JP4877478B2 - Zoom lens for image sensor - Google Patents

Description

  The present invention relates to a zoom lens for an image sensor that has a long back focus that allows a color separation prism to be inserted, is compact despite high magnification, and is suitable for use in a video camera or the like.

  In recent years, with the digitization of video decks and the like, video cameras are also required to have high image quality. As a means of improving image quality, the photographed light is divided into R (red), G (green), and B (blue) colors by a color separation prism, and three CCDs (Charge Coupled Devices) corresponding to each color independently. It is effective to use a multi-plate type that obtains high image quality by picking up images and superimposing the images. In such a multi-plate video camera, there is a strong demand for a zoom lens having a long back focus into which a color separation prism can be inserted and a high zoom ratio.

  That is, in such a multi-panel video camera, a relatively long back focus is required for disposing a color separation prism and the like as compared with a single-panel type that is a combination of a single CCD and a color filter, and color A long exit pupil distance that does not cause shading is necessary.

Incidentally, for example, Patent Document 1 discloses a zoom lens having a long back focus and a zoom ratio of about 10 times.
JP 07-270684 A

  However, the zoom lens disclosed in Patent Document 1 realizes a long back focus in which a color separation prism can be inserted. However, the number of lenses constituting the lens is relatively large, about 13 to 14, and the cost increases. There is a problem of causing an increase in weight.

  In view of such problems, an object of the present invention is to provide a zoom lens capable of forming a compact and high-quality image while having a sufficiently long back focus such that a color dispersion prism can be disposed, for example.

The zoom lens according to claim 1 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 and moving for zooming, and a positive refractive power. a third lens group having, and has a positive refractive power, in four lens rear-focusing type zoom lens made of a group of the fourth lens group which moves for correcting the positional change of the image plane during zooming ,
The first lens group includes a negative lens (L11), a positive lens (L12), and a positive lens (L13) from the object side to the object side, and the second lens group includes a negative lens (L21) and a negative lens from the object side. lens (L22), made of a positive lens (L23), the third lens group at least one surface is made from a single lens having a positive refractive power is aspheric (L31), the fourth lens group at least one or more sides And a negative lens (L41), a positive lens (L42), and a positive lens (L43) from the object side, and at least one Abbe of the positive lens of the first lens group. When the number is ν1, the Abbe number of the single lens (L31) is ν31, the focal length of the i-th lens group is fi, and the focal length of the negative lens (L41) in the fourth lens group is f4-
75.0 <ν1 (1)
40.0> ν31 (2)
0.8 <f4 / | f4- | <1.5 (3)
3.0 <| f1 / f2 | <6.0 (4)
The following conditional expression is satisfied.

  In the zoom lens of the present invention, the first lens group having positive refractive power, the second lens group having negative refractive power, the third lens group having positive refractive power, and the fourth lens having positive refractive power For example, when zooming from the wide-angle side to the telephoto side, the second lens group is moved to the image plane side, and the image plane variation caused by zooming is changed in the fourth lens group. A part or all of the object is corrected while being moved while having a convex locus on the object side. As a result, the space between the third lens group and the fourth lens group is effectively used to effectively shorten the entire lens length.

  The first lens group includes a negative lens (L11), a positive lens (L12), and a positive lens (L13) from the object side. With this configuration, the principal point position of the first lens group is located on the second lens group side, and the distance between the principal points of the first lens group and the second lens group at the wide angle end is shortened. Thus, the first lens unit is reduced in size.

  The second lens group includes a negative lens (L21), a negative lens (L22), and a positive lens (L23) from the object side. With such a configuration, fluctuations in distortion and coma at the wide-angle end can be suppressed.

  The third lens group includes a single lens (L31) having a positive refractive power, and both surfaces of the positive lens have aspherical shapes. By configuring the third lens group as described above, the third lens group can be configured as a single lens, and various aberrations with a large aperture of F number of about 1.8 can be corrected. In particular, the aspherical shape of the third lens group has a great effect on correcting spherical aberration.

  The fourth lens group includes a negative lens (L41), a positive lens (L42), and a positive lens (L43) from the object side, and the fourth lens group is a lens having at least one aspherical shape. Have. By adopting such a configuration, it is possible to correct the aberration with a small number of components of three and realize a long back focus.

