JPH0266509A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain high optical performance by providing four lens groups which have specific refracting power, respectively, and setting the refracting power and image formation magnification of 3rd and 4th groups as movement conditions of the respective lens groups in power variation. CONSTITUTION:This zoom lens has a 1st group with positive with positive refracting power, a 2nd group with negative refracting power a 3rd group with positive refracting power, and a 4th lens group with positive refracting power in order form the object side. Then when the magnification is varied from the wide-angle end to the telephoto end, the 1st and 4th groups are moved to the object side and at least one of the 2nd and 3rd groups is moved so that the gap between the 1st and 2nd groups decreases and the gap between the 3rd and 4th groups decreases while requirements shown by inequalities I, II, and III are met. In the inequalities I, II, and III, f3 and f4 are the focal lengths of the 3rd and 4th groups, fW and fT are the focal lengths of the whole system at the wide-angle end and telephoto end, and beta4W and beta4T are the image formation magnification values of the 4th group at the wide-angle end and telephoto end respectively. Consequently, the excellent optical performance is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a zoom lens, and in particular to a zoom lens that has a high variable power ratio and a wide angle of view with a long hack focus, suitable for photographic cameras, video cameras, etc. It is.

(Prior Technology) Conventionally, photographic cameras and video cameras have a high variable power ratio, a wide angle of view, and a space in which a quick return mirror is placed behind the lens system in photographic cameras.

For video cameras, there is a demand for a zoom lens with a long back focal length corresponding to the space in which various optical members such as a low-pass filter are arranged.

Examples of zoom lenses with a relatively wide angle of view with a variable magnification ratio of about 3x include those disclosed in Japanese Patent Application Laid-open No. 115411/1983 and Japanese Patent Application Laid-open No. 57-1989.
This is proposed in Japanese Patent No. 192918.

In this publication, in order from the object side, the first . 2nd, 3rd. It consists of a fourth lens group, and the first group, second group, and fourth group are moved, and the third group is fixed or slightly moved to change the magnification.The first group has a positive refractive power. A positive lead four-group zoom lens is disclosed.

Among these, in Japanese Patent Application Laid-Open No. 62-115411, the focal length is about 35 to 105 mm in terms of a 35 mm single-lens reflex camera, and the back focus is about 135% of the focal length at the wide-angle end.

Also, in Japanese Patent Application Laid-Open No. 57-192918, the focal length is 35
It is about 35 to 105 mm in terms of a single-lens reflex camera, and the back focus is about 104% of the focal length at the wide-angle end.

In general, in order to increase the angle of view at the wide-angle end of a high-power zoom lens, shortening the overall length of the lens and shortening the back focus is advantageous for correcting aberrations and downsizing the entire lens system. It is.

Furthermore, on the telephoto side, increasing the overall length of the lens is disadvantageous in terms of aberration correction.

However, positive lead type zoom lenses are the first
It is advantageous in shortening the overall length of the lens compared to a negative lead type zoom lens, which consists of a lens group with negative refractive power, but if you try to lengthen the back focus while achieving a high zoom ratio and wide angle of view, The total length of the lens increases, and aberration fluctuations due to zooming increase, making it very difficult to obtain good optical performance.

(Problems to be Solved by the Invention) The present invention consists of a zoom lens consisting of four lens groups each having a predetermined refractive power. By appropriately setting and configuring the imaging magnification etc. at the zoom position,
To provide a zoom lens having a high variable power, a wide angle of view, a relatively long back focus, and good optical performance over the entire variable power range.

(Means for solving the problem) From the object side, the first group has positive refractive power, and the second group has negative refractive power.
group, a third group with positive refractive power and a fourth group with positive refractive power.
It has two lens groups, and the first lens group changes the magnification from the wide-angle end to the telephoto end. the fourth group is moved toward the object side, and the distance between the first group and the second group is increased, and at least one of the second and third lens groups is moved toward the object side;
The distance between the second and third groups is decreased, and the distance between the third and fourth groups is decreased, and the focal lengths of the third and fourth groups are set to f3. f4. The focal lengths of the entire system at the wide-angle end and the telephoto end are fW and fT, respectively, and the imaging magnifications of the fourth group at the wide-angle end and the telephoto end are β4W and β4T, respectively.
When (f3/f4(1,9......
...(1) fT ・β 4W O, 32 f4/fTcO, 51...
...(3) must be satisfied.

(Example) FIGS. 1 to 3 are lens sectional views of numerical examples 1 to 3 of the present invention, respectively.

