JPH06250086A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain a zoom lens of high variable power ratio suitable for a television camera and having a variable power ratio of 8-30, a F-number of 1.7 and a large aperture by comprizing four lens groups and properly setting the lens constitution of the respective lens groups and an aspherical surface. CONSTITUTION:This zoom lens comprizes the first group F having a positive refractive power and fixed at the time of varying a power, the second group V having a negative refractive power for varying the power, the third group C having a negative refractive power and compensating the fluctuation of an image plane due to varying the power and the fixed fourth group R having a positive refractive power in order from the object side and the focal length fT and an F-number FNT of the whole system at the telescopic end, the focal length fi and the F-number Fni of the first group F, the image forming magnification of the second group V by varying the power, the maximum incident height h3m of an on-axis light beam to the third group C at the wide angle end and the moving locus of the third group C and the difference DELTAnu3 of an Abbe number of the materials of a negative lens and a positive lens of the third group C, having at least one positive lens and one negative lens, are properly set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and in particular, by appropriately using an aspherical surface as part of the lens system, the F number at the wide-angle end is 1.7 with a large aperture and a zoom ratio of 8 to 10. The present invention relates to a zoom lens suitable for a television camera, a photographic camera, a video camera and the like, which has good optical performance over the entire zoom range of about 30 and a high zoom ratio.

[0002]

2. Description of the Related Art Conventionally, a television camera or a camera for photography,
A zoom lens having a large aperture, a high zoom ratio and high optical performance is required for a video camera or the like.

Of these, particularly in a color television camera for broadcasting, operability and mobility are emphasized, and in response to the demand, the image pickup device has recently been a small CCD (solid-state image pickup device) of 2/3 inch or 1/2 inch. Is becoming mainstream.

Since the CCD has a substantially uniform resolving power over the entire image pickup range, a zoom lens using this CCD is required to have a substantially uniform resolving power from the center of the screen to the periphery of the screen.

For example, various aberrations such as astigmatism, distortion, and chromatic aberration of magnification are satisfactorily corrected, and it is desired that the entire screen has high optical performance. Further, it is required to have a high zoom ratio, be small and lightweight, and have a long back focus because a color separation system and various filters are arranged in front of the image pickup means.

In the zoom lens, from the object side, in order from the object side, a first group of positive refracting power for focusing (focusing), a second group of negative refracting power for zooming, and an image plane that varies with zooming. A so-called four-group zoom lens composed of four lens groups of a third lens group having a positive or negative refractive power for correcting the above and a fourth lens group having a positive refractive power for image formation has a relatively high zoom ratio and a large zoom lens. Since it is easy to adjust the aperture ratio, it is widely used in color television cameras for broadcasting.

Of the four-group zoom lens, an F number of 1.6
A large-aperture, high-magnification, four-group zoom lens having a zoom ratio of about 1.8 to about 20 and a zoom ratio of about 20 has been proposed in, for example, Japanese Patent Laid-Open No. 54-127322.

[0008]

The zoom lens has a large aperture ratio (F number 1.6 to 1.8), a high zoom ratio (variable ratio 15 to 20), and high optical performance over the entire zoom range. In order to obtain, it is necessary to properly set the refractive power and lens configuration of each lens group.

Generally, in order to obtain high optical performance with little aberration variation over the entire zooming range, it is necessary to increase the degree of freedom in aberration correction by increasing the number of lenses in each lens group, for example.

For this reason, if a zoom lens having a large aperture ratio and a high zoom ratio is to be achieved, the number of lenses will inevitably increase and the size of the entire lens system will increase.

Regarding the image forming performance, there is a problem that the image contrast at the center of the screen is the best, that is, the variation due to the so-called zooming of the best image plane. This is mainly due to the fluctuation of spherical aberration associated with zooming.

Generally, when the zoom ratio is changed to Z and the focal length at the wide-angle end is fW, the variation due to the zooming of the spherical aberration is fW '= from the wide-angle end where the spherical aberration is 0 as shown in FIG.
Up to around FW × Z ^1/4 , there is an under (minus) tendency with respect to the Gaussian image plane. And the zoom position fW ′ = f
If the ^{distance is} close to W × Z ^1/4 , the under amount becomes small, becomes 0 at a certain zoom position, and tends to be over (plus) this time.

Then, the F number becomes larger (the lens system becomes darker), and it becomes the most over (plus) in the vicinity of the zoom position (FNW / FNT) × fT at which F-drop starts, and when the zoom position is passed, the telephoto lens becomes a telephoto lens. The amount of over becomes small toward the end, and becomes almost 0 at the telephoto end.

Generally, the degree of coincidence between the variation due to zooming of the spherical aberration that influences the best image plane at the center of the screen and the variation due to zooming of the sagittal image plane and the meridional image plane that influences the best image plane around the screen is determined. A well-balanced control over the entire zoom range is important for obtaining high optical performance.

In particular, recently, in response to a demand for reduction in size, weight and wide angle of the zoom lens, it has been attempted to increase the refracting power of each lens group to make the entire zoom lens system a reduction system.

Among them, in the four-group zoom lens, the total power of the zoom lens system is reduced by strengthening the refracting power of the compensator (image surface variation correction group) which is the third group and reducing the reciprocating movement thereof. Therefore, the load on the image plane correction lens group tends to increase.

27, 28, and 29 show the wide-angle end (f = 10) and the middle (f = 19.6) in the 4-group zoom lens.
8) is an explanatory diagram showing a state when a light beam passes through the lens systems from the first group to the third group at the telephoto end (f = 150).