  Hereinafter, conditional expressions (1) to (4) will be described. Conditional expression (1) defines the Abbe number of the positive lens constituting the first lens group, and satisfies the conditional expression (1) with the negative lens in the first lens group having positive refractive power as a whole. By adopting a configuration including a positive lens using such a glass material, the secondary spectrum can be removed, and axial chromatic aberration generated near the telephoto end can be reduced. If the Abbe number decreases beyond the lower limit of the conditional expression, the correction of chromatic aberration near the telephoto end becomes insufficient.

  Conditional expression (2) is an expression that defines the Abbe number of the positive lens (L31) constituting the third lens group. By using a high dispersion material that satisfies the conditional expression (2), the fourth lens is obtained. Chromatic aberration that occurs in the group is corrected. If the Abbe number increases beyond the upper limit of the conditional expression, it becomes difficult to correct chromatic aberration occurring in the fourth lens group.

  Conditional expression (3) is an expression that defines the refractive power of the negative lens (L41) in the fourth lens group. If the lower limit is exceeded, it is difficult to realize a long back focus in which a color separation optical system can be inserted. . If the upper limit is exceeded, it will be difficult to correct spherical aberration. Furthermore, it is more preferable to satisfy conditional expression (7) described later.

  Conditional expression (4) defines the ratio of the refractive powers of the first lens group and the second lens group, and achieves a reduction in the size of the entire optical system while maintaining a high zoom ratio. The conditions for obtaining the imaging performance are determined. When the refractive power of the second lens group becomes weaker than the refractive power of the first lens group exceeding the upper limit of conditional expression (4), the amount of movement of the second lens group accompanying zooming increases, and the total lens length and It becomes difficult to reduce the ball diameter. Conversely, when the refractive power of the second lens group becomes stronger than the refractive power of the first lens group beyond the lower limit, it becomes difficult to correct various aberrations such as spherical aberration. Furthermore, it is more preferable to satisfy conditional expression (9) described later.

  In general, chromatic aberration is ideally corrected by each lens group alone, but it is very disadvantageous in terms of size and cost of the entire optical system to completely correct chromatic aberration by each lens group alone. Therefore, in such a lens type, the axial chromatic aberration generated in the first lens group is enlarged at the telephoto end by the second lens group which is a zoom unit. Further, when the zoom ratio is increased, axial chromatic aberration at the telephoto end is more generated, and in order to correct it, the first lens group and the second lens group must comprehensively correct, and as a result, Lateral chromatic aberration remains at an intermediate position between the wide-angle end and the telephoto end.

  In such a case, it is generally considered that the distance between the third lens group and the fourth lens group is sufficiently widened so that the light beam passes through a place away from the optical axis of the lens group.

  However, with such an arrangement, the fourth lens group requires a larger effective diameter, and the zoom lens becomes large. Enlarging the distance between the third lens group and the fourth lens group is also a factor in increasing the size.

  Therefore, in the zoom lens of the present invention, the distance between the third lens group and the fourth lens group is not widened, and the chromatic aberration of magnification in the direction in which the image height of the g-line becomes larger than the d-line in the fourth lens group, The lateral chromatic aberration is corrected in the direction in which the image height of the g-line becomes smaller than the d-line generated in the first lens group and the second lens group. As a result, axial chromatic aberration remains in the fourth lens group in the direction in which the g-line exceeds the d-line, but a high-dispersion glass that satisfies the conditional expression (2) is used in the third lens group. Thus, axial chromatic aberration in the direction opposite to that of the fourth lens group is generated to correct the axial chromatic aberration of the fourth lens group.

  Further, according to the present invention, the first lens group is formed by using a lens using a special low dispersion glass material or an anomalous dispersion glass material that satisfies the conditional expression (1), so that the first lens group is generated at the telephoto end. The axial chromatic aberration is reduced to some extent. As a result, the distance between the third lens group and the fourth lens group is further reduced, leading to a reduction in the size of the lens unit. Although this glass material is effective for both the positive lens (L12) and the positive lens (L13) constituting the first lens group, the front lens diameter can be reduced by using the positive lens (L12). On the other hand, the positive lens (L12) is often cemented with the negative lens (L11). Considering defects at the time of cementing, the special low-dispersion lens having a relatively high cost is preferably used as the positive lens (L13) alone. Cost increase can be mitigated.

