JP2009002991A - Variable power finder and imaging apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a variable power finder which easily attains a high zoom ratio while downsizing downsized an entire objective optical system and obtains an excellent optical performance in a variable power range from a wide angle end to a telephoto end. <P>SOLUTION: The variable power finder is equipped with the objective optical system, an image reversing optical system reversing an object image formed by the objective optical system and an eyepiece optical system. The objective optical system includes, in order from an object side to an observation side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power. When zooming, the second lens group, the third lens group and the fourth lens group move on an optical axis. When it is assumed that focal distances of the objective optical system at the wide angle end and the telephoto end are fw and fT respectively, the focal distance of the second lens group is f2 and the focal distance of the eyepiece optical system is fe, they satisfy conditions: 0.10<¾(f2)¾/√(fw×fT)<0.36 and 0.10<fw/fe<0.40. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a zoom finder and an image pickup apparatus using the same, and is suitable for, for example, a video camera and a digital camera.

  In recent years, many of the photographing systems used in digital still cameras have zoom ratios (magnification ratios) exceeding 3 times.

  For this reason, a finder mounted on a digital camera is required to be a zoom finder with a high zoom ratio (high zoom ratio) corresponding to the zoom ratio of the photographing system.

  In addition, since this zoom finder is incorporated into a small digital camera, it is required to have a small size and a structure that can easily obtain high optical performance.

  As a variable magnification finder, an object image (finder image) formed by an objective optical system having a variable magnification function is converted into an erect image by an image reversal optical system, and a real image type variable magnification finder for observing the erect image through an eyepiece is provided. Known (Patent Documents 1 and 2).

  Specifically, the objective optical system is composed of a large number of lens groups, and among these, a plurality of lens groups are moved in the optical axis direction to perform zooming (magnification), and an object image formed by the objective optical system. The magnification is changed variously.

  The object image at this time is an erect image through an image inverting optical system composed of a Porro prism and a plurality of prisms. This erect image is observed from the position of the eye point through an eyepiece.

  The objective optical system in Patent Documents 1 and 2 includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a positive refractive power. And a fourth lens group.

  Among them, in Patent Document 1, the first lens group and the fourth lens group are stationary, and the second lens group and the third lens group move in the optical axis direction, so that the diopter change and the diopter change accompanying the zooming (viewfinder). (Diopter change) is corrected.

In Patent Document 2, the first lens group is stationary, and the second lens group, the third lens group, and the fourth lens group are moved to correct magnification change and diopter change accompanying magnification change.
JP 2005-164993 A JP 2003-207722 A

  In the zoom finder disclosed in Patent Document 1, the first lens unit and the fourth lens unit do not move during zooming. The second lens group having a zooming function is moved to the observation side on the optical axis when zooming from the wide-angle end to the telephoto end.

  In order to correct the diopter change accompanying zooming, the third lens group is moved to the observation side independently of the second lens group. In Cited Document 1, an example of a magnification finder of about 4.6 times is given. In these zooming viewfinders, in order to obtain a high zooming ratio, the amount of movement of the second lens group having a zooming function is increased.

  As a result, the space in which the second lens group moves must be secured, and the total lens length (distance from the first lens surface to the final lens surface) of the objective optical system tends to be excessive.

  In general, at least two lens groups must be moved in order to correct zooming and diopter changes accompanying zooming.

  In Patent Document 1, since there is only one lens group having a zooming function, if an attempt is made to increase the zooming ratio, the amount of movement of the lens group must be increased, and the total lens length of the objective optical system is shortened. It becomes difficult.

  On the other hand, in Patent Document 2, a lens group having a zooming function is shared by two lens groups to realize a zooming finder having a zoom ratio of 3.6 times.

  Specifically, when zooming from the wide-angle end to the telephoto end, the second lens group having the main zooming function is moved to the observation side, and the third lens group having the sub-magnification function is moved to the object side. The fourth lens group moves to the object side to correct the diopter change accompanying zooming.

  In this case, since the third lens group moves to the object side during zooming, the distance between the third lens group and the fourth lens group at the telephoto end is increased.

  As a result, the amount of movement of the fourth lens group increases in order to reduce the distance between the third lens group and the fourth lens group in order to correct the diopter change associated with zooming.

  As a result, the total lens length of the objective optical system tends to be long at the telephoto end.

  An image pickup system used in recent digital still cameras has come to have a high zoom ratio.

  For this reason, if the zoom type of the objective optical system constituting the zoom finder and the lens configuration of each lens group are not set appropriately, it is difficult to obtain a high zoom ratio and high optical performance while reducing the size of the entire system. It becomes.

  It is an object of the present invention to provide a zoom finder that is easy to achieve a high zoom ratio while reducing the size of the entire objective optical system and that can provide good optical performance in the entire zoom range from the wide-angle end to the telephoto end. To do.

The zoom finder of the present invention includes an objective optical system, an image inversion optical system that inverts an object image formed by the objective optical system, and an eyepiece optical system that guides light to an observer through the image inversion optical system. In the variable magnification finder provided,
The objective optical system includes, in order from the object side to the observation side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a positive refraction. A fourth lens group having power, and during zooming, the second lens group, the third lens group, and the fourth lens group move on the optical axis;
When the focal lengths at the wide-angle end and the telephoto end of the objective optical system are fw and fT, the focal length of the second lens group is f2, and the focal length of the eyepiece optical system is fe,

It is characterized by satisfying the following conditions.

