JPS61121021A - Zoom lens with soft focus function - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens having a soft focus function, and in particular to a soft focus lens in which aberrations can be easily varied by a simple operation by moving a part of the lens group for variable magnification. The present invention relates to a zoom lens having functions.

Conventionally, methods to give a soft 7 orcus effect to photographed images include attaching a filter with a soft focus function to the front of the lens system, or attaching an optical element to the lens system as proposed in Japanese Patent Publication No. 1402/1982. There are methods of moving the lens inside the lens or adding an attachment lens as proposed in Japanese Utility Model Publication No. 57-9769. However, these methods have disadvantages in that it is difficult to provide a uniform soft focus effect over the entire screen, and operations to provide the soft focus effect, such as attaching and detaching optical members, are cumbersome. Japanese Patent Publication No. 52-7692
No. 1 and Japanese Unexamined Patent Publication No. 55-52013 propose a method of obtaining a soft focus effect by changing the air spacing in the lens system to continuously change aberrations, for example, spherical aberration. However, in these methods, the lens system itself is limited to special uses and is not suitable for general photography.

An object of the present invention is to provide a zoom lens with a soft focus function that can obtain a uniform soft focus effect over the entire screen with a simple operation of moving some lens groups in a normal lens system. shall be.

The main feature of a zoom lens having a soft focus function to achieve the object of the present invention is that it has at least two lens groups, lens group A and lens group B, in order from the object side, and at least the two lens groups A, In a zoom lens that changes magnification by moving B, lens group A
The lens surface R1R closest to the image plane and the lens surface R2y closest to the object side of lens group B are both composed of lenses with convex surfaces facing toward the object side, and by moving lens group A and lens group B at different ratios. This is because the aberrations are made variable.

In this way, the present invention generates aberrations, especially spherical aberrations, with a simple configuration by moving the two moving lens groups while maintaining a predetermined relationship when changing the magnification, thereby achieving an arbitrary soft focus effect. ing.

Next, the reason why the soft focus effect can be obtained in the present invention will be explained using FIGS. 1 to 3. In the figure, 4 corresponds to lens group A, 5 corresponds to lens group B, and 1.2.
3 is the image point of each lens group B, and lens groups A and B are arranged in an arbitrary zoom lens system. Although the figure shows lens group A as having negative refractive power and lens group B as having positive refractive power, the refractive power arrangement may be reversed.

FIG. 1 shows a normal photographing state in which various aberrations are well corrected and there is no soft 7 orcus effect.

FIG. 2 is a diagram when the lens group 5 is moved in a direction closer to the lens group 4 from the state shown in FIG.

The amount of spherical aberration generated on each surface is proportional to the fourth power of the height of incidence on the lens surface.
7 is incident at a lower position than the incident ray 6 in FIG. 1, and the negative spherical aberration generated in the lens group 5 is reduced. Therefore, as a result, positive spherical aberration occurs in the entire system, producing a soft focus effect.

However, the image point 2 of the lens group 5 moves from the position of the image point 1 in FIG. 1, and the image points of the lens groups located after the lens group 5 move. In other words, a shift in focus occurs.

FIG. 3 is a diagram in which the lens group 4 and the lens group 5 are brought closer to each other while the lens group 4 is also moved so that the image point 6 of the lens group 5 coincides with the position of the image point 1 in FIG. 1. That is, lens group 4
By moving the and lens group 5 at different ratios,
Mainly spherical aberration is generated without changing the focus position. In the present description, a case has been described in which the lens group 4 and the lens group 5 are brought closer to each other, but the same effect can be obtained by moving them farther apart.

It is desirable that the image delineation due to the soft focus effect be uniform over the entire screen. Expressing this from an aberration standpoint, the halo component due to spherical aberration is generated in approximately the same amount over the entire screen, and deterioration other than spherical aberration is kept extremely small.

In order to generate such an aberration, only spherical aberration can be generated by changing the air distance between two lens surfaces that are concentric with respect to the exit wind or the entrance pupil.

Generally, in a zoom lens, the pupil position changes in response to a change in focal length during zooming, and the difference between the light ray at the center of the luminous flux and the light ray passing through the center of the pupil is significantly different.

In other words, since the position where the center of the light flux intersects with the central optical axis changes with each image height, there is no longer a concentric lens surface, making it difficult to obtain uniform depiction over the entire screen.

