JPH1123965A - Rear focus type zoom lens and image pickup device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rear focus type zoom lens and an image pickup device using the zoom lens having excellent performance over the entire zoom area and the entire object distance while sufficiently securing a back focus space. SOLUTION: This zoom lens is provided with four lens groups, that is, a 1st group L1 having positive refractive power, a 2nd group L2 having negative refractive power, a 3rd group L3 having the positive refractive power and a 4th group L4 having the positive refractive power in this order from the object side, performs variable power from a wide angle end to a telephoto end by moving the 2nd group L2 to an image surface side and corrects the fluctuation of the image surface in accordance with the variable power by moving a part of or all of the 4th group L4. Furthermore, focusing is performed by moving a part of or all of the 4th group L4 and the 2nd group L2 is constituted of a 21st lens negative, a 22nd lens negative, a 23rd lens negative and a 24th lens positive.

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 an image pickup apparatus using the same, and more particularly, to providing a color separation prism on an image plane side used for an image pickup apparatus such as a video camera and a broadcast camera. The present invention relates to a small rear-focus type zoom lens having a long back focus as large as possible, a large aperture ratio, a high zoom ratio, and a short overall lens length, and an image pickup apparatus using the same.

[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 group other than the first group on the object side.

In general, a rear focus type zoom lens has a smaller effective diameter of the first lens group than a zoom lens which performs focusing by moving the first lens group, so that the entire lens system can be easily miniaturized, and close-up photographing 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.

[0005] Such a rear focus type zoom lens is disclosed in, for example, JP-A-62-215225, JP-A-62-220616, and JP-A-62-262.
No. 4213, JP-A-63-247316 and JP-A-4-43311 disclose, in order from the object side, 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. The zoom lens has four lens groups, a third lens group and a fourth lens group having a positive refractive power. The second lens group is moved to perform zooming, and the fourth lens group is moved to change the image plane due to zooming and focus. It is carried out.

Further, JP-A-4-43311, JP-A-4-153615, JP-A-5-19165, JP-A-5-27167 and JP-A-5-609.
No. 73 proposes a zoom lens having a short overall lens length in which the fourth lens group is constituted by one positive lens or two positive lenses. Japanese Patent Application Laid-Open No. 5-60974 discloses a fourth method.
There has been proposed a zoom lens in which a lens group includes two lenses, a positive lens and a negative lens.

JP-A-55-62419, JP-A-55-62419
JP-A-2-24213, JP-A-62-215225, JP-A-56-114920, JP-A-3-20
In Japanese Patent Application Laid-Open Nos. 0113, 4-242707, 4-343313, 5-297275, etc., the third lens unit and the fourth lens unit in the examples are respectively a positive lens and a negative lens. A zoom lens comprising two lenses is disclosed. On the other hand, with the recent high performance (digitalization) of video decks, various improvements have been made to the image quality of video cameras. One of them is color separation of an image by a color separation optical system. Such a zoom lens for a video camera has been proposed in, for example, JP-A-5-72474, JP-A-6-51199, JP-A-7-199069, and JP-A-7-270684.

[0008]

Generally, when a rear focus system is adopted in a zoom lens, the whole lens system can be reduced in size, quick focus can be achieved, and further, advantages such as easy close-up photographing can be obtained.

On the other hand, on the other hand, while ensuring a long back focus enough to dispose a color separation prism, fluctuations in aberrations during focusing are reduced, and high optical performance is obtained over the entire object distance from an object at infinity to an object at a short distance. If so, the lens configuration becomes very difficult.

Particularly, in a zoom lens having a large aperture ratio and a high zoom ratio, it is very difficult to obtain high optical performance over the entire zoom range and over the entire object distance while securing a long back focus.

[0011] JP-A-4-26811 and JP-A-4-26811
The zoom lens disclosed in Japanese Patent No. 88309 has a short back focus, and it is difficult to dispose a color separation prism.

JP-A-4-43311 and JP-A-4-43311
The zoom lenses disclosed in JP-A-153615, JP-A-5-19165, JP-A-5-27167 and JP-A-5-60973 have a zoom ratio of about 6 to 8 times, and more. If a zoom lens having a high zoom ratio is to be obtained, the chromatic aberration variation due to zooming becomes too large, and it becomes difficult to satisfactorily correct this.