A zoom lens according to a second aspect of the present invention is the zoom lens according to the first aspect, wherein the positive lens (L12) included in the first lens group satisfies the following conditional expression.
75.0 <ν1 (5)

  A zoom lens according to a third aspect of the present invention is the zoom lens according to the first or second aspect, wherein the second lens group includes a lens having at least one surface having an aspherical shape.

  Various aberrations can be corrected by providing at least one aspheric surface in the second lens group. The aspherical surface of the second lens group corrects off-axis aberrations, particularly distortion aberration, mainly caused by refraction of off-axis principal rays.

  According to a fourth aspect of the present invention, in the zoom lens according to any one of the first to third aspects, at least one of the negative lenses included in the second lens group is formed of an aspherical resin on a glass spherical surface. The composite aspherical lens is characterized in that it is a composite aspherical lens.

  When one or more of the negative lenses included in the second lens group is composed of a glass spherical lens and an aspheric resin, the choice of glass materials is widened compared to glass mold lenses and plastic lenses, and various aberrations are reduced. The correction effect is increased. In addition, by using a cemented lens, the assembly can be performed relatively easily compared to the case where each is a single lens.

  According to a fifth aspect of the present invention, in the zoom lens according to any one of the first to fourth aspects, the second lens group includes a cemented lens in which a negative lens (L22) and a positive lens (L23) are cemented. Features.

  A zoom lens according to a sixth aspect of the present invention is the zoom lens according to any one of the first to fifth aspects, wherein the first lens group includes a cemented lens in which a negative lens (L11) and a positive lens (L12) are cemented. Features.

A zoom lens according to a seventh aspect of the present invention is the zoom lens according to any one of the first to sixth aspects, wherein the third lens group satisfies the following conditional expression when the focal length at the wide angle end of the zoom lens is fw. It is characterized by doing.
6.0 <f3 / fw <13.0 (6)

  Conditional expression (6) defines the refractive power of the third lens group. If the lower limit of conditional expression (6) is exceeded, the refractive power of the third lens group becomes too strong, so that sufficient back focus can be secured. In addition, even if an aspherical surface is used, correction of spherical aberration becomes insufficient. If the upper limit is exceeded, shortening of the total lens length becomes insufficient. Furthermore, it is more preferable that conditional expression (10) described later is satisfied.

  A zoom lens according to an eighth aspect of the present invention is the zoom lens according to any one of the first to seventh aspects, wherein the third lens group is composed of a single lens having a positive refractive power having a double-sided aspheric shape. .

  According to a ninth aspect of the present invention, in the zoom lens according to any one of the first to eighth aspects, the third lens group is composed of a single plastic lens having a positive refractive power having a double-sided aspheric shape. It is characterized by.

  By configuring the third lens group with a single lens made of a plastic material, there are advantages that the cost and the weight are reduced as compared with the case of making the third lens group with a glass material.

  In a zoom lens according to a tenth aspect, in the invention according to any one of the first to ninth aspects, the fourth lens group includes a cemented lens in which a negative lens (L41) and a positive lens (L42) are cemented. Features.

  The zoom lens according to claim 11 is the invention according to any one of claims 1 to 10, wherein the positive lens (L43) included in the fourth lens group has an aspheric resin formed on a glass spherical surface. It is a composite aspherical lens.

  As for the lens having an aspherical shape used in the fourth lens group, the glass spherical lens and the aspherical resin are compounded in the same manner as the second lens group, so that the glass material is made in comparison with the glass mold lens and the plastic lens. Various types of options are expanded, and the effect of correcting various aberrations is increased. In addition, by using a cemented lens, the assembly can be performed relatively easily compared to the case where each is a single lens.

A zoom lens according to a twelfth aspect is the invention according to any one of the first to eleventh aspects, wherein the focal length at the wide angle end of the zoom lens is fw, and the air equivalent distance from the lens final surface to the image plane at the wide angle end. When Bfw is satisfied, the following conditional expression is satisfied.
2.5 <Bfw / fw <5.0 (7)

  Conditional expression (7) defines the back focus. If the value Bfw / fw falls below the lower limit of conditional expression (7), the backfocus becomes too short, and the space for inserting the color dispersion prism becomes insufficient. On the contrary, if the upper limit of conditional expression (7) is exceeded, the entire length of the entire lens is extended and the compactness is lost. Therefore, it is desirable to satisfy conditional expression (7).