  According to the present invention, it is possible to obtain a zoom finder that can easily reduce the size of the entire objective optical system and that can easily achieve a high zoom ratio and can provide good optical performance in the entire zoom range from the wide-angle end to the telephoto end.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a zoom finder and an image pickup apparatus having the same according to the present invention will be described below with reference to the drawings.

  The zoom finder of the present invention includes an objective optical system, an image reversal optical system that reverses an object image formed by the objective optical system, and an eyepiece optical system that guides light to an observer via the image reversal optical system. Yes.

  The objective optical system includes, in order from the object side to the observation side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a positive refractive power. A fourth lens unit having During zooming, the second lens group, the third lens group, and the fourth lens group move on the optical axis.

  FIG. 1 is a lens cross-sectional view at the wide-angle end (short focal length end) when the optical path of the variable magnification finder of Example 1 is developed. 2A, 2B, and 2C are aberration diagrams at the wide angle end, the intermediate zoom position, and the telephoto end (long focal length end) of the zoom finder according to the first embodiment.

  Example 1 is a real image type variable magnification finder having a finder magnification of -0.30 to -1.33 times.

  FIG. 3 is a lens cross-sectional view at the wide-angle end when the optical path of the zoom finder of Example 2 is developed. 4A, 4B, and 4C are aberration diagrams of the zoom finder of Example 2 at the wide-angle end, the intermediate zoom position, and the telephoto end.

  Example 2 is a real image type variable magnification finder having a finder magnification of -0.24 to -1.21 times.

  FIG. 5 is a lens cross-sectional view at the wide-angle end when the optical path of the zoom finder of Example 3 is developed. 6A, 6B, and 6C are aberration diagrams at the wide angle end, the intermediate zoom position, and the telephoto end of the zoom finder according to the third embodiment.

  Example 3 is a real image type variable magnification finder having a finder magnification of -0.30 to -1.34 times.

  FIG. 7 is a lens cross-sectional view at the wide-angle end when the optical path of the variable magnification finder of Example 4 is developed. 8A, 8B, and 8C are aberration diagrams of the zoom finder of Embodiment 4 at the wide-angle end, the intermediate zoom position, and the telephoto end.

  Example 4 is a real image type variable magnification finder having a finder magnification of -0.30 to -1.34 times.

  FIG. 9 is a lens cross-sectional view at the wide-angle end when the optical path of the variable magnification finder of Example 5 is developed. 10A, 10B, and 10C are aberration diagrams of the zoom finder of Example 5 at the wide-angle end, the intermediate zoom position, and the telephoto end.

  Example 5 is a real image type variable magnification finder having a finder magnification of -0.28 to -1.44 times.

  FIG. 11 is a schematic view of the main part of the optical system of the zoom finder of the present invention. FIG. 12 is a schematic diagram of a main part of a digital camera (imaging apparatus) having a zoom finder according to the present invention.

  The zoom finder of each embodiment is an optical system used in an imaging apparatus (optical apparatus). In the lens cross-sectional view, the left side is the object side and the right side is the observation side.

  Next, a lens cross-sectional view will be described.

  Go is an objective optical system that corrects magnification and diopter change accompanying magnification (finder diopter change) and has positive refractive power (optical power = reciprocal of focal length) as a whole.

  The objective optical system Go includes a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, a third lens unit L3 having a positive refractive power, and a fourth lens unit L4 having a positive refractive power. Has been. The objective optical system Go forms an object image (finder image) on a predetermined surface.

  Gr is an image reversal optical system, which has a triangular prism P1 and a roof prism P2, and inverts an object image formed by the objective optical system Go into an erect image.

  S1 is a field stop, which is provided at or near the position of the object image formed by the objective optical system Go. The field stop S1 limits the range of the finder field.

  Ge is an eyepiece optical system, and guides light from an object image that has been erected by the image reversal optical system Gr to an observer. The observer observes the object image from the eye point Ep through the eyepiece lens Ge.

  The arrows indicate the movement trajectory of each lens group for correcting the magnification change from the wide angle end to the telephoto end and the diopter change accompanying the magnification change.

  In each of the following embodiments, the zoom lens positions at the wide-angle end and the telephoto end (the second lens unit L2 and the fourth lens unit L4 in each example) can move on the optical axis in the mechanism. The zoom position when positioned at both ends of this range.

  Next, aberration diagrams will be described. In the aberration diagrams, d is the d line, F is the F line, and C is the C line.

  ΔM is a meridional image plane, and ΔS is a sagittal image plane.

  The lateral chromatic aberration is shown for the F and C lines.

  In the spherical aberration, H is the height of the entrance pupil, and ω is the angle of view of the incident light.

  Next, the refractive power arrangement of the objective optical systems of Examples 1 to 5 will be described.

  The objective optical system Go includes a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, a third lens unit L3 having a positive refractive power, and a fourth lens unit having a positive refractive power. The lens unit L4 is configured.

  The first lens unit L1 is a lens unit having a positive refractive power so as to have an imaging function, and the lens unit having a positive refractive power is preceded to reduce the outer shape of the lens.

  Since the second lens unit L2 is a lens unit having a negative refractive power, a zooming effect is provided by movement accompanying zooming, which will be described later.

  By making the third lens unit L3 a positive refractive power lens unit, diopter change (finder diopter change) associated with zooming is corrected by movement accompanying zooming, which will be described later.

  The fourth lens unit L4 is a lens unit having a positive refractive power, and plays a role of performing primary image formation on the field frame of light emitted from the third lens unit L3.

  Next, the movement accompanying zooming of each lens group constituting the objective optical system Go of each embodiment will be described.