JP-A-55-62419, JP-A-5-62419
In the zoom lens disclosed in JP-A-6-114920 and JP-A-3-200113, the first lens unit or the third lens unit is disclosed.
The lens barrel structure becomes complicated because the group moves with zooming,
There is a problem that it is difficult to achieve miniaturization.

In the zoom lenses disclosed in JP-A-4-242707, JP-A-4-343313, JP-A-5-297275, etc., the third lens unit has a large air gap. Further, since the negative lens in the third lens group has a weak refractive power, if it is applied to a zoom lens having a high zoom ratio, a large amount of chromatic aberration occurs in the third lens group, and it is difficult to sufficiently correct this. there were.

In the zoom lens proposed in Japanese Patent Application Laid-Open No. 5-297275, the meniscus negative lens in the third lens unit has a lens configuration with a strong concave surface facing the image surface side. Although effective, it is difficult to correct higher-order flare components generated by the positive lens with the negative lens, and it is difficult to increase the aperture and the zoom ratio.

The zoom lens proposed in JP-A-5-72474, JP-A-6-51199, JP-A-7-199069, and JP-A-7-270684 has a variable magnification ratio. It is about 10 to 12 times, and the zoom ratio is not always enough for use in a video camera.

The present invention employs a rear focus system and has a long back focus such that a color separation prism, an optical filter and the like can be arranged on the image plane side.
With a large aperture ratio and a high zoom ratio of 16 times, it is excellent over the entire zoom range from the wide-angle end to the telephoto end, and over the entire object distance from infinity to super close-up objects. It is an object of the present invention to provide a rear focus type zoom lens having optical performance and an imaging device using the same.

[0018]

According to 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 a part or all of the fourth group, and a part or the whole of the fourth group is moved to perform focusing. The second group is composed of a negative 21st lens and a negative 22nd lens. It comprises a lens, a negative twenty-third lens, and a positive twenty-fourth lens.

The image pickup apparatus according to the present invention is characterized in that (2-1) a rear focus type zoom lens having the configuration (1-1) and a color separation optical system on the image plane side are provided.

[0020]

FIG. 1 is a sectional view of an essential part of an image pickup apparatus having a rear focus type zoom lens according to a first embodiment of the present invention, and FIGS. FIG. 8 is an aberration diagram at a zoom position at a middle or telephoto end.

FIG. 5 is a sectional view of an essential part of a second embodiment of an image pickup apparatus having a rear focus type zoom lens according to the present invention.
FIGS. 6, 7 and 8 are aberration diagrams of the second embodiment at zoom positions at the wide-angle end, the middle position, and the telephoto end.

FIG. 9 is a sectional view of a main part of an image pickup apparatus having a rear focus type zoom lens according to a third embodiment of the present invention.
FIGS. 10, 11, and 12 show the wide-angle end, the middle,
FIG. 7 is an aberration diagram at a zoom position at a telephoto end.

FIG. 13 is a sectional view of an essential part of an image pickup apparatus having a rear focus type zoom lens according to a fourth embodiment of the present invention. FIGS. 14, 15, and 16 show a wide angle end, a middle position, and a telephoto end of the fourth embodiment. 4 is an aberration diagram at a zoom position of FIG.

FIG. 17 is a sectional view of a principal part of a fifth embodiment of an image pickup apparatus having a rear focus type zoom lens according to the present invention. FIGS. 18, 19 and 20 show wide-angle, middle and telephoto ends of the fifth embodiment. 4 is an aberration diagram at a zoom position of FIG.

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. GA is a protective glass provided as needed to protect the zoom lens,
GB is a glass block such as a color separation prism, a face plate, and a filter. IP is the image plane, CCD
And the like are arranged.

Each element from the first lens unit L1 to the protective glass GA constitutes one element of the zoom lens (zoom lens unit) ZL. The glass block GB and the imaging device are housed in the camera body CB. The zoom lens unit ZL is detachably attached to the camera body CB via a mount member C.

In this embodiment, when zooming from the wide-angle end to the telephoto end, the second lens unit is moved to the image plane side as indicated by an arrow, and the image plane fluctuation due to zooming is partly or entirely included in the fourth lens unit. In the present embodiment, all of them are corrected while moving along a convex locus toward the object side.

Also, a rear focus system is employed in which a part or the whole (all in the present embodiment) of 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. The first and third units are fixed during zooming and focusing.

In this embodiment, the fourth lens unit is moved to correct the image plane fluctuation caused by zooming, and the fourth lens unit is moved for focusing. In particular, curve 4 in FIG.
When zooming from the wide-angle end to the telephoto end, as shown in FIGS.
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 indicated by a straight line 4c in FIG.