In the figure, 1 is the first group with positive refractive power, ■ is the second group with negative refractive power, ■ is the third group with positive refractive power, and ■ is the fourth group with positive refractive power.

In this embodiment, when changing the magnification from the wide-angle end to the telephoto end, each lens group is moved as shown by the arrows.

That is, the first, third, and fourth groups are arranged such that the distance between the first and second groups increases, and the distance between the second and third groups and the distance between the third and fourth groups decrease. is moved toward the object side, and the second lens group is moved toward the object side or image plane side to change the magnification from the wide-angle end to the telephoto end. At this time, by setting the refractive powers of the third and fourth groups and the imaging conditions of the fourth group as shown in the above-mentioned conditional expressions (1) to (3), a long back focus can be ensured and a high zoom ratio can be achieved. The result is a zoom lens with high optical performance over the entire zoom range. In addition, the present invention provides positive,
By configuring the lens system from four lens groups with negative, positive, and positive refractive powers, fluctuations in various aberrations caused by zooming are made to cancel each other out. The magnification effect when changing the magnification from the wide-angle end to the telephoto end is mainly shared between the second and fourth lens groups, thereby easily achieving a zoom ratio of about 3 to 4 times. There is. When changing the magnification from the wide-angle end to the telephoto end, by moving the first group toward the object side, the overall length of the lens can be shortened at the wide-angle end, and the diameter of the front lens and the diameter of the final lens can be reduced to ensure off-axis luminous flux. This prevents the effective diameter from increasing. At the telephoto end, the overall length of the lens is longer than at the wide-angle end to provide a sufficiently large telephoto ratio and correct various aberrations in a well-balanced manner.

Next, the technical meaning of each of the above-mentioned conditional expressions will be explained.

Conditional expression (1) defines the ratio of the refractive powers of the third group and the fourth group.0 If the upper limit of conditional expression (1) is exceeded, the refractive power of the third group becomes the refractive power of the fourth group. If it becomes too weak against the third
The effect of aberration correction by the group becomes smaller, and aberration fluctuations due to zooming, mainly fluctuations in spherical aberration and lateral chromatic aberration, increase.6 When the lower limit of conditional expression (1) is exceeded, the refractive power of the third group becomes smaller than that of the fourth group. If the refractive power is too strong, it will be difficult to obtain a long back focus, which is one of the objects of the present invention.

Conditional expression (2) specifies the share of the fourth group's variable power ratio with respect to the variable power ratio of the lens system. If becomes too large, fluctuations in various aberrations occurring in the fourth group will increase, and
If the zoom ratio of the fourth group becomes too small by exceeding the lower limit of conditional expression (2), which is undesirable because the amount of movement associated with zooming of the lens group increases, the amount of movement of the second lens group increases accordingly. The double effect must be increased, i.e. the first group or the second group.
This is not good because the amount of movement of the groups has to be increased, and in particular the amount of movement of the first group, which has a large outer diameter, is increased, which is undesirable from the viewpoint of torque when changing magnification. If the ratio is increased, fluctuations in various aberrations occurring in the second group will increase,
It becomes difficult to cancel this aberration variation using other lens groups and correct it in a well-balanced manner.

Conditional expression (3) defines the ratio of the refractive power of the fourth group to the focal length of the entire system at the telephoto end.
) If the refractive power of the fourth group becomes too weak by exceeding the upper limit of The zero conditional expression (3
) If the refractive power of the fourth group becomes too strong, exceeding the lower limit of
Variations in various aberrations occurring in the group become large, especially coma aberration, and it becomes very difficult to cancel this out with other lens groups.

In this embodiment, in order to perform better aberration correction over the entire screen under the above conditions, the tj11
The third group consists of two positive lenses and one negative lens,
When the average refractive index of the positive lens material 41 and the average Atsube number are respectively NP and yP, and the refractive index and Atsube number of the negative lens material are NN and νN, then 0.2:1cNN-NP・・・・・・・・・・・・・・・
...(4) It is preferable to satisfy the conditional expression ν N yP.

In the present invention, by using two positive lenses in the third group, it is possible to use a material with a low refractive index for each. Conditional expression (4) is based on the materials of the positive and negative lenses in the third group. Six conditional expressions (
4) If the lower limit value is exceeded and the refractive index difference becomes too small,
Conditional expression (5), in which the Petzval sum increases in the negative direction and it is difficult to maintain a good image plane, defines the difference in the reciprocals of the Atbe numbers of the materials of the positive and negative lenses in the third group. This is mainly for correcting chromatic aberrations, especially lateral chromatic aberration of magnification at the wide-angle end.If the upper limit of conditional expression (5) is exceeded, the chromatic aberration of magnification of the G-line at the wide-angle end will be undervalued, and this will be reflected in other lenses. Conversely, if the lower limit of conditional expression (5) is exceeded, the axial chromatic aberration generated in the third group becomes large, making it difficult to correct it in a well-balanced manner. It's coming.