A zoom lens according to a thirteenth aspect of the invention according to any one of the first to twelfth aspects of the present invention satisfies the following conditional expression.
0.9 <f4 / | f4- | <1.3 (8)

A zoom lens according to a fourteenth aspect is characterized in that, in the invention according to any one of the first to thirteenth aspects, the following conditional expression is satisfied.
4.5 <| f1 / f2 | <6.0 (9)

A zoom lens according to a fifteenth aspect of the invention is characterized in that, in the invention according to any of the first to fourteenth aspects, the following conditional expression is satisfied.
8.5 <f3 / fw <13 (10)

  The zoom lens according to a sixteenth aspect is the invention according to any one of the first to fifteenth aspects, wherein a stop is disposed on the object side of the third lens group, and the stop is on the optical axis of the second lens group. The opening diameter varies depending on the position.

  In the present invention, the aperture diameter is reduced for reasons such as reducing the illuminance unevenness of the image plane while cutting off the harmful luminous flux that becomes the flare component, and making it easier to correct the aberration at the telephoto end and allow a design margin. Control can be performed according to the position of the second lens group on the optical axis.

  A zoom lens according to a seventeenth aspect is the invention according to any one of the first to sixteenth aspects, wherein focusing is performed from an infinitely distant object to a short-distance object by moving the fourth lens group in the optical axis direction. It is characterized by that.

  When photographing a short distance object from an object at infinity using the zoom lens of the present invention, if focusing is performed by moving the fourth lens group to the object side, focusing is performed by moving the first lens group. Compared with the zoom lens to be performed, there is an advantage that the effective diameter of the first lens group is reduced and the entire lens system can be easily downsized.

  A zoom lens according to an eighteenth aspect is characterized in that, in the invention according to any one of the first to seventeenth aspects, a color separation optical element is disposed on the image plane side of the fourth lens group.

  According to the present invention, it is possible to provide a zoom lens that can form a high-quality image that is compact and has a sufficiently long back focus such that a color dispersion prism can be disposed, for example.

Embodiments of the zoom lens according to the present invention will be described below with reference to the drawings, but are not limited thereto. Symbols used in each example are as follows.
f: Focal length F: F number ω: Half angle of view r: Radius of curvature of each lens surface d: Lens thickness or lens interval nd: Refractive index νd: Abbe number

  In each embodiment, the shape of the aspheric surface is expressed by the following “Equation 1” where the vertex of the surface is the origin, the X axis is taken in the optical axis direction, and the height in the direction perpendicular to the optical axis is h.

  In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10-02) is represented using E (for example, 2.5E-02).

Example 1
Table 1 shows lens data of the zoom lens according to the first example. FIG. 1 is a sectional view in the middle of the zoom lens according to the first example, and FIG. 2 is an aberration diagram of spherical aberration, astigmatism, and distortion of the zoom lens according to the first example. Here, FIG. 2A is an aberration diagram at the wide-angle end. FIG. 2B is an aberration diagram in the middle. FIG. 2C is an aberration diagram at the telephoto end. In the following aberration diagrams, in the spherical aberration diagram, the solid line represents the d line and the dotted line represents the g line, and in the astigmatism diagram, the solid line represents the sagittal image plane and the dotted line represents the meridional image plane.

  In FIG. 1, the rear focus type zoom lens according to the first exemplary embodiment includes a first lens group G1 having a positive refractive power and a second lens having a negative refractive power and moving for zooming in order from the object side. The four lenses of the group G2, the stop S, the third lens group G3 having positive refractive power, and the fourth lens group having positive refractive power and moving in order to correct the position change of the image plane at the time of zooming Including the group G4, an infrared cut filter IR + low-pass filter LF, a light separation prism ODP which is a color separation optical element, and a CCD cover glass CG are arranged on the image side.

  The first lens group G1 includes a negative lens L11, a positive lens L12, and a positive lens L13 from the object side to the object side. The second lens group G2 includes a negative lens L21, a negative lens L22, and a positive lens L23 from the object side. The third lens group G3 is composed of a single lens L31 having a positive refractive power having at least one aspheric surface, the fourth lens group has a lens having at least one aspheric surface, and is on the object side. Thus, the lens includes a negative lens L41, a positive lens L42, and a positive lens L43.