As shown in the figure, the incident height of the axial ray on the compensator C is the highest at the wide-angle end, and the focal length fM =
It rapidly decreases toward the zoom position of FW × Z ^1/4 .
Therefore, when the spherical aberration is not canceled in the compensator C at the wide-angle end and the over-component of the spherical aberration remains, the compensator C is corrected even if the spherical aberration is well corrected at the wide-angle end. Since the reciprocating motion is started and the incident height of the axial ray on the compensator C is drastically lowered, the spherical aberration is also drastically under. This tendency becomes more remarkable as the refractive power of the compensator C becomes stronger.

Particularly in the case of a zoom lens for which high specifications and high performance are required such as a zoom lens for broadcasting, the compensator C is composed of at least one negative lens and positive lens combination lens. Then, a diverging surface for spherical aberration correction is provided by a cemented lens, and a difference in refractive index of the medium is provided to correct aberration inside the compensator.

However, the correction of spherical aberration due to zooming and the correction of high-order chromatic aberration are insufficient, so that the number of lenses is increased or the refractive power of the lens group is weakened. For this reason, it has been very difficult to make the zoom lens compact and have high performance.

The present invention is a so-called four-group zoom lens,
After properly setting the refractive power and F number of each group, the change in imaging magnification due to the variator's magnification change, the locus of image point correction of the compensator, etc., an aspherical surface is formed on at least one lens surface of the compensator. The axial height and the off-axis luminous flux pass through the lens surface of the compensator so that the incident height satisfies the prescribed conditions that maximize the efficiency of the aspherical surface. Wide-angle end F that has high optical performance over the entire zoom range by reducing fluctuations in spherical aberration due to zooming and by correcting well-balanced fluctuations in astigmatism and curvature of field associated with zooming. It is an object of the present invention to provide a zoom lens having a large zoom ratio of about 1.7 and a zoom ratio of about 8 to 30 and a high zoom ratio.

[0022]

The zoom lens according to the present invention has a first positive refractive power which is fixed when zooming in order from the object side.
It has a group, a second group of negative refractive power for zooming, a third group of negative refractive power that corrects image plane variation due to zooming, and a fourth group of fixed positive refractive power, The focal length and the F number of the entire system at the ends are fT and FNT, the focal length and the F number of the i-th group are fi and FNi, respectively, and the second group is a region in which the image forming magnification includes the same magnification. The maximum incident height of the axial light flux at the wide-angle end on the third lens group is h3m, and the third lens group has at least one negative lens 31 and positive lens 32.
At the time of zooming from the wide-angle end to the telephoto end, it has a convex locus toward the object side, and at the telephoto end, it moves so as to be positioned on the image plane side compared to the wide-angle end, and the negative lens 31 and the positive lens 32 are moved. 1.09 <FNT <1.61 where FN1 = f1 / (fT / FNT) (1) -1.03 <f3 / f1 <-0. 37 (2) 1.43 <FN3 <2.13 However, FN3 = | (f3 / 2 × h3m) | A zoom lens featuring.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1, 2, 3, and 4 are lens cross-sectional views at the wide-angle end of Numerical Embodiments 1, 2, 3, and 4 to be described later, respectively. 5 to 9 are numerical example 1, FIGS. 10 to 14 are numerical example 2, and FIGS. 15 to 19 are numerical example 3.
20 to 24 are various aberration diagrams of Numerical Example 4.

In the figure, F is a focus group (front lens group) having a positive refractive power as the first group. 1 to 3, the entire focus group F is moved on the optical axis for focusing. In FIG. 4, the focus group F is composed of three lens groups, a front focus group F1 having a negative refractive power, a focus moving group F2 having a positive refractive power, and a rear focus group F3 having a positive refractive power. . Focusing with a change in the object distance is performed by moving the focus moving group F2 on the optical axis.

V is a variator of negative refracting power for zooming as the second lens unit, which is monotonically moved to the image plane side on the optical axis to change from the wide-angle end (wide) to the telephoto end (tele). We are changing the magnification. The variator V is used in a region in which the imaging magnification includes the same magnification when changing the magnification.

C is a compensator of negative refracting power as the third lens unit, which reciprocates so as to have a convex locus on the object side on the optical axis in order to correct the image plane variation due to zooming. ing.

SP is an aperture and R is a relay group having a positive refractive power as the fourth group. G is a color separation prism, an optical filter or the like, which is shown as a glass block in FIG.

Next, the features of the zoom lens of the present invention will be described.

The zoom lens of the present invention has a zoom ratio of about 8 to 30 times, and further, in order to realize a large aperture in the entire zoom range, the front lens group F first satisfies the conditional expression (1). It uses a bright lens system. The variator V is configured to pass a point where the image forming magnification is -1 (equal magnification) at the time of zooming, thereby adopting a zoom method in which a high variable magnification is provided.

Further, the compensator C first moves to the object side from the reference position at the wide-angle end and then moves to the image surface side from a certain focal length in the correction of the image-plane variation due to zooming from the wide-angle end to the telephoto end. At the telephoto end, a zoom method is adopted such that it exists closer to the image plane than the reference position at the wide-angle end.
Then, the refractive power of the compensator C is made to satisfy the conditional expression (2), thereby making it compact. Moreover, the effective F number value F of the compensator C
Keep N3 bright enough to satisfy conditional expression (3),
It is easy to increase the diameter.

