JPS61270718A - Telephoto zoom lens - Google Patents

Abstract

PURPOSE:To reduce both the variation of spherical abberration and image surface curve by dividing a focusing lens group arranged on the object side from variable power lens group into two divided groups, fixing the divided group arranged on the object side, moving the divided group arranged on the image side to attain focusing, and satisfying these lens groups with a prescribed condition. CONSTITUTION:The zoom lens is constituted of the variable power groups G2-G4 and the focusing lens group G1 arranged on the object side from the groups G1-G4. The focusing lens group G1 is divided into the 1st partial group L, and the 2nd partial group L2, the 1st partial group L1 arranged on the object side is fixed on an image surface and the 2nd partial group L2 arranged on the image side is moved along the optical axis to attain focusing. When the whole composite focal distance of the focusing lens group G1 is (f) and the focal distance of the 1st partial group L1 is f1, the lens groups are satisfied with the condition shown by the formula.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a zoom lens, and particularly to a so-called telephoto zoom lens whose angle of view at the wide-angle end is smaller than 45°.

(Background of the Invention) In general, the focusing method of a zoom lens is as follows:
A so-called front lens extension method is used in which a lens group placed closer to the object side than the lens group being moved for zooming is moved. However, with this system, aberration fluctuations due to focusing, especially fluctuations in spherical aberration and field curvature, are large at the telephoto end, and this tendency becomes more pronounced as the zoom ratio and aperture ratio become larger.

For example, as a focusing method for a telephoto zoom lens, as disclosed in Japanese Patent Publication No. 59-4688, the front lens is divided into four groups, positive, negative, positive, and negative, in order from the object side, and the third group is moved for focusing. A method has been proposed. However, in a specific example using this method, the zoom ratio is about 4,
B diameter ratio t: S, When trying to use this method with a zoom lens with a larger aperture ratio and a zoom ratio larger than L11, the front lens becomes larger and the front lens as a whole becomes smaller. In comparison, it is necessary to make the zooming section extremely small, and aberration fluctuations due to L11 zooming become large, making it difficult to realize a high-performance zoom lens.

(Object of the invention) The object of the invention is to have a large zoom ratio and a wide variable power range,
It is an object of the present invention to provide a telephoto zoom lens with little variation in aberrations due to focusing despite its large aperture ratio.

(Summary of the Invention) A telephoto zoom lens according to the present invention is constructed by dividing a focusing lens section located closer to the object side than the variable power lens group into two lens groups having positive refractive power, and The positive refractive power lens group is fixed to the image plane, and focusing is performed by moving the positive refractive power lens group on the image side along the optical axis.

Specifically, as shown in the lens configuration diagram (telephoto end state) of the embodiment in FIG.
I is the first lens with positive refractive power fixed to the image plane on the object side.
It is composed of a subgroup 1 and a second subgroup Lx that is movable along the optical axis on the image side, and the combined focal length of the entire focusing lens section is f, and the first subgroup L11 The focal length of fl.

When 5.0 < f I / f < 12.0 (
It satisfies the condition 1).

If the upper limit of this condition (1) is exceeded, the second subgroup L
Since the refractive power as a 0-focus lens section is concentrated on x, aberration fluctuations due to focusing are reduced by
In combination with this, it becomes difficult to correct. If the lower limit of this condition is exceeded,

Since the refractive power of the second subgroup L2 becomes too small, the amount of movement of the second subgroup for focusing becomes large (
This leads to an increase in the length of the L11 focusing lens group.

Further, since the burden of chromatic aberration on the first subgroup and the second subgroup increases, the L11 lens system becomes complicated and large, making it difficult to configure each subgroup with a simple lens configuration.

Furthermore, the first subgroup LI includes a negative meniscus lens component Lll with a convex surface facing the object side and a positive lens component Ll with a surface with a stronger curvature facing the object side! In addition, 8 in the first subgroup has a bonded positive lens component L13 with a surface with a stronger curvature facing the object side, and a biconvex positive lens component L■ with a surface with a stronger curvature facing the object side. It is desirable to have a configuration. The refractive index of the negative meniscus lens component L11 in the first subgroup is Na, and the radius of curvature of the image side lens surface is R.
a, the refractive index of the positive lens component L1t in the first partial group is Nb, the radius of curvature of the object side lens surface is Rb, and the image of the biconvex positive lens component LI4 on the image side in 8 of the first partial group. When the radius of curvature of the side lens surface is Re, 0.48<Ra
/ f < 0.72 (2) 0.48 <
Rh/r<0.72 (3)1
．． 8 < Rc / f < 2.6 (5
) is desirable.

