JP2010211056A - Inner zoom type and inner focus type zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a full length-fixed inner zoom type and inner focus type zoom lens having high optical performance in all the zoom area. <P>SOLUTION: The inner zoom type and inner focus type zoom lens includes, in order from an object side, a first lens group L1 having negative refractive power, a second lens group L2 having negative refractive power, a third lens group L3 having positive refractive power, a fourth lens group L4 having negative refractive power, and a fifth lens group L5 having positive refractive power. In zooming from a wide angle side to a telephoto side, L1 is fixed relative to an image surface, L2 moves to an optional position, L3 moves to the object side, space between L4 and L3 becomes larger on the telephoto side than on the wide angle side, and L5 moves to the object side so that space between L4 and L5 becomes smaller on the telephoto side than on the wide angle side. When focusing from subject distance infinity to a short-distance object, L2 moves to the object side. The zoom lens satisfies two conditional expressions concerning a focal length of a partial system. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a zoom lens particularly suitable for digital cameras, silver salt cameras, video cameras, and the like.

  Conventionally, as a four-group zoom lens having a zoom ratio of about 3 times, a so-called negative leading type four-group zoom having negative, positive, negative, and positive refractive power from the object side has been proposed. The negative leading type four-group zoom has features that it is easy to widen the angle of view and that it is easy to ensure the back focus. For example, Patent Document 1 and Patent Document 2 adopt this negative leading type four-group zoom system. As another method, there is a so-called positive leading four-group zoom having positive, negative, positive, and positive refractive powers from the object side. For example, in Patent Document 3 and Patent Document 4, the front-leading four-group zoom is employed, and the inner focus method is employed to maintain the performance at the time of focusing.

Japanese Patent Laid-Open No. 2005-92056

JP 2006-113572 A

JP 2007-127899 A

JP 2004-101739 A

  However, in general, the negative leading zoom lens adopts the front-lens payout method as the focus method, so the operability is impaired and the total length changes during zooming and focusing. There was a problem that was difficult.

  In addition, the front-end zoom lens has no change in the overall length during focusing because of the inner focus method, but there is a problem that the dust-proof and drip-proof measures are insufficient due to the change in the overall length during zooming.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a zoom lens that is optimal for dust and drip proofing measures by fixing the entire length during zooming and further making the inner focus.

In order to solve the above problems, in the present invention, in order from the object side, a first lens unit L1 having negative refractive power, a second lens unit L2 having negative refractive power, and a first lens unit having positive refractive power. A zoom lens including a three-lens group L3, a fourth lens group L4 having negative refractive power, and a fifth lens group L5 having positive refractive power, in zooming from the wide-angle side to the telephoto side The first lens group is fixed with respect to the image plane, the second lens group is moved to an arbitrary position, the third lens group is moved toward the object side, and the telephoto side is compared with the wide angle side. The distance between the fourth lens group and the third lens group is increased, and the fifth lens group is moved to the object side so that the distance between the fourth lens group and the fourth lens group is smaller on the telephoto side than on the wide angle side, and When focusing from infinity to a close object, the second lens unit L2 Go to side, to provide an inner zoom type and inner focus type zoom lens satisfies the following conditional expression.
2.3 <| f1 / f12w | <8.8 (1)
0.9 <| f2 / f12w | <2.7 (2)
However,
f1 is the focal length of the first lens group,
f2 is the focal length of the second lens group,
f12w is the focal length of the combined system of the first lens group and the second lens group at the wide angle end at infinity.

Further, it is preferable that the first lens group has at least one aspherical surface in which positive refractive power increases from the optical axis toward the periphery of the lens, or negative refractive power decreases.

In addition, it is preferable that the third lens group satisfies the following conditional expression.
0.8 <f3 / fw <1.8 (3)
However,
f3 is the focal length of the third lens group,
fw is the focal length at the wide angle end.

In addition, it is preferable that the fourth lens group satisfies the following conditional expression.
0.6 <| f4 / fw | <1.4 (4)
However,
f4 is the focal length of the fourth lens group,
fw is the focal length at the wide angle end.

