JP5866190B2 - Zoom lens and imaging device - Google Patents

Description

  The present invention relates to a zoom lens and an image pickup apparatus using the same, and more particularly to a zoom lens suitable for being applied to a camera that receives light by an image pickup device such as a surveillance camera, a video camera, a digital still camera, and a broadcast camera. The present invention relates to the imaging device used.

  Conventionally, for example, a positive / negative positive / positive four-group zoom lens is known as a high-quality, high-magnification zoom lens suitable for a surveillance camera, a video camera, a digital still camera, a broadcast camera, and the like. The positive / negative / positive / positive four-group zoom lens includes, in order from the object 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 positive refraction. A fourth lens group having power is arranged, and at the time of zooming from the wide-angle end to the telephoto end, the first lens group and the third lens group are fixed in the optical axis direction, and the second lens group is moved from the object side. The fourth lens unit moves in the optical axis direction so as to compensate for image plane variations caused by moving toward the image side, and has a focusing function.

  In recent years, it has been required to secure optical performance corresponding to a high-pixel imaging device and to maintain good performance even when focusing on a close range. In Patent Document 1 below, as a method for ensuring optical performance at the telephoto end, a system in which positive refractive power is dispersed by arranging three negative lenses and three positive lenses in the first lens group is known. Yes. Patent Document 2 below describes a configuration in which the second lens group G2 includes at least two negative lenses in a positive / negative / positive / positive four-group zoom lens.

JP 2010-139724 A JP 2010-102096 A

  However, the conventional zoom lenses described in Patent Documents 1 and 2 have not been able to obtain optical performance corresponding to a high-pixel imaging device while being small and compatible with high zooming. For example, with the configuration described in Patent Document 1, only a magnification of about 20 times can be obtained. Further, in the configuration described in Patent Literature 1, the negative refractive power is dispersed by the two-group configuration including, in order from the object side, a negative lens, a meniscus negative lens, and a cemented lens of a negative lens and a positive lens. In order to improve the performance by correcting the coma caused by the change in the angle of view at the wide-angle end, the chromatic aberration cannot be corrected sufficiently because the position of the positive lens is not appropriate, and the optical performance is satisfied. I couldn't. Even in the configuration described in Patent Document 2, a zoom lens having a high zoom ratio of about 30 times could not be configured.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to achieve downsizing and a high zoom ratio of about 30 times in a positive / negative / positive / positive 4 group zoom lens. It is an object of the present invention to provide a new and improved zoom lens and image pickup apparatus capable of achieving the above.

In order to solve the above-described problem, according to an aspect of the present invention, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a fixed to the image plane And a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and the first lens group and the third lens group at the time of zooming from the wide-angle end to the telephoto end. Is fixed in the optical axis direction, the second lens group moves from the object side to the image side and has a zooming action, and the fourth lens group varies in image plane position as the second lens group moves. In the zoom lens that moves in the optical axis direction so as to compensate for and has a focusing function, the first lens group includes one negative lens and three positive lenses in order from the object side. The lens group has at least three negative lenses and one positive lens, and the third lens group includes A positive lens and a cemented lens of a positive lens and a negative lens that are independent from the body side; and the fourth lens group includes at least one positive lens and a negative lens, and satisfies the following conditions: A zoom lens is provided.
0.03 <| f2 / ft | <0.08
5.8 <| f1 / f2 | <8.0
Where f1: focal length of the first lens group f2: focal length of the second lens group ft: focal length of the entire lens system at the telephoto end

The most object side positive lens constituting the third lens group has at least one surface including an aspherical shape, and the cemented surface of the cemented lens constituting the third lens group has a convex shape on the object side. Satisfy the following conditions.
0.15 <f3 / ft <0.35
0.4 <f31 / f3 <0.8
Where f3: focal length of the third lens group f31: focal length of the most object-side positive lens constituting the third lens group ft: focal length of the entire lens system at the telephoto end

  At least one of the positive lenses constituting the first lens group is made of a glass material having an Abbe number of 80 or more.