Among the aberrations that fluctuate due to zooming as shown in FIG. 26, the focal length is fM = fW × Z.
Spherical aberration that greatly fluctuates near the zoom position of ^1/4 is well corrected.

The incident height of the axial ray on the compensator C is highest at the wide-angle end as shown in FIGS.
The focal length fM = fW × Z ^1/4 sharply decreases toward the zoom position, and after the zoom position of the focal length fM, the incident height hardly changes.

However, if there is no F drop at the telephoto end and the position of the compensator C at the telephoto end is on the object side of the reference position at the wide-angle end, the incident height at the telephoto end becomes high again. For this reason, the position of the compensator C at the telephoto end is set to be closer to the image plane side than the reference position at the wide-angle end.

In particular, in this embodiment, by satisfying the F drop of the conditional expression (5) described later, the incident height at the telephoto end is suppressed to be low, and the effect of the aspherical surface acts on the wide angle side. 27 to 29 show an optical path at each zoom position of the optical system which is a part of the lens sectional view of FIG.

In the present invention, after the optical arrangement of such a zoom lens is provided, the compensator C which satisfies the above conditions is provided with a lens surface for spherical aberration correction or chromatic aberration correction. For this reason, the compensator is configured to have at least one negative lens 31 and positive lens 32, and is a cemented lens surface of these lenses or a diverging surface for spherical aberration correction due to a relatively small space.

At this time, not only the spherical aberration but also the Abbe number Δν3 of the medium of the lens element is set as in conditional expression (4) in order to increase the effect of correcting chromatic aberration. As a result, variations in chromatic aberration due to zooming are well corrected.

In the compensator C for the zoom lens according to the present invention, the effective F number FN3 is very bright, and the refracting power of the compensator is strengthened to reduce the space for reciprocating motion for image plane correction by zooming. . For this reason, the fluctuation of spherical aberration increases.

On the other hand, if the number of lenses is increased and the degree of freedom in design is increased, the axial rays before and after the compensator C are strong divergent rays, and the zoom lens becomes large. For this reason, if the compensator C is made up of only spherical lenses, it becomes difficult to increase the diameter.

Therefore, in this embodiment, at least one aspherical surface is provided in the compensator (third group), and the aspherical surface has a shape in which the negative refracting power becomes weaker toward the peripheral portion of the lens. 100% of diameter, 9
The amount of aspherical surface is divided by ΔX ₁₀ , ΔX ₉ , and Δ
When X ₇

[0040]

[Equation 1] I try to satisfy the following conditions.

As described above, in this embodiment, the conditional expression (a)
An aspherical surface satisfying at least one of compensator C
By providing it on one lens surface, the fluctuation of the remaining spherical aberration is canceled.

FIG. 26 is an explanatory diagram showing the variation of spherical aberration when the aspherical surface at this time is used. In this embodiment, in order to efficiently bring the effect of the aspherical surface into the wide-angle range in which the change is the largest and the angle falls under, the following conditional expression should be satisfied.

The focal lengths of the entire system at the wide-angle end are f-numbers fW and FNW, the zoom ratio is Z, and the focal length fM is the third group of axial luminous fluxes at the zoom position where fM = fW × Z ^1/4 . When the maximum incident height of Hm is hM, 0.9 <FNW / FNT (5) 1.08 <h3m / hM (6).

The aspherical surface applied to the compensator C in this embodiment has a shape in which the central portion of the aspherical surface is substantially spherical and the aspherical surface becomes larger toward the periphery in order to favorably correct high-order spherical aberration.

The conditional expressions (5) and (6) are the focal length fM from the wide-angle end in the zoom range in the zoom lens system.
= FW × Z ^{1/4 In} order to exert the effect of the aspherical surface only in a part of the zoom range up to the vicinity of the zoom position and to reduce the influence on spherical aberration and astigmatism as much as possible in other zoom regions. It is a thing.

In conditional expression (6), the entrance height h3m and the entrance height hM
A ratio of 1 near 1 indicates that the change in the incident height of the axial ray on the aspherical surface is small from the wide-angle end to the zoom position where the focal length is fM = fW × Z ^1/4. The correction effect will affect the entire zoom range.

This is because when the spherical aberration at the wide-angle end is corrected in the under direction by the aspherical surface, the focal length fM = fW × Z
The spherical aberration at the zoom position of ^{1/4 is} also affected by this aspherical surface and changes to the under direction, which is not good because the effect of correcting the fluctuation of the spherical aberration becomes weak.

Thus, in this embodiment, as shown in FIG.
As shown in (B), the aspherical lens surface is appropriately set to reduce the influence of spherical aberration on the telephoto side from the zoom intermediate range, correct spherical aberration on the wide-angle side, and adjust the entire zoom range. The spherical aberration is satisfactorily corrected over the range.

Next, numerical examples of the present invention will be shown. 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 gap from the object side, and Ni and νi are respectively from the object side of the i-th lens. The refractive index of glass and the Abbe number.