Conditions (2) to (5) are all for sharing aberrations between the first partial group L11 and the second partial group L2 so as to cancel aberration fluctuations due to focusing. At the telephoto end, where the aberration variation due to focusing is greatest, by configuring each subgroup as described above, the first
On the image side lens surface Ra of the negative meniscus lens component L11 in the subgroup, large positive spherical aberration and astigmatism occur,
Object side lens surface R of positive lens component L12 in the first subgroup
Large negative spherical aberration and astigmatism occur in b, and the sum of these aberrations occurring on both surfaces occurs on the image-side lens surface Re of the image-side double-convex positive lens component Lra in 8 of the first subgroups. The aberration is balanced so that the absolute value is almost equal with the opposite sign to that of the aberration.

When the second subgroup L11 is moved to focus on a close object,
The spherical aberration generated on the image side lens surface Ra of the negative meniscus lens component L11 in the first subgroup changes in the negative direction, and the astigmatism changes in the positive direction, and at the same time, the positive lens component in the first subgroup The spherical aberration generated on the object-side lens surface Rh of component L12 changes in the positive direction, and the astigmatism changes in the negative direction. As a result, the positive spherical aberration as the first subgroup is small, and the positive astigmatism becomes larger. On the other hand, when focusing on a short distance object, L11
In the 1st subgroup! The negative spherical aberration generated at the image-side lens surface Rc of the middle image-side positive lens component L14 is small, and the negative astigmatism is large. Therefore, aberration fluctuations due to focusing change in the direction of canceling each other out in the first partial group and the second partial group, and it becomes possible to correct the aberration fluctuations to extremely small values as a focusing lens group.

Even if the upper and lower limits of conditions (2), (3), and (5) are exceeded, the balance of aberrations generated at each of the above lens surfaces Ra, Rb, and Rc will be lost, and aberration fluctuations due to focusing will be reduced. I can't do anything. Also, condition (4)
is not satisfied, the absolute value of the aberration occurring between the image side lens surface Ra of the negative meniscus lens component L11 in the first partial group and the object side lens surface Rh of the positive lens component L12 in the first partial group is As a result, it becomes difficult to cancel out the aberration generated at the image-side lens surface Re of the image-side positive lens component LI4 in the second partial group Lt.

Furthermore, the laminated positive lens component LI3 in the second partial group Lt
The biconvex positive lens is made of so-called anomalous dispersion glass with an Abbe number of 80 or more or made of fluorite.The negative lens is made of lanthanum crown glass or lanthanum 1.
Preferably, it is flint type glass. By selecting such a glass material, it is possible to eliminate the secondary spectrum, which is a major cause of deteriorating the contrast of the image at the telephoto end of L11.

(Example) Examples according to the present invention will be described below.

FIG. 1 is a lens configuration diagram of an embodiment according to the present invention. This zoom lens includes, in order from the object side, a lens group G as a focusing lens group, a second lens group Gt with a negative refractive power as a variable magnification lens group, a third lens group G8 with a negative refractive power as well,
and a fourth lens group G# as a relay lens group. The fourth lens group G4 is composed of a front group Gy on the object side and a rear group G separated by a relatively large air gap, and the L11 rear group GII is linked to the movement of the third lens group G. It is movable. When changing the magnification from the wide-angle end to the telephoto end,
The second lens group G: moves linearly toward the image side, and the third lens group G: moves nonlinearly, drawing a trajectory with its convex surface facing the object side. The rear group GR in the group G4 moves nonlinearly so as to draw a locus with its convex surface facing the image side.

The lens group G't as a focusing lens group has the lens configuration as described above, and by moving t in the first subgroup L11 toward the object side along the optical axis by 15.2+w , it is possible to focus on objects as close as 2.5 - from the vertex of the frontmost lens surface.

