JP3097399B2 - Rear focus telephoto zoom lens - Google Patents

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 telephoto zoom lens, and more particularly, to a zoom ratio of 3 and an F number used for a photographic camera, video camera, electronic still camera, broadcast camera, etc. for 35 mm film. 2.8
The present invention relates to a rear focus type telephoto zoom lens having a large aperture ratio and a large focus ratio.

[0002]

2. Description of the Related Art Conventionally, a zoom lens such as a photographic camera or a video camera adopts a so-called inner focus type or rear focus type in which a lens group other than the first group on the object side is moved to perform focusing. Various proposals have been made. Hereinafter, the rear focus type is also included, including the inner focus type.

In general, a rear focus type zoom lens has a smaller effective diameter of the first lens unit (front lens diameter) than a zoom lens which moves and focuses the first lens unit, so that the size of the entire lens system can be easily reduced. In addition, close-up photography, particularly very close-up photography, is facilitated. Further, since the relatively small and light lens group is moved, the driving force (rotation torque) of the lens group is small, so that quick focusing can be performed. There are features such as.

For example, Japanese Patent Laid-Open Publication No. Sho 59-52215 discloses a rear focus type zoom lens having a first lens unit having a positive refractive power, a second lens unit having a negative refractive power for zooming, and a zoom lens. In a so-called four-unit zoom lens composed of four lens units, a third unit having a positive refractive power for correcting an image plane variation due to magnification, and a fourth unit having a positive refractive power, the third unit is moved. The focus is on. However, in this zoom lens, the moving space of the third lens group must be secured, and the overall length of the lens tends to increase.

In Japanese Patent Application Laid-Open Nos. 57-78514 and 59-33418, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a second lens unit having a positive refractive power are arranged in order from the object side. The zoom lens system includes four lens units including a third lens unit and a fourth lens unit having a positive refractive power having an imaging function. The second lens unit is moved to perform zooming, and the third lens unit is moved to change the image plane. The fluctuation has been corrected.

Then, the lens unit having a negative refractive power in the fourth unit is moved to the image plane side to focus on a short-distance object (hereinafter, referred to as "in-relay focusing type"). The focus-in-relay type is advantageous in auto-focusing because the weight of the focus lens group is light.

However, since the fourth group has a relatively weak refractive power, the aberration correction is satisfactorily performed, but the entire fourth group tends to become large.

In particular, the F-number is as dark as F4 to F8, and the amount of extension of the focus lens group increases, and if the close distance is shortened, it interferes with other lens groups on the long focal length side, resulting in a sufficient back focus. There was a problem that it was difficult to obtain.

[0009]

In general, when a rear focus system is employed in a zoom lens, the entire lens system is reduced in size and quick focusing becomes possible.

On the other hand, however, aberration fluctuation at the time of focusing becomes large, and it becomes very difficult to obtain high optical performance while miniaturizing the entire lens system over the entire object distance from an object at infinity to an object at a short distance. The problem arises. In particular, a telephoto zoom lens having a large aperture ratio has a problem that it becomes very difficult to obtain high optical performance over the entire zoom range and over the entire object distance.

According to the present invention, a wide-angle end is achieved while adopting the relay focusing method among the rear focusing methods, achieving a large aperture ratio of about F / 2.8, and miniaturizing the entire lens system, particularly the relay system. It is an object of the present invention to provide a rear-focusing telephoto zoom lens having excellent optical performance over the entire zoom range from the object to the telephoto end, and over the entire object distance from an object at infinity to an object at a short distance.

[0012]

A rear focus type telephoto zoom lens according to the present invention comprises a first group of positive refractive power, a second group of negative refractive power, and a second group of negative refractive power which are fixed during zooming in order from the object side. A fourth lens unit having a third lens unit having a positive refractive power and a fourth lens unit having a positive refractive power having an imaging function. The first to third units constitute a substantially afocal system. 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 accompanying zooming is performed by moving the third unit. The fourth unit is a positive refractor. A fourth lens unit having a fourth refractive power, a fourth lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power. -Shaped positive fourth A2 lens, both lens surfaces of which are concave negative fourth A
The fourth lens unit includes a third lens and a positive fourth A4 lens having a convex surface facing the object side. An air lens is formed between the fourth A2 lens and the fourth A3 lens.
The fourth lens subunit includes at least one positive lens. The fourth lens subunit has at least one positive lens, and moves the fourth lens subunit toward the image plane side to a short distance object. focusing performed, 0.4 and a focal length of the fourth group and the 4A group each f4, F4a, the average value of the refractive index of the material of the positive lens in said 4A group was _{N 4AP} <F4a /F4<0.8‥‥‥(1) 1.65 <N _4AP ‥‥‥ (2)