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 light traveling direction, and R as a paraxial radius of curvature.
When A, B, C, D, and E are aspherical coefficients, respectively

[0051]

[Equation 2] It is expressed by

Numerical Example 1 f = 10.0 fno = 1: 1.8 to 2.1 2 ω = 57.62 ° to 4.20 ° R 1 = 959.78 D 1 = 2.30 N 1 = 1.81265 ν 1 = 25.4 R 2 = 101.24 D 2 = 0.10 R 3 = 101.06 D 3 = 10.15 N 2 = 1.48915 ν 2 = 70.2 R 4 = -873.87 D 4 = 0.20 R 5 = 133.99 D 5 = 7.77 N 3 = 1.51825 ν 3 = 64.2 R 6 = -1406.74 D 6 = 0.00 R 7 = 99.83 D 7 = 6.79 N 4 = 1.60548 ν 4 = 60.7 R 8 = 368.44 D 8 = 0.20 R 9 = 70.69 D 9 = 6.76 N 5 = 1.69979 ν 5 = 55.5 R10 = 166.41 D10 = variable R11 = 60.98 D11 = 0.80 N 6 = 1.83945 ν 6 = 42.7 R12 = 16.22 D12 = 5.81 R13 = -29.73 D13 = 0.80 N 7 = 1.80811 ν 7 = 46.6 R14 = 47.69 D14 = 2.24 R15 = 35.80 D15 = 4.73 N 8 = 1.81265 ν 8 = 25.4 R16 = -28.90 D16 = 0.43 R17 = -25.06 D17 = 0.80 N 9 = 1.77621 ν 9 = 49.6 R18 = 142.67 D18 = Variable R19 = -26.07 D19 = 0.80 N10 = 1.79013 ν10 = 44.2 R20 = 30.87 D20 = 3.47 N11 = 1.85501 ν11 = 23.9 R21 = 736.14 D21 = Variable R22 = (Aperture) D22 = 1.40 R23 = -140.14 D23 = 3.57 N12 = 1.72794 ν12 = 38.0 R24 = -37.07 D24 = 0.20 R25 = 68.87 D25 = 4.98 N13 = 1.51314 ν13 = 60.5 R26 = -69.05 D26 = 0.20 R27 = 35.78 D27 = 9.49 N14 = 1.50229 ν14 = 66.0 R28 = -30.39 D28 = 1.66 N15 = 1.83932 ν15 = 37.2 R29 = 542.75 D29 = 15.69 R30 = -770.53 D30 = 4.69 N16 = 1.51314 ν16 = 60.5 R31 = -34.66 D31 = 0.20 R32 = 156.95 D32 = 1.40 N17 = 1.83932 ν17 = 37.2 R33 = 17.57 D33 = 7.55 N18 = 1.50014 ν18 = 65.0 R34 = -183.30 D34 = 0.20 R35 = 91.81 D35 = 5.69 N19 = 1.51977 ν19 = 52.4 R36 = -24.46 D36 = 1.40 N20 = 1.80811 ν20 = 46.6 R37 = 268.36 D37 = 0.30 R38 = 33.66 D38 = 5.54 N21 = 1.51977 ν21 = 52.4 R39 = -46.30 D39 = 4.73 R40 = ∞ D40 = 29.35 N22 = 1.60718 ν22 = 38.0 R41 = ∞ D41 = 16.20 N23 = 1.51825 ν23 = 64.2 R42 = ∞ Aspheric surface = R19

[0053]

[Table 1] Aspherical shape Reference spherical surface R = -26.074 Parameter FN1 = 1.091 Aspherical surface coefficient A = B = 0 FN3 = 1.433 C = 2.336 59 × 10 ^-8 f3 / f1 = -0.436 D = -2.17787 × 10 ^-10 FNW / FNT = 0.857 E = 6.77619 × 10 ^-13 Δν3 = 20.3 h3m / hM = 1.105 <Numerical Example 2> f = 8.50 fno = 1: 1.7 to 3.6 2 ω = 65.81 ° to 3.71 ° R 1 = -144.71 D 1 = 2.20 N 1 = 1.81265 ν 1 = 25.4 R 2 = 256.49 D 2 = 3.28 R 3 = 670.58 D 3 = 8.23 N 2 = 1.48915 ν 2 = 70.2 R 4 = -131.23 D 4 = 0.15 R 5 = 210.33 D 5 = 8.57 N 3 = 1.51825 ν 3 = 64.2 R 6 = -216.00 D 6 = 0.15 R 7 = 115.22 D 7 = 7.37 N 4 = 1.62287 ν 4 = 60.3 R 8 = -4024.89 D 8 = 0.15 R 9 = 69.19 D 9 = 5.27 N 5 = 1.73234 ν 5 = 54.7 R10 = 139.74 D10 = variable R11 = 62.27 D11 = 0.90 N 6 = 1.83945 ν 6 = 42.7 R12 = 16.10 D12 = 7.30 R13 = -44.83 D13 = 0.80 N 7 = 1.80811 ν 7 = 46.6 R14 = 40.62 D14 = 2.05 R15 = 30.61 D15 = 5.80 N 8 = 1.81265 ν 8 = 25.4 R16 = -35.85 D16 = 0.79 R17 = -28.53 D17 = 0.80 N 9 = 1.77621 ν 9 = 49.6 R18 = 137.04 D18 = Variable R19 = -31.47 D19 = 0.90 N10 = 1.77621 ν10 = 49.6 R20 = 43.74 D20 = 2.77 N11 = 1.85501 ν11 = 23.9 R21 = -1447.41 D21 = Variable R22 = (Aperture) D22 = 2.30 R23 = 515.99 D23 = 4.32 N12 = 1.55099 ν12 = 45.8 R24 = -45.85 D24 = 0.20 R25 = 117.89 D25 = 4.19 N13 = 1.51825 ν13 = 64.2 R26 = -69.14 D26 = 0.20 R27 = 47.78 D27 = 7.72 N14 = 1.48915 ν14 = 70.2 R28 = -37.07 D28 = 1.20 N15 = 1.83945 ν15 = 42.7 R29 = 380.52 D29 = 30.00 R30 = 340.64 D30 = 4.29 N16 = 1.51825 ν16 = 64.2 R31 = -43.67 D31 = 0.20 R32 = 238.15 D32 = 1.40 N17 = 1.81077 ν17 = 41.0 R33 = 19.74 D33 = 7.12 N18 = 1.51314 ν18 = 60.5 R34 = -284.16 D34 = 0.20 R35 = 103.90 D35 = 5.28 N19 = 1.51314 ν19 = 60.5 R36 = -28.83 D36 = 1.40 N20 = 1.83945 ν20 = 42.7 R37 = -6948.66 D37 = 0.20 R38 = 35.36 D38 = 5.86 N21 = 1.51825 ν21 = 64.2 R39 = -53.78 D39 = 5.00 R40 = ∞ D40 = 30.00 N22 = 1.60718 ν22 = 38.0 R41 = ∞ D41 = 16.20 N23 = 1.51825 ν23 = 64.2 R42 = ∞ Aspherical surface = R21