  In the first lens group G1, the negative lens L11 and the positive lens L12 are cemented lenses that are cemented with each other. The positive lens L12 uses a special low dispersion glass material or an anomalous dispersion glass material.

  The negative lens L22 included in the second lens group G2 is a compound aspherical lens in which an aspherical resin PL is formed on a glass spherical surface on the object side. In the second lens group G2, the negative lens L22 and the positive lens L23 are cemented lenses that are cemented with each other. The positive lens L31 of the third lens group G3 is a single glass mold lens with positive refractive power having a double-sided aspheric shape. In the fourth lens group G4, the negative lens L41 and the positive lens L42 are cemented lenses that are cemented with each other. The positive lens L43 included in the fourth lens group G4 is a compound aspherical lens in which an aspherical resin PL is formed on a glass spherical surface on the object side.

  As it goes from the wide-angle end to the telephoto end, the first lens group G1 is fixed, the second lens group G2 moves to the image side along the optical axis direction, the third lens group G3 is fixed, The lens group G4 is moved so as to return to the image side after moving toward the object side along the optical axis direction, thereby performing focusing from an infinite object to a short distance object. The aperture stop S disposed on the object side of the third lens group G3 has a configuration in which the aperture diameter changes depending on the position of the second lens group G2 on the optical axis. And description is abbreviate | omitted.

(Example 2)
Table 2 shows lens data of the zoom lens according to the second example. FIG. 3 is a cross-sectional view in the middle of the zoom lens according to the second embodiment, and FIG. 4 shows aberration diagrams of spherical aberration, astigmatism, and distortion of the zoom lens according to the second embodiment. Here, FIG. 4A is an aberration diagram at the wide-angle end. FIG. 4B is an aberration diagram in the middle. FIG. 4C is an aberration diagram at the telephoto end.

  In FIG. 3, the rear focus type zoom lens according to the second embodiment includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens having a negative refractive power and moving for zooming. The four lenses of the group G2, the stop S, the third lens group G3 having positive refractive power, and the fourth lens group having positive refractive power and moving in order to correct the position change of the image plane at the time of zooming Including the group G4, an infrared cut filter IR + low-pass filter LF, a light separation prism ODP which is a color separation optical element, and a CCD cover glass CG are arranged on the image side.

  The first lens group G1 includes a negative lens L11, a positive lens L12, and a positive lens L13 from the object side to the object side. The second lens group G2 includes a negative lens L21, a negative lens L22, and a positive lens L23 from the object side. The third lens group G3 is composed of a single lens L31 having a positive refractive power having at least one aspheric surface, the fourth lens group has a lens having at least one aspheric surface, and is on the object side. Thus, the lens includes a negative lens L41, a positive lens L42, and a positive lens L43.

  In the first lens group G1, the negative lens L11 and the positive lens L12 are cemented lenses that are cemented with each other. The positive lens L12 uses a special low dispersion glass material or an anomalous dispersion glass material.

  The negative lens L21 included in the second lens group G2 is a composite aspheric lens in which an aspheric resin PL is formed on a glass spherical surface on the image side. In the second lens group G2, the negative lens L22 and the positive lens L23 are cemented lenses that are cemented with each other. The positive lens L31 of the third lens group G3 is a single plastic lens having positive refractive power and a double-sided aspheric shape. In the fourth lens group G4, the negative lens L41 and the positive lens L42 are cemented lenses that are cemented with each other. The positive lens L43 included in the fourth lens group G4 is a compound aspherical lens in which an aspherical resin PL is formed on a glass spherical surface on the object side.

  As it goes from the wide-angle end to the telephoto end, the first lens group G1 is fixed, the second lens group G2 moves to the image side along the optical axis direction, the third lens group G3 is fixed, The lens group G4 is moved so as to return to the image side after moving toward the object side along the optical axis direction, thereby performing focusing from an infinite object to a short distance object. The aperture stop S disposed on the object side of the third lens group G3 has a configuration in which the aperture diameter changes depending on the position of the second lens group G2 on the optical axis. And description is abbreviate | omitted.

(Example 3)
Table 3 shows lens data of the zoom lens according to the third example. FIG. 5 is a cross-sectional view in the middle of the zoom lens according to Example 3, and FIG. 6 is an aberration diagram of spherical aberration, astigmatism, and distortion of the zoom lens according to Example 3. Here, FIG. 6A is an aberration diagram at the wide-angle end. FIG. 6B is an aberration diagram in the middle. FIG. 6C is an aberration diagram at the telephoto end.

