JP3264949B2 - Zoom lens with short overall length - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable-magnification lens having a large aperture ratio and a high zoom ratio, which has a short overall length and uses a rear focus in a four-group configuration.

[0002]

2. Description of the Related Art In recent years, video cameras have been significantly reduced in size and weight and cost has been remarkably advanced, and the camcorder market has been greatly activated and is rapidly spreading to general users. A video camera mainly includes an electric circuit board, an actuator (mechanical) system, and an optical system. Conventionally, miniaturization and cost reduction have been promoted, especially in the electric system in recent years. Thus, the miniaturization of the imaging optical system has been rapidly progressing. The miniaturization and cost reduction of the imaging optical system is achieved by a new zoom (magnification) that makes effective use of the development of imager miniaturization technology, rotation target aspherical surface processing technology, and TTL automatic focusing technology.
It is currently being done by the development of types.
As an example of the new zoom lens, Japanese Patent Application Laid-Open No. 62-24 / 1987
No. 213, JP-A-62-178917, JP-A-62-278.
No. 215225, etc., but there is no limit to the need for reduction in size and weight, and in particular, the need for further reduction in the overall length and diameter of the front lens is high.

In JP-A-62-2423, JP-A-62-178917, and JP-A-62-215225, a rear focus method or a method in which a compensator group is arranged in a group behind a stop is used. However, this method has the surprising potential of reducing the overall length and the diameter of the front lens. In particular, JP-A-6
Japanese Patent Application Laid-Open No. 2-178917 shows that the number of components can be greatly reduced by using an aspherical surface in the image forming system, and that aberration correction can be sufficiently performed. However, the ability to reduce the size is hardly exploited, and the overall length and the front lens diameter are not much different from the classic lens configuration.

[0004]

The problem to be solved by the present invention is as follows:
No. 178917 has a first positive refractive power.
A third lens, which is composed of only a variable power system consisting of a second group having a negative refractive power and a positive single lens having an aspheric surface, and which is always fixed;
A group, having at least one negative lens, consisting of two or three lenses as a whole, and an imaging system consisting of a movable fourth group for adjusting the focal position at the time of zooming and a change in subject distance, etc. It is composed. As described above, by adopting the rear focus and the aspherical surface also serving as a compensator, the number of components can be reduced to 10 or less, thereby reducing the extra space, so that the diameter of the front lens can be significantly reduced, and the overall length can be reduced. Can also be shortened. However, although the power of the first lens group should have been easily increased by rear focus, the power of the second lens group is still loose because it is hardly done. Also,
Since the third group became a single ball, it was difficult to converge the light flux enough to emit it almost afocal, and the fourth group had to increase the focal length, Back focus can not be shortened, total length,
The diameter of the front lens is not sufficiently reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to provide a variable power system comprising a first lens unit having a positive refractive power and a second lens unit having a negative refractive power; Of a variable power lens composed of a third lens unit having a constant refractive power and a fourth lens unit having a positive refractive power and a movable fourth lens unit for adjusting the focal position and for adjusting the focal position. Setting of appropriate paraxial arrangement for each group,
Further, by devising the lens configuration of the third and fourth lens units, the number of lens elements is 10 or less, the total length is extremely short, the front lens diameter is small, the size is small and light, and the cost is large. An object of the present invention is to provide a zoom lens having a high zoom ratio.

[0006]

In order to achieve the above object, a variable power lens having a short overall length according to the present invention has a first lens unit having a positive refractive power and a negative lens having a negative refractive power in order from the object side. A variable power system consisting of two groups of a second lens group movable at the time of zooming; a third lens group having a positive refractive power and always fixed; And an imaging system composed of two movable fourth lens groups.
The lens group has a non-uniformity such that, in order from the object side, the amount of deviation toward the object side monotonically increases with respect to a spherical surface having a strong convergence on the object side and a radius of curvature near the optical axis as the distance from the optical axis increases. The fourth lens group includes: a positive lens having a spherical surface; and a negative meniscus lens having a concave surface facing the image side.
In a lens system composed of a biconvex lens having an aspheric surface and a negative meniscus lens, the conjugate distance (conjugate) of the imaging system synthesized by the third lens unit and the fourth lens unit is further reduced. Thus, the overall length is shortened, and therefore, the following conditions are satisfied.

