JP2004109961A - Viewfinder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a viewfinder which has a compact constitution while having a long focal length and demonstrates a satisfactory performance. <P>SOLUTION: The viewfinder is provided with a first lens group having a positive optical power and a second lens group having a negative optical power, in order from the observer side, and either of the first lens group and the second lens group is moved along an optical axis to correct diopter. Since the viewfinder is constituted of two lens groups in this manner, diopter can be corrected by moving only one of the first lens group and the second lens group, and the extent of movement can be made smaller than that for movement of moving an entire system. Thus the viewfinder is made compact as the whole, and the variance of magnifications is reduced because change of the visual angle at the time of diopter correction is reduced. Since the viewfinder is constituted of two lens groups, a principal point position on the entrance pupil side is brought closer to an entrance pupil position so that the distortion can be reduced. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a viewfinder mounted on an imaging apparatus, and more particularly to a viewfinder having a relatively large focal length suitable for mounting on a high-resolution television camera or the like.
[0002]
[Prior art]
2. Description of the Related Art In general, an imaging device such as a video camera or a television camera is provided with an electronic viewfinder (hereinafter simply referred to as a viewfinder) that allows a user to look in order to observe an image displayed on an image display surface. The conventional viewfinder for a television camera has a simple configuration such as a single-group configuration including one lens or a single-group configuration including two lenses. In the viewfinder having such a configuration, the diopter is adjusted by moving the entire system back and forth along the optical axis.
[0003]
An example of a viewfinder having a single-group structure is described in Japanese Patent Application Laid-Open No. H11-163,837. Further, for example, there is also a viewfinder having a three-unit / one-group configuration described in Patent Document 2.
[0004]
[Patent Document 1]
Japanese Utility Model Publication No. 5-41271
[Patent Document 2]
JP-A-2002-10112
[0005]
[Problems to be solved by the invention]
In recent years, for example, as represented by an HD (High Definition) camera used for digital broadcasting, the resolution of an imaging device has been remarkably increased. Therefore, in the viewfinder mounted on the imaging device, the focal length of the viewfinder is inevitably increased in order to cope with higher resolution.
[0006]
However, in the one-group configuration as described in Patent Document 1, when the focal length of the viewfinder exceeds, for example, 100 mm, the amount of lens movement when performing diopter correction increases, and the viewfinder becomes large. I will. Further, in this case, an increase in the amount of movement of the lens causes an increase in magnification variation when performing diopter correction. In addition, it is difficult to satisfactorily correct distortion particularly in the single-unit configuration.
[0007]
In the viewfinder described in Patent Literature 2, one lens located closest to the viewer and two subsequent lenses have a positive focal length. Therefore, the focal length is inevitably short (33.73 mm), and it is difficult to increase the focal length.
[0008]
The present invention has been made in view of such a problem, and an object of the present invention is to provide a viewfinder that has a compact configuration and exhibits good performance even if it has a large focal length.
[0009]
[Means for Solving the Problems]
A viewfinder according to a first aspect of the present invention is a viewfinder for observing an image display surface, and includes, in order from an observer side, a positive first lens group and a negative second lens group, One of the first lens group and the second lens group is configured to be able to correct diopter by moving along the optical axis. Here, the positive lens group is a lens group having a positive refractive power (power) as a whole, and the negative lens group is a lens group having a negative refractive power as a whole.
[0010]
A viewfinder according to a second aspect of the present invention is a viewfinder for observing an image display surface, and includes, in order from an observer side, a positive first lens group and a negative second lens group, The first lens group is configured to be able to correct diopter by moving along the optical axis.
[0011]
A viewfinder according to a third aspect of the present invention is a viewfinder for observing an image display surface, and includes, in order from an observer side, a positive first lens group and a negative second lens group, The second lens group is configured to be able to correct diopter by moving along the optical axis.
[0012]
In the viewfinder according to the first to third aspects of the present invention, since the above-described two-group configuration is employed, the diopter correction is performed by moving one of the first lens group and the second lens group. And the amount of movement can be suppressed to be smaller than when the entire system is moved. For this reason, a change in the viewing angle at the time of diopter correction can be reduced. In addition, with the two-group configuration, the principal point position on the entrance pupil side becomes closer to the eye point (entrance pupil position), so that distortion can be reduced.
[0013]
It is preferable that the viewfinder according to the second aspect of the present invention be configured so as to satisfy the following conditional expressions (1) and (2).
0.4 <| f1 / f | <0.75 (1)
0.5 <| f2 / f | <1.8 (2)
Here, f indicates the focal length of the entire system, f1 indicates the focal length of the first lens group, and f2 indicates the focal length of the second lens group. By satisfying these conditional expressions (1) and (2), appropriate power distribution can be performed, and spherical aberration, astigmatism, and distortion can be favorably corrected.
[0014]
In the viewfinder according to the third aspect of the present invention, it is desirable to configure so as to satisfy the following conditional expressions (3) and (4).
0.4 <| f1 / f | <0.6 (3)
0.5 <| f2 / f | <0.8 (4)
Here, f indicates the focal length of the entire system, f1 indicates the focal length of the first lens group, and f2 indicates the focal length of the second lens group. By satisfying these conditional expressions (3) and (4), appropriate power distribution can be performed, and spherical aberration, astigmatism, and distortion can be favorably corrected.
[0015]
In the viewfinder according to the second and third aspects of the present invention, the first lens group includes a positive cemented lens including a negative first lens and a positive second lens, and has the following conditional expression (5). It is desirable to configure so as to satisfy ()).
n12> 1.8 (5)
Here, n12 is the refractive index of the second lens. By satisfying conditional expression (5), the radius of curvature of the second lens can be increased to some extent, so that occurrence of spherical aberration can be reduced.
[0016]
In the viewfinder according to the second and third aspects of the present invention, the first lens group is constituted by a positive cemented lens including a negative first lens and a positive second lens, and a positive single lens. It may be. As described above, by adding a positive single lens to the first lens group, it is possible to reduce the power burden on the positive cemented lens and reduce the occurrence of spherical aberration.