Incidentally, in the zoom lens according to the present invention, the second group and the third group are moved when changing the magnification, but the second group or the third group is moved.
It is sufficient if at least one of the groups can be moved, but it is preferable to have more fixed groups in order to simplify the lens barrel structure and prevent performance deterioration due to manufacturing errors. The zoom system in which the third group is fixed has the advantage that the diaphragm can be fixed before or after the 3nth group during zooming, which is preferable in terms of lens barrel structure. On the other hand, a zoom system in which the second group is fixed and the third group is moved has the advantage that the second group, which has the strongest refractive power, is fixed, so that performance deterioration due to manufacturing errors can be reduced.

Next, numerical examples of the present invention will be shown.
i is the radius of curvature of the first lens surface from the object side, D
i is the first lens thickness and air gap from the object side, Ni
and νi are the refractive index and Abbe number of the glass of the first lens, respectively, in order from the object side.

Further, Table 1 shows the relationship between each of the above-mentioned conditional expressions and various numerical values in the numerical examples.

Numerical Examples l F Dew 36.0-102 Rl-116,99 R2-51,91 R3-755,56 R4 Dew 41. S'l R5-73,79 R6854,50 R7-16,45 88 kick-96,89 89-36,33 RIO-23,49 R11 snow-319,39 R12 through-41,34 Old 3-61.88 R14-58,86 R15-147-99 8I6- 49.63 R17--21,65 FNOIll: 3.5-4.5 2ω-62,0-2
4.0D I=2.0N l-1,805
18F 1-25.40 2= 10.5
N2=1.59680y2-
55.5Dff-0,2 D4=5.0 N3-1.69680
y 3-55.505 = variable D 6- 1.5 N 4 = 1.80400
y 4-46. l1D7-6.8 D8= 1.5 N S-1,
77250y 5- 49.609 0.9 DIG 4. ON 6-1. l14S68 Jiro 2ff, 9D11- 1.2 012- 1. sN? -1,77250 Shear 49.5013- Variable 014- 3.5 Ni1-1.56444
νIl-43,8015-0,2 D16=4.5 N! -1. l10
729 F 9- 49.2017=
1. s Nl0-1.83400
ylO-37,2118-85,62 Old 9er 3fu, 95 R20 tan 3360.23 R21--74,83 R22-44,23 R23 tumor-135,77 ■24--35.89 R25 騨269.5O R26 layer - 75,26 D2 ko depth N11-1.11040O N12 Oka 1.805111 N13-1.7725O N14-1.7725 (1 Shi11 Tan 46.6 y12 Fuji 25.4 Shi1:l-49,6 114 rin 4g, 6 Numerical Example 2 F-35,9~1004 R1 rich 188.81 D l-R2 electric 62.
82 D 2- R3～-604,16D 3- R4-49,0804th R5-150,1405 Proverb R6-56,44 R6- R7 So-called 15.78 D 7- 1 8-115.73 D 8暉R9 Proverb 5
1.92 D'1-RIO-22,15DI
[l- R11-239,64DIl- RI2--35.64 012- R13~ 51.40 Dl3- 1114 wealth 73.27 0+4 proverb RI5--5
:1.72 Dl5-R16-53,20Dl6- RI7--24.09 Dl, 7-arm FNO-1:3
．． S~4.5 2ω-62,0~24. :12.0
N l-1,805+8 ν 1 25.49.5 82-1.6968 [1ν 2
55.50.2 6.0 N 3-1.69680 ν
]-55,5 variable 1.5 N4 votes 1.80400
ν 4 servings 45.57.0 1, s NSSi280400 5 46
,60.9 4.0 N 6-1.114566
ν 6 穣 23.91.22 1.5 N7 votes 1.80400 Schiff wealth 46
．． 6 variable 3.0 N 8-1.56444 ν8-4
3.80.2 4.0 N 9-1.5:1172
ν 9 proverbs 480g0.5 R1 [1--23,3] Old 9 proverbs: 128. [1l R20-37,10 R21-435,62 122--76,26 R23-42,50 R24-189,18 R25 Frost-29,7 [l R26-173,09 R27--59,15 Dla bed 1.5 D19# Variable R20 depth 3.0 R21-1,98 R22 wing 3.0 D23■ 2. I R24-3,4 R25 Cao 0.2 R26 Ken 3.0 NIO Building 1.834of1 N11-1.7570O NI2 Station 1.80518 N13-1.6223O N14 Cloud 1.622 GoroylO Island 37.2 Shi11謔47.8 ν12 family 25.4 ν13 electric 53.2 ν14-53.2 Numerical example 3 F tan 36.0~+33.0 Rl-135,06D l frag R2-57,7802- R]] fable-619 []SD 3-R4-55,1
3D4 scale R5-113, 44D S- R6 Otori 61.48 D 6 R7-17, 8I D7 filter R8-109, +5 D 8- R9 @ 44.49 R9- RIO-25, 48 DIO Yuki R11-627, 39 DIl - R12--41,420+2 wealth RI3-81.83 D13 weight R14-106,580+4 electric RI5--52.52 Dl5- 816- 54.77 D16 bite RI7 ■-2
5,98[117 Akebono FNO-1:3.5~4.5 2ω-62,O~18
．． 52.0 XI 1.80518 ν
I-25,411,5N 2-1.69680
ν 2-55.50.2 5.0 N 3 wealth 1.59680
ν 3 denominations 55.5 variable 1, s N 4-1.77250 y 4-
49. li7.4 1.5 N S-1,77250ν5-49.6
1.0 4, ON6 1.84666 Jiro 23.91.
2 1.5 N? -1.77250
y 7- 49.6 variable 38 N8 fog 1.56444 y 8 error 43,
80.2 4.5 N 9-1.51256 ν9-4
5.91, s N10-1.113400
Shiro Gen 37.2R1B-1159,52 RI9 Korea 42.10 R20s813.78 R21--79,49 822-47,58 R2 Ko-1711,89 R24--34,37 R2S Korea 309.20 R26 Frost -110,13 019 snow 2l- R22 same R23 糟R24藏N11-1.7725O N12 1.8051+1 Nl"!-1.71:100 N14-1.69680 ν11-49.6 し12 proverb 25.4 ν13 -51.8 ν14-55.5 (Table-1) (Effects of the invention) According to Undeveloped 1, as mentioned above, there are four lens groups with a predetermined refractive power, the movement conditions of each lens group during zooming, and especially 3. By setting the refractive power and imaging magnification of the 4th group,
It is possible to achieve a zoom lens that has a high zoom ratio of ~4x, a wide angle of view, a predetermined back focus, and high optical performance.