(1) 0.45 <f _34S / (f _W f _T ) ^1/2 <0.9 (2) 0.18 <β _4T <0.36 (3) 0.5 <r ₃₁ / ｛ (N ₃₁ -1) (f _W f _T ) ^1/2 ｝ <1.0 (4) 0.4 <r ₃₄ / {(n ₃₄ -1) (f _W f _T ) ^1/2 ｝ <0. 8 (5) 0.24 <D _III / (f _W f _T ) ^1/2 <0.5 where f _W and f _T are the focal lengths of the entire system at the wide angle end and the telephoto end, respectively, and f _34S is the entire system. Focal length of (f _W f _T ) ^1/2
Is the combined focal length of the third and fourth lens groups when focusing on an object point at infinity, β _4T is the magnification of the fourth lens group when focusing on an object point at infinity at the telephoto end, and r ₃₁ is the third lens. The radius of curvature of the surface closest to the object side of the group near the optical axis, r ₃₄ is the radius of curvature of the surface closest to the image side of the third lens group, and n ₃₁ and n ₃₄ are the positive lens and the negative lens of the third lens group, respectively. refractive index of the medium, D _III is the distance, up to the vertex of the surface closest to the image side from the vertex of the most object side surface of the third lens group.

[0008]

The meaning and operation of each condition of the present invention will be described below. The point of the configuration of the present invention is that a negative lens having a strong divergence on the image side surface is disposed closest to the image side of the third lens group, and further, a strong convergence is formed on the most object side surface of the third lens group. The third lens group and the fourth lens group can be used without deteriorating the focusing performance.
The point is that the conjugate distance (conjugate) of the imaging system synthesized by the lens groups is greatly reduced, and the overall length of the variable power lens is shortened.

In the case of employing the rear focus method, it is preferable that the light beam emitted from the third lens group be substantially afocal in order to reduce the fluctuation of aberration during focusing to a level that does not cause a practical problem. On the other hand, as the focal length of the fourth lens group becomes shorter, the overall back focus length becomes shorter, and the overall length can be shortened.

Here, the magnification of the afocal portion formed by the first to third lens groups is β _A ,
When the focal length of the lens group and f _IV, the focal length f of the entire system is a f = beta _A f _IV, to reduce the f _IV beta
It turns out that _A should be increased. On the other hand, β _A
When the focal length of the lens unit f _1, the magnification of the second lens group beta _II, the focal length of the third lens group and f _III, the _{β A = f I β II /} f III. By the way, f _I and β _II is The smaller the f _I β
_{Since II} tends to be large, consider reducing the value of f _III to increase β _A. If f _III is reduced, the principal point of the third lens group must be closer to the image point by the zooming unit, and therefore, mechanical interference between the second lens group and the third lens group occurs. It will be easier. Therefore, the third lens group may be configured such that the principal point of the third lens group is located closer to the second lens group than the lens is located. In other words, in order from the object side (the second lens group side), a total of two lenses including a positive lens having a strong curvature on the object side and a negative lens having a strong curvature on the image side (the conventional example uses only one positive lens) Therefore, there was a limit in moving the principal point to the second lens unit side, and as in the embodiment, a positive meniscus lens having a strong curvature had to be used, which was not preferable in terms of aberration correction.) By forming the object-side surface of the positive lens, which has a strong power, with an aspheric surface whose curvature monotonously decreases toward the periphery of the lens, it is possible to particularly suppress the occurrence of spherical aberration. As described above, the fourth lens group also has a high power, and particularly has a high off-axis ray height. Therefore, in order to suppress the generation of coma, the curvature monotonously decreases as the surface on the object side moves toward the lens periphery. It is a positive single lens composed of an aspheric surface. Note that the afocal need not be strict, and a slightly convergent light flux within a range in which aberration variation during focusing is acceptable can further shorten the back focus and shorten the overall length of the lens system. It is desirable to define not only f _III but also the combined focal length of the third lens unit and the fourth lens unit and the magnification of the fourth unit as in the conditions (1) and (2).