The video camera (imaging device) of the present invention comprises at least the zoom lens, a color separation element, an image pickup element corresponding to each color divided by the color separation element, an image pickup signal processing circuit and the like. .

In this embodiment, the second negative refractive power for zooming is used.
As described above, the group is composed of the four lenses having a predetermined refractive power, so that aberration fluctuations accompanying zooming can be satisfactorily corrected to facilitate a high zoom ratio.

As described above, the zoom lens of this embodiment is composed of four lens groups as a whole, and the moving conditions of each lens group during zooming and focusing and the lens configuration of the second group are appropriately set. As a result, high optical performance is obtained over the entire zoom range and the entire object distance while securing a predetermined back focus.

In particular, the second lens unit includes, in order from the object side, a negative 21st lens, a negative 22nd lens, a negative 23rd lens, and a positive 2nd lens.
It consists of four lenses. In other words, in order to increase the magnification, the power of the second lens unit having a zooming action is increased so that the magnification changes with a small amount of movement. At this time, if the negative power of the second lens unit is excessively increased, the Petzval sum increases in the negative direction, and the image plane falls. In addition, the movement of the second lens unit for zooming causes the coma aberration and astigmatism to fluctuate greatly, making it difficult to correct these fluctuation aberrations. For this purpose, three negative lenses are used to reduce the sharing of each lens, thereby reducing the Petzval sum.

Further, by arranging the negative lens in a concentrated manner on the object side, the position of the front principal point of the second group can be made closer to the object side, and the principal point distance between the first and second groups can be reduced. Is shortened. Then, the first lens unit can approach the stop, and the off-axis light beam that determines the diameter of the first lens unit (front lens) is
The height passing through the first group is reduced, thereby reducing the diameter of the first group.

Further, in order to sufficiently correct the chromatic aberration at the telephoto end, three negative lenses and one positive lens are used.

Next, the features of another lens configuration of the rear focus type zoom lens of the present invention will be described.

(A1) Since the present invention aims at a high zoom ratio as described above, it is desirable that aberrations caused by zooming be canceled in the first and second units. However, the manner of occurrence of aberrations due to zooming differs between the first and second groups, and tends to be overcorrected at the wide-angle end.

Therefore, in the present invention, when the focal length of the i-th lens unit is fi, 0.16 <| f2 / f1 | <0.20 (1) is satisfied.

When the value exceeds the upper limit of conditional expression (1), the Petzval sum increases in the negative direction, and the image plane tends to largely fall to the plus side, which is not preferable. Conversely, if the lower limit value is exceeded, it is necessary to increase the moving distance of the second lens unit for high zooming, which leads to an increase in the diameter of the front lens and an increase in the overall length of the lens.

(A2) It is desirable that aberrations that fluctuate with zooming should be sufficiently suppressed in the second lens unit.

Therefore, in the present invention, when the focal length of the i-th lens unit is fi and the focal length of the 22nd lens is f22, the condition of 3.03 <f22 / f2 <8.03 (2) is satisfied. I am satisfied.

Conditional expression (2) is for correcting variations in spherical aberration and coma due to zooming in a well-balanced manner.

When the value exceeds the upper limit of conditional expression (2), the spherical aberration becomes under at the telephoto end (telephoto end), and the correction becomes insufficient. Conversely, if the lower limit value is exceeded, a large amount of inward coma aberration occurs at the wide end (wide angle end), leading to deterioration of performance, which is not good.

(A3) In order to satisfactorily correct aberration fluctuations caused by zooming, when the focal lengths of the 23rd and 24th lenses are f23 and f24, respectively, 0.87 <| f23 / f24 | < The condition 1.51） (3) is satisfied.

This conditional expression (3) is for favorably correcting coma aberration and axial chromatic aberration mainly occurring in the second lens unit. By composing the negative 23rd lens and the positive 24th lens in the second group with a single lens, the air lens formed between them is used for aberration correction, and thus the aberration correction is favorably performed. .

If the upper limit of conditional expression (3) is exceeded, spherical aberration at the telephoto end will be undercorrected, and introvertive coma will occur, which is not preferable. Conversely, if the value exceeds the lower limit, axial chromatic aberration is overcorrected, which is not good.