[0054]

[Table 2] Aspherical shape Reference spherical surface R = -1447.410 Parameter FN1 = 1.601 Aspherical surface coefficient A = B = C = D = E = 0 FN3 = 2.031 D = 9.80814 × 10 ^-13 f3 / f1 = -0.595 FNW / FNT = 0.472 Δν3 = 25.7 h3m / hM = 1.131 <Numerical Example 3> f = 11.0 fno = 1: 1.7 to 2.75 2ω = 53.13 ° to 1.91 ° R 1 = 834.14 D 1 = 5.30 N 1 = 1.72311 ν 1 = 29.5 R 2 = 188.89 D 2 = 1.06 R 3 = 189.46 D 3 = 16.52 N 2 = 1.49845 ν 2 = 81.6 R 4 = -616.13 D 4 = 0.25 R 5 = 291.81 D 5 = 8.16 N 3 = 1.48915 ν 3 = 70.2 R 6 = 722.87 D 6 = 0.25 R 7 = 160.89 D 7 = 9.91 N 4 = 1.48915 ν 4 = 70.2 R 8 = 330.43 D 8 = 0.25 R 9 = 165.17 D 9 = 10.96 N 5 = 1.51825 ν 5 = 64.2 R10 = 536.33 D10 = variable R11 = 67.85 D11 = 1.70 N 6 = 1.82017 ν 6 = 46.6 R12 = 29.05 D12 = 10.17 R13 = -51.01 D13 = 1.60 N 7 = 1.77621 ν 7 = 49.6 R14 = 69.63 D14 = 2.05 R15 = 50.83 D15 = 5.22 N 8 = 1.81265 ν 8 = 25.4 R16 =- 72.19 D16 = 1.01 R17 = -49.10 D17 = 1.00 N 9 = 1.77621 ν 9 = 49.6 R18 = 168.38 D18 = Variable R19 = -52.40 D19 = 1.70 N10 = 1.74679 ν10 = 49.3 R20 = 67.42 D20 = 4.00 N11 = 1.93306 ν11 = 21.3 R21 = 348.95 (Aperture) D21 = Variable R22 = -1923.50 D22 = 5.86 N12 = 1.62287 ν12 = 60.3 R23 = -47.39 D23 = 0.20 R24 = 131.09 D24 = 4.36 N13 = 1.48915 ν13 = 70.2 R25 = -162.09 D25 = 0.20 R26 = 58.62 D26 = 9.70 N14 = 1.48915 ν14 = 70.2 R27 = -46.27 D27 = 2.10 N15 = 1.83932 ν15 = 37.2 R28 = 154.20 D28 = 35.97 R29 = 68.25 D29 = 6.28 N16 = 1.51825 ν16 = 64.2 R30 = -118.74 D30 = 0.20 R31 = 141.42 D31 = 2.20 N17 = 1.77621 ν17 = 49.6 R32 = 32.68 D32 = 9.37 N18 = 1.59143 ν18 = 61.2 R33 = -85.02 D33 = 0.20 R34 = 41.73 D34 = 6.33 N19 = 1.48915 ν19 = 70.2 R35 = -68.89 D35 = 2.20 N20 = 1.74795 ν20 = 44.8 R36 = 35.35 D36 = 1.90 R37 = 59.88 D37 = 2.54 N21 = 1.80811 ν21 = 46.6 R38 = 151.93 D38 = 6.00 R39 = ∞ D39 = 30.00 N22 = 1.60718 ν22 = 38.0 R40 = ∞ D40 = 16.20 N23 = 1.51825 ν23 = 64.2 R41 = ∞ aspheric surface = R19

[0055]