  The first lens unit L1 is not moved during zooming (magnification change) in order to simplify the mechanical configuration.

  Generally, in order to correct the magnification change and diopter change accompanying the magnification change, it is necessary to move at least two lens groups.

  When the zooming function of the entire system is borne by one lens group, the moving amount of the lens group having the zooming function increases, and the total lens length (distance from the first lens surface to the image side) becomes long.

  Therefore, in each embodiment, at the time of zooming, the three lens groups are moved, and the zooming function is shared by a plurality of groups so that the entire lens length is shortened while ensuring a predetermined zoom ratio.

  At this time, during zooming from the wide-angle end to the telephoto end, the lens group having the largest zoom ratio is referred to as a main zoom lens group, and the lens group having the next zoom ratio is referred to as a sub-magnification lens group.

  In each embodiment, the second lens unit L2 is a main variable magnification lens unit, the fourth lens unit L4 is a sub-variable lens unit, and the variable magnification function is shared by the two lens units.

  Specifically, the second lens unit L2 moves to the observation side monotonously during zooming from the wide angle end to the telephoto end.

  The fourth lens unit L4 moves along a locus convex toward the object side so as to shorten the distance from the second lens unit L2.

  The sign of the movement amount of the lens group is a positive sign for the movement amount to the observation side and a negative sign for the movement amount to the object side.

  If the amount of movement of the second lens unit L2 is too large during zooming, the total length of the objective optical system Go increases.

  Conversely, if the amount of movement of the second lens unit L2 is too small, it is difficult to obtain a desired zoom ratio (zoom ratio).

  Similarly, if the moving amount of the fourth lens unit L4 is too small during zooming, the zooming share of the fourth lens unit L4 becomes too small, and it becomes difficult to obtain a desired zooming ratio.

  Conversely, if the amount of movement of the fourth lens unit L4 is too large, the total length of the objective optical system Go increases.

  Therefore, in each embodiment, the refractive power of the second lens unit L2 having the main zooming function and the fourth lens unit L4 having the secondary zooming function and the moving direction and the moving amount accompanying zooming are appropriately set. . As a result, the entire lens system is reduced in size and has a high zoom ratio (high zoom ratio).

  Next, the movement of the third lens unit L3 will be described.

  The third lens unit L3 moves to the observation side so as to reduce the distance from the second lens unit L2 during zooming from the wide-angle end to the telephoto end. Thereby, the diopter change accompanying the zooming is corrected while shortening the total length of the objective optical system Go at the wide-angle end.

  Regarding the moving direction of the third lens unit L3, the distance from the second lens unit L2 can also be reduced by moving the third lens unit L3 to the object side during zooming from the wide-angle end to the telephoto end.

  However, with this combination, it is necessary to ensure a sufficient distance between the second lens unit L2 and the third lens unit L3 at the wide angle end so that the second lens unit L2 and the third lens unit L3 do not interfere at the telephoto end.

  As a result, the overall length of the objective optical system Go increases. Therefore, in each embodiment, the third lens unit L3 is moved to the observation side so as to satisfy conditional expression (4) described later.

  Next, the lens configuration of each lens group constituting the objective optical system Go of each embodiment will be described.

  The first lens unit L1 is composed of a biconvex positive lens, which corrects spherical aberration well on the telephoto side.

  The second lens unit L2 is composed of a biconcave negative lens, which corrects image plane variation due to the angle of view satisfactorily.

  The third lens unit L3 includes a meniscus positive lens having a convex surface directed toward the object side, and thereby corrects spherical aberration and astigmatism favorably.

  The fourth lens unit L4 is composed of a biconvex positive lens, and mainly corrects spherical aberration favorably.

  Each lens group has one or more aspheric surfaces, and by performing aberration correction of the on-axis light beam and the off-axis light beam independently, good optical performance is achieved with a small number of lenses.

  In addition, each lens group is configured by a lens made of a single plastic material to facilitate manufacture.

  In each example, the objective optical system Ge is configured as described above, and the real image type transformation having high optical performance is achieved by appropriately setting the moving direction and moving amount of the second to fourth lens groups accompanying zooming. You've got a double viewfinder.

  Next, the configuration of the image inverting optical system Gr of each embodiment 1 will be described.

  The image inverting optical system Gr includes a triangular prism P1 and a roof prism P2 as shown in FIG.

  The triangular prism P1 causes the light beam from the objective optical system Go to be incident from the incident surface P1a, and is temporarily reflected to the object side by the first reflecting surface P1b.

  Then, the light is totally reflected by the total reflection surface P1c which also serves as the incident surface P1a, the optical path is bent, and the light is emitted from the emission surface P1d and guided to the primary imaging surface S1a where the field frame (field stop) S1 is located.

  The exit surface P1d has an appropriate positive refractive power, and acts as a field lens that converts the light beam into a condensed light beam or a parallel light beam.

  S1 is a field frame indicating the finder field range, and is provided on the primary imaging surface or in the vicinity thereof (near the exit surface P1d of the triangular prism P1), and includes a mechanical configuration or display means such as liquid crystal.

  The roof prism P2 converts the object image formed in the vicinity of the exit surface P1d of the triangular prism P1 into an upright image by inverting it vertically and horizontally.

  That is, the roof prism P2 causes the light beam from the triangular prism P1 to be incident from the incident surface P2a, totally reflected by the surface P2b, and then totally reflected (or reflected) by the roof surface P2c.

  Then, the light is totally reflected by the incident surface P2a, emitted from the surface P2b, and guided to the eyepiece lens (eyepiece optical system) Ge.

