JPH11305129A - Rear focus type zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain the miniaturization of a whole lens system by providing four lens groups having positive, negative, positive and positive refraction power in order from the side of an object, and satisfying specified conditions. SOLUTION: Four lens groups of 1st group G1 having positive refractive power, 2nd group G2 having negative refractive power, 3rd group G3 having positive refractive poser and 4th group G4 having positive refractive power are provided in order from the object side. Then magnification from a wide angle end to a telescopic end is performed by moving the 2nd group L2 to an image surface side. In this case, the fluctuation of an image surface caused by the magnification is corrected by moving the 4th group L4 and focusing is performed by moving the 4th group G4. The 1st group L1 is composed of three lenses, the 2nd group L2 is composed of three lenses, the 3rd group G3 is composed of one lens and the 4th group L4 is composed of a negative 41st lens and a positive 42nd lens, respectively. In this case, when the focal distances of the whole system at the wide angle end and telescopic end are respectively defined as fw and fT and the curvature radiuses on the surface of the 41st lens on the image surface side and the surface of the 42nd lens on the object side are respectively defined as R41b and R42a, the inequalities are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear focus type zoom lens, and more particularly to a zoom ratio of 15 to 1 used for a photographic camera, a video camera, a broadcast camera and the like.
8, a rear-focusing zoom lens having a simple configuration with a large number of lenses having a large aperture ratio and an F-number of about 1.6 at the wide-angle end and having a small number of lenses.

[0002]

2. Description of the Related Art In recent years, as home video cameras and the like have become smaller and lighter, remarkable progress has been made in miniaturization of zoom lenses for image pickup. Emphasis is placed on simplification.

As one means for achieving these objects, there is known a so-called rear focus type zoom lens which performs focusing by moving a lens unit other than the first unit on the object side.

In general, a rear focus type zoom lens has a smaller effective diameter of the first group than a zoom lens which moves and focuses the first group, so that the entire lens system can be easily miniaturized, and close-up photography can be performed. In particular, since extremely close-up photography is facilitated and the relatively small and lightweight lens group is moved, the driving force of the lens group is small and quick focusing can be performed.

In order to reduce the weight of the entire lens system and to facilitate manufacture, various zoom lenses using a lens (plastic lens) made of a plastic material in some lens groups have been proposed.

As such a rear-focusing type zoom lens, for example, in Japanese Patent Application Laid-Open No. Sho 62-24213, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a positive lens having a positive refractive power are arranged in order from the object side. The zoom lens has four lens units, a third unit and a fourth unit having a positive refractive power. The first and third units are fixed, and the second unit is moved in one direction to perform zooming. The lens unit is moved so as to correct the image plane fluctuation accompanying zooming, and the fourth unit is moved to perform focusing. The first unit is composed of two positive lenses and one negative lens, and the second group is composed of one positive lens. A rear-focusing zoom lens consisting of a total of ten lenses, a lens and two negative lenses, a third lens group consisting of one positive lens and one negative lens, and a fourth lens group consisting of one positive lens and one negative lens Has been disclosed.

In Japanese Patent Application Laid-Open No. 3-33710, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power and having a zooming function by moving on the optical axis are arranged in order from the object side.
A group, a third group composed of an aspheric lens having a positive refractive power and having a light-condensing action, and a light source that keeps an image plane, which fluctuates due to movement of the second group and an object, at a fixed position from the reference plane. A zoom lens that moves on an axis and includes a fourth group including an aspheric lens, wherein the third and fourth groups have a relatively large air gap, three first groups, and a second group. Discloses a zoom lens having nine lenses, that is, three lenses in the third group, one lens in the third group, and two lenses in the fourth group, of which two aspheric lenses made of glass material are used.

In Japanese Patent Publication No. 6-60971, in order from the object side, a first lens unit having a positive focal length and being fixed at all times, and having a negative focal length and movable only during zooming. A second lens unit as a variator, a third lens unit having a positive focal length and being fixed at all times, and a focusing unit which is an imaging system and corrects a change in a focal position generated at the time of zooming, and A fourth lens unit that moves as a whole, and a zoom lens including at least one aspheric lens in the third lens unit or the fourth lens unit.
A zoom lens comprising three lenses, three lenses in a third lens group, and three lenses in a fourth lens group, that is, a total of 11 lenses is disclosed.