[0017]
In the viewfinder according to the second and third aspects of the present invention, the first lens group includes a positive cemented lens including a negative first lens and a positive second lens, and the second lens group includes It is desirable that the zoom lens be composed of a negative single lens and further satisfy the following conditional expression (6).
| {(N−1) / r} (1 / ν11) − (1 / ν12)} + 1 / (ν21 · f21) | <5.0 × 10 ^-4 [1 / mm] (6)
Here, n is the average refractive index of the first lens and the second lens, r is the radius of curvature of the joint surface between the first lens and the second lens, ν11 is the Abbe number of the first lens, and ν12 is the Abbe number of the second lens. The number, ν21, is the Abbe number of the negative single lens, and f21 is the focal length of the negative single lens. By satisfying conditional expression (6), the amount of chromatic aberration generated can be suppressed to a practically acceptable level.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0019]
[First Embodiment]
First, the configuration of a viewfinder according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 shows an example of a lens configuration of a viewfinder 1 according to the present embodiment. In FIG. 1, the side indicated by the symbol Zeye is the observation side (also referred to as the observer side or the entrance pupil side), while the side indicated by the symbol Zimg is the observation image side. The symbol Simg is an image display surface of a CRT (cathode-ray tube) or an LCD (liquid crystal display: liquid crystal display). The symbol Ri indicates an eye point (entrance pupil position). P. Is the first, and shows the radius of curvature on the i-th (i = 1 to 6) optical surface that sequentially increases toward the observation image side. The symbol Di indicates a surface interval on the optical axis between the i-th optical surface and the (i + 1) -th optical surface. Further, the symbol Lj is the eye point E. P. The j-th (j = 1 to 3) lenses sequentially increasing from the side to the observation image side are shown. The configuration example shown in FIG. 1 corresponds to the lens configuration of Example 1 (FIG. 6) described later.
[0020]
The viewfinder 1 shown in FIG. 1 is suitable for mounting on an image pickup apparatus compatible with a high resolution, such as an HD camera for digital broadcasting, and allows a user to be displayed on an image display surface such as an LCD. This is for observing the enlarged image. As shown in FIG. 1, the viewfinder 1 includes a first lens group G1 having a positive refractive power as a whole and a second lens having a negative refractive power as a whole along an optical axis Z1 from the observer side. And a group G2. The first lens group G1 is configured to be able to correct diopter by moving in the Z direction on the optical axis Z1.
[0021]
It is desirable that the viewfinder 1 be configured to satisfy the following conditional expressions (1) and (2) in order to secure compactness with good aberration performance. Here, f indicates the focal length of the entire viewfinder 1, f1 indicates the focal length of the first lens group G1, and f2 indicates the focal length of the second lens group G2.
0.4 <| f1 / f | <0.75 (1)
0.5 <| f2 / f | <1.8 (2)
[0022]
The first lens group G1 is a cemented lens composed of a negative first lens L1 and a positive second lens L2 having a positive refractive power in order from the entrance pupil side, and satisfies the following conditional expression (5). It is desirable to be constituted. Here, n12 is the refractive index of the second lens L2.
n12> 1.8 (5)
[0023]
The first lens L1 has, for example, a meniscus shape with the convex surface facing the entrance pupil side. The second lens L2 has, for example, a lens shape in which both surfaces are convex.
[0024]
The second lens group G2 includes a single lens L3 having a negative refractive power. This single lens L3 has, for example, a meniscus shape with a concave surface facing the entrance pupil side.
[0025]
It is desirable that the viewfinder 1 is further configured to satisfy the following conditional expression (6). Here, n indicates the average refractive index of the first lens L1 and the second lens L2, and r indicates the radius of curvature of the joint surface between the first lens L1 and the second lens L2. ν11 indicates the Abbe number of the first lens L1, ν12 indicates the Abbe number of the second lens L2, and ν21 indicates the Abbe number of the negative single lens L3. Further, f21 indicates the focal length of the negative single lens L3.
| {(N−1) / r} (1 / ν11) − (1 / ν12)} + 1 / (ν21 · f21) | <5.0 × 10 ^-4 [1 / mm] (6)
[0026]
Next, an optical function and an effect provided by the viewfinder 1 having the above configuration will be described.
[0027]
Since the viewfinder 1 has a two-group configuration including a first positive lens group G1 and a second negative lens group G2, unlike the viewfinder described in Patent Document 2, a long focal length is ensured. Becomes possible. Further, since the diopter correction can be performed by moving only the first lens group G1 in the Z direction while the second lens group G2 is fixed, the movement amount of the first lens group G1 is limited to the entire system. Can be suppressed to a smaller value than when diopter correction is performed. This is because the amount of lens movement required for diopter correction is proportional to the square of the focal length of the entire moving lens portion. That is, in a single-group viewfinder, f ² When the diopter correction requiring a movement of / 1000 mm is performed by the viewfinder 1 having a two-group configuration, the diopter correction is the square of the focal length of the first lens group G1 (f1). ² / 1000 mm. Since the focal length f1 of the first lens group G1 is shorter than the focal length f of the entire viewfinder system, the movement amount (f1) of the first lens group G1. ² / 1000 mm is smaller. For this reason, even if the focal length of the entire viewfinder 1 becomes large, it is possible to keep the entire size compact.
[0028]
By the way, in general, when the diopter correction is performed by moving the view finder, the viewing angle of the observation image changes, so that the magnification of the observation image changes. For example, when the lens moves to the entrance pupil side, the viewing angle of the observation image becomes small, so that the magnification becomes small. Conversely, when the lens moves to the observation image side, the viewing angle increases, so that the magnification increases. The viewfinder 1 of the present embodiment has a two-group configuration, in which only the first lens group G1 is moved and the amount of movement is reduced, so that the change in the viewing angle during diopter correction is smaller than when the entire system is moved. Can be reduced. Therefore, a change in magnification of the observation image can be suppressed to a small value.
[0029]
Furthermore, in the viewfinder 1, distortion can be reduced by adopting a two-group configuration. In the case where the viewfinder has a positive single-unit configuration, the principal point position on the entrance pupil side and the eye point E.E. P. , The pincushion type distortion is likely to occur. However, by adopting the two-group configuration, the principal point position on the entrance pupil side becomes the eye point E. P. , The distortion can be reduced.