  The second lens group includes two negative lenses in order from the object side, and a cemented lens of a positive lens having a convex surface facing the object side and a negative lens.

The fourth lens group is composed of a cemented lens of a positive lens and a negative lens in order from the object side. The positive lens constituting the fourth lens group has at least one surface including an aspherical shape, and satisfies the following conditions: To do.
0.08 <f4 / ft <0.25
Where f4: focal length of the fourth lens group ft: focal length of the entire lens system at the telephoto end

  In order to solve the above problems, according to another aspect of the present invention, an imaging apparatus including the above zoom lens is provided.

  According to the present invention, it is possible to achieve a reduction in size and a high zoom ratio of about 30 times in a positive / negative / positive / positive 4 group zoom lens.

It is lens sectional drawing in the wide angle end of Numerical Example 1 of this invention. FIG. 6 is an aberration diagram at the wide-angle end according to Numerical Example 1 of the present invention. FIG. 6 is an aberration diagram at an intermediate zoom position according to Numerical Example 1 of the present invention. FIG. 6 is an aberration diagram at the telephoto end according to Numerical Example 1 of the present invention. It is lens sectional drawing in the wide angle end of Numerical Example 2 of this invention. FIG. 6 is an aberration diagram at the wide-angle end according to Numerical Example 2 of the present invention. FIG. 9 is an aberration diagram at an intermediate zoom position according to Numerical Example 2 of the present invention. It is an aberration diagram in the telephoto end of Numerical Example 2 of the present invention. It is lens sectional drawing in the wide angle end of Numerical Example 3 of this invention. It is an aberration diagram in the wide angle end of Numerical Example 3 of the present invention. FIG. 10 is an aberration diagram at an intermediate zoom position according to Numerical Example 3 of the present invention. It is an aberration diagram in the telephoto end of Numerical Example 3 of the present invention. It is lens sectional drawing in the wide angle end of Numerical Example 4 of this invention. It is an aberration diagram in the wide angle end of Numerical Example 4 of the present invention. FIG. 10 is an aberration diagram at an intermediate zoom position according to Numerical Example 4 of the present invention. It is an aberration diagram in the telephoto end of Numerical Example 4 of the present invention. It is lens sectional drawing in the wide angle end of Numerical Example 5 of this invention. It is an aberration diagram in the wide angle end of Numerical Example 5 of the present invention. FIG. 10 is an aberration diagram at an intermediate zoom position according to Numerical Example 5 of the present invention. It is an aberration diagram in the telephoto end of Numerical Example 5 of the present invention.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  FIG. 1 is a schematic diagram illustrating a zoom lens according to the present embodiment. The imaging apparatus according to the present embodiment includes the zoom lens illustrated in FIG. 1 and an imaging element having an imaging surface on which a subject image is formed by the zoom lens. FIG. 1 shows a zoom lens according to Numerical Example 1 described later. As shown in FIG. 1, in order from the object side (left side in FIG. 1), a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens having a positive refractive power. The lens group G3 includes a fourth lens group G4 having a positive refractive power, and the stop SP is disposed on the most object side of the third lens group G3.

G shown in FIG. 1 is an optical block corresponding to an optical filter, a face plate, or the like. IP is an image plane, and when used as a photographing optical system for a surveillance camera, a video camera, or a digital still camera, a solid-state imaging device (such as a CCD sensor or a CMOS sensor) (
When the imaging surface of the photoelectric conversion element is a silver salt film camera, the film surface corresponds to IP.

  When zooming from the wide-angle end to the telephoto end, the second lens group G2 is moved to the image plane side as indicated by an arrow. At this time, the first lens group G1 and the third lens group G3 are fixed in the optical axis direction, and the fourth lens group G4 moves so as to correct the variation of the image plane position accompanying the movement of the second lens group G2. And moves to the object side when focusing on a short distance. A solid curve 4a and a dotted curve 4b of the fourth lens group G4 shown in FIG. 1 are images when zooming from the wide-angle end to the telephoto end when focusing on an infinitely distant object and a short-distance object, respectively. The movement trajectory for correcting the surface fluctuation is shown.