In Japanese Patent Application Laid-Open No. 6-34882, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power are sequentially arranged from the object side.
The zoom lens has four lens groups: a group, a third group having a positive refractive power, and a fourth group having a positive refractive power. The second group is moved to perform zooming, and the fourth group is moved to zoom. Focus and image plane fluctuation due to And the third group counting from the object side of the first group
The first lens, the first lens counted from the object side of the second group, and one lens of the third group are made of a plastic material.

[0010]

Generally, when a rear focus system is employed in a zoom lens, the entire lens system can be reduced in size, quick focusing can be performed, and further, close-up photographing can be easily performed. .

The rear focus type zoom lens proposed in the above-mentioned Japanese Patent Application Laid-Open No. Sho 62-24213 has a zoom ratio of about 5 times, which is not always sufficient.
In order to secure a high zoom ratio with a zoom ratio of 15 to 18, there is a problem that the entire lens system becomes very large.

Also, the zoom lens of the rear focus type proposed in Japanese Patent Application Laid-Open No. 3-33710 and Japanese Patent Publication No. 6-60971 does not always have a sufficient zoom ratio, and an aspherical surface is formed on a lens made of glass. Although an aspherical lens made of a glass material is being used, it is easy to manufacture the aspherical lens made of a plastic material.

The zoom ratio of the rear focus type zoom lens proposed in Japanese Patent Application Laid-Open No. Hei 6-34882 is not always sufficient, and if the zoom ratio is set to about 15 to 18, the entire lens system becomes large. There was a problem.

In addition, since plastic is used where high-index glass is used, the position of the front principal point of the second lens group changes greatly, causing the first lens group to become larger, and the second lens group to become larger.
This also led to an increase in the size of the first lens in the group. In addition, the curvature of the first lens of the second group on the image surface side, which has been tight in the related art, is further increased, and the thickness deviation ratio is increased, so that the production is also difficult.

Further, since plastic is used for a portion having a high refractive power, even if the focus movement due to temperature is canceled on the design value, the temperature of the solid-state imaging device or the like which is actually the image plane becomes high. There is a problem that a temperature difference occurs between the object side and the image side of the lens, and a focus shift occurs due to the temperature.

According to the present invention, when a high zoom ratio of 15 to 18 is to be achieved while adopting the rear focus method, the size of the entire lens system can be reduced by appropriately setting the lens configuration of each lens unit. The objective is to provide a rear-focusing zoom lens with good optical performance over the entire zoom range from the wide-angle end to the telephoto end, and over the entire object distance from an object at infinity to a very close object. .

[0017]

According to a first aspect of the present invention, there is provided a rear focus type zoom lens comprising: (1-1) a first unit having a positive refractive power, a second unit having a negative refractive power, and a positive refraction in order from the object side. Power third
Group, and a fourth lens unit having a positive refractive power, a fourth lens unit. The second lens unit is moved to the image plane side to perform zooming from the wide-angle end to the telephoto end. The movement is corrected by moving the fourth group, and the focus is moved by moving the fourth group. The first group has three lenses, the second group has three lenses, and the third group has one lens. The fourth lens group includes a negative first lens and a positive second lens. The focal lengths of the entire system at the wide-angle end and the telephoto end are respectively fW and fT. When the radius of curvature of the object-side lens surface of the forty-second lens is R41b and R42a, respectively.

[0018]

(Equation 5) -0.08 <(R41b-R42a) / (R41b + R42a) ≦ 0 ‥‥‥ (2a)

(1-2) The first group of positive refractive power, the second group of negative refractive power, the third group of positive refractive power, and the fourth group of positive refractive power in order from the object side. The second lens group,
The lens unit is moved to the image plane side to perform zooming from the wide-angle end to the telephoto end, and the image plane fluctuation due to zooming is corrected by moving the fourth unit, and the fourth unit is moved to focus. The first group has three lenses, the second group has three lenses, and the third group has three lenses.
The group consists of one lens, the fourth group consists of a negative No. 41 lens and a positive No. 42 lens made of plastic material, and the focal lengths at the wide-angle end and the telephoto end of the entire system are respectively fW and fT.
When the radii of curvature of the lens surface on the image surface side of the lens and the radius of curvature of the lens surface on the object side of the forty-second lens are R41b and R42a, respectively.