  Next, the configuration of the eyepiece optical system Ge of each example will be described.

  The eyepiece lens Ge is composed of a single lens having a positive refractive power.

  The eyepiece lens Ge guides light from the object image formed by the objective optical system Go to the eye point Ep via the prisms P1 and P2. The observer observes an erect object image from the eye point Ep through the eyepiece lens Ge.

  In order to construct a wide-field and compact zoom finder, it is necessary to increase the eyepiece magnification of the eyepiece optical system Ge to some extent and appropriately distribute the refractive power between the objective optical system Go and the eyepiece optical system Ge.

  However, if the eyepiece magnification is excessively large with respect to the objective optical system Go, a lot of distortion aberration occurs in the eyepiece lens Ge.

  On the other hand, if the eyepiece magnification is extremely small, the objective optical system Go becomes large in order to achieve a wide field of view.

  In each embodiment, by appropriately setting the eyepiece magnification with respect to the objective optical system Go, the entire zoom finder can be made compact while having a wide field of view.

  The focal length at the wide-angle end of the objective optical system Go is fw, and the focal length at the telephoto end is fT.

  The focal lengths of the first lens unit L1, the second lens unit L2, the third lens unit L3, and the fourth lens unit of the objective optical system are sequentially set as f1, f2, f3, and f4. Let the focal length of the eyepiece optical system be fe.

  The amount of movement of the third lens unit L3 during zooming from the wide-angle end to the telephoto end is m3 (however, the sign of the amount of movement is positive for movement toward the observation side and vice versa).

The imaging magnifications at the wide-angle end and the telephoto end of the first lens unit L1 are β1w and β1t.
The imaging magnifications at the wide-angle end and the telephoto end of the second lens unit L2 are β2w and β2t.
The imaging magnifications at the wide-angle end and the telephoto end of the third lens unit L3 are β3w and β3t.
The imaging magnifications at the wide-angle end and the telephoto end of the fourth lens unit L4 are β4w and β4t.

  The zoom ratio Z of the objective optical system Go

And

The zoom ratio Z4 of the fourth lens unit L4 is Z4 = β4t / β4w
And

  At this time, the zoom finder of each embodiment satisfies the conditional expressions (1) and (2), so that the entire objective optical system can be reduced in size, and the high zoom ratio can be easily achieved from the wide-angle end to the telephoto end. Excellent optical performance is obtained in the entire zoom range up to.

  When one or more of conditional expressions (3) to (6) are further satisfied, a more preferable zoom finder can be realized.

  Next, the technical meaning of each conditional expression will be described.

  Conditional expression (1) defines the focal length of the second lens unit L2 with respect to the focal length of the intermediate zoom position of the objective optical system Go.

  When the lower limit of conditional expression (1) is exceeded, the focal length of the second lens unit L2 becomes short, that is, the refractive power of the second lens unit L2 becomes excessive, and the Petzval sum increases to the negative side.

  As a result, an excessive tendency of the curvature of field is excessively increased, and it is difficult to correct this.

  When the upper limit of conditional expression (1) is exceeded, the focal length of the second lens unit L2 becomes long, that is, the refractive power of the second lens unit L2 becomes too small.

  Since the second lens unit L2 has a zooming function, if the refractive power of the second lens unit L2 becomes excessive, the amount of movement of the second lens unit L2 increases in order to obtain a desired zoom ratio.

  At this time, in order to prevent the second lens unit L2 and the third lens unit L3 from interfering at the telephoto end, a sufficient interval between the second lens unit L2 and the third lens unit L3 must be secured at the wide angle end. Don't be. As a result, the overall length of the objective optical system Go increases at the wide-angle end.

  In conditional expression (1), it is more preferable to set the numerical range as follows.

  Conditional expression (2) defines the relationship between the focal length at the wide-angle end of the objective optical system Go and the focal length of the eyepiece optical system Ge.

  When the lower limit of conditional expression (2) is exceeded, if the focal length of the objective optical system Go is constant, the focal length of the eyepiece optical system Ge becomes excessive, that is, the eyepiece magnification becomes low. For this reason, it becomes difficult to obtain a desired finder magnification.

  Further, when the focal length of the eyepiece optical system Ge is constant, that is, when the eyepiece magnification is constant, the focal length of the objective optical system Go is too short, so that the refractive power of each lens group must be increased. As a result, in order to achieve the desired optical performance, the refractive power of the lens group must be dispersed to a plurality of lenses, which results in an increase in the number of constituent lenses.

  If the upper limit of conditional expression (2) is exceeded, if the focal length of the objective optical system Go is constant, the focal length of the eyepiece optical system Ge will be too short, and a lot of pincushion distortion will occur in the eyepiece optical system Ge. So not good.

  In conditional expression (2), it is more preferable to set the numerical range as follows.

  Conditional expression (3) defines the focal length of the first lens unit L1 with respect to the focal length at the wide-angle end of the objective optical system Go.

  When the lower limit of conditional expression (3) is exceeded, the focal length of the first lens unit L1 becomes short, that is, the refractive power of the first lens unit L1 becomes excessive, and the axial chromatic aberration is insufficiently corrected at the telephoto end.

  When the upper limit of conditional expression (3) is exceeded, the focal length of the first lens unit L1 becomes long, that is, the refractive power of the first lens unit L1 becomes too small.

  In this case, since the force for bending the light beam that passes through the first lens unit L1 is too small, the height of the light beam that passes through the first lens unit L1 increases, and the front lens diameter increases.

  In the conditional expression (3), it is more preferable to set the numerical range as follows.