[0030]
Conditional expressions (1) and (2) define appropriate power ranges of the first lens group G1 and the second lens group G2. If the lower limits of conditional expressions (1) and (2) are not reached, the powers of the first lens group G1 and the second lens group G2 become too strong, and spherical aberration, astigmatism, and distortion cannot be corrected. On the other hand, if the upper limit is exceeded, the powers of the first lens group G1 and the second lens group G2 become weak, and the amount of movement of the first lens group G1 becomes large during diopter correction. As a result, the compactness of the entire viewfinder 1 is lost.
[0031]
When the viewfinder has a two-group configuration including a positive lens group G1 and a negative lens group G2, it is necessary to increase the power of the positive lens group G1 as compared with the case of a single-group positive lens group. Since the curvature of the lens sphere must be reduced, the amount of spherical aberration generated increases. To correct this, conditional expression (5) defines the magnitude of the refractive index n12 of the second lens L2. By setting the refractive index n12 to be larger than 1.8, the radius of curvature of the spherical surface of the lens can be maintained to some extent, so that the spherical aberration can be suppressed. On the other hand, when the refractive index n12 is 1.8 or less, it is difficult to sufficiently correct spherical aberration.
[0032]
Conditional expression (6) represents the first term on the left side.
{(N-1) / r} (1 / ν11)-(1 / ν12)}
Represents the chromatic aberration that occurs on the cemented surface r of the first lens group G1, and the second term on the left-hand side
1 / (ν21 · f21)
Represents chromatic aberration generated in the second lens group G2. By canceling each other and satisfying conditional expression (4), the amount of chromatic aberration generated in the entire viewfinder 1 can be suppressed to a practically acceptable level. When the value exceeds the range of the conditional expression (6), the chromatic aberration increases, and the observed image deteriorates.
[0033]
Further, since the second lens group G2 is fixed and the first lens group G1 is movable, a sufficient back focus can be secured. Thus, for example, another optical component such as a deflection mirror for deflecting the optical path can be arranged between the second lens group G2 and the image plane.
[0034]
As described above, the viewfinder 1 according to the present embodiment has a two-group configuration including the first positive lens group G1 and the second negative lens group G2, and only the first positive lens group G1. Is moved at the time of diopter correction, so that even with the viewfinder 1 having a large focal length, the overall size can be kept compact and the change in magnification of the observed image can be suppressed. In addition, since equations (1), (2), (5) and (6) are satisfied, spherical aberration, astigmatism, distortion, chromatic aberration, and the like can be suppressed, and good aberration performance is exhibited. can do.
[0035]
[Second embodiment]
Next, a second embodiment of the present invention will be described. In the following description, portions that are substantially the same as the components in the first embodiment are given the same reference numerals, and descriptions thereof will be omitted as appropriate.
[0036]
2 and 3 show examples of lens configurations of the viewfinders 2 and 3 according to the present embodiment, respectively. In the first embodiment, the viewfinder 1 in which the first lens group G1 includes one set of cemented lenses has been described. On the other hand, in the present embodiment, viewfinders 2 and 3 in which the first lens group G1 includes one set of cemented lenses and one single lens will be described. The configuration example shown in FIG. 2 corresponds to the lens configuration of Example 2 (FIG. 11) described later, and the configuration example shown in FIG. 3 corresponds to the lens configuration of Example 3 (FIG. 12) described later. I have. 2 and 3, the symbol Ri indicates the eye point E.E. P. Is the first, and shows the radius of curvature on the i-th (i = 1 to 8) optical surface that sequentially increases toward the observation image side. The symbol Di indicates a surface interval on the optical axis between the i-th optical surface and the (i + 1) -th optical surface. Further, the symbol Lj is the eye point E.E. P. The j-th (j = 1 to 4) lenses sequentially increasing from the side to the observation image side are shown.
[0037]
Like the viewfinder 1, the viewfinders 2 and 3 according to the present embodiment shown in FIGS. 2 and 3 are particularly suitable for being mounted on an imaging device compatible with a high resolution, such as an HD camera for digital broadcasting. This is intended for a user to magnify and observe an image displayed on an image display surface such as an LCD. As shown in FIGS. 2 and 3, the viewfinder 1 has a first lens group G1 having a positive refractive power as a whole and a second lens group having a negative refractive power as a whole along the optical axis Z1 in order from the observer side. And two lens groups G2. The first lens group G1 is configured to be able to correct diopter by moving along the optical axis Z1.
[0038]
The viewfinders 2 and 3 are preferably configured to satisfy the following conditional expressions (1) and (2) in order to ensure good aberration performance and compactness. Here, f indicates the focal length of the entire viewfinder 2, 3, f1 indicates the focal length of the first lens group G1, and f2 indicates the focal length of the second lens group G2.
0.4 <| f1 / f | <0.75 (1)
0.5 <| f2 / f | <1.8 (2)
[0039]
The first lens group G1 includes, in order from the entrance pupil side, a cemented lens including a first negative lens L1 and a second positive lens L2 having a positive refractive power, and a single lens L3 having a positive refractive power. The first lens L1 has, for example, a meniscus shape with the convex surface facing the entrance pupil side. The second lens L2 has, for example, a lens shape in which both surfaces are convex. The single lens L3 has, for example, a plano-convex shape or a biconvex shape.
[0040]
The second lens group G2 includes a single lens L4 having a negative refractive power. The single lens L4 has, for example, a lens shape in which both sides are concave.