[0020]

(Equation 6) -0.08 <(R41b-R42a) / (R41b + R42a) ≦ 0 ‥‥‥ (2a)

The rear focus type zoom lens according to the second aspect of the present invention is characterized in that (2-1) the first lens having a positive refractive power in order from the object side.
Group, a second group having a negative refractive power, a third group having a positive refractive power, and a fourth group having a positive refractive power. The second group is moved to the image plane side. The zooming is performed from the wide-angle end to the telephoto end, and the image plane fluctuation caused by the zooming is corrected by moving the fourth unit, and the fourth unit is moved to perform focusing. It is characterized by comprising an aspheric lens having a refractive power of 0 or very weak and a positive lens, and the entire system is constituted by one aspheric lens and nine spherical lenses.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 4 are sectional views of a rear focus type zoom lens according to a first embodiment of the present invention at the wide-angle end in numerical examples 1 to 4 described later, and FIGS. ~ 4
FIG.

FIGS. 9 to 13 are sectional views at the wide-angle end of numerical examples 5 to 9 of the rear focus type zoom lens according to the second invention. FIGS. 14 to 18 show aberrations of the numerical examples 5 to 9. FIG. In the aberration diagrams, (A) is the wide-angle end, (B)
Indicates the telephoto end. Hereinafter, the first invention and the second invention are collectively referred to as the present invention.

In the figure, L1 is a first group having a positive refractive power, L2 is a second group having a negative refractive power, L3 is a third group having a positive refractive power, and L4 is a fourth group having a positive refractive power. . SP denotes an aperture stop, which is arranged in front of the third lens unit L3. G is a glass block such as a face plate or a filter, and IP is an image plane.

In this embodiment, when zooming from the wide-angle end to the telephoto end, the second lens unit is moved to the image surface side as indicated by an arrow, and the image surface fluctuation due to zooming is changed by projecting the fourth lens unit to the object side. The movement is corrected while having the trajectory.

Also, a rear focus system is employed in which the fourth unit is moved on the optical axis to perform focusing. A solid line curve 4a and a dotted line curve 4b of the fourth lens group shown in the same figure show the image plane fluctuation caused by zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at a short distance, respectively. The movement locus for correction is shown. In the numerical examples of the present invention, the first and third units are fixed during zooming and focusing, but may be moved together with the stop during zooming to further reduce the size of the entire lens system.

In the present embodiment, the fourth unit is moved to correct the image plane fluctuation caused by zooming, and the fourth unit is moved to perform focusing. In particular, as shown by the curves 4a and 4b in the figure, the zoom lens is moved so as to have a convex trajectory toward the object side when zooming from the wide angle end to the telephoto end. Thereby, the space between the third and fourth units is effectively used, and the overall length of the lens is effectively reduced.

In this embodiment, for example, when focusing from an object at infinity to an object at a short distance at the telephoto end, the fourth unit is moved forward as shown by a straight line 4c in FIG.

In the first and second aspects of the present invention, the effective diameter of the first lens unit is prevented from increasing when the object distance that can be photographed is shortened, based on the above-described configuration. Also, by specifying the lens configuration of each lens group as described above, especially by appropriately setting the position of the lens made of plastic material on the optical axis, it is possible to simplify the entire lens system and to make it easier to manufacture the zoom lens. The aberration fluctuation accompanying the above is corrected well.

The zoom lens of the present invention has a zoom ratio of 15 to
Since the zoom ratio is as high as 18 times, the amount of movement of the fourth unit during zooming is relatively large, and the variation in aberrations due to zooming tends to increase. At the same time, the amount of movement of the fourth unit for focusing at the telephoto end also increases, and it becomes difficult to correct aberration fluctuations caused by focusing from an object at infinity to a close object.

Therefore, in the present invention, the fourth unit is constituted by a negative meniscus 41th lens having a convex surface facing the object side and a positive 42th lens having both lens surfaces convex. 1a) and (2a) are satisfied, whereby aberration fluctuations during zooming and focusing are satisfactorily corrected.

In particular, in the first invention, the forty-second lens is constituted by an aspheric lens made of a plastic material which is easy to manufacture.
Thereby, the aspherical surface effect is favorably exhibited.

The material referred to as plastic in the present embodiment is, for example, an acrylic resin (eg, polymethylmethacrylete: PMMA) which is light-transmitting and relatively inexpensive, polycarbonate (Polycarbonete: PC), a styrene resin (eg, Styrene-Acrylonitriteresin: SAN), polystyrene resin (for example, Polystyrene: PSt) or amorphous polyolefin (for example, Amorphous-Polyolefin: APO). In this embodiment, an organic material may be used instead of plastic.