[Table 3] Aspherical surface Reference spherical surface R = -52.400 Parameter FN1 = 1.595 Aspherical coefficient A = B = 0 FN3 = 1.947 C = 6.36551 × 10 ^-10 f3 / f1 = -0.367 D = -2.23017 × 10 ^-12 FNW / FNT = 0.618 E = 2.29897 × 10 ^-15 Δν3 = 28.0 h3m / hM = 1.144 Numerical Example 4 f = 6.50 fno = 1: 1.7 to 1.88 2 ω = 80.5 ° to 12.1 ° R 1 = 61.13 D 1 = 2.50 N 1 = 1.77621 ν 1 = 49.6 R 2 = 32.50 D 2 = 17.51 R 3 = 465.72 D 3 = 2.00 N 2 = 1.64254 ν 2 = 60.1 R 4 = 55.73 D 4 = 11.31 R 5 = -93.76 D 5 = 2.00 N 3 = 1.64254 ν 3 = 60.1 R 6 = -540.14 D 6 = 0.20 R 7 = 83.20 D 7 = 5.90 N 4 = 1.76168 ν 4 = 27.5 R 8 = -3243.08 D 8 = 5.70 R 9 = 167.64 D 9 = 7.64 N 5 = 1.48915 ν 5 = 70.2 R10 = -85.86 D10 = 9.17 R11 = 241.58 D11 = 2.00 N 6 = 1.81265 ν 6 = 25.4 R12 = 42.25 D12 = 9.22 N 7 = 1.48915 ν 7 = 70.2 R13 = 1729.81 D13 = 0.20 R14 = 127.61 D14 = 8.69 N 8 = 1.48915 ν 8 = 70.2 R15 = -68.28 D15 = 0.20 R16 = 50.95 D16 = 4.45 N 9 = 1.79025 ν 9 = 50.0 R17 = 136.34 D17 = Variable R18 = 45.39 D18 = 0.90 N10 = 1.83945 ν10 = 42.7 R19 = 17.32 D19 = 4.79 R20 = -33.93 D20 = 0.90 N11 = 1.80811 ν11 = 46.6 R21 = 28.59 D21 = 1.33 R22 = 29.87 D22 = 3.10 N12 = 1.81265 ν12 = 25.4 R23 = -51.93 D23 = 0.64 R24 = -35.29 D24 = 0.90 N13 = 1.77621 ν13 = 49.6 R25 = -948.20 D25 = variable R26 = -33.14 D26 = 1.00 N14 = 1.71615 ν14 = 53.8 R27 = 43 .95 D27 = 2.85 N15 = 1.79191 ν15 = 25.7 R28 = 695.80 D28 = Variable R29 = (Aperture) D29 = 1.05 R30 = 210.62 D30 = 3.83 N16 = 1.57047 ν16 = 42.8 R31 = -44.84 D31 = 0.20 R32 = 100.51 D32 = 3.74 N17 = 1.50014 ν17 = 65.0 R33 = -76.46 D33 = 0.20 R34 = 87.32 D34 = 6.90 N18 = 1.50014 ν18 = 65.0 R35 = -26.52 D35 = 1.40 N19 = 1.83945 ν19 = 42.7 R36 = -441.81 D36 = 32.29 R37 = -267.84 D37 = 4.47 N20 = 1.57047 ν20 = 42.8 R38 = -41.12 D38 = 0.20 R39 = 485.78 D39 = 1.50 N21 = 1.83932 ν21 = 37.2 R40 = 28.73 D40 = 7.64 N22 = 1.51977 ν22 = 52.4 R41 = -120.25 D41 = 0.20 R42 = 75.81 D42 = 6.49 N23 = 1.48915 ν23 = 70.2 R43 = -36.57 D43 = 1.60 N24 = 1.83932 ν24 = 37.2 R44 = -365.87 D44 = 0.20 R45 = 51.72 D45 = 5.69 N25 = 1.51825 ν25 = 64.2 R46 = -64.48 D46 = 8.00 R47 = ∞ D47 = 55.50 N26 = 1.51825 ν26 = 64.2 R48 = ∞ Aspherical surface = R26

[0056]

[Table 4] Aspherical shape Reference spherical surface R = -33.140 Parameter FN1 = 1.316 Aspherical coefficient A = B = 0 FN3 = 2.129 C = 9.138 43 × 10 ^-10 f3 / f1 = -1.304 D = -6.95659 × 10 ^-14 FNW / FNT = 0.904 E = 1.13899 × 10 ^-14 Δν3 ＝ 28.1 h3m / hM ＝ 1.085 Next, features of each numerical example of the present invention will be described.

Numerical Embodiment 1 shown in FIG. 1 has a zoom ratio of more than 15 times, and R1 to R10 are front lens groups F for focusing, which have a function of connecting an object point to the variator V, The ball group F has a loose positive power as a whole.

R11 to R18 are variators that mainly contribute to zooming, and monotonously move to the side surface when zooming from wide to tele, and pass an imaging magnification of -1 (one-time) on the way. .

R19 to R21 are compensators mainly having an image point correcting action associated with zooming, and have a negative power.
Upon zooming from wide to tele, it moves from the wide-angle end reference position to the object side, moves from a certain focal length to the image side, and exists at the telephoto end on the image side of the wide-angle end reference position. SP (R2
2) is a diaphragm.

R23 to R39 are relay groups having an image forming action, and R40 to R42 are glass blocks equivalent to color separation prisms.

When the F number FN1 of the front lens group is defined as FN1 = f1 / (fT / FNT) as a target for increasing the aperture, FN1 = 1.091 in this embodiment. When the F number of the front lens group is maintained over the entire zoom range, and the F number at the wide end is FNW = 1.8 and a long back focus is maintained, the F number of the compensator C is FN3 = f3 / (2 × h3m). If defined as F
The large aperture ratio is N3 = 1.433.

For these large aperture ratios, in the front lens group, one negative lens and four positive lenses are used for correction in order to correct spherical aberration on the tele side.

Generally, it is preferable that the compensator C and the variator V have a simple lens structure and a small block thickness in order to downsize the entire zoom lens system and save power in the drive system. Therefore, compensator C
It is desirable to reduce the number of lenses as much as possible.