Looking at the specific configuration of each group, the Luns group G is, in order from the object side, a negative meniscus lens L with a convex surface facing the object side, a positive lens L with a surface with a stronger curvature facing the object side, and so on. A first subgroup L, which has a positive refractive power when combined, consists of a positive lens LI3 and a biconvex positive lens LI4, which are laminated with a convex surface facing the object side, and a second subgroup, which has a positive refractive power when combined.
It is composed of subgroups. The second lens group G is
In order from the object side, there is a negative meniscus lens Li with its convex surface facing the object side, and a bonded negative lens Lt with its surface with stronger curvature facing the image side! , a laminated negative lens L with a surface with a stronger curvature facing the object side. Karana L11 third lens group G3 is
It consists of a bonded negative lens L with a concave surface facing the object side. , and the fourth lens group G as a relay group
4 is a front group GF, a rear group G movable along the optical axis, and a L11 front group GF, which is a positive lens with a surface of stronger curvature facing the image side in order from the object side L41 a biconvex positive lens L4t
, laminated positive lens L with the surface with stronger curvature facing the object side
. , a positive lens L44 with a surface with a stronger curvature facing the object side.
The L11 rear group Gll consists of a negative lens L4S with a surface with a stronger curvature facing the image side, and a laminated meniscus lens L4 with a concave surface facing the object side, and a laminated meniscus lens L4S with a concave surface facing the object side in order from the object side. It consists of a negative meniscus lens L4'F, a biconvex positive lens L41, and a positive lens L49 with a surface with a stronger curvature facing toward the object side. A parallel plane member P corresponding to a color separation prism or various filters is arranged between the fourth lens group G4 and the image plane (2).

Table 1 below shows the specifications of this example. In the table, the leftmost number indicates the order from the object side, and the refractive index and Atsbe number are d
Value for the line (λ-587.6n+*) l upper focal path Mf-24~275 Zoom ratio 11.5F
Number 1.8”-2,8 (Table 1 = continued) Regarding the above example, at the wide-angle end (f=24), at the middle (f-
120) and the telephoto end (f=275) are shown in Figs. 2A, 2B, and 2c in order. In the aberration diagram, the reference ray is the C line (λ = 546.1n
11) In the L11 spherical aberration diagram, astigmatism diagram, and lateral chromatic aberration diagram, g-line (λ = 435.8 nm) and C-line (λ
=656.3na+) is also written. Further, in the spherical aberration diagram, the amount of violation of the sine condition is also indicated by a broken line.

In addition, by moving only the second component in the lens group Gl, in each focal length state of the wide-angle end (f = 24), intermediate (f - 120), and telephoto end (f = 275),
Various aberration diagrams when focusing on an object distance of 2.5 m+ are shown in Figures 3A, 3B, and 3C in order.

In this example, a lens with a length of 69IIIffi and a refractive index of 1.60881 is provided between the fourth lens group G4 and the image plane toner.
, a prison corresponding to a parallel plane member P with an Atsube number of 59,
The L11 was designed to include this, and filters, etc. are arranged.

According to these aberration diagrams, it has a wide zooming range with a zoom ratio of 11.5, and an F number of 1.8 to 2.8 (telephoto end).
Despite being a telephoto zoom lens with such a large zoom ratio and large aperture ratio, it can be used over a wide range of magnification, and even when focused on objects as close as 2.5m at each focal length. It is clear that various aberrations are corrected extremely well. The L11 maintains excellent imaging performance that warmly surpasses not only conventional video camera zoom lenses, but also 351Ill-eye reflex camera zoom lenses. It can be seen that it has sufficiently good performance as a commercially available product.

In Table 2 below, in order to show the aberration balance during focusing in the lens group G1 of the above embodiment, the results are shown for the infinity focus state and the close focus state for an object distance of 2.5 m. In Table 2, which shows the third-order aberration coefficients at each lens surface (both at the telephoto end), ■ is spherical aberration, ■ is coma, ■ is astigmatism, ■ is Benzbar sum, and ■ is distortion aberration. represents each third-order aberration coefficient, and the leftmost number represents the order of each lens surface in the lens group G1 from the object side. Then, the first subgroup and the second subgroup of the Luns group G,
The subtotal of aberration coefficients for each subgroup and the total sum for the entire system are also shown.