Next, the features of the configuration of the first invention will be described. In the first invention, of the four lens groups, the first group has three lenses, the second group has three lenses, the third group has one positive lens with both lens surfaces being convex, and the fourth group has a negative 41st lens. And a positive 42th lens made of a plastic material.

The zoom lens is set so as to satisfy the conditional expressions (1a) and (2a), whereby high optical performance is obtained over the entire zoom range while achieving high zoom ratio.

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

The conditional expression (1a) relates to the 42nd lens made of the fourth group of plastic materials. Conditional expression (1
If the radius of curvature of the lens surface on the object side of the forty-second lens is loosened beyond the upper limit of a), there arises a problem that chromatic aberration at the wide-angle end becomes largely under. Conversely, if the radius of curvature is reduced below the lower limit, the 42nd lens will be close to a hemisphere, which causes a problem that manufacturing becomes difficult.

Conditional expression (2a) relates to an air lens formed between the negative first lens and the positive second lens in the fourth unit. When the value exceeds the upper limit of conditional expression (2a),
If the lens surface on the image plane side of one lens is too tight, a problem arises in that the off-axis light beam at the wide angle end causes total reflection on the lens surface on the image plane side of the 41st lens. Further, a problem arises that a ghost occurs due to surface reflection between the image plane side of the 41st lens and the object side surface of the 42nd lens.

As described above, the conditional expressions (1a) and (2a) are conditions for satisfying that the zoom lens has a high zoom ratio and a small size and low cost.

[0040]

(Equation 7) −0.06 <(R41b−R42a) / (R41b + R42a) ≦ 0 ‥‥‥ (2aa)

In the first aspect of the invention, the rear focus of a small and simple lens structure having good optical performance from the wide-angle end to the telephoto end and over the entire object distance while preventing the entire lens system from being enlarged. In order to obtain the zoom lens of the formula, at least one of the following conditions should be satisfied.

(A-1) The second group and the third group each have a lens made of one plastic material.

(A-2) The second group has a lens made of a plastic material provided with an aspherical surface.

According to the constitutions (a-1) and (a-2), the zoom ratio having high optical performance in which the astigmatism and distortion accompanying the zooming are satisfactorily corrected while the size of the entire lens system is reduced. A zoom lens having a high zoom ratio of 16 or more can be easily achieved.

(A-3) The focal length of the i-th lens unit is fi, and the distance between the third lens unit and the fourth lens unit at the telephoto end at infinity is D34.
When T∞

[0046]

(Equation 8) Satisfying the following conditions.

Conditional expression (3a) relates to the distance between the third and fourth units in an object at infinity at the telephoto end. If the distance between the third lens unit and the fourth lens unit is widened beyond the upper limit value of the conditional expression (3a), the height of off-axis luminous flux incident on the fourth lens unit becomes high, it becomes difficult to correct aberration, and the effective diameter of the fourth lens unit becomes large. As a result, the off-axis light flux at the wide angle end is totally reflected.
Conversely, if the distance is smaller than the lower limit and the distance becomes narrow, it becomes difficult to secure the amount of extension of the lens unit by focusing on the object closest to the fourth unit, and the fourth lens unit for securing the F-number light beam from the third unit. The effective diameter of the group increases, and here again, a problem arises in that the off-axis light flux at the wide-angle end is totally reflected.

Condition (4a) relates to the focal length of the second lens unit. If the focal length of the second lens unit becomes shorter than the lower limit of conditional expression (4a), the Petzval sum increases in the under direction, and it becomes difficult to correct aberrations such as image plane tilt. Conversely, if the focal length of the second lens unit becomes longer than the upper limit, the amount of movement of the second lens unit will increase, and the diameter of the front lens will increase too much.

Conditional expression (5a) relates to the ratio of the focal length of the third lens unit to the focal length of the fourth lens unit, and is used to achieve a compact optical system after the stop and maintain good optical performance. . If the focal length of the third lens unit becomes shorter than the lower limit of conditional expression (5a), it becomes difficult to correct the change in spherical aberration due to zooming or during focusing. In addition, problems such as difficulty in securing a sufficient back focus, shortening of the exit pupil at the intermediate zoom position, and an increase in the amount of movement of the fourth lens unit, resulting in a large variation in aberrations during zooming and focusing. Conversely, if the focal length of the third lens group becomes longer than the upper limit, the divergence of the light beam emitted from the third lens group becomes large, the effective diameter of the fourth lens group becomes large, and the lens becomes heavy, so that focusing cannot be performed smoothly. Problems arise.