[0041]
It is desirable that the viewfinders 2 and 3 are further configured to satisfy the following conditional expression (6). Here, n indicates the average refractive index of the first lens L1 and the second lens L2, and r indicates the radius of curvature of the joint surface between the first lens L1 and the second lens L2. ν11 indicates the Abbe number of the first lens L1, ν12 indicates the Abbe number of the second lens L2, and ν21 indicates the Abbe number of the negative single lens L4. Further, f21 indicates the focal length of the negative single lens L4.
| {(N−1) / r} (1 / ν11) − (1 / ν12)} + 1 / (ν21 · f21) | <5.0 × 10 ^-4 [1 / mm] (6)
[0042]
In the viewfinders 2 and 3 having the above-described configurations, the first lens group G1 and the negative second lens group G2 are used to correct spherical aberration that increases due to the two-group configuration. Positive power is divided by increasing the number of lenses constituting the lens group G1. That is, the power necessary for the entire first lens group G1 is distributed to the cemented lens (L1 + L2) and the single lens L3. Therefore, the power load on the cemented lens (L1 + L2) is reduced, and the spherical aberration generated by the cemented lens (L1 + L2) is reduced. Therefore, even when the refractive index n12 of the second lens L2 is small (for example, 1.8 or less), it is possible to satisfactorily correct the spherical aberration. Other functions and effects are the same as those of the first embodiment.
[0043]
[Third Embodiment]
Next, a third embodiment of the present invention will be described. In the following description, portions that are substantially the same as the components in the first and second embodiments are given the same reference numerals, and descriptions thereof will be omitted as appropriate.
[0044]
FIG. 4 shows a lens configuration example of the viewfinder 4 according to the present embodiment. In the first and second embodiments, the viewfinder 1 capable of correcting diopter by moving the first lens group G1 on the optical axis Z1 has been described. On the other hand, in the present embodiment, a description will be given of the viewfinder 4 configured so that the diopter can be corrected by moving the second lens group G2 in the Z direction on the optical axis Z1. The configuration example shown in FIG. 4 corresponds to the lens configuration of a fourth embodiment (FIG. 19) described later.
[0045]
The viewfinder 4 shown in FIG. 4 includes the same first lens group G1 and second lens group G2 as the viewfinder 1 in the first embodiment. However, the difference is that the second lens group G2 is configured to be able to correct diopter by moving in the Z direction on the optical axis Z1.
[0046]
It is desirable that the viewfinder 4 be configured to satisfy the following conditional expressions (3) and (4) in order to secure compactness with good aberration performance. Here, f indicates the focal length of the entire viewfinder 4, f1 indicates the focal length of the first lens group G1, and f2 indicates the focal length of the second lens group G2.
0.4 <| f1 / f | <0.6 (3)
0.5 <| f2 / f | <0.8 (4)
[0047]
Similar to the viewfinder 1, the first lens group G1 is a cemented lens having a positive refractive power including a negative first lens L1 and a positive second lens L2 in order from the entrance pupil side. It is desirable to be configured to satisfy 5). Here, n12 is the refractive index of the second lens L2.
n12> 1.8 (5)
[0048]
The second lens group G2 includes a single lens L3 having a negative refractive power, similarly to the viewfinder 1.
[0049]
It is desirable that the viewfinder 4 be further configured to satisfy the following conditional expression (6).
| {(N−1) / r} (1 / ν11) − (1 / ν12)} + 1 / (ν21 · f21) | <5.0 × 10 ^-4 [1 / mm] (6)
[0050]
Next, the optical function and effect provided by the viewfinder 4 having the above configuration will be described.
[0051]
Since the viewfinder 4 has a two-group configuration including the first positive lens group G1 and the second negative lens group G2, unlike the viewfinder described in Patent Document 2, a long focal length is ensured. Becomes possible. Furthermore, since it is possible to perform diopter correction by moving only the second lens group G2 in the Z direction while the first lens group G1 is fixed, the viewfinder is similar to the first embodiment. 4. Even if the focal length of the whole becomes large, the whole size can be kept compact.
[0052]
Further, the viewfinder 4 has a two-group configuration, in which only the second lens group G2 is moved to reduce the amount of movement, so that a change in the viewing angle during diopter correction is reduced as compared with the case where the entire system is moved. be able to. Therefore, a change in magnification of the observation image can be suppressed to a small value.
[0053]
Conditional expressions (3) and (4) define appropriate power ranges of the first lens group G1 and the second lens group G2. If the lower limits of conditional expressions (3) and (4) are exceeded, the powers of the first lens group G1 and the second lens group G2 become too strong, and spherical aberration, astigmatism, and distortion cannot be corrected. On the other hand, if the upper limit is exceeded, the powers of the first lens group G1 and the second lens group G2 become weak, and the amount of movement of the first lens group G1 becomes large during diopter correction. As a result, the compactness of the entire viewfinder 4 is lost.
[0054]
Further, since the first lens group G1 is fixed and the second lens group G2 is movable, the hermeticity of the viewfinder 4 can be ensured, and the entry of dust and the like from the outside into the viewfinder 4 can be avoided. be able to.
[0055]
As in the first embodiment, the viewfinder 4 has a two-group configuration, so that distortion can be reduced. In addition, since the viewfinder 4 satisfies Expression (7), spherical aberration can be suppressed. Further, since the viewfinder 4 satisfies Expression (8), chromatic aberration can be suppressed.
[0056]
As described above, the viewfinder 4 according to the present embodiment has a two-group configuration including the first positive lens group G1 and the second negative lens group G2, and includes only the second positive lens group G2. Is moved at the time of diopter correction, so that even with the viewfinder 4 having a large focal length, the overall size can be kept compact and the change in magnification of the observed image can be suppressed. Further, since the viewfinder 4 satisfies the expressions (5) to (8), it is possible to suppress spherical aberration, astigmatism, distortion, chromatic aberration, and the like, and to exhibit good aberration performance. .
[0057]
[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described. In the following description, the same reference numerals are given to substantially the same components as the components in the second and third embodiments, and the description will be appropriately omitted.
[0058]
FIG. 5 shows a lens configuration example of the viewfinder 5 according to the present embodiment. In the second embodiment, the first lens group G1 is configured to be able to correct the diopter by moving on the optical axis Z1, and the first lens group G1 includes one set of a cemented lens and one lens. The viewfinders 2 and 3 configured with a single lens have been described. In the third embodiment, the diopter can be corrected by moving the second lens group G2 on the optical axis Z1, and the first lens group G1 includes one set of cemented lenses. The viewfinder 4 configured as described above has been described. On the other hand, in the present embodiment, the diopter can be corrected by moving the second lens group G2 on the optical axis Z1, and the first lens group G1 is composed of a set of cemented lenses and The viewfinder 5 composed of a single lens will be described. The configuration example shown in FIG. 5 corresponds to a lens configuration of a later-described embodiment 5 (FIG. 24).