  The first lens group G1 includes a meniscus negative lens having a convex surface facing the object side, a cemented lens of a positive lens having a convex surface facing the object side, and two positive lenses having a convex surface facing the object side. Has been. The second lens group G2 includes, in order from the object side, two negative lenses, and a cemented lens of a positive lens and a negative lens having a convex surface facing the object side.

  The third lens group G3 includes an independent positive lens having an aspheric shape on the object side in order from the object side, and a cemented lens of a positive lens and a negative lens. The fourth lens group G4 includes a cemented lens of a positive lens having an aspheric shape on the object side and a negative lens in order from the object side.

Hereinafter, this embodiment will be described in detail. The zoom lens according to the present embodiment includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a diaphragm fixed to the image plane, and a positive refractive power. A third lens group having a positive refractive power and a fourth lens group having a positive refractive power, the first lens group and the third lens group being fixed in the optical axis direction upon zooming from the wide-angle end to the telephoto end, The second lens group moves from the object side to the image side to have a zooming action, and the fourth lens group is in the direction of the optical axis so as to compensate for variations in the image plane position accompanying the movement of the second lens group. In a zoom lens having a focusing function while moving to
The first lens group includes, in order from the object side, one negative lens and three positive lenses, and the second lens group includes at least three negative lenses and one positive lens, The three lens group has a cemented lens of a positive lens, a positive lens, and a negative lens that are independent from the object side in order, and the fourth lens group has at least one positive lens and a negative lens, and the following conditions are satisfied. It is characterized by satisfaction.
0.03 <| f2 / ft | <0.08 (Condition 1)
5.8 <| f1 / f2 | <8.0 (Condition 2)

  Here, f1 represents the focal length of the first lens group, f2 represents the focal length of the second lens group, and ft represents the focal length of the entire lens system at the telephoto end.

  By disposing at least three positive lenses constituting the first lens group, positive refractive power is dispersed, and correction of spherical aberration, particularly at the telephoto end, is facilitated. Further, the use of a glass material having an Abbe number of 80 or more for the positive lens facilitates correction of longitudinal chromatic aberration and lateral chromatic aberration, particularly at the telephoto end.

  The second lens group includes at least three negative lenses and one positive lens to disperse the negative refractive power and correct coma that occurs with changes in the angle of view at the wide-angle end. However, high performance has been achieved. Desirably, by arranging a cemented lens of a positive lens and a negative lens, correction of aberrations such as chromatic aberration can be corrected satisfactorily, and furthermore, the influence of assembly errors during manufacturing can be reduced, and stable optical quality can be obtained. be able to.

  Since the third lens group has at least one surface including an aspherical shape, it is possible to satisfactorily correct off-axis aberrations that occur during zooming. Further, the third lens group includes two positive lenses and a negative lens, so that chromatic aberration generated in the third lens group can be corrected well, and the principal point position of the third lens group can be set to the object side. Since they can be arranged, the distance from the third lens group to the image plane can be reduced, which contributes to miniaturization. Further, the negative lens constituting the third lens group is a meniscus negative lens having a strong curvature on the image plane side, thereby facilitating correction of spherical aberration. The negative lens constituting the third lens group is a positive lens. By using the cemented lens, the distance between the principal point of the third lens group and the most object-side positive lens is widened, and it becomes easy to ensure stable optical performance during manufacturing.

  The fourth lens group is composed of a cemented lens of a positive lens and a negative lens, so that it is possible to satisfactorily correct on-axis aberrations that occur during zooming. Furthermore, the simplification of the configuration by joining makes it possible to reduce the weight of the fourth lens group, which is the movable lens group, and to perform the focusing operation at high speed. Desirably, by having at least one aspheric surface, it becomes easy to satisfactorily correct spherical aberration occurring in the fourth lens group.

  Conditional expression (1) defines the focal length of the second lens group and the focal length of the entire lens system at the telephoto end. If the refractive power of the second lens group becomes weaker than the upper limit value of conditional expression (1), the amount of movement during zooming increases, the total length becomes longer, and it becomes difficult to reduce the size, which is not preferable. Further, if the refractive power of the second lens unit is increased beyond the lower limit of conditional expression (1), it is difficult to satisfactorily correct aberration fluctuations during zooming from the wide-angle end state to the telephoto end state. Absent.