On the other hand, as described above, the F-number FN3 of the compensator C becomes very bright, so that it becomes difficult to correct spherical aberration in the compensator group C, especially from the wide-angle end to the focal length fM = fw × Z
^The spherical aberration changes greatly at the zoom position of ^1/4 .

Therefore, in this embodiment, the compensator C is used.
The first lens is composed of a cemented lens made up of a negative lens 31 having a relatively high refractive index on both lens surfaces and a positive lens 32 having a convex surface facing the object side, thereby suppressing the occurrence of spherical aberration.

Further, when the difference between the Abbe numbers of the front and rear materials is Δν3, Δν3 = 20.3 is set on the cemented lens surface to have an effect of improving chromatic aberration.

The aspherical surface is provided on the R19 surface, and the above conditional expression (6) is h3m / hM = 1.105. The direction of the aspherical surface is such that the negative power becomes weaker as the on-axis incident height becomes higher, so that abrupt changes in the aspherical shape are avoided and the fluctuation of spherical aberration is efficiently performed from low-order to high-order regions. For the correction, only the aspherical surface coefficients C, D and E are used to mainly correct the spherical aberration. The aspherical amount at this time is about 18 μm, which is 100% of the effective diameter.

Numerical embodiment 2 of FIG. 2 has a zoom ratio of 20 times. Compared to Numerical Embodiment 1, the lens configuration is substantially the same, but an angle of view at the wide-angle end of 2ω65.8 ° and a zoom ratio of 20 are achieved by appropriate selection of the power arrangement.

At this time, while the amount of movement of the compensator C is increased, the variation of spherical aberration in the entire zoom range is suppressed with a small amount of aspherical surface. At this time, the compensator C
The aspherical surface in is applied to the R21 surface, h3m / hM
= 1.131.

The direction of the aspherical surface is such that the negative power becomes weaker as the on-axis incident height becomes higher, but in order to obtain a larger effect with a small amount of aspherical surface, the aspherical surface is introduced as compared with Numerical Embodiment 1. Has a higher refractive index.

Numerical example 3 in FIG. 3 is a very high-magnification zoom lens having a zoom ratio of 30 times, but the F number FNT at the tele end is 2.75, which is very bright.

As a solution for reducing the variation of the spherical aberration in the present embodiment, the movement amount is large and the power is f3 / f1 =-.
The point is to search for a compensator solution that is very strong at 0.367.

First, the compensator is composed of a cemented lens composed of a negative lens whose both lens surfaces are concave and a positive lens whose convex surface facing the object side, and the refractive index difference between the media before and after the cemented lens surface is 0.18 or more. The effect of the diverging surface of the spherical aberration is increased by holding it.

At this time, the achromatism inside the compensator group C is the difference Δν in Abbe number between the media before and after the cemented lens surface.
3 is separated to Δν3 = 28.0 to suppress spherical aberration and chromatic aberration in a well-balanced manner.

Numerical Embodiment 4 shown in FIG. 4 is a very wide-angle zoom lens having a zoom ratio of about 8 times and an angle of view 2ω = 80.5 ° at the wide-angle end.

R1 to R17 are the front lens group (focus group F), R1 to R8 are the front group fixed focus group F1 which is fixed for zooming and focusing and has a negative power (refractive power) as a whole, and R9 ~ R10 is a focus movement group F2 for focusing, having positive power,
R11 to R17 are rear focus fixed groups that have a positive power and are fixed during zooming and focusing. R1-R
The front lens group F has a function of connecting an object point to the variator V by 17, and the whole front lens group F has a positive power.

R18 to R25 mainly contribute to zooming, and when zooming from wide to tele, the variator V monotonously moves to the image plane side and passes the imaging magnification of -1 (actual magnification) on the way.
Is. R26 to R28 are compensators, which are mainly compensators having an image point correcting action associated with zooming, have negative power, and when zooming from wide to tele, move from the wide-angle end reference position to the object side, It moves to the image side from a certain focal length, and exists at the telephoto end to the image side from the wide-angle end reference position. SP (R29) is a diaphragm.

R30 to R46 are a relay group having an image forming action, and R47 to R48 are glass blocks equivalent to color separation prisms.

The front lens group F number FN1 is FN1 = 1.3
16 、 Compensator C effective F number FN3 is F
N3 = 2.129, which is a large diameter, but the ratio of the entrance height h3m to the entrance height hM is as small as h3m / hM = 1.085, so the spherical aberration on the wide-angle side can be controlled freely on the aspherical surface. In order to expand the degree and improve the efficiency of the aspherical surface, C, D and E are used among the aspherical surface coefficients in the aspherical surface formula. Aberration correction is satisfactorily performed by separating the Abbe number difference Δν3 to 28.1. The amount of aspherical surface at this time is about 2.1 μm at the height of the R26 surface.

[0080]

As described above, according to the present invention, in the so-called four-group zoom lens, the refractive power and F-number value of each lens group are appropriately set, and the axial light flux is incident when passing through the lens surface. High is at least 1 that satisfies the specified conditional expression
By applying an aspherical surface to the two lens surfaces, fluctuations in spherical aberration due to zooming are reduced, and in addition, fluctuations in off-axis aberrations such as astigmatism, field curvature, and distortion aberrations due to zooming are well balanced. However, it is possible to achieve a zoom lens having a high zoom ratio with a wide-angle end F number of about 1.7 and a zoom ratio of about 8 to 30, which has high optical performance over the entire zoom range.

[Brief description of drawings]

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

FIG. 2 is a lens cross-sectional view at a wide-angle end according to Numerical Example 2 of the present invention.