[0013]

1 to 4 are sectional views of a lens at a wide angle end according to Numerical Examples 1 to 4 of the present invention. 5 to 16 show aberration diagrams of Numerical Examples 1 to 4 of the present invention. In the aberration diagram (A)
Is an object at infinity, and (B) is an object distance of 1.5 m.

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, L4
Denotes a fourth group (relay group) having a positive refractive power.

SP is an aperture. The fourth lens unit L4 includes three lens units, a fourth lens unit having a positive refractive power, a fourth lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power. First group L1
Up to the third lens unit L3, a substantially afocal system is constituted as a whole.

At the time of zooming from the wide-angle end to the telephoto end, the second lens unit L2 is moved to the image plane side as indicated by an arrow, and the image plane fluctuation caused by zooming is corrected by moving the third lens unit L3 to the convex shape toward the image plane side. The movement is corrected so as to have a locus.

The first lens unit L1 and the fourth lens unit L4 are fixed during zooming.

Further, a rear focus type is employed in which the fourth lens unit L4F is moved on the optical axis to perform focusing.

In the present invention, when focusing from an object at infinity to an object at a close distance, the fourth lens unit L4F is moved to the image plane side.

In the present embodiment, the effective lens diameter of the first group is increased by adopting the rear focus method as described above in comparison with a conventional four-group zoom lens in which the first group is extended and focused. Prevention.

In this embodiment, the first lens unit L1 is a meniscus negative eleventh lens unit having a concave surface facing the image surface side in order from the object side.
The lens is composed of three lenses, a positive twelfth lens and a positive thirteenth lens, both lens surfaces of which are convex.

The second lens unit L2 has at least three negative lenses as a whole. The third unit L3 is configured to include a positive lens and a meniscus negative lens having a concave surface facing the object side. The first to third groups are substantially afocal as a whole.

By configuring each lens unit in this way, aberration fluctuations caused by zooming can be satisfactorily corrected in the first to third units, and high optical performance can be maintained over the entire zooming range.

Then, it is sufficient that the aberration fluctuation at the time of focusing in the fourth lens unit is corrected by the fourth lens unit alone.

In general, in a four-unit zoom lens, the relay unit of the fourth unit is provided with a lens unit having a positive refractive power at the front and a lens unit having a negative refractive power at the rear in order to shorten the total lens length. A telephoto system (telephoto system) is formed.

Taking spherical aberration as an example,
A negative spherical aberration occurs in the front lens unit having a positive refractive power,
The spherical aberration is corrected as a whole by canceling out the positive spherical aberration generated by the rear lens unit having a negative refractive power.

At this time, when focusing is performed by moving the rear lens unit having a negative refractive power as a focus lens unit and moving on the optical axis, the focus lens is moved to the image plane side as the subject becomes closer. The incident height of the axial ray into the lens is reduced. For this reason, the occurrence of positive spherical aberration is reduced, and the spherical aberration is insufficiently corrected for the entire relay system.

Therefore, in the present invention, as described above, the fourth lens unit L4 is divided into three lenses, that is, a fourth lens unit having a positive refractive power, a fourth lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power. The fourth lens group is moved to the image plane side as a focus lens to focus from an object at infinity to a close object.

The lens configuration is such that the spherical aberration generated in the fourth lens unit A is positively displaced so as to cancel out the negative displacement of the spherical aberration of the fourth lens unit F (focus lens) as the subject distance becomes shorter.

In this way, the spherical aberration at the time of focusing in the fourth F group of the fourth group is corrected so as not to be insufficiently corrected.

In particular, in the fourth A group, in order from the object side, a fourth A1 lens with both lens surfaces convex, a positive meniscus fourth A2 lens with the convex surface facing the object side, and a fourth lens with both lens surfaces concave.
An A3 lens and a positive fourth A4 lens having a convex surface facing the object side, and a negative air lens formed between the fourth A2 lens and the fourth A3 lens.
Positive spherical aberration is generated in a better balance than in the A group.