[0059]
The viewfinder 5 according to the present embodiment shown in FIG. 5 includes a first lens group G1 and a second lens group G2 along the optical axis Z1, like the viewfinders 1 to 4. However, the diopter can be corrected by moving the second lens group G2 in the Z direction along the optical axis Z1.
[0060]
It is desirable that the viewfinder 5 be configured to satisfy the following conditional expressions (3) and (4) in order to secure compactness with good aberration performance. Here, f indicates the focal length of the entire viewfinder 5, f1 indicates the focal length of the first lens group G1, and f2 indicates the focal length of the second lens group G2.
0.4 <| f1 / f | <0.6 (3)
0.5 <| f2 / f | <0.8 (4)
[0061]
The configuration of the first lens group G1 and the second lens group G2 is the same as that of the viewfinder 2. Specifically, the first lens group G1 includes, in order from the entrance pupil side, a cemented lens including a negative first lens L1 and a positive second lens L2 having a positive refractive power, and a single lens having a positive refractive power. L3. The first lens L1 has, for example, a meniscus shape with the convex surface facing the entrance pupil side. The second lens L2 has, for example, a lens shape in which both surfaces are convex. The single lens L3 has, for example, a plano-convex shape or a biconvex shape. The second lens group G2 includes a single lens L4 having a negative refractive power. The single lens L4 has, for example, a lens shape in which both sides are concave.
[0062]
It is desirable that the viewfinder 5 be further configured to satisfy the following conditional expression (6).
| {(N−1) / r} (1 / ν11) − (1 / ν12)} + 1 / (ν21 · f21) | <5.0 × 10 ^-4 [1 / mm] (6)
[0063]
In the viewfinder 5 configured as described above, similarly to the second embodiment, the power necessary for the entire first lens group G1 is distributed to the cemented lens (L1 + L2) and the single lens L3. Therefore, the power load on the cemented lens (L1 + L2) is reduced, and the spherical aberration generated by the cemented lens (L1 + L2) is reduced. Therefore, similarly to the viewfinders 2 and 3, it is possible to satisfactorily correct the spherical aberration even when the refractive index n12 of the second lens L2 is small (for example, 1.8 or less). Other functions and effects are the same as in the third embodiment.
[0064]
【Example】
Next, several examples of the viewfinder according to each of the above embodiments will be described.
[0065]
<Example 1>
First, a numerical example of the first embodiment will be described. FIGS. 6A and 6B show lens data as Example 1 corresponding to the viewfinder 1 (FIG. 1) in the first embodiment. FIG. 6A shows a basic data portion of the lens data of these examples, and FIG. 6B shows the values of the surface intervals D1 and D4 that fluctuate due to diopter adjustment.
[0066]
The column of the surface number Si in FIG. 6A indicates the number corresponding to each surface of the lens in FIG. The column of the radius of curvature Ri indicates a value corresponding to the symbol Ri attached to FIG. 1, and the column of the surface interval Di indicates a value corresponding to the symbol Di assigned to FIG. The unit of the value of the radius of curvature Ri and the surface interval Di is millimeter (mm). The columns of the refractive index nj and the Abbe number νj indicate the eye point E.E. P. The values of the refractive index and Abbe number of the j-th (j = 1 to 3) lens Lj from d side (due to 587.6 nm) are shown. The focal length f of the entire viewfinder 1 is 150.0 mm. In FIG. 6A, ν1 (= 25.46) corresponds to a specific example of “ν11” in the conditional expression (6) of the present invention, and ν2 (= 42.98) corresponds to the conditional expression (6) of the present invention. ) Corresponds to a specific example of “ν12”, and ν3 (= 64.20) corresponds to a specific example of “ν21” in the conditional expression (6) of the present invention. Further, n2 corresponds to “n12” in conditional expression (5) of the present invention.
[0067]
In FIG. 6B, a correction of 0 dpt is a case where no diopter correction is performed. The diopter of −2.5 dpt indicates a case where the first lens group G1 is moved to the observation image side to perform correction, and the diopter of +1.0 dpt is corrected by moving the first lens group G1 to the entrance pupil side. Is performed.
[0068]
FIG. 7 shows numerical values corresponding to the above-mentioned conditional expressions (1), (2), (5) and (6) in Example 1 together with numerical values in Examples 2 and 3 described later. Things. As shown in FIG. 7, the first embodiment satisfies the conditional expressions (1), (2), (5) and (6).
[0069]
The lens movement amount necessary for correcting the diopter by 1 dpt is approximately F, where F is the focal length of the entire moving lens portion. ² / 1000mm. Accordingly, when the focal length f of the entire viewfinder is 150.0 mm (F = f), the lens movement amount in the single-unit configuration is 150. ² / 1000, which is about 22.5 mm. On the other hand, in the viewfinder 1, since the focal length f1 of the first lens group G1 is 78 mm (Example 1) (F = f1), the lens movement amount is 78. ² At / 1000, it becomes about 6.1 mm, which is much smaller. As described above, it has been found that the total size can be reduced by adopting the two-group configuration.
[0070]
FIGS. 8A to 8C are aberration diagrams respectively showing the spherical aberration, astigmatism, and distortion (distortion) of the viewfinder 1 when the diopter is 0 dpt in the first embodiment. Similarly, FIGS. 9A to 9C are aberration diagrams when the diopter is −2.5 dpt, and FIGS. 10A to 10C are aberration diagrams when the diopter is +1.0 dpt. is there. 8 to 10 show values for the d-line (wavelength 587.6 nm), C-line (wavelength 656.3 nm), and F-line (wavelength 486.1 nm). Astigmatism indicates a value for the d-line.
[0071]
As can be seen from the lens data and the aberration diagrams described above, the viewfinder 1 of Example 1 has a compact overall size even with a large focal length of 150.0 mm, and favorably corrects various aberrations. Thus, the optimum performance for a high-resolution imaging device is obtained. Specifically, in the first embodiment, the diopter can be corrected by 1 dpt by moving the first lens group G1 by about 6.1 mm while the focal length f of the entire system is 150.0 mm.