  In FIG. 5, the rear focus type zoom lens of Example 3 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens having a negative refractive power and moving for zooming. The four lenses of the group G2, the stop S, the third lens group G3 having positive refractive power, and the fourth lens group having positive refractive power and moving in order to correct the position change of the image plane at the time of zooming Including the group G4, an infrared cut filter IR + low-pass filter LF, a light separation prism ODP which is a color separation optical element, and a CCD cover glass CG are arranged on the image side.

  The first lens group G1 includes a negative lens L11, a positive lens L12, and a positive lens L13 from the object side to the object side. The second lens group G2 includes a negative lens L21, a negative lens L22, and a positive lens L23 from the object side. The third lens group G3 is composed of a single lens L31 having a positive refractive power having at least one aspheric surface, the fourth lens group has a lens having at least one aspheric surface, and is on the object side. Thus, the lens includes a negative lens L41, a positive lens L42, and a positive lens L43.

  In the first lens group G1, the negative lens L11 and the positive lens L12 are cemented lenses that are cemented with each other. The positive lens L12 uses a special low dispersion glass material or an anomalous dispersion glass material.

  The positive lens L31 of the third lens group G3 is a single glass mold lens with positive refractive power having a double-sided aspheric shape. The positive lens L43 included in the fourth lens group G4 is a compound aspherical lens in which an aspherical resin PL is formed on a glass spherical surface on the object side.

  As it goes from the wide-angle end to the telephoto end, the first lens group G1 is fixed, the second lens group G2 moves to the image side along the optical axis direction, the third lens group G3 is fixed, The lens group G4 is moved so as to return to the image side after moving toward the object side along the optical axis direction, thereby performing focusing from an infinite object to a short distance object. The aperture stop S disposed on the object side of the third lens group G3 has a configuration in which the aperture diameter changes depending on the position of the second lens group G2 on the optical axis. And description is abbreviate | omitted.

Example 4
Table 4 shows lens data of the zoom lens according to the fourth example. FIG. 7 is a cross-sectional view in the middle of the zoom lens according to Example 4, and FIG. 8 is an aberration diagram of spherical aberration, astigmatism, and distortion of the zoom lens according to Example 4. Here, FIG. 8A is an aberration diagram at the wide-angle end. FIG. 8B is an aberration diagram in the middle. FIG. 8C is an aberration diagram at the telephoto end.

  In FIG. 7, the rear focus type zoom lens of Example 4 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens having a negative refractive power and moving for zooming. The four lenses of the group G2, the stop S, the third lens group G3 having positive refractive power, and the fourth lens group having positive refractive power and moving in order to correct the position change of the image plane at the time of zooming Including the group G4, an infrared cut filter IR + low-pass filter LF, a light separation prism ODP which is a color separation optical element, and a CCD cover glass CG are arranged on the image side.

  The first lens group G1 includes a negative lens L11, a positive lens L12, and a positive lens L13 from the object side to the object side. The second lens group G2 includes a negative lens L21, a negative lens L22, and a positive lens L23 from the object side. The third lens group G3 is composed of a single lens L31 having a positive refractive power having at least one aspheric surface, the fourth lens group has a lens having at least one aspheric surface, and is on the object side. Thus, the lens includes a negative lens L41, a positive lens L42, and a positive lens L43.

  In the first lens group G1, the negative lens L11 and the positive lens L12 are cemented lenses that are cemented with each other. The positive lens L13 uses a special low dispersion glass material or an anomalous dispersion glass material.

  The negative lens L22 included in the second lens group G2 is a compound aspherical lens in which an aspherical resin PL is formed on a glass spherical surface on the object side. In the second lens group G2, the negative lens L22 and the positive lens L23 are cemented lenses that are cemented with each other. The positive lens L31 of the third lens group G3 is a single glass mold lens with positive refractive power having a double-sided aspheric shape. In the fourth lens group G4, the negative lens L41 and the positive lens L42 are cemented lenses that are cemented with each other. The positive lens L43 included in the fourth lens group G4 is a compound aspherical lens in which an aspherical resin PL is formed on a glass spherical surface on the object side.

