopter +2 Dpt. In the spherical aberration diagram, the solid line indicates the value on the d line, the broken line indicates the value on the C line, and the alternate long and short dash line indicates the value on the F line. In the astigmatism diagram, the solid line indicates the value on the sagittal image plane and the broken line indicates the value on the tangential image plane. Is shown.

  Table 10 shows specific numerical values of the optical system in the fourth embodiment shown in FIG.

  In Numerical Example 4, the third surface (the surface on the observer side of the first lens L1 of the eyepiece optical system Gf of the finder), the fifth surface (the surface on the observer side of the second lens L2 of the eyepiece optical system Gf), The sixth surface (the object side surface of the first lens group G1 of the finder adapter Ga4) and the ninth surface (the surface on the observer side of the second lens group G2 of the finder adapter Ga4) are formed as aspherical surfaces. Table 11 shows the aspheric coefficients of these surfaces.

  In the finder adapter Ga4 according to the fourth embodiment, the second lens group G2 moves on the optical axis to correct the fine fur diopter. Accordingly, the surface distances d7 (D2) and d9 (D3) are variable. Therefore, in addition to the reference diopter (-1 Dpt) in Numerical Example 3, the numerical values of the surface distances d7 and d9 when the diopter is -4Dpt and the diopter + 2Dpt are shown in Table 12.

  FIG. 14 shows a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram at a reference diopter (−1 Dpt), FIG. 15 at a diopter −4 Dpt, and FIG. 16 at a diopter +2 Dpt. In the spherical aberration diagram, the solid line indicates the value on the d line, the broken line indicates the value on the C line, and the alternate long and short dash line indicates the value on the F line. In the astigmatism diagram, the solid line indicates the value on the sagittal image plane and the broken line indicates the value on the tangential image plane. Is shown.

  Table 13 shows the numerical data of the conditional expressions (1), (2), (3) and (4) in the numerical examples described above.

  As described above, according to the present invention, it is possible to continuously correct the finder diopter, and to obtain an easy-to-see finder adapter with little optical performance and pupil diameter fluctuation accompanying diopter correction. it can.

  It should be noted that the specific shapes, configurations, and numerical values shown in the respective embodiments and numerical examples described above are merely examples of the implementation performed in the practice of the present invention, and as a result, the present invention. The technical scope should not be interpreted in a limited way.

  It can be used for a camera having only a diopter fixed for the purpose of downsizing, etc., enables continuous correction of diopter, provides a good field of view, and does not hinder downsizing.

FIG. 2 to FIG. 4 show a first embodiment of a finder adapter of the present invention, and this figure shows a configuration of an optical system. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration corresponding to -1Dpt (reference diopter). It is a figure which shows the spherical aberration, astigmatism, and distortion aberration corresponding to -4Dpt. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration corresponding to + 2Dpt. 6 to 8 show a second embodiment of the finder adapter of the present invention, and this figure shows a configuration of an optical system. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration corresponding to -1Dpt (reference diopter). It is a figure which shows the spherical aberration, astigmatism, and distortion aberration corresponding to -4Dpt. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration corresponding to + 2Dpt. FIG. 10 to FIG. 12 show a third embodiment of the finder adapter of the present invention, and this figure is a diagram showing the configuration of the optical system. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration corresponding to -1Dpt (reference diopter). It is a figure which shows the spherical aberration, astigmatism, and distortion aberration corresponding to -4Dpt. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration corresponding to + 2Dpt. FIG. 14 to FIG. 16 show a first embodiment of a finder adapter of the present invention, and this figure shows a configuration of an optical system. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration corresponding to -1Dpt (reference diopter). It is a figure which shows the spherical aberration, astigmatism, and distortion aberration corresponding to -4Dpt. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration corresponding to + 2Dpt. FIG. 4 is a partially cutaway perspective view showing an example in which the finder adapter according to the present invention is configured to be mounted on a finder of a digital camera.

Explanation of symbols

  Gf: finder eyepiece optical system, Ga1: finder adapter, Ga2: finder adapter, Ga3: finder adapter, Ga4: finder adapter, G1: first lens group, G2: second lens group

Claims (8)

A finder adapter to be mounted behind the eyepiece optical system in the finder optical system,
In order from the object side, the first lens group having a negative refractive power and a second lens group having a positive refractive power,
A finder adapter characterized by continuously correcting the finder diopter by moving the first lens group in the optical axis direction and satisfying the following conditional expressions (1), (2) and (3): .
(1) 2.5 <f1 + f2 <5.0
(2) 150 <| f1 · f2 | <600
(3) | f1 / f2 |> 0.8
However,
f1: The focal length of the first lens group f2: The focal length of the second lens group. 2. The finder adapter according to claim 1, wherein each of the first lens group and the second lens group includes one lens and satisfies the following conditional expression (4).
(4) | R11 | · L / n <55
However,
R11: Radius of curvature of the entrance-side surface of the lens constituting the first lens group n: Refractive index at the d-line of the lens constituting the first lens group of the finder adapter L: From the exit surface of the final lens of the finder adapter to the finder adapter The air-converted distance on the optical axis to the entrance surface of the lens constituting the first lens group when the first lens group is located closest to the observer side. A finder adapter to be mounted behind the eyepiece optical system in the finder optical system,
In order from the object side, the first lens group having a negative refractive power and a second lens group having a positive refractive power,
A finder adapter characterized by continuously correcting the finder diopter by moving the second lens group in the optical axis direction and satisfying the following conditional expressions (1), (2) and (3): .
(1) 2.5 <f1 + f2 <5.0
(2) 150 <| f1 · f2 | <600
(3) | f1 / f2 |> 0.8
However,
f1: The focal length of the first lens group f2: The focal length of the second lens group. 4. The finder adapter according to claim 3, wherein each of the first lens group and the second lens group includes one lens and satisfies the following conditional expression (4).
(4) | R11 | · L / n <55
However,
R11: Radius of curvature of the entrance-side surface of the lens constituting the first lens group n: Refractive index at the d-line of the lens constituting the first lens group of the finder adapter L: From the exit surface of the final lens of the finder adapter to the finder adapter The air-converted distance on the optical axis to the entrance surface of the lens constituting the first lens group. The finder adapter according to claim 1, further comprising an eye cup. The finder adapter according to claim 2, wherein an eye cup is provided. The finder adapter according to claim 3, wherein an eye cup is provided. The finder adapter according to claim 4, wherein an eye cup is provided.

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