  Conditional expression (4) is an expression that defines the focal length of the third lens unit L3 with respect to the amount of movement associated with zooming of the third lens unit L3.

  When the lower limit of conditional expression (4) is exceeded, the focal length of the third lens unit L3 becomes short, that is, the refractive power of the third lens unit L3 becomes excessive.

  As a result, the correction of spherical aberration is insufficiently corrected at the telephoto end.

  When the upper limit of conditional expression (4) is exceeded, the focal length of the third lens unit L3 becomes long, that is, the refractive power of the third lens unit L3 becomes too small.

  As a result, it becomes difficult to sufficiently correct the diopter change accompanying the increase in zoom.

  In conditional expression (4), it is more preferable to set the numerical range as follows.

  Conditional expression (5) defines the focal length of the fourth lens unit L4 with respect to the focal length of the intermediate zoom position of the objective optical system Go.

  When the lower limit of conditional expression (5) is exceeded, the focal length of the fourth lens unit L4 becomes excessive, that is, the refractive power of the fourth lens unit L4 becomes excessive.

  For this reason, in order to achieve the desired optical performance, the refractive power of the fourth lens unit L4 must be shared by two or more lenses, and the objective optical system Go becomes larger.

  If the upper limit of conditional expression (5) is exceeded, the focal length of the fourth lens unit L4 becomes excessive, that is, the refractive power of the fourth lens unit L4 becomes excessively small.

  Since the fourth lens unit L4 is a lens unit having a zooming function, the amount of movement of the fourth lens unit L4 increases in order to obtain a desired zoom ratio.

  When the first lens unit L1 is fixed, the total length of the objective optical system Go is increased at the wide-angle end or the telephoto end by the amount of movement of the fourth lens unit L4. As a result, the objective optical system Go is enlarged. come.

  In conditional expression (5), it is more preferable to set the numerical range as follows.

  Conditional expression (6) defines the zoom ratio of the fourth lens unit L4 with respect to the zoom ratio of the entire objective optical system Go.

  If the lower limit of conditional expression (6) is exceeded, the zoom ratio of the fourth lens unit L4 becomes too small. Therefore, in order to obtain a desired zoom ratio, another lens group that shares the zoom ratio, that is, It is necessary to increase the zoom ratio of the two lens unit L2.

  When the zoom ratio of the second lens unit L2 is increased, the refractive power of the second lens unit L2 becomes excessively strong, so that a lot of barrel distortion is generated.

  If the upper limit of conditional expression (6) is exceeded, the zoom ratio of the fourth lens unit L4 becomes excessive. If the zoom ratio of the fourth lens unit L4 is excessive, the amount of movement of the fourth lens unit L4 increases and the overall length of the objective optical system Go increases.

  In conditional expression (6), it is more preferable to set the numerical range as follows.

  As described above, according to each embodiment, the objective optical system Go is divided into the first lens unit L1 having a positive refractive power, the second lens unit L2 having a negative refractive power, and the third lens having a positive refractive power. The lens unit L3 includes a fourth lens unit L4 having a positive refractive power. Then, by appropriately arranging the movement direction and movement amount associated with zooming of the second lens group L2, the third lens group L3, and the fourth lens group L4, a variable magnification finder that can easily achieve a reduction in thickness and a high zoom ratio. Have gained.

  Next, numerical examples of the respective embodiments of the present invention will be shown.

  The meanings of symbols used in each numerical example are as follows.

  In the numerical example, A is the finder magnification, ω is the half angle of view of the finder, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air spacing in order from the object side. is there. Ni and νi are respectively the refractive index and Abbe number at the wavelength of 587.6 nm of the material of the i-th lens in order from the object side.

  When the aspherical shape is x with respect to the surface apex, the displacement in the optical axis direction at the position of the height H from the optical axis,

It is represented by

Where R is a radius of curvature, k is a conic constant, and B, C, D, and E are aspherical coefficients. [E + X] means [× 10 ^{+ x} ], and [eX] means [× 10 ^−x ].

  R1 to R8 correspond to the objective optical system Go. R9 and R10 correspond to the triangular prism P1. R12 to R15 correspond to the roof prism P2. R16 and R17 correspond to the eyepiece optical system Ge.

  Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.

[Numerical Example 1]
A = -0.30 to -1.33 ω = 23.59 ° to 5.61 °
* R1 = 8.138 D1 = 1.91 N1 = 1.49171 ν1 = 57.40
R2 = -18.121 D2 = variable
* R3 = -2.768 D3 = 0.60 N3 = 1.58306 ν3 = 30.23
R4 = 3.29 D4 = variable
* R5 = 3.295 D5 = 1.01 N5 = 1.49171 ν5 = 57.40
* R6 = 10.960 D6 = variable
* R7 = 7.258 D7 = 1.47 N7 = 1.49171 ν7 = 57.40
* R8 = -3.983 D8 = variable
R9 = ∞ D9 = 8.22 N9 = 1.57090 ν9 = 33.80
R10 = -24.500 D10 = 0.15
R11 = ∞ D11 = 1.20
R12 = ∞ D12 = 15.37 N12 = 1.57090 ν12 = 33.80
R13 = ∞ D13 = 0.10
R14 = ∞ D14 = 0.20
R15 = ∞ D15 = 0.09
* R16 = 16.780 D16 = 1.60 N16 = 1.49171 ν16 = 57.40
R17 = -9.084 D17 = 16.00
R18 = Eyepoint