2 (3' of Luns G1,) [Infinity focus state] I n II [IV Vl
1.287-0.380 0.112 0.
029-0.0422(Ra)-227,87487,
790-33,822-0,94213,0663(R
h) 191.125 -73.369 28.16
5 0.070 -10.8395 3.267
-1.060 0.344 0.040-0.12
56 -10.388 4.545 -1.988
-0.009 0.8747 0.027
0.001 0.000-0.018-0.0018
2.619-0.827 0.261 0.
022-0.0'1 complete system -0,223-0,1550
, 1320, 016-0, 367 [Distance focus state] I II III IV
Vl 1.8757-0.744 0.
295 0.029-0.1292(Ra)-205
,56999,016-47,693-0,09423
,0173(Rb) 173.188 -83.169
39.940 0.070 -19.2145
4.360-1.867 0.800 0.0
40-0.3606 -7.619 4.152-
2.263-0. f109 1.2387 -0.
018 0.003 -0.001 -0.018
-0.0048 3.823-1.608 0.
676 0.047-0.304 Whole system 0.214
-0.148 0.107 0.016-0.43
2. From the aberration coefficient table above, it is clear that each lens surface R as described above is due to the fact that the lens group G1 as a focusing lens group according to the present invention is composed of a first subgroup and a second subgroup with positive refractive power. , , Rb, and the state of aberration variation in R can be read. That is, it can be seen that the aberrations generated on each of these surfaces are generated so as to skillfully cancel each other out through focusing, and the fluctuations in the entire L11 system are suppressed to extremely small fluctuations.

(However, the signs of the actual aberrations and the above aberration coefficients are reversed.) In this example, the negative lens Lll in the first subgroup in the lens group Gl is made of lanthanum flint glass, Positive lens L
l! L11 second made of phosphate crown glass
Together with the selection of the glass material of the bonded positive lens in the subgroup, it greatly contributes to the correction of the secondary spectrum, and as shown in the aberration diagrams of L11 Figs. Corrected in a well-balanced manner.

(Effects of the Invention) As described above, according to the present invention, although the zoom ratio is large and the aperture ratio is large, aberration fluctuations due to focusing, especially fluctuations in spherical aberration and field curvature, are small, and the total It is possible to realize a telephoto zoom lens that maintains excellent imaging performance even when focusing on close objects in the magnification range.

Since the first subgroup L1 is fixed with respect to the image plane, it is possible to construct a lens barrel with excellent impact resistance and dust resistance. When the camera is mounted on a camera, there is no need to rotate the front lens, so there is the advantage that focusing can be performed without changing the filter effect in the desired direction.

[Explanation of symbols of main parts]

G,... Third lens group G,... Third lens group Gt... Second lens group G4... Fourth lens group L11... Positive refractive power first partial group L1 in the third lens group
1t...Positive refractive power second subgroup in the Luns group Applicant
Nippon Kogaku Kogyo Co., Ltd. Representative Patent Attorney Takashi Watanabe Male spherical aberration Fractional aberration Distortion aberration Lateral chromatic aberration Figure 2A Spherical aberration Radical distortion Distortion aberration Figure 2B Spherical aberration Radical curvature Distortion aberration Figure 2C Spherical aberration a curvature Distortion aberration No. 3A Spherical aberration Rokuen Takkyoku Distortion aberration P Lateral chromatic aberration No. 3B Spherical aberration Rokumen Yoshikoku Distortion aberration Lateral chromatic aberration No. 3Q Procedure correction document □ September IO date, 1985

Claims (1)

[Scope of Claims] (1) A zoom lens having a variable magnification lens group and a focusing lens group disposed on the object side of the variable magnification lens group, both of which have positive refractive power. The structure is divided into a first subgroup and a second subgroup, and of the two subgroups, the first subgroup on the object side is fixed to the image plane, and the second subgroup on the image side is fixed to the optical axis. Focus by moving along the
When the combined focal length of the entire focusing lens group is f and the focal length of the first partial group L_1 is f_1, the following condition is satisfied: 5.0<f_1/f<12.0(1) A telephoto zoom lens. (2) The first partial group L_1 has a negative meniscus lens component L_1_1 with a convex surface facing the object side and a positive lens component L_1_2 with a surface with a stronger curvature facing the object side, and the second partial group L_2 has a negative meniscus lens component L_1_1 with a convex surface facing the object side. It has a bonded positive lens component L_1_3 with a surface with a stronger curvature facing the side and a biconvex positive lens component L_1_4 with a surface with a stronger curvature facing the object side,
The refractive index of the negative meniscus lens component L_1_1 in the first subgroup is Na, the radius of curvature of the image side lens surface is Ra, and the refractive index of the positive lens component L_1_2 in the first subgroup is Nb.
, the radius of curvature of the object-side lens surface is Rb, and the second subgroup L
When the radius of curvature of the image side lens surface of the image side biconvex positive lens component L_1_4 in _2 is Rc, 0.48<Ra/f<0.72 (2) 0.48<Rb/f<0. 72(3) (Nb-1)/Rb<(Na-1)/Ra(4)1.8
Claim 1, characterized in that it satisfies the condition <Rc/f<2.6(5)
Telephoto zoom lens described in section.