(1) 0.45 <f _34S / (f _W f _T ) ^1/2 <0.9 (2) 0.18 <β _4T <0.36 Here, the lower limit of the condition (1) is exceeded. In addition, mechanical interference between the second lens group and the third lens group easily occurs, which is not preferable. If the upper limit is exceeded, the overall length is not shortened, and the object of the present invention cannot be achieved. If the lower limit of the condition (2) is exceeded, it is not advantageous in shortening the back focus. If the upper limit of the condition (2) is exceeded, the focus adjustment ability of the fourth lens unit is reduced, and a space is required for a large amount of movement. In contrast to miniaturization, aberration fluctuations during zooming and focusing increase. For the above reasons, the upper and lower limits of the conditions (1) and (2) were set.

The above-mentioned functional interference can be made less likely to occur by satisfying the following conditions (3) to (5). _{(3) 0.5 <r 31 /} {(n 31 -1) (f W f T) 1/2} <1.0 (4) 0.4 <r 34 / {(n 34 -1) (f ^{_{W f T) 1/2} <0.8}} (5) 0.24 <D III / (f W f T) 1/2 <0.5 where condition (3) exceeds the lower limit of (4) Even if only the principal point of the third lens group comes closer to the second lens group and the focal length of the third lens group is shortened, mechanical interference with the second lens group hardly occurs, but the aspherical surface Introduces a limit to the correction of spherical aberration. On the other hand, if the upper limit is exceeded, the functional interference is likely to occur, and the focal length of the third lens group must be increased. By the way, if the distance between the converging surface closest to the object side and the diverging surface closest to the image side in the third lens group is large, the principal point of the third lens group is changed to the second lens group without reducing r ₃₁ and r _34. It is preferable because it is easy to approach, but if this interval is too large, on the contrary, the relay section (third
The total length of the lens system and the fourth lens group) becomes longer,
On the contrary, it does not meet the purpose of the present invention. Condition (5) is a condition that defines this.

Further, in order to shorten the total length of the relay section,
It is preferable that the air gap between the third lens group and the fourth lens group be as short as possible. This air space is used as a space in which the fourth lens group moves for focal adjustment accompanying zooming and movement of an object point. In order to make this as short as possible, it is ideal to arrange the power of each group so as to reduce the amount of movement of the fourth lens group.
Since the magnification of the lens group is set to a slightly larger side, the movement amount is slightly larger. Therefore, condition (6) is set. (6) 0.25 <D _34T / (f _W f _T ) ^1/2 <0.5 Here, D _34T is between the third lens unit and the fourth lens unit at the telephoto end when focused on an object point at infinity. Is the on-axis air spacing.

When the value exceeds the upper limit of the condition (6), the total length tends to be long. When the value exceeds the lower limit, it becomes necessary to increase the power of the second lens unit.

Next, it is considered to shorten the zooming portion formed by the first lens unit and the second lens unit. This is the first
It is also effective to reduce the diameter of the lens group. The total length of the zoom section is the total thickness of the first lens group, the total thickness of the second lens group,
Then, it is determined by the moving space of the second lens group. First, consider reducing the movement space of the second lens group. As the method, (i) shorten the focal length of the second lens group, (ii) increase the magnification of the second lens group,
There are things. The effect is larger in (ii). However, in order to realize (ii), the power of the first lens unit must be increased, and when the second lens unit exceeds the same magnification, the third lens unit starts to reduce the magnification, and the multiplication effect is reduced. To increase the magnification of the second lens group too much, because the trajectory of the fourth lens group becomes steeper on the telephoto side, so that the moving space of the fourth lens group is required including focusing. I can't do that either. Therefore, it is better to implement both in a well-balanced manner. Therefore, it is desirable to satisfy the conditions (7) and (8).

(7) 0.25 <| f _II | / (f _W f _T ) ^1/2 <0.5 (8) 0.2 <| β _IIS | f _W / (f _W f _T ) ^{1 / 2} <0.4 where f _II is the focal length of the second lens group, β _IIS is the focal length of the entire system at f = (f _W f _T ) ^1/2 and the focal length at infinity object point focusing. This is the magnification of the two lens groups.