Next, the features of the lens configuration of the fourth group A will be described.

In the reference state (object at infinity), the fourth A
The negative spherical aberration generated on the image surface side of each of the first lens, the fourth A2 lens, and the fourth A3 lens is canceled by the positive spherical aberration generated mainly on the object side lens surface of the fourth A3 lens. It is in a state where it has been well corrected.

Subsequently, when focusing is performed on the object side at a short distance, the spherical aberration is negatively displaced between the object-side lens surface of the fourth A1 lens and the object-side and image-side lens surfaces of the fourth A4 lens. A large positive displacement is made on the lens surface on the image plane side of the fourth A3 lens, and the entire relay system is made positively displaced.

The positive displacement in the entire relay system is because the first to third groups have been well corrected for aberrations but have negative displacement of the weak crown of spherical aberration.

The behavior of coma and astigmatism is the same as the behavior of substantially spherical aberration, and the fluctuations of these various aberrations are well corrected in the same manner as described above.

Then, various aberrations in the reference state (object at infinity) are satisfactorily corrected by the fourth lens unit (positive lens) disposed behind the fourth lens unit, and fluctuations such as coma and astigmatism are satisfactorily corrected. doing.

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

Conditional expression (1) relates to the ratio of the refractive power of the fourth group A in the relay system to the refractive power of the entire relay system.
In particular, it is for controlling the amount of positive displacement of spherical aberration.

If the refractive power of the fourth unit A is weakened beyond the upper limit value of the conditional expression (1), it is advantageous for aberration correction, but it is not good because the back focus becomes long and the entire lens system becomes large.

Further, the amount of extension of the focus lens (fourth lens unit) increases, and rapid auto-focusing cannot be performed.

On the other hand, when the lower limit of conditional expression (1) is exceeded, the fourth
When the refractive power of the group increases, the lens system becomes compact, and the amount of extension of the focus lens also decreases. The correction becomes largely insufficient, and when focusing on a short-distance object, a sufficient amount of positive displacement of spherical aberration cannot be obtained.As a result, the aberration is deteriorated over the entire object distance from an object at infinity to a short-distance object. Absent.

Conditional expression (2) is for satisfying conditional expression (1) with respect to the average refractive index of the material of the positive lens in the fourth group A, and for further correcting various aberrations favorably.

When the refractive index is higher than the upper limit of conditional expression (2), the spherical aberration and the coma can be easily corrected. However, since the value of Petzval sum is displaced in the negative direction,
This is not good because the entire image plane is overcorrected and the astigmatic difference increases.

Conversely, if the refractive index is reduced below the lower limit of conditional expression (2), the value of Petzval sum for obtaining desired field curvature and astigmatism becomes advantageous, but spherical aberration is reduced. It is not good because it gets worse in both the next and higher orders.

In the present invention, the fourth lens unit is composed of a cemented lens in which a low-dispersion positive lens and a high-dispersion negative lens are cemented, and the chromatic aberration variation during focusing is corrected well.

In the present invention, in order to favorably correct axial and lateral chromatic aberrations, it is preferable to use anomalous dispersion high-dispersion glass for the first lens unit and the third lens unit.

If the stop SP is arranged on the object side of the fourth lens unit, it is advantageous for one stop of the off-axis light beam.
It is preferable to dispose it between the A3 lens and the fourth A4 lens because the aperture diameter becomes small.

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.

The relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples is shown in Table 1. (Numerical Example 1) Fno = 1: 2.94 2ω = 33.25 ° to 12.18 ° R 1 = 182.94 D 1 = 2.90 N 1 = 1.80518 ν 1 = 25.4 R 2 = 104.66 D 2 = 8.60 N 2 = 1.49700 ν 2 = 81.6 R 3 = -678.85 D 3 = 0.20 R 4 = 78.93 D 4 = 8.80 N 3 = 1.49700 ν 3 = 81.6 R 5 = 1149.35 D 5 = Variable R 6 = -1206.57 D 6 = 4.30 N 4 = 1.64769 ν 4 = 33.8 R 7 = -56.23 D 7 = 1.50 N 5 = 1.54664 ν 5 = 61.5 R 8 = 61.49 D 8 = 4.54 R 9 = -93.03 D 9 = 1.50 N 6 = 1.48749 ν 6 = 70.2 R10 = 47.27 D10 = 3.80 N 7 = 1.80518 ν 7 = 25.4 R11 = 146.44 D11 = 3.19 R12 = -73.76 D12 = 1.50 N 8 = 1.77250 ν 8 = 49.6 R13 = 121.23 D13 = Variable R14 = 136.20 D14 = 4.80 N 9 = 1.49700 ν 9 = 81.6 R15 =- 72.64 D15 = 0.20 R16 = 163.29 D16 = 7.00 N10 = 1.64448 ν10 = 61.0 R17 = -45.53 D17 = 1.60 N11 = 1.86536 ν11 = 42.5 R18 = -311.73 D18 = Variable R19 = 124.34 D19 = 4.80 N12 = 1.71300 ν12 = 53.8 R20 = -107.80 D20 = 0.15 R21 = 51.12 D21 = 3.60 N13 = 1.71300 ν13 = 53.8 R22 = 134.97 D22 2.01 R23 = -160.27 D23 = 1.80 N14 = 1.62184 ν14 = 26.0 R24 = 50.12 D24 = 6.45 R25 = (aperture) D25 = 0.59 R26 = 81.20 D26 = 4.90 N15 = 1.71300 ν15 = 53.8 R27 = -481.43 D27 = 1.10 R28 = 786.31 D28 = 3.00 N16 = 1.80518 ν16 = 25.4 R29 = -91.15 D29 = 1.50 N17 = 1.77250 ν17 = 49.6 R30 = 46.86 D30 = 18.15 R31 = 585.19 D31 = 3.40 N18 = 1.48749 ν18 = 70.2 R32 = -66.20

[0051]

[Table 1] (Numerical Example 2) Fno = 1: 2.91 2ω = 33.41 ° to 12.11 ° R 1 = 124.23 D 1 = 2.80 N 1 = 1.84666 ν 1 = 23.8 R 2 = 88.90 D 2 = 0.15 R 3 = 87.29 D 3 = 9.55 N 2 = 1.49700 ν 2 = 81.6 R 4 = -603.14 D 4 = 0.12 R 5 = 88.28 D 5 = 6.03 N 3 = 1.49700 ν 3 = 81.6 R 6 = 248.49 D 6 = Variable R 7 = 365.57 D 7 = 1.40 N 4 = 1.65160 ν 4 = 58.5 R 8 = 37.79 D 8 = 8.63 R 9 = -116.73 D 9 = 1.40 N 5 = 1.65160 ν 5 = 58.5 R10 = 44.82 D10 = 4.11 N 6 = 1.84666 ν 6 = 23.9 R11 = 363.87 D11 = 3.00 R12 = -46.04 D12 = 1.40 N 7 = 1.69680 ν 7 = 55.5 R13 = -111.79 D13 = Variable R14 = 144.20 D14 = 8.10 N 8 = 1.49700 ν 8 = 81.6 R15 = -33.26 D15 = 1.40 N 9 = 1.94383 ν 9 = 40.2 R16 = -48.79 D16 = Variable R17 = (Aperture) D17 = 1.00 R18 = 64.06 D18 = 5.37 N10 = 1.83481 ν10 = 42.7 R19 = -152.13 D19 = 0.15 R20 = 34.60 D20 = 4.08 N11 = 1.60311 ν11 = 60.7 R21 = 88.45 D21 = 2.34 R22 = -228.21 D22 1.80 N12 = 1.84666 ν12 = 23.8 R23 = 37.87 D23 = 13.20 R24 = 179.59 D24 = 2.84 N13 = 1.88300 ν13 = 40.8 R25 = -107.94 D25 = 1.10 R26 = 342.49 D26 = 4.01 N14 = 1.80518 ν14 = 25.4 R27 = -42.13 D27 = 1.50 N15 = 1.80400 ν15 = 46 .6 R28 = 38.26 D28 = 16.11 R29 = 122.59 D29 = 7.62 N16 = 1.50936 ν16 = 54.2 R30 = -34.12 D30 = 6.85 R31 = -32.63 D31 = 1.80 N17 = 1.85425 ν17 = 33.1 R32 = -166.63 D32 = 0.42 R33 = 45.16 D33 = 4.88 N18 = 1.48749 ν18 = 70.2 R34 = 225.83