Aspheric coefficient
R1 K = 1.92651E + 00 B = -8.19997E-04 C = -7.41171E-06
D = -1.23721E-06 E = 0.00000E + 00
R3 K = 8.40036E + 05 B = 4.60857E-05 C = 1.99522E-03
D = -4.55166E-04 E = 0.00000E + 00
R5 K = -2.10797E + 00 B = 3.30115E-03 C = 1.83923E-04
D = -8.70731E-05 E = 0.00000E + 00
R6 K = -4.24494E + 01 B = 6.59969E-03 C = 5.67238E-04
D = -2.12951E-04 E = 0.00000E + 00
R7 K = -5.92649E + 00 B = -5.78993E-03 C = 1.25133E-03
D = -2.52564E-04 E = 0.00000E + 00
R8 K = 6.45446E-02 B = -1.84264E-03 C = 1.15300E-03
D = -2.23999E-04 E = 0.00000E + 00
R16 K = 3.79650E + 00 B = -4.47796E-04 C = 5.04578E-06
D = -2.43568E-07 E = 0.00000E + 00

Wide angle Medium telephoto
D2 1.37 4.95 6.31
D4 3.22 1.32 0.49
D6 3.60 0.62 0.84
D8 1.06 2.35 1.60

Start surface Focal length 1st lens group 1 11.70
Second lens group 3 -2.49
Third lens group 5 9.19
Fourth lens group 7 5.47
Inversion optics 9 42.91
Eyepiece optics 16 12.24


[Numerical Example 2]
A = -0.24 to -1.21 ω = 27.77 ° to 6.23 °
* R1 = 8.494 D1 = 1.88 N1 = 1.49171 ν1 = 57.40
R2 = -16.505 D2 = variable
* R3 = -2.581 D3 = 0.70 N3 = 1.58306 ν3 = 30.23
R4 = 3.231 D4 = variable
* R5 = 3.415 D5 = 0.99 N5 = 1.49171 ν5 = 57.40
* R6 = 11.251 D6 = variable
* R7 = 6.964 D7 = 1.63 N7 = 1.49171 ν7 = 57.40
* R8 = -3.823 D8 = variable
R9 = ∞ D9 = 8.22 N9 = 1.57090 ν9 = 33.80
R10 = -24.500 D10 = 0.45
R11 = ∞ D11 = 1.20
R12 = ∞ D12 = 15.37 N12 = 1.57090 ν12 = 33.80
R13 = ∞ D13 = 0.10
R14 = ∞ D14 = 0.20
R15 = ∞ D15 = 0.09
* R16 = 16.780 D16 = 1.60 N16 = 1.49171 ν16 = 57.40
R17 = -9.084 D17 = 16.00
R18 = Eyepoint

Aspheric coefficient
R1 K = 1.95417E + 00 B = -7.53692E-04 C = -7.30731E-06
D = -1.08053E-06 E = 0.00000E + 00
R3 K = 6.37652E + 05 B = 3.38109E-04 C = 1.75822E-03
D = -2.94358E-04 E = 0.00000E + 00
R5 K = -3.26232E + 00 B = 5.82559E-03 C = 0.00000E + 00
D = 0.00000E + 00 E = 0.00000E + 00
R6 K = -3.24027E + 01 B = 6.87170E-03 C = 0.00000E + 00
D = 0.00000E + 00 E = 0.00000E + 00
R7 K = -3.57935E + 00 B = -5.43247E-03 C = 1.30608E-03
D = -2.95406E-04 E = 0.00000E + 00
R8 K = 4.42447E + 06 B = -1.86098E-03 C = 1.08098E-03
D = -2.38860E-04 E = 0.00000E + 00
R16 K = 3.79650E + 00 B = -4.47796E-04 C = 5.04578E-06
D = -2.43568E-07 E = 0.00000E + 00

Wide angle Medium telephoto
D2 1.03 4.58 6.24
D4 3.34 1.35 0.85
D6 4.39 0.86 0.69
D8 0.57 2.54 1.55

Start surface Focal length 1st lens group 1 11.70
Second lens group 3 -2.36
Third lens group 5 9.57
Fourth lens group 7 5.28
Inversion optics 9 42.91
Eyepiece optics 16 12.24

[Numerical Example 3]
A = -0.30 to -1.34 ω = 23.70 ° to 5.67 °
* R1 = 7.091 D1 = 2.10 N1 = 1.49171 ν1 = 57.40
R2 = -16.629 D2 = variable
* R3 = -1.930 D3 = 0.70 N3 = 1.58306 ν3 = 30.23
R4 = 2.607 D4 = variable
* R5 = 2.609 D5 = 1.62 N5 = 1.49171 ν5 = 57.40
* R6 = 76.767 D6 = variable
* R7 = 9.156 D7 = 1.56 N7 = 1.49171 ν7 = 57.40
* R8 = -3.516 D8 = variable
R9 = ∞ D9 = 8.22 N9 = 1.57090 ν9 = 33.80
R10 = -24.500 D10 = 0.45
R11 = ∞ D11 = 1.20
R12 = ∞ D12 = 15.37 N12 = 1.57090 ν12 = 33.80
R13 = ∞ D13 = 0.10
R14 = ∞ D14 = 0.20
R15 = ∞ D15 = 0.09
* R16 = 16.780 D16 = 1.60 N16 = 1.49171 ν16 = 57.40
R17 = -9.084 D17 = 16.00
R18 = Eyepoint