Further, it is preferable that the fifth lens group satisfies the following conditional expression.
0.9 <f5 / fw <2.1 (5)
However,
f5 is the focal length of the fifth lens group,
fw is the focal length at the wide angle end.

Further, it is preferable in terms of mechanical structure that the third lens group and the fifth lens group perform the same movement during zooming.

Further, it is preferable in terms of the mechanical structure that the aperture stop is disposed between the third lens group and the fourth lens group and performs the same movement as the third lens group or the fourth lens group during zooming. .

Further, it is preferable that a flare cut stop fixed in zooming is provided on the image plane side of the fifth lens group.

  The fifth lens group preferably has at least one aspheric surface.

Preferably, each of the third lens group, the fourth lens group, and the fifth lens group has at least one cemented lens.

According to the present invention, it is possible to provide an inner zoom type and inner focus type zoom lens that has high optical performance in the entire zoom range and has a fixed overall length.

It is a lens block diagram in the wide angle end of Example 1 of this invention. It is a longitudinal aberration figure at the time of infinity focusing in the wide angle end of Example 1 of the present invention. It is a longitudinal aberration figure at the time of infinity focusing in the telephoto end of Example 1 of the present invention. It is a lateral aberration figure at the time of infinity focusing in the wide angle end of Example 1 of the present invention. It is a lateral aberration figure at the time of infinity focusing in the telephoto end of Example 1 of the present invention. It is a lens block diagram in the wide angle end of Example 2 of this invention. It is a longitudinal aberration figure at the time of infinity focusing in the wide-angle end of Example 2 of the present invention. It is a longitudinal aberration figure at the time of infinity focusing in the telephoto end of Example 2 of the present invention. It is a lateral aberration figure at the time of infinity focusing in the wide-angle end of Example 2 of the present invention. It is a lateral aberration figure at the time of infinity focusing in the telephoto end of Example 2 of the present invention. It is a lens block diagram in the wide angle end of Example 3 of this invention. It is a longitudinal aberration figure at the time of infinity focusing in the wide-angle end of Example 3 of the present invention. It is a longitudinal aberration figure at the time of infinity focusing in the telephoto end of Example 3 of the present invention. It is a transverse aberration figure at the time of infinity focusing in the wide angle end of Example 3 of the present invention. It is a lateral aberration figure at the time of infinity focusing in the telephoto end of Example 3 of the present invention. It is a lens block diagram in the wide angle end of Example 4 of this invention. It is a longitudinal aberration figure at the time of infinity focusing in the wide-angle end of Example 4 of the present invention. It is a longitudinal aberration figure at the time of infinity focusing in the telephoto end of Example 4 of the present invention. It is a transverse aberration figure at the time of infinity focusing in the wide angle end of Example 4 of the present invention. It is a lateral aberration figure at the time of infinity focusing in the telephoto end of Example 4 of the present invention. It is a lens block diagram in the wide angle end of Example 5 of this invention. It is a longitudinal aberration figure at the time of infinity focusing in the wide angle end of Example 5 of this invention. It is a longitudinal aberration figure at the time of infinity focusing in the telephoto end of Example 5 of the present invention. It is a transverse aberration figure at the time of infinity focusing in the wide angle end of Example 5 of the present invention. It is a lateral aberration figure at the time of infinity focusing in the telephoto end of Example 5 of the present invention. It is a lens block diagram in the wide angle end of Example 6 of this invention. It is a longitudinal aberration figure at the time of infinity focusing in the wide angle end of Example 6 of this invention. It is a longitudinal aberration figure at the time of infinity focusing in the telephoto end of Example 6 of this invention. It is a transverse aberration figure at the time of infinity focusing in the wide angle end of Example 6 of the present invention. It is a lateral aberration figure at the time of infinity focusing in the telephoto end of Example 6 of this invention.

  Hereinafter, an inner zoom type and inner focus type zoom lens according to an embodiment of the present invention will be described.