  As it goes from the wide-angle end to the telephoto end, the first lens group G1 is fixed, the second lens group G2 moves to the image side along the optical axis direction, the third lens group G3 is fixed, The lens group G4 is moved so as to return to the image side after moving toward the object side along the optical axis direction, thereby performing focusing from an infinite object to a short distance object. The aperture stop S disposed on the object side of the third lens group G3 has a configuration in which the aperture diameter changes depending on the position of the second lens group G2 on the optical axis. And description is abbreviate | omitted.

(Example 5)
Table 5 shows lens data of the zoom lens according to the fifth example. FIG. 9 is a cross-sectional view in the middle of the zoom lens according to Example 5, and FIG. 10 is an aberration diagram of spherical aberration, astigmatism, and distortion of the zoom lens according to Example 5. Here, FIG. 10A is an aberration diagram at the wide-angle end. FIG. 10B is an aberration diagram in the middle. FIG. 10C is an aberration diagram at the telephoto end.

  In FIG. 9, the rear focus type zoom lens of Example 5 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens having a negative refractive power and moving for zooming. The four lenses of the group G2, the stop S, the third lens group G3 having positive refractive power, and the fourth lens group having positive refractive power and moving in order to correct the position change of the image plane at the time of zooming Including the group G4, an infrared cut filter IR + low-pass filter LF, a light separation prism ODP which is a color separation optical element, and a CCD cover glass CG are arranged on the image side.

  The first lens group G1 includes a negative lens L11, a positive lens L12, and a positive lens L13 from the object side to the object side. The second lens group G2 includes a negative lens L21, a negative lens L22, and a positive lens L23 from the object side. The third lens group G3 is composed of a single lens L31 having a positive refractive power having at least one aspheric surface, the fourth lens group has a lens having at least one aspheric surface, and is on the object side. Thus, the lens includes a negative lens L41, a positive lens L42, and a positive lens L43.

  In the first lens group G1, the negative lens L11 and the positive lens L12 are cemented lenses that are cemented with each other. The positive lens L12 uses a special low dispersion glass material or an anomalous dispersion glass material.

  The negative lens L22 included in the second lens group G2 is a compound aspherical lens in which an aspherical resin PL is formed on a glass spherical surface on the object side. In the second lens group G2, the negative lens L22 and the positive lens L23 are cemented lenses that are cemented with each other. The positive lens L31 of the third lens group G3 is a single glass mold lens with positive refractive power having a double-sided aspheric shape. In the fourth lens group G4, the negative lens L41 and the positive lens L42 are cemented lenses that are cemented with each other. The positive lens L43 included in the fourth lens group G4 is a compound aspherical lens in which an aspherical resin PL is formed on a glass spherical surface on the object side.

  As it goes from the wide-angle end to the telephoto end, the first lens group G1 is fixed, the second lens group G2 moves to the image side along the optical axis direction, the third lens group G3 is fixed, The lens group G4 is moved so as to return to the image side after moving toward the object side along the optical axis direction, thereby performing focusing from an infinite object to a short distance object. The aperture stop S disposed on the object side of the third lens group G3 has a configuration in which the aperture diameter changes depending on the position of the second lens group G2 on the optical axis. And description is abbreviate | omitted.

  Table 6 shows values of the respective examples corresponding to the conditional expressions.

FIG. 3 is a cross-sectional view in the middle of the zoom lens according to Example 1; FIG. 3 is an aberration diagram of spherical aberration, astigmatism, and distortion of the zoom lens according to Example 1; FIG. 6 is a cross-sectional view in the middle of a zoom lens according to Example 2; FIG. 6 is an aberration diagram of spherical aberration, astigmatism, and distortion of the zoom lens according to Example 2; FIG. 6 is a cross-sectional view in the middle of a zoom lens according to Example 3; FIG. 9 is an aberration diagram of spherical aberration, astigmatism, and distortion of the zoom lens according to Example 3; FIG. 10 is a cross-sectional view of the middle of a zoom lens according to Example 4; FIG. 9 is an aberration diagram of spherical aberration, astigmatism, and distortion of the zoom lens according to Example 4; FIG. 10 is a cross-sectional view of the middle of a zoom lens according to Example 5; FIG. 10 is an aberration diagram of spherical aberration, astigmatism, and distortion of the zoom lens according to Example 5;