Aspheric coefficient
R1 K = 9.76085E-01 B = -8.04180E-04 C = -1.05015E-05
D = -8.17938E-07 E = 0.00000E + 00
R3 K = 5.44929E + 05 B = 1.57735E-02 C = 1.71213E-04
D = -1.02686E-03 E = 0.00000E + 00
R5 K = -2.58843E + 00 B = 6.16679E-03 C = 0.00000E + 00
D = 0.00000E + 00 E = 0.00000E + 00
R6 K = -2.17546E + 04 B = 8.43760E-03 C = 0.00000E + 00
D = 0.00000E + 00 E = 0.00000E + 00
R7 K = 6.61466E + 00 B = -1.39016E-02 C = 1.42835E-03
D = -2.36324E-04 E = 0.00000E + 00
R8 K = 1.21759E + 00 B = -2.68895E-03 C = 2.09427E-03
D = -1.34856E-04 E = 0.00000E + 00
R16 K = 3.79650E + 00 B = -4.47796E-04 C = 5.04578E-06
D = -2.43568E-07 E = 0.00000E + 00

Wide angle Medium telephoto
D2 1.44 5.00 6.09
D4 2.04 1.10 0.46
D6 3.33 0.29 0.55
D8 0.41 0.83 0.12

Start surface Focal length 1st lens group 1 10.41
Second lens group 3 -1.80
Third lens group 5 5.46
Fourth lens group 7 5.39
Inversion optics 9 42.91
Eyepiece optics 16 12.24


[Numerical Example 4]
A = -0.30 to -1.34 ω = 23.73 ° to 5.66 °
* R1 = 7.633 D1 = 2.10 N1 = 1.49171 ν1 = 57.40
R2 = -16.043 D2 = variable
* R3 = -2.229 D3 = 0.70 N3 = 1.58306 ν3 = 30.23
R4 = 3.03 D4 = variable
* R5 = 3.024 D5 = 1.30 N5 = 1.49171 ν5 = 57.40
* R6 = 22.180 D6 = variable
* R7 = 10.623 D7 = 1.42 N7 = 1.49171 ν7 = 57.40
* R8 = -3.740 D8 = variable
R9 = ∞ D9 = 8.22 N9 = 1.57090 ν9 = 33.80
R10 = -24.500 D10 = 0.45
R11 = ∞ D11 = 1.20
R12 = ∞ D12 = 15.37 N12 = 1.57090 ν12 = 33.80
R13 = ∞ D13 = 0.10
R14 = ∞ D14 = 0.20
R15 = ∞ D15 = 0.09
* R16 = 16.780 D16 = 1.60 N16 = 1.49171 ν16 = 57.40
R17 = -9.084 D17 = 16.00
R18 = Eyepoint

Aspheric coefficient
R1 K = 1.05300E + 00 B = -7.21020E-04 C = -1.16332E-05
D = -4.61290E-07 E = 0.00000E + 00
R3 K = 7.18420E + 04 B = 3.12957E-03 C = 2.25276E-03
D = -6.78191E-04 E = 0.00000E + 00
R5 K = -2.86111E + 00 B = 6.88098E-03 C = 0.00000E + 00
D = 0.00000E + 00 E = 0.00000E + 00
R6 K = -8.07155E + 02 B = 9.16235E-03 C = 0.00000E + 00
D = 0.00000E + 00 E = 0.00000E + 00
R7 K = 3.07171E + 00 B = -1.02817E-02 C = 1.70018E-03
D = -2.15025E-04 E = 0.00000E + 00
R8 K = 5.84951E-01 B = -1.17771E-03 C = 1.22288E-03
D = -1.37370E-04 E = 0.00000E + 00
R16 K = 3.79650E + 00 B = -4.47796E-04 C = 5.04578E-06
D = -2.43568E-07 E = 0.00000E + 00

Wide angle Medium telephoto
D2 1.35 4.94 5.99
D4 2.96 1.53 0.71
D6 3.38 0.47 0.61
D8 0.79 1.55 1.18

Start surface Focal length 1st lens group 1 10.84
Second lens group 3 -2.10
Third lens group 5 6.97
Fourth lens group 7 5.81
Inversion optics 9 42.91
Eyepiece optics 16 12.24


[Numerical Example 5]
A = -0.28 to -1.44 ω = 26.71 ° to 5.42 °
R 1 = 9.442 D 1 = 3.00 N 1 = 1.491710 ν 1 = 57.4
R 2 = -48.981 D 2 = variable
R 3 = -4.436 D 3 = 1.00 N 2 = 1.632000 ν 2 = 23.0
R 4 = 3.204 D 4 = Variable
R 5 = 3.581 D 5 = 1.30 N 3 = 1.491710 ν 3 = 57.4
R 6 = 14.794 D 6 = Variable
R 7 = 5.737 D 7 = 1.70 N 4 = 1.491710 ν 4 = 57.4
R 8 = -6.596 D 8 = variable
R 9 = ∞ D 9 = 8.22 N 5 = 1.570 900 ν 5 = 33.8
R10 = -24.500 D10 = 0.15
R11 = ∞ D11 = 1.20
R12 = ∞ D12 = 15.4 N 6 = 1.570900 ν 5 = 33.8
R13 = ∞ D13 = 0.10
R14 = ∞ D14 = 0.20
R15 = ∞ D15 = 0.09
R16 = 16.781 D16 = 1.60 N 7 = 1.491710 ν 5 = 57.4
R17 = -9.084 D17 = 16.00
R18 = Eyepoint