It is preferable to set the numerical range of conditional expression (1) so as to satisfy the following conditional expression (1a).
0.05 <| f2 / ft | <0.065 (Condition 1a)

  Conditional expression (2) defines the focal length of the first lens group and the focal length of the second lens group. If the upper limit of conditional expression (2) is exceeded and the refractive power of the first lens group becomes weak, the entire length of the zoom lens becomes longer, and further, the lens diameter of the first lens group has to be increased, thereby achieving miniaturization. This is not preferable because it becomes difficult. If the lower limit of conditional expression (2) is exceeded and the refractive power of the first lens unit becomes strong, it will be difficult to correct spherical aberration at the telephoto end, and it will not be possible to achieve high performance.

It is preferable to set the numerical range of conditional expression (2) so as to satisfy the following conditional expression (2a).
6.0 <| f1 / f2 | <7.0 (Condition 2a)

More desirably, the third lens group preferably satisfies the following conditions.
0.15 <f3 / ft <0.35 (Condition 3)
0.4 <f31 / f3 <0.8 (Condition 4)

  Here, f3 represents the focal length of the third lens group, f31 represents the focal length of the most object-side positive lens constituting the third lens group, and ft represents the focal length of the entire lens system at the telephoto end.

  Conditional expression (3) defines the focal length of the third lens group and the focal length of the entire lens system at the telephoto end. If the upper limit of conditional expression (3) is exceeded, the refractive power of the third lens group becomes too weak, and in order to maintain the refractive power of the entire third lens group and fourth lens group, the fourth lens group. Therefore, it is difficult to correct aberrations such as astigmatism and coma. If the lower limit value of conditional expression (3) is exceeded, the refractive power of the third lens group becomes too strong, and large aberrations such as spherical aberration occur.

It is preferable that the numerical range of conditional expression (3) is set so as to satisfy the following conditional expression (3a).
0.2 <f3 / ft <0.3 (Condition 3a)

  Conditional expression (4) is an expression that defines the focal length of the most object side positive lens and the third lens group constituting the third lens group. If the upper limit value of conditional expression (4) is exceeded, the refractive power of the most object-side positive lens constituting the third lens group becomes too weak, and the total length of the zoom lens becomes long, which is not preferable. If the lower limit of conditional expression (4) is exceeded, the refractive power of the most object-side positive lens constituting the third lens group becomes too strong, and large aberrations such as spherical aberration occur, which is not preferable.

Preferably, the numerical range of conditional expression (4) is preferably set so as to satisfy the following conditional expression (4a).
0.55 <f31 / f3 <0.7 (Condition 4a)
More desirably, the fourth lens group preferably satisfies the following conditions.
0.08 <f4 / ft <0.25 (Condition 5)

  Here, f4 represents the focal length of the fourth lens group, and ft represents the focal length of the entire lens system at the telephoto end.

  Conditional expression (5) defines the focal length of the fourth lens group and the focal length of the entire lens system at the telephoto end. When the refractive power of the fourth lens group becomes weaker than the upper limit value of the conditional expression (5), the payout amount at the time of focusing of the fourth lens group becomes large, and the distance between the third lens group and the fourth lens group is shortened. It is difficult to reduce the size. If the lower limit of conditional expression (5) is exceeded and the refractive power of the fourth lens group becomes strong, it is difficult to satisfactorily correct aberration fluctuations during zooming from the wide-angle end state to the telephoto end state.

It is preferable to set the numerical range of conditional expression (5) so as to satisfy the following conditional expression (5a).
0.1 <f4 / ft <0.16 (Condition 5a)

  As described above, in the zoom lens according to the present embodiment, by appropriately configuring each lens group, the optical performance corresponding to the high-pixel image sensor is ensured while the zoom ratio is as high as about 30. The miniaturization is realized while maintaining the performance.