FIG. 3 is a lens cross-sectional view at a wide-angle end according to Numerical Example 3 of the present invention.

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

FIG. 5 is a focal length f = 10 of Numerical Embodiment 1 of the present invention.
Aberration diagram

FIG. 6 is a focal length f = 1 according to the first numerical embodiment of the present invention.
Aberration diagram of 9.68

FIG. 7: Focal length f = 40 of Numerical Embodiment 1 of the present invention
Aberration diagram

FIG. 8 is a focal length f = 10 of Numerical Embodiment 1 of the present invention.
0 aberration diagram

FIG. 9 is a focal length f = 15 of Numerical Embodiment 1 of the present invention.
0 aberration diagram

FIG. 10 shows a focal length f = 8.
Aberration diagram of 5

FIG. 11 is a focal length f = 1 of the second numerical embodiment of the present invention.
Aberration diagram of 7.98

FIG. 12 is a focal length f = 34 of Numerical Embodiment 2 of the present invention.
Aberration diagram

FIG. 13 shows a focal length f = 68 according to the second numerical embodiment of the present invention.
Aberration diagram

FIG. 14 is a focal length f = 17 of Numerical Embodiment 2 of the present invention.
0 aberration diagram

FIG. 15 is a focal length f = 11 of Numerical Embodiment 3 of the present invention.
Aberration diagram

FIG. 16 is a focal length f = 2 of Numerical Embodiment 3 of the present invention.
Aberration diagram of 5.74

FIG. 17: Focal length f = 66 of Numerical Example 3 of the present invention
Aberration diagram

FIG. 18 is a focal length f = 19 of Numerical Example 3 of the present invention.
8 aberration diagram

FIG. 19 is a focal length f = 33 of Numerical Embodiment 3 of the present invention.
0 aberration diagram

FIG. 20 shows the focal length f = 6.
Aberration diagram of 5

FIG. 21 is a focal length f = 1 of the numerical value example 4 according to the present invention.
0.92 aberration diagram

FIG. 22 is a focal length f = 2 of Numerical Embodiment 4 of the present invention.
2.75 aberration diagram

FIG. 23 is a focal length f = 39 of Numerical Embodiment 4 of the present invention.
Aberration diagram

FIG. 24 is a focal length f = 52 of Numerical Embodiment 4 of the present invention.
Aberration diagram

FIG. 25 is an explanatory diagram showing a change in spherical aberration of a conventional four-group zoom lens due to zooming.

FIG. 26 is an explanatory diagram showing a variation of spherical aberration of the zoom lens according to the present invention due to zooming.

FIG. 27 is an explanatory diagram showing optical paths of light beams from the first group to the third group of the zoom lens.

FIG. 28 is an explanatory diagram showing optical paths of light beams from the first group to the third group of the zoom lens.

FIG. 29 is an explanatory diagram showing optical paths of light fluxes from the first group to the third group of the zoom lens.

[Explanation of symbols]

 F First group (focus group) F1 Front group fixed focus group F2 Focus moving group F3 Rear group focus fixed group V Second group (variator) C Third group (Compensator) R Fourth group (Relay group) G Glass block SP aperture e e line ΔS sagittal image plane ΔM meridional image plane

Claims (3)

[Claims] 1. A first lens unit having a fixed positive refracting power, a second lens unit having a negative refracting power for zooming, and a negative lens unit for correcting an image plane variation due to zooming, in order from the object side during zooming. It has a third lens group having a refractive power and a fourth lens group having a fixed positive refractive power, and the focal length and the F number of the entire system at the telephoto end are fT and FNT, and the focal length and the F number of the i-th group are respectively. fi, FNi, the second group has an imaging magnification that changes in a region including a unity magnification upon zooming, and the maximum incident height of the axial light flux on the third group at the wide-angle end is h3m, and the third group The group has at least one negative lens 31 and positive lens 32, has a convex locus toward the object side during zooming from the wide-angle end to the telephoto end, and has an image at the telephoto end compared to the wide-angle end. 1.09 <FN1 <1.6 when the difference between the Abbe numbers of the materials of the negative lens 31 and the positive lens 32 is Δν3. However, FN1 = f1 /
(FT / FNT) −1.03 <f3 / f1 <−0.37 1.43 <FN3 <2.13 However, FN3 = | f3 /
A zoom lens characterized by satisfying a condition of (2 × h3m) | 20 <Δν3. 2. The third group has at least one aspherical surface, and the aspherical surface has a shape in which the negative refracting power becomes weaker toward the lens peripheral portion, and the aspherical surface has a lens effective diameter of 10% or less. , 90%, 70% of the aspherical amount is ΔX
Assuming ₁₀ , ΔX ₉ and ΔX ₇ , 2.9 × 10 ⁻⁷ <ΔX ₇ /f3<1.15×10 ⁻⁴ 2.13 × 10 ⁻⁶ <ΔX ₉ /f3<3.32×10 ⁻⁴ 2. The zoom lens according to claim 1, wherein the condition of 5.29 × 10 ⁻⁶ <ΔX ₁₀ /f3<5.06×10 ⁻⁴ is satisfied. 3. The focal length of the entire system at the wide-angle end is f-number fW and FNW, the zoom ratio is Z, and the focal length fM.
Is hM = fW × Z ^1/4 where hM is the maximum incident height of the axial light flux on the third lens group, the condition 0.9 <FNW / FNT 1.08 <h3m / hM is satisfied. The zoom lens according to claim 1, wherein