The inner zoom type and inner focus type zoom lens according to this embodiment includes, in order from the object side, a first lens unit L1 having a negative refractive power, a second lens unit L2 having a negative refractive power, and a positive lens unit. An inner zoom type and inner focus type zoom lens composed of a third lens unit L3 having refractive power, a fourth lens unit L4 having negative refractive power, and a fifth lens unit L5 having positive refractive power In zooming from the wide-angle side to the telephoto side, the first lens group is fixed with respect to the image plane, the second lens group moves to an arbitrary position, and the third lens group moves to the object side. An object in which the distance between the fourth lens group and the third lens group is larger on the telephoto side than on the wide angle side, and the distance between the fourth lens group and the fourth lens group is smaller on the telephoto side than on the wide angle side. Move to the side In addition, when focusing from an infinite object distance to a close object, the second lens unit L2 moves toward the object side, and satisfies the following conditional expression: an inner zoom type and an inner focus type zoom lens .
2.3 <| f1 / f12w | <8.8 (1)
0.9 <| f2 / f12w | <2.7 (2)
However,
f1 is the focal length of the first lens group,
f2 is the focal length of the second lens group,
f12w is the focal length of the combined system of the first lens group and the second lens group at the wide-angle end at infinity.

Conditional expression (1) defines the focal length of the first lens group, and is for achieving both miniaturization and high performance. If the lower limit of conditional expression (1) is exceeded and the focal length of the first lens group becomes shorter in absolute value, it becomes difficult to correct negative distortion on the wide angle side.

  If the upper limit of conditional expression (1) is exceeded and the focal length of the first lens unit is increased in absolute value, it is difficult to reduce the front lens diameter.

  Conditional expression (2) defines the focal length of the second lens group, and is to achieve both high performance and miniaturization as in conditional expression (1). If the lower limit value of conditional expression (2) is exceeded and the focal length of the second lens group becomes shorter in absolute value, it becomes difficult to correct aberration fluctuations during focusing, particularly spherical aberration. In addition, since the zooming burden after the third group becomes large, the movement amount after the third group increases, and it becomes difficult to secure the space. Furthermore, an increase in the amount of movement increases the variation of the open F value during zooming, and it becomes difficult to secure a predetermined open F value unless the aperture diameter is variable.

  If the upper limit of conditional expression (2) is exceeded and the focal length of the second lens group is increased in absolute value, it is advantageous for aberration correction, but the amount of extension for focusing increases, and the first It is difficult to secure a focus space between the lens group and the second lens group, which is disadvantageous for downsizing.

  The first lens group has at least one aspheric surface in which the positive refractive power increases from the optical axis toward the lens periphery or the negative refractive power decreases, thereby reducing negative distortion aberration correction on the wide angle side. Realized by the number of lenses. In addition, by making the first lens group negative and positive in order from the object side, it becomes easier to correct negative distortion on the wide-angle side without increasing the front lens diameter.

The third lens group satisfies the following conditional expression.
0.8 <f3 / fw <1.8 (3)
However,
f3 is the focal length of the third lens group,
fw is the focal length at the wide angle end.

  In the zoom lens according to the present invention, the F-number light beam diverging from the first lens group and the second lens group is incident on the third lens group as an F-number light beam having a large diameter, so that spherical aberration on the telephoto side is particularly generated. It becomes easy to do. Accordingly, it is necessary to appropriately set the focal length of the third lens group.

  Based on the above, if conditional expression (3) exceeds the lower limit value and the focal length of the third lens group becomes short, the apparent F value of the third lens group becomes small, and it is difficult to correct spherical aberration on the telephoto side. Become.

If the upper limit of conditional expression (3) is exceeded and the focal length of the third lens group is increased, it is difficult to obtain a telephoto type refractive power arrangement on the telephoto side, and it becomes difficult to ensure a high zoom ratio. .

The fourth lens group is characterized by satisfying the following conditional expression.
0.6 <| f4 / fw | <1.4 (4)
However,
f4 is the focal length of the fourth lens group,
fw is the focal length at the wide angle end.

In the zoom lens of the present invention, on the wide angle side, the first lens group, the second lens group, the third lens group, and the fourth lens group synthesis system have negative refractive power, and the fifth lens group has positive refractive power. It has a so-called retrofocus type configuration. On the telephoto side, the first lens group, the second lens group, and the third lens group synthesis system have a positive refractive power, and the fourth lens group and the fifth lens group synthesis system have a negative refractive power. It takes a telephoto type configuration.