Explanation of symbols

G1 to G5 Lens group IR Infrared cut filter LP Low pass filter ODP Color separation prism CG Cover glass S Aperture stop

Claims (18)

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 moving for zooming, a third lens group having a positive refractive power, and a positive lens has a refractive power, the four lens rear focus type imaging element zoom lens made of a group of the fourth lens group which moves for correcting the positional change of the image plane during zooming,
The first lens group includes a negative lens (L11), a positive lens (L12), and a positive lens (L13) from the object side to the object side, and the second lens group includes a negative lens (L21) and a negative lens from the object side. lens (L22), made of a positive lens (L23), the third lens group at least one surface is made from a single lens having a positive refractive power is aspheric (L31), the fourth lens group at least one or more sides And a negative lens (L41), a positive lens (L42), and a positive lens (L43) from the object side, and at least one Abbe of the positive lens of the first lens group. When the number is ν1, the Abbe number of the single lens (L31) is ν31, the focal length of the i-th lens group is fi, and the focal length of the negative lens (L41) in the fourth lens group is f4-
75.0 <ν1 (1)
40.0> ν31 (2)
0.8 <f4 / | f4- | <1.5 (3)
3.0 <| f1 / f2 | <6.0 (4)
A zoom lens for an image sensor, wherein the following conditional expression is satisfied. The zoom lens for an image sensor according to claim 1, wherein the positive lens (L12) included in the first lens group satisfies the following conditional expression.
75.0 <ν1 (5)   3. The zoom lens for an image sensor according to claim 1, wherein the second lens group includes a lens having at least one surface having an aspheric shape. 4.   4. The compound aspherical lens according to claim 1, wherein at least one of the negative lenses included in the second lens group is a compound aspherical lens in which an aspherical resin is formed on a glass spherical surface. The zoom lens for imaging elements as described.   The zoom lens for an image sensor according to claim 1, wherein the second lens group includes a cemented lens in which a negative lens (L22) and a positive lens (L23) are cemented.   The zoom lens for an image sensor according to any one of claims 1 to 5, wherein the first lens group includes a cemented lens in which a negative lens (L11) and a positive lens (L12) are cemented. The zoom lens for an image sensor according to any one of claims 1 to 6, wherein the third lens group satisfies the following conditional expression when a focal length at a wide angle end of the zoom lens is fw. .
6.0 <f3 / fw <13.0 (6)   The zoom lens for an image pickup device according to any one of claims 1 to 7, wherein the third lens group includes a single lens having a positive refractive power and a double-sided aspheric shape.   The zoom lens for an image pickup device according to any one of claims 1 to 8, wherein the third lens group includes a single plastic lens having a positive refractive power having a double-sided aspheric shape.   The zoom lens for an image sensor according to any one of claims 1 to 9, wherein the fourth lens group includes a cemented lens in which a negative lens (L41) and a positive lens (L42) are cemented.   The positive lens (L43) included in the fourth lens group is a composite aspherical lens in which an aspherical resin is formed on a glass spherical surface, according to any one of claims 1 to 10. Zoom lens for image sensor. 12. The zoom lens according to claim 1, wherein the following conditional expression is satisfied, where a focal length at the wide-angle end of the zoom lens is fw and an air-converted distance from the final lens surface to the image plane at the wide-angle end is Bfw. 2. A zoom lens for an image sensor according to claim 1.
2.5 <Bfw / fw <5.0 (7) The zoom lens for an image sensor according to claim 1, wherein the following conditional expression is satisfied.
0.9 <f4 / | f4- | <1.3 (8) The zoom lens for an image sensor according to claim 1, wherein the following conditional expression is satisfied.
4.5 <| f1 / f2 | <6.0 (9) The zoom lens for an image sensor according to claim 1, wherein the following conditional expression is satisfied.
8.5 <f3 / fw <13 (10)   16. The aperture according to claim 1, wherein an aperture is disposed on the object side of the third lens group, and the aperture of the aperture changes depending on the position on the optical axis of the second lens group. Zoom lens for image sensors.   The zoom lens for an image sensor according to any one of claims 1 to 16, wherein focusing is performed from an object at infinity to an object at a short distance by moving the fourth lens group in an optical axis direction.   The zoom lens for an image sensor according to claim 1, wherein a color separation optical element is disposed on the image plane side of the fourth lens group.

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