[0052]

[Table 2] (Numerical Example 3) Fno = 1: 2.94 2ω = 33.25 ° to 12.18 ° R 1 = 186.34 D 1 = 2.90 N 1 = 1.80518 ν 1 = 25.4 R 2 = 105.37 D 2 = 8.60 N 2 = 1.49700 ν 2 = 81.6 R 3 = -773.73 D 3 = 0.20 R 4 = 77.56 D 4 = 8.80 N 3 = 1.49700 ν 3 = 81.6 R 5 = 1390.83 D 5 = Variable R 6 = -1599.93 D 6 = 4.30 N 4 = 1.64769 ν 4 = 33.8 R 7 = -57.59 D 7 = 1.50 N 5 = 1.56278 ν 5 = 60.7 R 8 = 60.51 D 8 = 4.20 R 9 = -152.18 D 9 = 1.50 N 6 = 1.48749 ν 6 = 70.2 R10 = 53.89 D10 = 3.80 N 7 = 1.80518 ν 7 = 25.4 R11 = 203.82 D11 = 3.32 R12 = -67.75 D12 = 1.50 N 8 = 1.77250 ν 8 = 49.6 R13 = 142.01 D13 = Variable R14 = 178.35 D14 = 4.80 N 9 = 1.49700 ν 9 = 81.6 R15 =- 81.52 D15 = 0.20 R16 = 108.35 D16 = 7.00 N10 = 1.78734 ν10 = 59.7 R17 = -47.85 D17 = 1.60 N11 = 1.91933 ν11 = 46.1 R18 = 350.29 D18 = Variable R19 = 228.50 D19 = 4.80 N12 = 1.71300 ν12 = 53.8 R20 =- 88.75 D20 = 0.15 R21 = 57.12 D21 = 3.60 N13 = 1.71300 ν13 = 53.8 R22 = 211.20 D22 1.79 R23 = -134.50 D23 = 1.80 N14 = 1.62468 ν14 = 22.3 R24 = 76.90 D24 = 5.96 R25 = (aperture) D25 = 0.56 R26 = 79.87 D26 = 4.90 N15 = 1.71300 ν15 = 53.8 R27 = -18583.45 D27 = 1.10 R28 = 1160.75 D28 = 3.00 N16 = 1.80518 ν16 = 25.4 R29 = -72.61 D29 = 1.50 N17 = 1.77250 ν17 = 49.6 R30 = 44.53 D30 = 16.17 R31 = -2222.47 D31 = 3.40 N18 = 1.48749 ν18 = 70.2 R32 =- 64.26

[0053]

[Table 3] (Numerical Example 4) Fno = 1: 2.94 2ω = 33.25 ° to 12.18 ° R 1 = 200.87 D 1 = 2.90 N 1 = 1.80518 ν 1 = 25.4 R 2 = 109.37 D 2 = 8.50 N 2 = 1.49700 ν 2 = 81.6 R 3 = -705.95 D 3 = 0.20 R 4 = 76.30 D 4 = 8.90 N 3 = 1.49700 ν 3 = 81.6 R 5 = 1124.16 D 5 = Variable R 6 = -678.29 D 6 = 5.20 N 4 = 1.64769 ν 4 = 33.8 R 7 = -48.11 D 7 = 1.50 N 5 = 1.56536 ν 5 = 60.6 R 8 = 57.32 D 8 = 3.83 R 9 = -183.10 D 9 = 1.50 N 6 = 1.48749 ν 6 = 70.2 R10 = 47.90 D10 = 3.60 N 7 = 1.80518 ν 7 = 25.4 R11 = 169.02 D11 = 3.70 R12 = -54.84 D12 = 1.50 N 8 = 1.77250 ν 8 = 49.6 R13 = 158.88 D13 = Variable R14 = 124.91 D14 = 4.30 N 9 = 1.49700 ν 9 = 81.6 R15 =- 80.33 D15 = 0.20 R16 = 122.99 D16 = 7.20 N10 = 1.64294 ν10 = 92.0 R17 = -43.00 D17 = 1.60 N11 = 1.90148 ν11 = 46.9 R18 = -219.82 D18 = Variable R19 = 137.08 D19 = 4.40 N12 = 1.90293 ν12 = 36.2 R20 = -102.16 D20 = 0.15 R21 = 52.42 D21 = 3.10 N13 = 1.80000 ν13 = 46.0 R22 = 132.18 D22 1.86 R23 = -171.41 D23 = 1.80 N14 = 1.84666 ν14 = 23.8 R24 = 54.60 D24 = 4.24 R25 = (aperture) D25 = 1.47 R26 = 83.74 D26 = 3.60 N15 = 1.77250 ν15 = 49.6 R27 = -1192.87 D27 = 1.10 R28 = 434.14 D28 = 3.10 N16 = 1.80518 ν16 = 25.4 R29 = -90.25 D29 = 1.50 N17 = 1.78110 ν17 = 48.8 R30 = 45.46 D30 = 17.83 R31 = 456.83 D31 = 3.30 N18 = 1.48749 ν18 = 70.2 R32 = -74.13