Based on the above, if the upper limit value of conditional expression (4) is exceeded and the focal length of the fourth lens unit is increased in absolute value, it becomes difficult to adopt a telephoto type configuration on the telephoto side, so a high zoom ratio is ensured. It becomes difficult.

Further, if the lower limit value of conditional expression (4) is exceeded and the focal length of the fourth lens group becomes shorter in absolute value, it becomes difficult to adopt a retrofocus type configuration on the wide angle side. Furthermore, since the focal length of the fourth lens group is shortened in absolute value, it becomes difficult to correct distortion and coma that occur in the entire zoom range.

The fifth lens group is characterized by satisfying the following conditional expression.
0.9 <f5 / fw <2.1 (5)
However,
f5 is the focal length of the fifth lens group,
fw is the focal length at the wide angle end.

  In the zoom lens of the present invention, the focal length is obtained by adopting a retrofocus type configuration on the wide-angle side and distributing the refractive power so that the rear principal point of the entire system is arranged on the image plane side with respect to the fifth lens group. Against the back focus.

  Based on the above, if the upper limit value of conditional expression (5) is exceeded and the focal length of the fifth lens group becomes long, it becomes difficult to adopt a retrofocus type configuration on the wide-angle side, and it becomes difficult to ensure back focus. Furthermore, since the amount of movement during zooming increases, it becomes difficult to reduce the size.

If the lower limit of conditional expression (5) is exceeded and the focal length of the fifth lens group is shortened, it is advantageous for miniaturization. Since it passes through and receives stronger refractive power, it is difficult to correct lateral chromatic aberration, astigmatism, and coma.

Since the third lens group and the fifth lens group move in the same way during zooming, the third lens group and the fifth lens group can be integrated in terms of the mechanical structure. As a result, the number of parts can be reduced and the size and weight associated therewith can be reduced, and the relative decentration between the third lens group and the fifth lens group due to manufacturing errors can be suppressed. Deterioration can be kept small.

The aperture stop is disposed between the third lens group and the fourth lens group, and in zooming, the same movement as the third lens group or the fourth lens group is performed, so that the amount of peripheral light is secured and the coma aberration is secured. Can be corrected satisfactorily.

By providing a fixed flare-cut stop for zooming on the image plane side of the fifth lens group, unnecessary rays at the peripheral angle of view can be cut off on the telephoto side, and the image quality can be improved.

  In the zoom lens of the present invention, in the fifth lens group, the light beam passes through the peripheral portion of the lens more as it reaches the peripheral angle of view. Therefore, in order to effectively correct coma and astigmatism, in the fifth lens group, the negative refractive power increases from the optical axis toward the lens periphery, or the positive refractive power decreases. It is preferable to provide one aspherical surface.

Since each of the third lens group, the fourth lens group, and the fifth lens group has at least one cemented lens, axial chromatic aberration and chromatic aberration of magnification in zooming can be favorably maintained.

Hereinafter, an inner zoom and inner focus type zoom lens according to a numerical example will be described with reference to the drawings.

FIG. 1 is a lens configuration diagram at the wide-angle end of an inner zoom and inner focus type zoom lens according to the first embodiment.

Table 1 below shows specifications of the inner zoom and inner focus type zoom lens according to the first embodiment. In [Overall specifications], f represents a focal length, Fno represents an F number, and 2ω represents an angle of view (unit: °). In [lens specifications], the first column N is the order of the lens surfaces counted from the object side, the second column r is the radius of curvature of the lens surfaces, the third column d is the lens surface interval, and the fourth column n is d-line ( The refractive index at the wavelength λ = 587.6 nm), the fifth column ν represents the Abbe number at the d-line (wavelength λ = 587.6 nm). R = 0.0000 represents a plane, Bf represents the back focus, the diaphragm represents the diaphragm surface, the flare-cut diaphragm represents the flare-cut diaphragm surface, the symbol * represents an aspheric surface, and the refractive index of air n = 1.0000. Omits the description. [Variable interval at infinity shooting] indicates the focal length f and the variable interval. [Conditional Expression Corresponding Value] indicates the corresponding value of each conditional expression. [Aspherical data] represents the aspherical coefficient and the conic coefficient when the surface number N and the shape of the aspherical surface are expressed by the following equations.