[0072]
<Examples 2 and 3>
Next, numerical examples of the viewfinders 2 and 3 in the second embodiment will be described with reference to FIGS.
[0073]
FIGS. 11A and 11B show lens data as Example 2 corresponding to the viewfinder 2 (FIG. 2) in the second embodiment. Similarly, FIGS. 12A and 12B show lens data as Example 3 corresponding to the viewfinder 3 (FIG. 3) in the second embodiment. FIGS. 11 (A) and 12 (A) show the basic data portion of the lens data of these examples, and FIGS. 11 (B) and 12 (B) show the diopter adjustment. The values of the fluctuating surface distances D1 and D6 are shown. The meaning of each item in the lens data shown in FIGS. 11A and 11B and FIGS. 12A and 12B is the same as that in FIGS. 6A and 6B, and will not be described here. Omitted. However, the columns of the refractive index nj and the Abbe number νj indicate the eye point E.E. P. The values of the refractive index and Abbe number of the j-th (j = 1 to 4) lens Lj with respect to the d-line (wavelength 587.6 nm) from the side of are shown. In FIGS. 11A and 12A, ν1 corresponds to one specific example of “ν11” in conditional expression (6) of the present invention, and ν2 corresponds to “ν12” in conditional expression (6) of the present invention. This corresponds to one specific example, and ν4 corresponds to one specific example of “ν21” in the conditional expression (6) of the present invention.
[0074]
In Example 2, the focal length f of the entire system was set to 150.0 mm. In Example 3, f was set to 97.4 mm. As shown in FIG. 7, the second and third embodiments also satisfy the conditional expressions (1), (2) and (6).
[0075]
Regarding the movement amount when the diopter is corrected by 1 dpt, since the focal length f1 of the first lens group G1 in the second embodiment is 72 mm, the lens movement amount is about 5.2 (= 72). ² / 1000) mm, which is much smaller than the lens movement in the single-unit configuration. Similarly, since the focal length f1 of the first lens group G1 in the third embodiment is 70 mm, the lens movement amount is about 4.9 (= 70). ² / 1000) mm, and the lens movement amount 9.5 (= 97.4) in the one-unit configuration. ² / 1000) mm. As described above, it has been found that the total size can be reduced by adopting the two-group configuration.
[0076]
13A to 13C are aberration diagrams respectively showing the spherical aberration, astigmatism, and distortion (distortion) of the viewfinder 2 when the diopter is 0 dpt in the second embodiment. Similarly, FIGS. 14A to 14C are aberration diagrams at a diopter of −2.5 dpt in the second embodiment, and FIGS. 15A to 15C are diopter +1.0 dpt in the second embodiment. FIG. 7 is an aberration diagram for the case of FIG. FIGS. 16 to 18 are aberration diagrams for the diopter of 0, −2.5, and +1.0 dpt in the third embodiment. The target wavelengths are the same as in the first embodiment.
[0077]
As can be seen from the lens data and the aberration diagrams described above, the viewfinders 2 and 3 of Embodiments 2 and 3 have a large focal length and a compact overall size, and various aberrations are well corrected. Therefore, the optimum performance is obtained for a high-resolution imaging device. Specifically, in Example 2, the diopter can be corrected by 1 dpt by moving the first lens group G1 by about 5.2 mm while the focal length f of the entire system is 150.0 mm. In the third embodiment, the diopter can be corrected by 1 dpt by moving the first lens group G1 by about 4.9 mm while the focal length f of the entire system is 97.4 mm.
[0078]
<Example 4>
Next, numerical examples of the viewfinder 4 according to the third embodiment will be described with reference to FIGS. FIGS. 19A and 19B show lens data as Example 4 corresponding to the viewfinder 4 (FIG. 4). FIG. 19A shows the basic data portion of the lens data of these examples, and FIG. 19B shows the values of the surface intervals D4 and D6 that fluctuate due to diopter adjustment. Since the meaning of each item in the lens data shown in FIGS. 19A and 19B is the same as that in FIGS. 6A and 6B, the description is omitted here. However, in FIG. 19A, ν1 (= 25.46) corresponds to a specific example of “ν11” in the conditional expression (6) of the present invention, and ν2 (= 42.98) corresponds to the conditional expression of the present invention. Ν3 (= 64.20) corresponds to a specific example of “ν12” in the conditional expression (6) of the present invention. Further, n2 corresponds to “n12” in conditional expression (5) of the present invention. The focal length f of the entire viewfinder 4 was set to 150.0 mm.
[0079]
FIG. 20 shows numerical values corresponding to the above-mentioned conditional expressions (3) to (6) in Example 4 together with numerical values in Example 5 described later. As shown in FIG. 20, the fourth embodiment satisfies the conditional expressions (3) to (6).
[0080]
Regarding the amount of movement when the diopter is corrected by 1 dpt, since the focal length f2 of the second lens group G2 in Example 4 is -99.3 mm, the amount of movement of the lens is (-99.3). ² / 1000) becomes about 9.9 mm, and the lens movement amount 22.5 (= 150) in the one-unit configuration. ² / 1000) mm. As described above, it was confirmed that the total size can be reduced by adopting the two-group configuration.
[0081]
FIGS. 21A to 21C are aberration diagrams respectively showing the spherical aberration, astigmatism, and distortion (distortion) of the viewfinder 4 when the diopter is 0 dpt in the fourth embodiment. Similarly, FIGS. 22A to 22C are aberration diagrams when the diopter is −2.5 dpt, and FIGS. 23A to 23C are aberration diagrams when the diopter is +1.0 dpt. is there. The target wavelengths are the same as in the first embodiment.
[0082]
As can be seen from the lens data and the aberration diagrams described above, the viewfinder 4 of Example 4 has a compact overall size even with a large focal length of 150.0 mm, and favorably corrects various aberrations. Thus, the optimum performance for a high-resolution imaging device is obtained. Specifically, in Example 4, the diopter can be corrected by 1 dpt by moving the second lens group G2 by about 9.9 mm while the focal length f of the entire system is 150.0 mm.