Next, the total thickness of the first lens unit and the second lens unit will be considered. Of course, it is better to make them thin together. By the way, when these are made thinner, not only the overall length is reduced, but also the position of the entrance pupil can be made shallower in addition to the reduced moving space of the second lens group, which can contribute to the reduction of the front lens diameter. . In addition, the power of the first lens group can be increased or reduced as the diameter becomes smaller. From the above, it is desirable to satisfy the conditions (9) and (10).

(9) 0.35 <D _I / (f _W f _T ) ^1/2 <0.7 (10) 0.27 <D _II / (f _W f _T ) ^1/2 <0.54 Here Where D _I is the distance from the vertex of the most object side surface of the first lens group to the vertex of the most image side surface, and D _II is the distance from the vertex of the most object side surface of the second lens group to the most image surface. It is the distance to the top of the side surface.

Above the lower limit of the above condition (7), aberration fluctuation due to zooming tends to increase, and above the upper limit, the amount of movement of the second lens unit tends to increase, or This requires a large space for moving the group, which is not preferable. With respect to the condition (8), if the lower limit value is exceeded, the zooming effect is small for the moving amount, and if the upper limit value is exceeded, a large moving space of the fourth lens unit is required or the power of the first lens unit is required. Is too strong, and aberrations at the telephoto end are likely to be worse. For conditions (9) and (10),
Exceeding these lower limits will make it difficult to secure the rim of the positive lens or weakening the power and lengthening the overall length. Exceeding these upper limits will tend to increase the overall length of the zoom section. Not only does this increase the diameter of the first lens group.

[0020]

Next, embodiments 1 and 2 of the zoom lens according to the present invention will be described.
Will be described. Although lens data of each embodiment will be described later, FIGS. 1 and 2 show lens cross sections of the first and second embodiments at the wide-angle end (W), the standard state (S), and the telephoto end (T), respectively.

In any of the embodiments, the first lens group G1 includes, in order from the object side, a cemented lens of a negative meniscus lens having a convex surface facing the object side and a biconvex lens, and a positive lens having a convex surface facing the object side. In the first embodiment, the second lens group G2 includes, in order from the object side, a negative meniscus lens having a convex surface facing the object side, and a bi-concave lens and a positive meniscus having a convex surface facing the object side. The second embodiment includes, in order from the object side, a biconcave lens and a cemented lens of a biconcave lens and a positive meniscus lens having a convex surface facing the object side. In each embodiment, the third lens group G3 is composed of a biconvex lens having a stronger curvature on the object side and a negative meniscus lens having a convex surface facing the object side. Group G4 is Example 1 consists of cemented lens of a double convex lens and a negative meniscus lens, Example 2,
It consists of a cemented lens of a negative meniscus lens and a biconvex lens.

With respect to the aspherical surface, the first embodiment uses two surfaces, the most object side surface of the third lens group G3 and the most object side surface of the fourth lens group G4. ,
The most object side surface of the third lens group G3 and the fourth lens group G
4 is used for two of the most image-side surfaces. The nineteenth to twenty-third surfaces in each embodiment indicate optical members such as filters.

In the following, the symbols are the same as above,
f is the focal length of the entire system, F _NO is the F number, ω is the half angle of view,
r _1, r ₂ ... is the radius of curvature, d _1, d ₂ ... the spacing between the lens surfaces, n _d1, n _d2 ... d-line refractive index of each lens of the lens surfaces, ν _d1, ν _d2 ... Is the Abbe number of each lens, and the aspherical shape is represented by the following equation, where x is the optical axis direction and y is the direction orthogonal to the optical axis. ^{x = (y 2 / r)} / [1+ {1-P (y 2 / r 2)} 1/2] + A 4 y 4 + A 6 y 6 + A 8 y 8 where, r is a paraxial radius of curvature, P Is the conic coefficient, A ₄ , A ₆ , A ₈
Is an aspheric coefficient.