Aspheric coefficient
R1 k = -3.92781e-01 B = -1.73125e-05 C = -2.77642e-06 D = 1.36697e-07
E = -3.77678e-09
R3 k = -3.01910e + 00 B = 5.81595e-03 C = -4.67941e-04 D = 1.78431e-05
E = 0.00000e + 00
R6 k = -6.67064e + 01 B = 6.82407e-03 C = -4.41289e-05 D = 0.00000e + 00
E = 0.00000e + 00
R7 k = 2.47816e + 00 B = -3.65828e-03 C = -7.47374e-05 D = -9.44132e-07
E = 0.00000e + 00
R8 k = -1.11835e + 01 B = -3.61111e-03 C = 3.43326e-04 D = 7.54838e-06
E = 0.00000e + 00
R16 k = 3.79650e + 00 B = -4.47796e-04 C = 5.04578e-06 D = -2.43568e-07
E = 0.00000e + 00



Wide angle Medium telephoto
D2 1.06 4.85 8.79
D4 4.56 3.09 1.48
D6 6.63 3.43 0.97
D8 1.17 2.05 2.19

Start surface Focal length 1st lens group 1 16.38
Second lens group 3 -2.80
Third lens group 5 9.26
Fourth lens group 7 6.54
Inversion optics 9 42.91
Eyepiece optics 16 12.24

  Next, an embodiment in which the zoom finder showing Embodiments 1 to 5 is applied to a digital still camera (imaging device) will be described with reference to FIG.

  12A is a front view, and FIG. 12B is a cross-sectional view.

In FIGS. 12A and 12B, reference numeral 10 denotes a camera body. Reference numeral 11 denotes a photographing lens.
Reference numeral 12 denotes a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor that receives a subject image formed by the photographing optical system 11 and is built in the camera body. Information corresponding to the subject image photoelectrically converted by the solid-state imaging device 12 is recorded in a memory (not shown). Reference numeral 13 denotes a zoom finder for observing a subject image. The zoom finder 13 is a real image type zoom finder as shown in the first to fifth embodiments.

  Thus, by applying the zoom finder of the present invention to an imaging apparatus such as a digital still camera, a small imaging apparatus can be realized.

Sectional view of the lens of the zoom finder of Example 1 of the present invention Aberration diagram at the wide-angle end of Example 1 of the present invention Aberration diagram at the intermediate zoom position in Example 1 of the present invention Aberration diagram at the telephoto end according to the first embodiment of the present invention. Sectional view of the lens of the zoom finder of Example 2 of the present invention Aberration diagram at the wide-angle end of Example 2 of the present invention Aberration diagram at the intermediate zoom position in Embodiment 2 of the present invention Aberration diagram at the telephoto end according to the second embodiment of the present invention. Lens cross-sectional view of the zoom finder of Example 3 of the present invention Aberration diagram at the wide-angle end of Example 3 of the present invention Aberration diagram at the intermediate zoom position in Embodiment 3 of the present invention Aberration diagram at telephoto end of Embodiment 3 of the present invention Lens cross-sectional view of the zoom finder of Example 4 of the present invention Aberration diagram at the wide-angle end of Example 4 of the present invention Aberration diagram at the intermediate zoom position in Embodiment 4 of the present invention Aberration diagram at the telephoto end according to the fourth embodiment of the present invention. Sectional view of the zoom finder lens of Example 5 of the present invention Aberration diagrams at the wide-angle end of Example 5 of the present invention Aberration diagrams at the intermediate zoom position in Example 5 of the present invention Aberration diagrams at the telephoto end according to the fifth embodiment of the present invention. Sectional view of the principal part of the optical system of the zoom finder of the present invention Schematic diagram of essential parts of an imaging apparatus having a zoom finder of the present invention

Explanation of symbols

ΔM: Meridional image plane ΔS: Sagittal image plane Go ... Objective optical system Gr ... Reverse optical system Ge ... Eyepiece optical system L1 ... First lens group L2 ... Second lens group L3 ... Third lens group L4 ... Fourth lens group S1 ... View frame Ep ... Eyepoint

Claims (7)

In a variable magnification finder comprising an objective optical system, an image inverting optical system that inverts an object image formed by the objective optical system, and an eyepiece optical system that guides light to an observer through the image inverting optical system,
The objective optical system includes, in order from the object side to the observation side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a positive refraction. A fourth lens group having power, and during zooming, the second lens group, the third lens group, and the fourth lens group move on the optical axis;
When the focal lengths at the wide-angle end and the telephoto end of the objective optical system are fw and fT, the focal length of the second lens group is f2, and the focal length of the eyepiece optical system is fe,

A zoom finder characterized by satisfying the following conditions. When the focal length of the first lens group of the objective optical system is f1,

The zoom finder according to claim 1, wherein the following condition is satisfied. The focal length of the third lens unit of the objective optical system is f3, the amount of movement of the third lens unit in zooming from the wide-angle end to the telephoto end is m3, and the sign of the amount of movement is positive for the movement toward the observation side. When

The zoom finder according to claim 1 or 2, wherein the following condition is satisfied. When the focal length of the fourth lens group of the objective optical system is f4,

The zoom finder according to claim 1, 2 or 3, wherein the following condition is satisfied. The zoom ratio from the wide-angle end to the telephoto end of the objective optical system is Z, the zoom ratio of the fourth lens group is Z4, and the imaging magnifications at the wide-angle end and the telephoto end of the fourth lens group are β4w and β4t, respectively. age,
Z4 = β4t / β4w
And when

The zoom finder according to any one of claims 1 to 4, wherein the following condition is satisfied.   6. The zoom finder according to claim 1, wherein each of the first lens group to the fourth lens group of the objective optical system is composed of a lens made of a single plastic material.   An imaging apparatus comprising: the variable magnification finder according to claim 1; and a photographing optical system.

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