x = (h ² / r) / [1+ {1− (1 + k) (h / r) ² } ^1/2 ] + Ah ⁴ + Bh ⁶ + Ch ⁸ + Dh ¹⁰

Where x is a shift in the optical axis direction at a position of height h from the optical axis with respect to the vertex of the surface, k is a conic coefficient, and A, B, C, and D are aspherical coefficients. Where r is the radius of curvature of the reference sphere. Further, “E−n” indicates “× 10 ⁻ⁿ ”, for example “−4.7168E-06” indicates “−4.7168 × 10 ⁻⁶ ”. Since these symbols are the same in the following embodiments, the description after the second embodiment will be omitted.

  In all the following values, the described focal length f, radius of curvature r, lens surface interval d, and other lengths are “mm” unless otherwise specified, but proportional expansion of the optical system Even in proportional reduction, the same optical performance can be obtained, and the present invention is not limited to this. Since these symbols are the same in the following embodiments, the description after the second embodiment will be omitted.

  The following table shows the specifications of the inner zoom and inner focus type zoom lens according to the first embodiment.

  FIG. 2 is a longitudinal aberration diagram of the inner zoom and inner focus type zoom lens according to Example 1 when focusing at infinity at the wide-angle end. FIG. 3 is a longitudinal aberration diagram when focusing on infinity at the telephoto end according to the first embodiment. FIG. 4 is a transverse aberration diagram for Example 1 upon focusing on infinity at the wide-angle end. FIG. 5 is a transverse aberration diagram when focusing on infinity at the telephoto end according to Example 1.

  In each aberration diagram, Fno is the F number, Y is the image height, C is the C line (wavelength λ = 656.3 nm), d is the d line (wavelength λ = 587.6 nm), and g is the g line (wavelength λ = 435). .8 nm), ΔM represents a meridional image plane, and ΔS represents a sagittal image plane. Since these symbols are the same in the following embodiments, description thereof will be omitted.

FIG. 6 is a lens configuration diagram at the wide-angle end of the inner zoom and inner focus type zoom lens according to the second embodiment.

  The following table shows the specifications of the inner zoom and inner focus type zoom lens according to the second embodiment.

  FIG. 7 is a longitudinal aberration diagram of the inner zoom and inner focus type zoom lens according to Example 2 when focusing at infinity at the wide-angle end. FIG. 8 is a longitudinal aberration diagram when focusing on infinity at the telephoto end according to Example 2. FIG. 9 is a transverse aberration diagram for Example 2 upon focusing on infinity at the wide-angle end. FIG. 10 is a transverse aberration diagram when focusing on infinity at the telephoto end according to Example 2.

FIG. 11 is a lens configuration diagram at the wide-angle end of the inner zoom and inner focus type zoom lens according to the third embodiment.

  The following table shows the specifications of the inner zoom and inner focus type zoom lens according to Example 3.

  FIG. 12 is a longitudinal aberration diagram of the inner zoom and inner focus type zoom lens according to Example 3 when focusing at infinity at the wide-angle end. FIG. 13 is a longitudinal aberration diagram when focusing on infinity at the telephoto end according to Example 3. FIG. 14 is a transverse aberration diagram for Example 3 upon focusing on infinity at the wide-angle end. FIG. 15 is a transverse aberration diagram for Example 3 upon focusing on infinity at the telephoto end.

FIG. 16 is a lens configuration diagram of an inner zoom and inner focus type zoom lens according to Example 4 at the wide-angle end.

  The following table shows the specifications of the inner zoom and inner focus type zoom lens according to Example 4.