(A4) In order to lengthen the back focus, which is one of the objects of the present invention, the lens closest to the object side of the third group is made concave on the object side. That is, the third group for making the luminous flux diverged by the second group substantially afocal is of a retro type, and the principal point position of the third group is arranged away from the second group, whereby the second group and the second group are arranged. The distance between the principal points of the third lens unit and the third lens unit is further increased, and the height of the axial ray incident on the third lens unit is further increased. As a result, the focal length of the fourth lens group for setting the focal length of the entire system to a predetermined amount can be increased, and the back focus as a working distance is extended.

That is, since the light flux exiting the third lens group is substantially afocal, the length of the back focus is substantially the same as the focal length of the fourth lens group when calculated using the principal point system. Therefore, in order to fix the focal length of the entire system and lengthen the focal length of the fourth lens group, it is understood that the height h of the axial light in the third lens group should be increased as shown in FIG. Further, the lens surface closest to the object side in the third group faces the object side with a strong concave surface,
The third group can receive the light flux diverging from the group without generating higher-order spherical aberration.

(A5) In Numerical Examples 1 and 3, the third lens unit is composed of two lenses: a negative lens having both concave lens surfaces and a positive lens having both convex lens surfaces. It constitutes a lens group. Further, the negative lens has a strong concave surface on the object side and plays a role of keeping the principal point position of the third group away from the second group. Therefore, the focal length of the fourth group is made longer, and thus the back focus is made longer. Have contributed.

In Numerical Embodiments 2 and 4, the third lens unit includes a negative cemented lens in which a negative lens and a positive lens are cemented as a whole, and a negative cemented lens having a concave lens surface on the object side and an image surface, and a convex cemented lens having both lens surfaces. It consists of a positive lens, and constitutes a retro-type positive lens group as a whole. Further, the cemented lens has a strong concave surface on the object side, and the principal point position of the third group is set to the second
It plays a role in keeping it away from the lens group, and contributes to increasing the focal length of the fourth lens group and thus increasing the back focus.

In Numerical Example 5, the third lens unit includes a negative cemented lens in which the negative lens and the positive lens are cemented as a whole, and a negative cemented lens having a concave lens surface on the object side and an image plane, and a positive lens and a negative lens. As a whole, the lens surfaces on the object side and the image plane side are made of a positive cemented lens having a convex surface, and a retro-type positive lens group is constituted as a whole. Further, the negative cemented lens has a strong concave surface on the object side, plays a role of keeping the principal point position of the third unit away from the second unit, and makes the focal length of the fourth unit longer, and thus the back focus. Contributes to lengthening

(A6) The fourth unit is composed of a positive lens having both lens surfaces convex, and a cemented lens having convex lens surfaces on the object side and the image side, and satisfactorily corrects aberration fluctuations during focusing. I have. In particular, in order to favorably correct chromatic aberration, at least one cemented lens is provided in the fourth group. As described above, with the improvement of the image quality of the video camera, chromatic aberration which has not been a problem in the past, especially chromatic aberration of magnification, has become a problem, and it has become possible to satisfactorily correct it.

(A7) The radius of curvature of the lens surface closest to the object side in the third group is R31, the focal length of the third group is f3, and the negative lens on the object side of the third group (a cemented lens in the case of a cemented lens).
When the focal length of the lens is f31, -0.5 <R31 / f3 <-0.2 {(4) 0.7 <R31 / f31 <1.3} (5)

Both of the conditional expressions (4) and (5) appropriately set the curvature of the lens surface on the object side of the third lens unit and appropriately distribute the refractive power of the third lens unit while maintaining a long back focus. The purpose is to achieve high performance.

If the upper limit of conditional expressions (4) and (5) is exceeded, it is difficult to sufficiently maintain the back focus, which is the object of the present invention.
It becomes difficult to correct high-order spherical aberration generated when the light beam diverging from the group enters the third group, and it becomes difficult to achieve high performance.

(A8) No matter where the aperture stop is located in the optical system, the object of the present invention is not hindered. When the aperture stop is located between the negative lens and the positive lens of the third group, the peripheral portion of the lens group is used. Is large, and the diaphragm space can be most easily obtained in view of the system configuration. In order to reduce the size of the first lens unit in order to promote the miniaturization of the lens, the position of the entrance pupil must be pushed forward of the lens. Therefore, for such a purpose, it is desirable that the aperture stop be arranged closest to the object side of the third lens unit.

When the space between the third lens unit and the fourth lens unit can be widened, it is preferable to dispose the aperture stop closest to the image plane side of the third lens unit because the exit pupil can be made longer.