  According to the present embodiment, in an imaging apparatus such as a surveillance camera, a video camera, a digital still camera, etc., the zoom ratio is as high as about 30, and it is small in size from the wide-angle end to the telephoto end and from infinity to the close range. A zoom lens capable of maintaining good optical performance corresponding to a high-pixel imaging device can be obtained.

  Hereinafter, specific examples of the present embodiment will be described. Numerical Examples 1 to 5 shown below are specific examples that meet the above conditional expressions. In each numerical example, the surface number i indicates the order of the optical surfaces from the object side. ri represents the radius of curvature of the i-th optical surface, di represents the distance between the i-th surface and the (i + 1) -th surface, and ndi and νdi represent the refractive index and Abbe number of the material of the i-th optical member with respect to the d-line, respectively. . The back focus (BF) is a value obtained by converting the distance from the last lens surface to the paraxial image surface into air. The total lens length is a value obtained by adding back focus (BF) to the distance from the front lens surface to the final lens surface.

  The unit of length is mm. Further, when K is a conic constant, A4, A6, A8, and A10 are aspherical coefficients, and the displacement in the optical axis direction at the position of the height H from the optical axis is x with respect to the surface vertex, the aspherical shape Can be represented by the following equation.

However, R is a curvature radius. Further, for example, the display of “E-Z” means “10 ^−Z ”. f is a focal length, Fno is an F number, and ω is a half angle of view.

  The table shown below shows a conditional expression correspondence table for each numerical example. Each numerical value indicates a value defined by each conditional expression. Thus, all the numerical examples satisfy each conditional expression.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

G1 1st lens group G2 2nd lens group G3 3rd lens group G4 4th lens group G Glass block such as CCD face plate and low-pass filter SP Aperture IP Imaging surface d d-line g g-line ΔM Meridional image surface ΔS Sagittal Image surface ω Half angle of view Fno F number

Claims (5)

In order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a stop fixed with respect to the image plane, a third lens group having a positive refractive power, a positive and a fourth lens group having a refractive power, upon zooming from the wide angle end to the telephoto end, the first lens group and the third lens group is fixed in the optical axis direction, the second lens group is an object side The fourth lens group moves in the optical axis direction so as to compensate for the variation in the image plane position accompanying the movement of the second lens group, and has a focusing function. In a zoom lens having
The first lens group includes, in order from the object side, one negative lens and three positive lenses, the second lens group includes at least three negative lenses and one positive lens, The three lens group has a cemented lens of a positive lens, a positive lens, and a negative lens that are independent from the object side in order, and the fourth lens group has at least one positive lens and a negative lens, and the following conditions are satisfied. satisfied, among the positive lens constituting the first lens group, at least one Abbe number and said Rukoto with 80 or more glass materials, the zoom lens.
0.03 <| f2 / ft | <0.08
5.8 <| f1 / f2 | <8.0
Where f1: focal length of the first lens group f2: focal length of the second lens group ft: focal length of the entire lens system at the telephoto end The most object side positive lens constituting the third lens group has at least one surface including an aspherical shape, and the cemented surface of the cemented lens constituting the third lens group has a convex shape on the object side. The zoom lens according to claim 1, wherein the following condition is satisfied.
0.15 <f3 / ft <0.35
0.4 <f31 / f3 <0.8
Where f3: focal length of the third lens group f31: focal length of the most object-side positive lens constituting the third lens group ft: focal length of the entire lens system at the telephoto end   3. The second lens group according to claim 1, wherein the second lens group includes two negative lenses in order from the object side, a cemented lens of a positive lens having a convex surface facing the object side, and a negative lens. Zoom lens.   The fourth lens group is composed of a cemented lens of a positive lens and a negative lens in order from the object side. The positive lens constituting the fourth lens group has at least one surface including an aspherical shape, and satisfies the following conditions: The zoom lens according to claim 1, wherein the zoom lens is a zoom lens.
  0.08 <f4 / ft <0.25
Where f4: focal length of the fourth lens group
      ft: focal length of the entire lens system at the telephoto end   An imaging apparatus comprising the zoom lens according to claim 1.

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