As described above, conditional expressions (3a) and (4)
a) and (5a) are conditions for satisfying good optical performance by reducing the front lens diameter while shortening the overall length of the lens with a simple configuration.

[0051]

(Equation 9) Good to be.

(A-4) The focal length of the i-th lens unit is fi, and the combined focal length of the first to third lens units at the telephoto end is f.
When 123T is satisfied, the following condition is satisfied: 0.2 <fT / f123T <0.7 {(6a) -8 <f1 / f2 <-4} (7a).

The conditional expression (6a) relates to the degree of parallelism (afocal degree) of the axial light beam emitted from the third lens unit.
When the convergence of the on-axis light flux becomes higher than the upper limit value of the conditional expression (6a), the astigmatism difference at a close object becomes large, and the meridional image plane becomes insufficiently corrected. Conversely, if the divergence of the on-axis light beam is increased beyond the lower limit, the incident height of the light incident on the fourth lens unit is increased, and a problem that a large amount of spherical aberration occurs.

Conditional expression (7a) relates to the focal length of the first and second units, and is intended to achieve compactness of the entire lens system and maintain good optical performance.
Exceeding the lower limit of conditional expression (7a) increases the focal length of the second lens unit, and shortens the focal length of the first lens unit. This increases the amount of movement of the second lens unit, thereby reducing the overall length and the front lens diameter. It becomes difficult. In addition, there is also a problem that the amount of movement of the fourth lens unit near the telephoto end increases, and the fluctuation of aberration during zooming increases.
Conversely, if the value exceeds the upper limit, it becomes difficult to satisfactorily correct various aberrations such as distortion.

(A-5) Preferably, the numerical ranges of the conditional expressions (1a) to (7a) in the first invention are further set as follows in view of aberration correction.

[0056]

(Equation 10) −0.05 <(R41b−R42a) / (R41b + R
42a) ≦ 0

[0057]

[Equation 11] 0.4 <fT / f123T <0.6-7 <f1 / f2 <-4 Next, the features of the configuration of the second invention will be described. In the second aspect of the present invention, the third lens group among the four lens groups having the basic configuration is made of a plastic material and has a refractive power of 0 or very weak (for example, a focal length of 30 times or more of the focal length fW at the wide-angle end of the entire system) ) And an aspheric lens and a positive lens. And one aspherical lens and 9 as a whole lens system
It is characterized by comprising two spherical lenses.

Thus, the front lens diameter can be reduced in size and weight to secure a high zoom ratio (15 times or more), and simplification and reduction in size and weight including the mechanism can be achieved over the entire zoom range and all object distances. Achieving a rear focus zoom lens with good optical performance.

In the second aspect of the invention, the rear focus of a small and simple lens configuration having good optical performance from the wide-angle end to the telephoto end and over the entire object distance while preventing the entire lens system from being enlarged. In order to obtain the zoom lens of the formula, at least one of the following conditions should be satisfied.

(B-1) The first group is composed of three lenses, the second group is composed of three lenses, the third group is composed of two lenses, and the fourth group is composed of two lenses.

(B-2) When the focal length of the i-th lens unit is fi and the focal length at the wide-angle end of the entire system is fW: -3 <f2 / fW <-0.5 (1b) 4 <f3 / f4 <2.5 ‥‥‥ (2b)

The technical meanings of conditional expressions (1b) and (2b) are the same as the technical meanings of conditional expressions (4a) and (5a) in the first invention. In order to obtain even better optical performance while achieving a high zoom ratio, the conditional expressions (1b) and (2b) must satisfy the following condition: -2.5 <f2 / fW <-0.6０．６ (1bb) 5 <f3 / f4 <2.2 ‥‥‥ (2bb)

(B-3) The aspherical lens is provided with a positioning pin. An aspherical lens made of a plastic material has a shape close to a parallel flat plate because the refractive power is weak or small. For this reason, a positioning pin is provided to prevent the front and back of the lens from being mistaken during assembly.