In the present embodiment, the diameter of the front lens, which is the first lens group, is reduced by disposing the third lens element closest to the object side.

(A9) In the present embodiment, the third lens unit is constituted by a negative lens unit and a positive lens unit, so that the exit pupil is lengthened.
The light rays emitted from the third lens group are made telecentric, and the angle of the light rays incident on the color separation prism disposed at the rear is made gentle. As a result, the change in the reflection characteristics due to the wavelength of the color separation system is eliminated, and the color separation is faithfully performed, and the color reproducibility of the image is greatly improved.

(A10) Since the zoom lens of the present invention has a high zoom ratio, the focal length at the telephoto end becomes extremely long, and the performance at and near the telephoto end is greatly affected by the second lens unit. Therefore, the optical performance is improved by arranging an aspherical surface in the fourth lens unit.

Since the aspherical surface basically aims at correcting spherical aberration, it is desirable that the aspherical surface has a shape in which the positive refractive power becomes weaker toward the periphery of the lens.

(A11) When the focal length of the fourth lens unit is f4, the distance between the third lens unit and the fourth lens unit when focusing on an object at infinity at the telephoto end is D34T, and the focal length at the wide-angle end is fW. 7 <f4 / fW <5.8 ‥‥ (6) 0.2 <D34T / f4 <0.94 ‥‥ (7)

The conditional expressions (6) and (7) are for achieving high performance, high zoom ratio, and large diameter while securing a predetermined back focus.

Conditional expression (6) optimizes the length of the back focus. When the value exceeds the upper limit, the back focus becomes unnecessarily long and the overall length becomes longer. When the value exceeds the lower limit, the object of the present invention is achieved. It becomes difficult to secure a certain sufficiently long back focus.

Conditional expression (7) is for optimizing the relationship between the movable space of the fourth unit for focusing and the focal length at the telephoto end. If the lower limit value is exceeded, it is not possible to secure a sufficient space for focusing, which impairs the operability of the zoom lens.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the radius of curvature of the ith lens surface in order from the object side, Di is the ith lens thickness and air spacing in order from the object side, and Ni and νi are the ith lens in order from the object side. Are the refractive index and Abbe number of the glass. The aspherical shape has a radius of curvature R at the center of the lens surface, the optical axis direction (the traveling direction of light) is the X axis, the direction perpendicular to the optical axis is the Y axis,
When B, C, D and E are each aspheric coefficients

[0068]

(Equation 1) This is represented by “E-0X” means “× 10 ^−X ”.

Further, R24 to R24 in Numerical Examples 1 and 3
R25, R25 to R26 in Numerical Examples 2 and 4, R26 to R27 in Numerical Example 5, etc. are protective glass parts,
R26 to R29 in Numerical Embodiments 1 and 3, R27 to R30 in Numerical Embodiments 2 and 4, and R28 to R31 in Numerical Embodiment 5 indicate glass blocks such as a color separation prism, an optical filter, and a face plate.

[0070]

[Outside 1]

[0071]

[Outside 2]

[0072]

[Outside 3]

[0073]

[Outside 4]

[0074]

[Outside 5]

[0075]

[Table 1]

[0076]

According to the present invention, as described above, by setting each element, the color separation prism and the optical filter can be arranged on the image plane side while adopting the rear focus method. Has a back focus,
With a large aperture ratio and a high zoom ratio of 16 times, it is excellent over the entire zoom range from the wide-angle end to the telephoto end, and over the entire object distance from infinity to super close-up objects. A rear focus type zoom lens having optical performance and an imaging device using the same can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a first embodiment of an imaging apparatus having a rear focus zoom lens according to the present invention;

FIG. 2 is an aberration diagram at a wide-angle end of an imaging device having a rear-focusing zoom lens according to a first embodiment of the present invention.

FIG. 3 is an intermediate aberration diagram of Embodiment 1 of the imaging apparatus having the rear focus zoom lens of the present invention.

FIG. 4 is an aberration diagram at a telephoto end of an image pickup apparatus including a rear-focus type zoom lens according to a first embodiment of the present invention.

FIG. 5 is a sectional view of a principal part of a second embodiment of an imaging apparatus having a rear focus zoom lens according to the present invention;

FIG. 6 is an aberration diagram at a wide-angle end of an imaging apparatus having a rear focus zoom lens according to a second embodiment of the present invention.

FIG. 7 is an intermediate aberration diagram of Embodiment 2 of the imaging apparatus having the rear focus type zoom lens of the present invention.