[Brief explanation of the drawing]

1 to 3 are lens sectional views of numerical examples 1 to 3 of the present invention, and Figures 4 to M48 are various aberration diagrams of numerical examples 1 to 3 of the present invention. In the aberration diagrams, (A) shows the wide-angle end, (B) shows the telephoto end, and 111, m, and fV are the 1st... Second. Third. The fourth group, arrows indicate the movement direction of each lens group as the zoom is changed from the wide-angle end to the telephoto end, ΔS is the sagittal image plane, and ΔM is the meridional image plane.

Claims (1)

[Claims] (1) In order from the object side, the first group has a positive refractive power, the second group has a negative refractive power, the third group has a positive refractive power, and the fourth group has a positive refractive power.
The lens group has four lens groups, and for changing magnification from the wide-angle end to the telephoto end, the first and fourth groups are moved toward the object side, and at least one of the second and third lens groups is moved toward the object side. The distance between the first group and the second group is increased, the distance between the second group and the third group is decreased, and the distance between the third group and the fourth group is decreased;
The focal lengths of the third and fourth groups are f3 and f4, respectively, the focal lengths of the entire system at the wide-angle end and the telephoto end are fW and fT, respectively, and the imaging magnifications of the fourth group at the wide-angle end and the telephoto end are respectively β4W
, β4T, then 1<f3/f4<1.9 0.5<(fW・β4T)/(fT・β4W)<0.8
A zoom lens that satisfies the following condition: 50.32<f4/fT<0.51. (2) The third group has two positive lenses and one negative lens, and the average refractive index and average Abbe number of the materials of the two positive lenses are @NP@ and @νP@, respectively. , where the refractive index and Abbe number of the material of the one negative lens are NN and νN, respectively, the conditional expression is 0.23<NN-@NP@ 0<1/νN-1/@νP@0.01 The zoom lens according to claim 1, wherein the zoom lens satisfies the following.