(B-4) The focal length of the i-th lens unit is fi, the focal lengths at the wide-angle end and the telephoto end of the entire system are fW and fT, respectively, and the combined focal lengths of the first to third units at the telephoto end. Distance f1
23T, when the distance between the third unit and the fourth unit in the case of an object at infinity at the telephoto end is D34T∞-0.1 <fT / f123T <0.7 ‥‥‥ (3b) -6.5 <f1 / F2 <-3 (4b)

[0065]

(Equation 12) Satisfying the following conditions. Here, conditional expression (3)
The technical meanings of b), (4b) and (5b) are the same as the technical meanings of conditional expressions (6a), (7a) and (3a) of the first invention.

(B-5) It is preferable from the viewpoint of aberration correction that the numerical ranges of the conditional expressions (1b) to (5b) in the second invention are further set as follows.

-2 <f2 / fW <-1.2 0.6 <f3 / f4 <2 0.1 <fT / f123T <0.6-6.5 <f1 / f2 <-4.5

[0068]

(Equation 13) (b-6) Similar effects can be obtained by providing an aspheric lens on the image plane side of the positive lens in place of the object side of the positive lens of the third group.

In the first and second inventions, it is preferable that the plastic lens and the lens barrel are integrally formed.
According to this, it is easy to simplify the lens barrel.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air spacing from the object side, and Ni and νi are the i-th lens surfaces in order from the object side. The refractive index and Abbe number of glass. In the numerical examples, the last two lens surfaces are glass blocks such as a face plate and a filter. In addition, the table shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples. The aspherical shape has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis, a positive traveling direction of light, and R as a paraxial radius of curvature, K, B, C, D,
When E and F are each aspheric coefficients,

[0071]

[Equation 14] It is represented by the following equation. "E-0x" is "10-x"
Means

[0072]

[Outside 1]

[0073]

[Outside 2]

[0074]

[Outside 3]

[0075]

[Outside 4]

[0076]

[Outside 5]

[0077]

[Outside 6]

[0078]

[Outside 7]

[0079]

[Outside 8]

[0080]

[Outside 9]

[0081]

[Table 1]

[0082]

[Table 2]

[0083]

According to the present invention, when the zoom ratio is increased to 15 to 18 while the rear focus method is employed as described above, by appropriately setting the lens configuration of each lens unit. , A rear-focusing zoom with good optical performance over the entire zoom range from the wide-angle end to the telephoto end while miniaturizing the entire lens system, and over the entire object distance from the object at infinity to the very close object Lens can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens at a wide angle end according to Numerical Embodiment 1 of the present invention.

FIG. 2 is a sectional view of a lens at a wide-angle end according to a second numerical embodiment of the present invention.

FIG. 3 is a sectional view of a lens at a wide-angle end according to a third numerical embodiment of the present invention;

FIG. 4 is a sectional view of a lens at a wide-angle end according to a fourth embodiment of the present invention.

FIG. 5 is an aberration diagram at a wide angle end and a telephoto end according to Numerical Embodiment 1 of the present invention.

FIG. 6 is an aberration diagram at a wide angle end and a telephoto end according to Numerical Embodiment 2 of the present invention.

FIG. 7 is an aberration diagram at a wide angle end and a telephoto end according to Numerical Embodiment 3 of the present invention.

FIG. 8 is an aberration diagram at a wide angle end and a telephoto end according to Numerical Embodiment 4 of the present invention.

FIG. 9 is a sectional view of a lens at a wide angle end according to Numerical Example 5 of the present invention.

FIG. 10 is a sectional view of a lens at a wide angle end according to Numerical Example 6 of the present invention.

FIG. 11 is a sectional view of a lens at a wide angle end according to Numerical Example 7 of the present invention.

FIG. 12 is a lens cross-sectional view at a wide angle end according to Numerical Example 8 of the present invention.

FIG. 13 is a sectional view of a lens at a wide angle end according to a ninth embodiment of the present invention.

FIG. 14 is an aberration diagram at a wide angle end and a telephoto end according to Numerical Example 5 of the present invention.

FIG. 15 is an aberration diagram at a wide angle end and a telephoto end according to Numerical Embodiment 6 of the present invention.

FIG. 16 is an aberration diagram at a wide angle end and a telephoto end according to Numerical Example 7 of the present invention.

FIG. 17 is an aberration diagram at a wide angle end and a telephoto end according to Numerical Example 8 of the present invention;

FIG. 18 is an aberration diagram at a wide angle end and a telephoto end according to Numerical Example 9 of the present invention.