[0083]
<Example 5>
Next, a numerical example of the viewfinder 5 according to the fourth embodiment will be described with reference to FIG. 20 and FIGS.
[0084]
FIGS. 24A and 24B show lens data as Example 5 corresponding to the viewfinder 5 (FIG. 5) in the fourth embodiment. FIG. 24A shows the basic data portion of the lens data of these examples, and FIG. 24B shows the values of the surface intervals D6 and D8 that fluctuate due to diopter adjustment. The meanings of the respective items in the lens data shown in FIGS. 24A and 24B are the same as those in FIGS. 11A and 11B, and a description thereof will be omitted. However, the columns of the refractive index nj and the Abbe number νj indicate the eye point E.E. P. The values of the refractive index and Abbe number of the j-th (j = 1 to 4) lens Lj with respect to the d-line (wavelength 587.6 nm) from the side of are shown. In FIG. 24A, ν1 corresponds to a specific example of “ν11” in conditional expression (6) of the present invention, and ν2 corresponds to a specific example of “ν12” in conditional expression (6) of the present invention. And ν4 corresponds to a specific example of “ν21” in the conditional expression (6) of the present invention.
[0085]
In the fifth embodiment, the focal length f of the entire system is set to 150.0 mm, and as shown in FIG. 20, the fifth embodiment also satisfies the conditional expressions (3), (4) and (6).
[0086]
Regarding the movement amount when the diopter is corrected by 1 dpt, since the focal length f2 of the second lens group G2 in the fifth embodiment is -85.5 mm, the lens movement amount is about 7.3 (= (-85.5). ² / 1000) mm, which is 22.5 (= 150) ² / 1000) mm. As described above, it has been found that the total size can be reduced by adopting the two-group configuration.
[0087]
FIGS. 25A to 25C are aberration diagrams respectively illustrating spherical aberration, astigmatism, and distortion (distortion) of the viewfinder 5 when the diopter is 0 dpt in the fifth embodiment. Similarly, FIGS. 26A to 26C are aberration diagrams for the diopter of −2.5 dpt in the fifth embodiment, and FIGS. 27A to 27C are diopter +1.0 dpt in the fifth embodiment. FIG. 7 is an aberration diagram for the case of FIG.
[0088]
As can be seen from the lens data and the aberration diagrams described above, the viewfinder 5 of Example 5 has a compact overall size even with a large focal length of 150.0 mm, and favorably corrects various aberrations. Thus, the optimum performance for a high-resolution imaging device is obtained. Specifically, in Example 5, the diopter can be corrected by 1 dpt by moving the second lens group G2 by about 7.3 mm while the focal length f of the entire system is 150.0 mm.
[0089]
As described above, the present invention has been described with reference to some embodiments and examples. However, the present invention is not limited to the above embodiments and examples, and can be variously modified. For example, the values of the radius of curvature R, the surface interval D, the refractive index n, and the Abbe number ν of each lens component are not limited to the values shown in the above-described numerical examples, and can take other values. Further, the present invention is not limited to application to a broadcast television camera, but may be applied to, for example, a home video camera.
[0090]
【The invention's effect】
As described above, according to the viewfinder of the first or ninth aspect, the first lens group includes the first positive lens group and the second negative lens group in order from the observer side. Alternatively, one of the second lens groups is configured to be able to correct diopter by moving along the optical axis. This makes it possible to keep the entire size compact even when having a large focal length, and to suppress a change in magnification of the observed image at the time of diopter correction. Further, the use of the two-group configuration can suppress the distortion as compared with the case of the one-group configuration, and can exhibit good aberration performance.
[0091]
According to the viewfinder of any one of claims 2 or 3 or claims 6 to 9, the positive first lens group and the negative second lens are arranged in order from the observer side. The first lens group is configured to be able to correct diopter by moving along the optical axis. This makes it possible to keep the entire size compact even when having a large focal length, and to suppress a change in magnification of the observed image at the time of diopter correction. Further, the use of the two-group configuration can suppress the distortion as compared with the case of the one-group configuration, and can exhibit good aberration performance. Further, since the second lens group is fixed and the first lens group can be moved, a sufficient back focus can be secured. For example, another optical component is arranged between the second lens group and the image plane. can do.
[0092]
In particular, according to the view finder of the third aspect, since the configuration is such that the conditional expressions (1) and (2) are satisfied, more favorable aberration performance, particularly, spherical aberration, astigmatism and distortion are excellent. , A viewfinder corrected to be obtained can be obtained.
[0093]
According to the viewfinder of any one of claims 4 to 9, the viewfinder includes, in order from the observer side, a first positive lens group and a second negative lens group, and the second lens The group was configured to be able to correct diopter by moving along the optical axis. This makes it possible to keep the entire size compact even when having a large focal length, and to suppress a change in magnification of the observed image at the time of diopter correction. Further, the use of the two-group configuration can suppress the distortion as compared with the case of the one-group configuration, and can exhibit good aberration performance. Further, since the first lens group is fixed and the second lens group is movable, it is possible to secure the hermeticity of the entire viewfinder system, and to prevent dust from entering the viewfinder from the outside. it can.
[0094]
In particular, according to the view finder of the fifth aspect, since the configuration is such that the conditional expressions (3) and (4) are satisfied, more favorable aberration performance, particularly, spherical aberration, astigmatism and distortion are excellent. , A viewfinder corrected to be obtained can be obtained.
[0095]
Further, according to the viewfinder of the present invention, the first lens group is a positive cemented lens composed of a negative first lens and a positive second lens, and the refractive index of the second lens is conditional expression ( Since the configuration satisfies item 5), it is possible to obtain a viewfinder in which spherical aberration is particularly well corrected.
[0096]
Further, according to the viewfinder of the present invention, the first lens group is constituted by a positive cemented lens composed of a negative first lens and a positive second lens, and a positive single lens. Therefore, it is possible to obtain a viewfinder in which spherical aberration is particularly well corrected without using a lens having a high refractive index for the first lens group.