[0024] Example _{1 f = 6.180~16.963~46.560 F NO = 1.43} ~ 1.53 ~ 2.09 ω = 27.0 ~10.5 ~ 3.9 ° r 1 = 36.7641 d 1 = 0.9000 n d1 = 1.84666 ν d1 = 23.78 r 2 = 21.6262 d _{2 = 5.2000 n d2 = 1.56873 ν} d2 = 63.16 r 3 = -342.4667 d 3 = 0.1500 r 4 = 20.4358 d 4 = 3.6000 n d3 = 1.60311 ν d3 = 60.70 r 5 = 89.9418 d 5 = ( variable) r ₆ = 627.3688 _{d 6 = 0.8000 n d4 = 1.77250} ν d4 = 49.66 r 7 = 6.9069 d 7 = 3.2000 r 8 = -11.2525 d 8 = 0.7000 n d5 = 1.48749 ν d5 = 70.20 r 9 = 9.6531 d 9 = 2.3000 n d6 = 1.84666 ν _{d6 = 23.78 r 10 = 40.7966 d} 10 = ( variable) r ₁₁ = ∞ _{(stop) d 11 = 1.4000 r 12 =} 8.5945 ( _{aspherical) d 12 = 5.6251 n d7 =} 1.67790 ν d7 = 55.33 r 13 = -54.1689 d _{13 = 0.1500 r 14 = 20.7894 d} 14 = 0.8000 n d8 = 1.84666 ν d8 = 23.78 r 15 = 8.0407 d 15 = ( variable) r ₁₆ = 11.6746 _{(aspherical) d 16 = 3.8000 n d9 =} 1.67790 ν d9 = 55.33 r ₁₇ = -12.5493 d ₁₇ = 0.8000 n _d10 = 1.84666 ν _d10 = 23.78 r ₁₈ = -24.9166 d ₁₈ = _{(Variable) r 19 = ∞ d 19 =} 1.6000 n d11 = 1.51633 ν d11 = 64.15 r 20 = ∞ d 20 = 4.4000 n d12 = 1.54771 ν d12 = 62.83 r 21 = ∞ d 21 = 1.8100 r _{22 = ∞ d 22 = 0.6000 n} d13 = 1.48749 ν d13 = 70.20 r 23 = ∞ zoom interval Aspherical coefficients twelfth surface _{P = 1 A 4 = -0.19862 ×} 10 -3 A 6 = -0.68296 × 10 -6 A 8 = -0.31665 × 10 -7 16th surface _{P = 1 A 4 = -0.10959 ×} 10 - ³ A ₆ = -0.25511 x 10 ^-5 A ₈ = 0.32731 x 10 ^-7 .

[0025] Example _{2 f = 6.180~16.963~46.560 F NO = 1.43} ~ 1.53 ~ 2.09 ω = 27.0 ~10.5 ~ 3.9 ° r 1 = 34.0391 d 1 = 0.9000 n d1 = 1.84666 ν d1 = 23.78 r 2 = 20.6946 d _{2 = 5.2000 n d2 = 1.56873 ν} d2 = 63.16 r 3 = -2729.7316 d 3 = 0.1500 r 4 = 22.1731 d 4 = 3.6000 n d3 = 1.60311 ν d3 = 60.70 r 5 = 115.8380 d 5 = ( variable) r ₆ = - _{757.7591 d 6 = 0.8000 n d4 =} 1.77250 ν d4 = 49.66 r 7 = 7.4251 d 7 = 3.1000 r 8 = -11.9281 d 8 = 0.7000 n d5 = 1.48749 ν d5 = 70.20 r 9 = 9.7645 d 9 = 2.2000 n d6 = 1.84666 ν _d6 = 23.78 r ₁₀ = 33.7506 d ₁₀ = (variable) r ₁₁ = ∞ (aperture) d ₁₁ = 1.4000 r ₁₂ = 8.9543 (aspherical surface) d ₁₂ = 4.9108 n _d7 = 1.67790 ν _d7 = 55.33 r ₁₃ = -295.3634 _{d 13 = 0.1500 r 14 = 19.8561} d 14 = 0.8000 n d8 = 1.84666 ν d8 = 23.78 r 15 = 9.4738 d 15 = ( _{variable) r 16 = 9.6299 d 16 =} 0.8000 n d9 = 1.84666 ν d9 = 23.78 r 17 = 6.4176 d ₁₇ = 4.3000 n _d10 = 1.67790 ν _d10 = 55.33 r ₁₈ = -69.384 2 (aspherical) d ₁₈ = _{(Variable) r 19 = ∞ d 19 =} 1.6000 n d11 = 1.51633 ν d11 = 64.15 r 20 = ∞ d 20 = 4.4000 n d12 = 1.54771 ν d12 = 62.83 r 21 = ∞ d 21 = _{1.8100 r 22 = ∞ d 22 =} 0.6000 n d13 = 1.48749 ν d13 = 70.20 r 23 = ∞ zoom interval Aspherical surface twelfth surface P = 1 A ₄ = -0.16512 × 10 ^-3 A ₆ = -0.29 135 × 10 ^-6 A ₈ = -0.22075 × 10 ^-7 18th surface P = 1 A ₄ = 0.24808 × 10 ^-3 A ₆ = 0.36334 × 10 ⁻⁵ A ₈ = −0.445678 × 10 ⁻⁷ .