[Explanation of symbols]

 L1 First lens unit L2 Second lens unit L3 Third lens unit L4 Fourth lens unit SP Aperture IP Image plane d d line gg line ΔS Sagittal image plane ΔM Meridional image plane

Claims (11)

[Claims] 1. A first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power. The second unit is moved to the image plane side to perform zooming from the wide-angle end to the telephoto end, and the image plane fluctuation due to zooming is corrected by moving the fourth unit. The focus is moved by moving the group, and the first group is 3
The second group is composed of three lenses, the third group is composed of one lens, and the fourth group is composed of a negative 41 lens and a positive 42 lens, and has a focal point at the wide-angle end and the telephoto end of the entire system. The distances are fW and fT, respectively, and the radii of curvature of the image-side lens surface of the 41st lens and the object surface lens surface of the 42nd lens are R41.
b, R42a −0.08 <(R41b−R42a) / (R41b + R
42a) A rear focus type zoom lens, characterized by satisfying the following condition: ≤0. 2. Four lens groups of a first group having a positive refractive power, a second group having a negative refractive power, a third group having a positive refractive power, and a fourth group having a positive refractive power, in this order from the object side. The second unit is moved to the image plane side to perform zooming from the wide-angle end to the telephoto end, and the image plane fluctuation due to zooming is corrected by moving the fourth unit. The focus is moved by moving the group, and the first group is 3
One lens, the second group includes three lenses, the third group includes one lens, and the fourth group includes a negative 41th lens and a positive 42th lens made of a plastic material. When the focal lengths at the telephoto end are fW and fT, respectively, and the radii of curvature of the image surface side lens surface of the 41st lens and the object surface lens surface of the 42nd lens are R41b and R42a, respectively. −0.08 <(R41b−R42a) / (R41b + R
42a) A rear focus type zoom lens, characterized by satisfying the following condition: ≤0. 3. The rear focus zoom lens according to claim 1, wherein each of the second group and the third group has a lens made of one plastic material. 4. The rear focus type zoom lens according to claim 1, wherein said second group has a lens made of a plastic material having an aspherical surface. 5. The focal length of the i-th lens unit is fi, and the distance between the third lens unit and the fourth lens unit at the telephoto end at infinity is D34T∞.
Then, 4. The method according to claim 1, wherein the following condition is satisfied.
Or a rear focus type zoom lens of 4. 6. The focal length of the i-th lens unit is fi, and the combined focal length of the first to third lens units at the telephoto end is f12.
The rear focus zoom according to any one of claims 1 to 5, wherein a condition of 0.2 <fT / f123T <0.7-8 <f1 / f2 <-4 is satisfied when 3T is set. lens. 7. Four lens groups of a first group having a positive refractive power, a second group having a negative refractive power, a third group having a positive refractive power, and a fourth group having a positive refractive power are arranged in this order from the object side. The second unit is moved to the image plane side to perform zooming from the wide-angle end to the telephoto end, and the image plane fluctuation due to zooming is corrected by moving the fourth unit. Focusing is performed by moving the group, and the third group is made up of an aspherical lens made of plastic material and having a very low refractive power of 0 or very low, and a positive lens, and the entire system is made up of one aspherical lens and nine spherical lenses. A rear-focus type zoom lens characterized by: 8. The first group includes three lenses, and the second group includes three lenses.
The rear focus type zoom lens according to claim 7, wherein one lens, the third group includes two lenses, and the fourth group includes two lenses. 9. When the focal length of the i-th lens unit is fi and the focal length at the wide-angle end of the entire system is fW, -3 <f2 / fW <-0.5 0.4 <f3 / f4 <2.5. 9. The rear focus type zoom lens according to claim 7, wherein the following condition is satisfied. 10. The rear focus type zoom lens according to claim 7, wherein said aspherical lens is provided with a positioning pin. 11. The focal length of the i-th lens unit is fi, the focal lengths at the wide-angle end and the telephoto end of the entire system are fW and fT, respectively, and the combined focal length of the first to third units at the telephoto end is f12.
When the distance between the third unit and the fourth unit at 3T and an object at infinity at the telephoto end is D34T∞, −0.1 <fT / f123T <0.7 −6.5 <f1 / f2 <−3 Equation 4 10. The following conditions are satisfied:
Or 10 rear focus zoom lenses.