[0097]
Further, according to the viewfinder of the present invention, the first lens group includes a positive cemented lens including at least a negative first lens and a positive second lens, and the second lens group includes a negative single lens. Since the zoom lens is constituted by a lens and further satisfies the conditional expression (6), it is possible to obtain a viewfinder in which the amount of chromatic aberration generated is suppressed to a practically acceptable level.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating one configuration example of a viewfinder according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view illustrating a configuration example of a viewfinder according to a second embodiment of the present invention.
FIG. 3 is a cross-sectional view illustrating another configuration example of the viewfinder according to the second embodiment of the present invention.
FIG. 4 is a cross-sectional view illustrating another configuration example of a viewfinder according to a third embodiment of the present invention.
FIG. 5 is a cross-sectional view illustrating another configuration example of a viewfinder according to a fourth embodiment of the present invention.
FIG. 6 is an explanatory diagram showing one embodiment (embodiment 1) of the viewfinder shown in FIG. 1;
FIG. 7 is an explanatory diagram showing data of a conditional expression satisfied by the viewfinder according to the first to third embodiments.
FIG. 8 is an aberration diagram showing various aberrations in the case of a diopter of 0 dpt in the viewfinder of Example 1.
FIG. 9 is an aberration diagram showing various aberrations at a diopter of −2.5 dpt in the viewfinder of Example 1.
FIG. 10 is an aberration diagram showing various aberrations at a diopter of +1.0 dpt in the viewfinder of Example 1.
FIG. 11 is an explanatory diagram showing one example (Example 2) of the viewfinder shown in FIG. 2;
FIG. 12 is an explanatory diagram showing one example (Example 3) of the viewfinder shown in FIG. 3;
FIG. 13 is an aberration diagram showing various aberrations at a diopter of 0 dpt in the viewfinder of Example 2.
14 is an aberration diagram showing various aberrations at a diopter of −2.5 dpt in the viewfinder of Example 2. FIG.
15 is an aberration diagram showing various aberrations at a diopter of +1.0 dpt in the viewfinder of Example 2. FIG.
FIG. 16 is an aberration diagram showing various aberrations in the case of a diopter of 0 dpt in the viewfinder of Example 3.
FIG. 17 is an aberration diagram showing various aberrations at a diopter of −2.5 dpt in the viewfinder of Example 3.
FIG. 18 is an aberration diagram showing various aberrations at a diopter of +1.0 dpt in the viewfinder of Example 3.
FIG. 19 is an explanatory diagram illustrating an example (Example 4) of the viewfinder illustrated in FIG. 4;
FIG. 20 is an explanatory diagram illustrating data of conditional expressions satisfied by viewfinders according to Examples 4 and 5.
FIG. 21 is an aberration diagram showing various aberrations at a diopter of 0 dpt in the viewfinder of Example 4;
FIG. 22 is an aberration diagram showing various aberrations at a diopter of −2.5 dpt in the viewfinder of Example 4.
FIG. 23 is an aberration diagram showing various aberrations at a diopter of +1.0 dpt in the viewfinder of Example 4;
FIG. 24 is an explanatory diagram showing an example (Example 5) of the viewfinder shown in FIG. 5;
FIG. 25 is an aberration diagram showing various aberrations at a diopter of 0 dpt in the viewfinder of Example 5;
FIG. 26 is an aberration diagram showing various aberrations at a diopter of −2.5 dpt in the viewfinder of Example 5;
FIG. 27 is an aberration diagram showing various aberrations at a diopter of +1.0 dpt in the viewfinder of Example 5.
[Explanation of symbols]
R1 to R8: radius of curvature, D1 to D8: surface interval, G1, G2: lens group, L1 to L4: lens component, Z1: optical axis.

Claims (9)

A viewfinder for observing an image display surface,
In order from the observer side, a positive first lens group and a negative second lens group are provided,
A viewfinder characterized in that one of the first lens group and the second lens group is configured to be able to correct diopter by moving along an optical axis. A viewfinder for observing an image display surface,
In order from the observer side, a positive first lens group and a negative second lens group are provided,
A viewfinder, wherein the first lens group is configured to be able to correct diopter by moving along an optical axis. 3. The viewfinder according to claim 2, further configured to satisfy the following conditional expressions (1) and (2).
0.4 <| f1 / f | <0.75 (1)
0.5 <| f2 / f | <1.8 (2)
However,
f: focal length of the entire system f1: focal length of the first lens group f2: focal length of the second lens group A viewfinder for observing an image display surface,
In order from the observer side, a positive first lens group and a negative second lens group are provided,
A viewfinder, wherein the second lens group is configured to be able to correct diopter by moving along an optical axis. 5. The viewfinder according to claim 4, wherein the viewfinder is configured to satisfy the following conditional expressions (3) and (4).
0.4 <| f1 / f | <0.6 (3)
0.5 <| f2 / f | <0.8 (4)
However,
f: focal length of the entire system f1: focal length of the first lens group f2: focal length of the second lens group The said 1st lens group is a positive cemented lens which consists of a negative 1st lens and a positive 2nd lens, Comprising: It is comprised so that conditional formula (5) below may be satisfied. The viewfinder according to claim 3 or claim 5.
n12> 1.8 (5)
However,
n12: The refractive index of the second lens. The first lens group includes:
A positive cemented lens comprising a negative first lens and a positive second lens;
6. The viewfinder according to claim 3, comprising a positive single lens. The first lens group includes a positive cemented lens including at least a first negative lens and a second positive lens,
The second lens group includes a negative single lens,
6. The viewfinder according to claim 3, wherein the view finder is configured to satisfy the following conditional expression (6).
| {(N−1) / r} (1 / ν11) − (1 / ν12)} + 1 / (ν21 · f21) | <5.0 × 10 ⁻⁴ [1 / mm] (6)
However,
n: average refractive index of the first lens and the second lens r: radius of curvature ν11 of the junction surface between the first lens and the second lens: Abbe number ν12 of the first lens: Abbe number ν21 of the second lens: negative Abbe number f21 of a single lens: The focal length of a negative single lens. The viewfinder according to any one of claims 1 to 8, wherein the viewfinder is used for a television camera.

Images