FIG. 8 is an aberration diagram at a telephoto end of an image pickup apparatus having a rear focus zoom lens according to a second embodiment of the present invention.

FIG. 9 is a sectional view of a main part of a third embodiment of an imaging apparatus having a rear focus type zoom lens according to the present invention;

FIG. 10 is an aberration diagram at a wide-angle end of an imaging device having a rear-focusing zoom lens according to a third embodiment of the present invention.

FIG. 11 is an intermediate aberration diagram of Embodiment 3 of the imaging apparatus having the rear focus zoom lens of the present invention.

FIG. 12 is an aberration diagram at a telephoto end of an imaging apparatus having a rear-focusing zoom lens according to a third embodiment of the present invention.

FIG. 13 is a cross-sectional view of a principal part of a fourth embodiment of the imaging apparatus having the rear focus zoom lens according to the present invention;

FIG. 14 is an aberration diagram at a wide-angle end of an imaging device including a rear-focusing zoom lens according to a fourth embodiment of the present invention.

FIG. 15 is an intermediate aberration diagram of Embodiment 4 of the imaging apparatus having the rear focus zoom lens of the present invention.

FIG. 16 is an aberration diagram at a telephoto end of an imaging apparatus including a rear-focusing zoom lens according to a fourth embodiment of the present invention.

FIG. 17 is a sectional view of an essential part of a fifth embodiment of an imaging apparatus having a rear focus type zoom lens according to the present invention;

FIG. 18 is an aberration diagram at a wide angle end of an imaging apparatus including a rear focus zoom lens according to a fifth embodiment of the present invention.

FIG. 19 is an intermediate aberration diagram of Embodiment 5 of the imaging apparatus including the rear focus zoom lens of the present invention.

FIG. 20 is an aberration diagram at a telephoto end of an imaging apparatus including a rear-focusing zoom lens according to a fifth embodiment of the present invention.

FIG. 21 is an explanatory diagram of an optical path of an image pickup apparatus having a rear focus type zoom lens 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 g g-line S Sagittal image plane M Meridional image plane GA, GB Glass block

Claims (10)

[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 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 caused by zooming is corrected by moving part or all of the fourth lens unit. At the same time, a part or all of the fourth group is moved to perform focusing, and the second group is composed of a negative twenty-first lens, a negative twenty-second lens, a negative twenty-third lens, and a positive twenty-fourth lens. This is a rear focus zoom lens. 2. The rear focus zoom lens according to claim 1, wherein a condition 0.16 <| f2 / f1 | <0.20 is satisfied when a focal length of the i-th lens unit is fi. . 3. The apparatus according to claim 2, wherein the focal length of the i-th lens unit is fi,
3. The rear focus type zoom lens according to claim 1, wherein a condition of 3.03 <f22 / f2 <8.03 is satisfied when a focal length of the two lenses is f22. 4. The lens system according to claim 1, wherein a condition of 0.87 <| f23 / f24 | <1.51 is satisfied when the focal lengths of the 23rd lens and the 24th lens are f23 and f24, respectively. , 2 or 3 rear focus zoom lenses. 5. A lens according to claim 1, wherein the lens closest to the object side of the third group has a concave surface facing the object side.
Rear focus type zoom lens of 3 or 4. 6. The apparatus according to claim 1, wherein the fourth group includes a cemented lens having a positive refractive power.
Rear focus type zoom lens as described in the item. 7. The twenty-first lens has a meniscus shape with a convex surface facing the object side, the twenty-second lens has a meniscus shape with a convex surface facing the object side, or both lens surfaces have a concave surface, and the twenty-third lens has a The rear focus zoom lens according to any one of claims 1 to 6, wherein the lens surface on the object side comprises a concave surface, and the 24th lens has both lens surfaces comprising convex surfaces. 8. The third lens unit includes a single or cemented lens having concave lens surfaces on the object side and the image surface side and a single or cemented lens having convex lens surfaces on the object side and the image surface side. The rear focus type zoom lens according to any one of claims 1 to 7, wherein: 9. The fourth lens unit according to claim 1, wherein the fourth lens unit comprises a positive lens having both convex surfaces, and a cemented lens having convex surfaces on the object side and the image side. 1
Rear focus type zoom lens as described in the item. 10. An image pickup apparatus comprising: the rear focus type zoom lens according to claim 1; and a color separation optical system on an image plane side thereof.