  FIG. 17 is a longitudinal aberration diagram of the inner zoom and inner focus type zoom lens according to Example 4 when focusing at infinity at the wide-angle end. FIG. 18 is a longitudinal aberration diagram when focusing on infinity at the telephoto end according to Example 4. FIG. 19 is a transverse aberration diagram for Example 4 upon focusing on infinity at the wide-angle end. FIG. 20 illustrates lateral aberrations at the telephoto end of Example 4 when focusing on infinity.

FIG. 21 is a lens configuration diagram at the wide-angle end of the inner zoom and inner focus type zoom lens according to the fifth embodiment.

  The following table shows the specifications of the inner zoom and inner focus type zoom lens according to Example 5.

  FIG. 22 is a longitudinal aberration diagram of the inner zoom and inner focus type zoom lens according to Example 5 when focusing at infinity at the wide-angle end. FIG. 23 is a longitudinal aberration diagram when focusing on infinity at the telephoto end according to Example 5. FIG. 24 is a transverse aberration diagram for Example 5 upon focusing on infinity at the wide-angle end. FIG. 25 is a transverse aberration diagram for Example 5 upon focusing on infinity at the telephoto end.

FIG. 26 is a lens configuration diagram of an inner zoom and inner focus type zoom lens according to Example 6 at the wide-angle end.

  The following table shows the specifications of the inner zoom and inner focus type zoom lens according to Example 6.

  FIG. 27 is a longitudinal aberration diagram of the inner zoom and inner focus type zoom lens according to Example 6 when focusing at infinity at the wide-angle end. FIG. 28 is a longitudinal aberration diagram when focusing on infinity at the telephoto end according to Example 6. FIG. 29 is a transverse aberration diagram for Example 6 upon focusing on infinity at the wide-angle end. FIG. 30 is a transverse aberration diagram for Example 6 upon focusing on infinity at the telephoto end.

L1 1st lens group L2 2nd lens group L3 3rd lens group L4 4th lens group L5 5th lens group S Aperture stop FC1 Flare cut stop FC2 Flare cut stop I Image plane d d line C C line g g line Fno F Number ΔS Sagittal image plane ΔM Meridional image plane Y Image height

Claims (5)

In order from the object side, a first lens unit L1 having negative refractive power;
A second lens unit L2 having negative refractive power;
A third lens unit L3 having a positive refractive power;
A fourth lens unit L4 having negative refractive power;
An inner zoom type and inner focus type zoom lens composed of a fifth lens unit L5 having positive refractive power,
In zooming from the wide-angle side to the telephoto side, the first lens group is fixed with respect to the image plane, the second lens group moves to an arbitrary position, the third lens group moves to the object side, The distance between the fourth lens group and the third lens group increases on the telephoto side with respect to the wide angle side, and the distance between the fourth lens group and the fourth lens group decreases on the telephoto side with respect to the wide angle side. The inner lens type wherein the second lens unit L2 moves toward the object side and satisfies the following conditional expression: Inner focus type zoom lens.
2.3 <| f1 / f12w | <8.8 (1)
0.9 <| f2 / f12w | <2.7 (2)
However,
f1 is the focal length of the first lens group,
f2 is the focal length of the second lens group,
f12w is the focal length of the combined system of the first lens group and the second lens group at the wide angle end at infinity. 2. The inner zoom according to claim 1, wherein the first lens group has at least one aspheric surface in which positive refractive power increases from the optical axis toward the periphery of the lens or negative refractive power decreases. Type and inner focus type zoom lens. The zoom lens of the inner zoom type and the inner focus type according to claim 1, wherein the third lens group satisfies the following conditional expression.
0.8 <f3 / fw <1.8 (3)
However,
f3 is the focal length of the third lens group,
fw is the focal length at the wide angle end. 4. The inner zoom type and inner focus type zoom lens according to claim 1, wherein the fourth lens group satisfies the following conditional expression. 5.
0.6 <| f4 / fw | <1.4 (4)
However,
f4 is the focal length of the fourth lens group,
fw is the focal length at the wide angle end. The inner zoom type and inner focus type zoom lens according to any one of claims 1 to 4, wherein the fifth lens group satisfies the following conditional expression.
0.9 <f5 / fw <2.1 (5)
However,
f5 is the focal length of the fifth lens group,
fw is the focal length at the wide angle end.

Images