In the first and second embodiments, spherical aberration, astigmatism, distortion, chromatic aberration of magnification, and coma (meridional) at the wide-angle end (W), the standard state (S), and the telephoto end (T).
Are shown in the aberration diagrams of FIGS. 3 and 4, respectively.

Further, the above-mentioned conditions (1) to
The value of (10) is shown in the following table.

[0028]

As described above, the variable power lens of the present invention includes a variable power system including the first lens group having a positive refractive power and the second lens group having a negative refractive power, and a positive lens. In a variable power lens composed of an imaging system including a third lens group that has a refractive power and is always fixed, and a fourth lens group that has a positive refractive power and is movable for adjusting magnification and focal position. , While devising the paraxial arrangement of the imaging system and the configuration of the actual lens shape and arrangement, etc., by introducing an aspherical surface in part, the overall length is extremely short, and a variable power lens with good aberration Is made possible. This variable magnification lens has 10 components, a magnification ratio of 8 times, an F value at the wide angle end, and an angle of view of 1.
Even though it is 4,54 °, overall length is extremely short and 10.2f _W about even when filters is inserted.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens at a wide angle end (W), a standard state (S), and a telephoto end (T) according to a first embodiment.

FIG. 2 is a lens sectional view similar to FIG. 1 of Example 2.

FIG. 3 is an aberration diagram showing spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma (meridional) at the wide-angle end (W), the standard state (S), and the telephoto end (T) in Example 1. .

FIG. 4 is an aberration diagram similar to FIG. 3 of the second embodiment.

[Explanation of symbols]

 G1 first group G2 second group G3 third group G4 fourth group

Claims (1)

(57) [Claims] 1. A zooming system comprising, in order from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power and movable during zooming, and a positive lens system. A third lens group having a refractive power and being fixed at all times, and an imaging system including a fourth lens group having a positive refractive power and movable for zooming and for focusing, and The three lens groups are arranged such that, in order from the object side, the surface on the object side has strong convergence and the amount of deviation toward the object side monotonically increases with respect to a spherical surface having a radius of curvature near the optical axis as the distance from the optical axis increases. The fourth lens group is composed of a positive lens composed of an aspheric surface and a negative meniscus lens having a concave surface facing the image side. The fourth lens group is a lens system composed of a biconvex lens having an aspheric surface and a negative meniscus lens. And a variable-power lens having a short overall length, satisfying the following conditions: (1) _{.45 <f 34S / (f W} f T) 1/2 <0.9 (2) 0.18 <β 4T <0.36 (3) 0.5 <r 31 / {(n 31 -1) ( f _W f _T ) ^1/2 ｝ <1.0 (4) 0.4 <r ₃₄ / ｛(n ₃₄ −1) (f _W f _T ) ^1/2 ｝ <0.8 (5) 0.24 _{<D III / (f W f} T) 1/2 <0.5 , however, f _W, f _T each wide angle end, the focal length of the entire system at the telephoto end, f _34S is the focal length of the entire system (f _W f _T ) ^1/2 is the composite focal length of the third and fourth lens groups when focusing on an object point at infinity, β _4T is the magnification of the fourth lens group when focusing on an object point at infinity at the telephoto end, r ₃₁ is the radius of curvature, r ₃₄ is the radius of curvature, n _31, n ₃₄ and the third lens group each most image side surface of the third lens group near the optical axis of the most object side surface of the third lens group of the positive lens and the negative lens refractive index of the medium, D _III is the most object side surface of the third lens group Distance from the top to the vertex of the surface closest to the image side, a.