[0054]

[Table 4]

[0055]

As described above, according to the present invention, while employing the relay-in-focus method among the rear-focus methods,
The F / 2.8 lens is designed to have a large aperture ratio and the entire lens system, especially the relay system, is reduced in size, while covering the entire zoom range from the wide-angle end to the telephoto end. It is possible to achieve a rear focus telephoto zoom lens having excellent optical performance over the entire object distance.

[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 Numerical Embodiment 3 of the present invention.

FIG. 4 is a sectional view of a lens at a wide angle end according to Numerical Example 4 of the present invention.

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

FIG. 6 is an intermediate aberration diagram of the numerical example 1 of the present invention.

FIG. 7 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention.

FIG. 8 is an aberration diagram at a wide angle end according to Numerical Example 2 of the present invention.

FIG. 9 is an intermediate aberration diagram of the numerical example 2 of the present invention.

FIG. 10 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention.

FIG. 11 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 12 is an intermediate aberration diagram of the numerical example 3 of the present invention.

FIG. 13 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

FIG. 14 is an aberration diagram at a wide angle end according to Numerical Example 4 of the present invention.

FIG. 15 is an intermediate aberration diagram of the numerical example 4 of the present invention.

FIG. 16 is an aberration diagram at a telephoto end in Numerical Example 4 of the present invention.

[Explanation of symbols]

 L1 1st group L2 2nd group L3 3rd group L4 4th group L4A 4A group L4F 4F group L4B 4B group SP SP stop d d line gg line S. C Sine condition ΔS Sagittal image plane ΔM Meridional image plane

Claims (3)

(57) [Claims] 1. A first lens unit having a fixed positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a positive refractive power having an imaging function. The fourth group has four lens groups. The first to third groups constitute a substantially afocal system, and the second group is moved to the image plane side to move from the wide-angle end to the telephoto end. The zooming is performed, and the image plane variation accompanying the zooming is performed by moving the third unit, and the fourth unit is a fourth lens unit having a positive refractive power.
A fourth lens unit having a negative refractive power, a fourth lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power. The fourth lens unit includes a fourth A1 lens having both lens surfaces convex, and a meniscus-shaped positive lens having a convex surface facing the object side. 4A2
A lens, a negative 4A3 lens having both concave lens surfaces and a positive 4A4 lens having a convex surface facing the object side, and an air lens is formed between the 4A2 lens and the 4A3 lens; The fourth lens unit includes a cemented lens in which a positive fourth lens and a negative fourth lens are cemented.
The 4B group has at least one positive lens,
The fourth group F is moved to the image plane side to focus on an object at a short distance, and the focal lengths of the fourth group and the fourth group A are set to f4 and f4, respectively.
A, satisfying the condition: 0.4 <f4A / f4 <0.8 1.65 <N _4AP , where N _4AP is the average value of the refractive indices of the materials of the positive lens in the 4A group. Rear focus telephoto zoom lens. 2. The rear focus telephoto zoom lens according to claim 1, wherein an aperture is arranged on the object side of said fourth group. 3. The rear-focusing telephoto zoom lens according to claim 1, wherein an aperture is arranged between said fourth A3 lens and said fourth A4 lens.