Therefore, in the present invention, in order to obtain a soft focus effect, lens surfaces corresponding to concentric lens surfaces are defined as lens surface R1R of lens group A closest to the image plane and lens surface R2F of lens group B closest to the object side. By arranging the diaphragm behind the lens surface R2F and changing the distance between the lens surface R1R and the lens surface R27, a good soft focus effect is obtained over the entire screen.

In the present invention, particularly preferably, the lens surface R1
The radius of curvature of R is RA, the refractive index of the object-side medium of lens surface R1H is NA, and the radius of curvature of lens surface R2F is RB.

The refractive index of the medium on the image side of lens surface 121F is NB, and the maximum value of the change in the air gap between lens surface R1R and lens surface R2F, which is changed to make the aberration variable, is When the focal length of the system is /T, the following condition is satisfied: 0.8 < - < 2.2 (1) RB.

Next, the above-mentioned technical meaning will be explained using FIGS. 4 and 5.

In FIGS. 4 and 5, 9 is the lens surface R1u, and 10 is the lens surface R21! , 12.15 is the central ray of the off-axis beam, and 11, 13, 14, and 16 are marginal rays.

FIG. 4 shows that by making the normal line of the light l112 exiting the lens surface 9 almost coincident with the normal line of the lens surface 10, even if the distance between the lens surfaces 9 and 10 changes, the aberration corresponding to off-axis spherical aberration can be reduced. I try not to change anything other than that. In terms of aberrations, it is preferable to set the aberration within a range of ±15 degrees with respect to the normal; if the aberration is outside this range, other aberrations will occur, which is not preferable.

For example, as shown in FIG. 5, if the difference in direction between the light ray 15 exiting the lens surface 9 and the normal line to the lens surface 9 is large, if the distance between the lens surfaces 9 and 10 changes, the lens surface
The absolute amount and amount of change in the aberration of the light ray refracted by the lens surface 10 increases, and coma aberration, astigmatism, etc. change greatly, degrading the image.

In other words, if the radius of curvature of lens surface 9 and lens surface 10 falls outside the range of conditional expression (1), large aberrations other than spherical aberration will occur from each lens surface, as explained in FIGS. 4 and 5. This is not preferable because it causes deterioration of the entire image.

Conditional expression (2) concerns the amount of change in the refractive power of the air lens formed by lens surface 9 and lens surface 10, and sets the refractive power of the air lens appropriately with respect to the amount of change in the air gap between both lens surfaces. This reduces the occurrence of various aberrations other than spherical aberration, as described above.

If conditional expression (2) is not met, astigmatism and coma aberration will occur,
This is not preferable because it significantly degrades the image performance around the screen.

In this example, a zoom lens with a large magnification ratio and a large change in the angle of view is shown. Distance range is limited. In the embodiment, soft focus is performed near the telephoto end.

However, a configuration that satisfies the conditional expression over the entire zoom range is also possible.Next, we will discuss the numerical implementation of the present invention when applied to a zoom lens that moves six lens groups during zooming and achieves a high zoom ratio. Show the side.

In the numerical examples, Ri is the radius of curvature of the th lens surface from the object side, Di is the thickness and air gap of the th lens surface from the object side, and N( and νt are the curvature radius of the th lens surface from the object side, respectively). These are the refractive index and Atsube number of the lens glass.

Numerical Example 1 f-36,0~66.5 FNO-4,1R1-60
,68D I-1,9N 1-1.69680 Si1-
55.5R2-23, 29D 2-78 R3-179, 97D 3-17 N 2-1.65
844 v 2-50.914- 47.06 D
4-Variable R5-52,59D 5-3.08 N! -1.
75520y 3-27.5R6-56,55D
6-Variable R7-34,09D 7-2.9 N 4-1620
41 u 4-60.3R8-210,82D 8-
01 R9-30,6609-5,0M S-1,60311
u 5-60.7R10 (51,58D10 San 1
．． 7 aperture Dll-12 R11-25, 37Dl2-4.0 N 6-1.
58913 v 6-61.0R12-4190D
l3-13 R13--71,91Dl4-1.9 N 7-1.
80518117-25.4R14-20,31Dl5
-4.85 R15-120, 58Dl6-2.8 M 8-1
62588 v 8-55.7116--29.0
6 Normal) X-MurGt D 4-4.54 D 6
-50.47-0.5 Soft focus photography Teha D 4-5. O.D.
6-4.435 Numerical Example 2 f-29,0~53.8 FNO-5,6~4.6
R1-111,08D I-5,24N 1-1.65
844 v 1-50.9R2-5320,68D
2-0.2R3-132,92D 5-1.43
N 2-1.80610 v 2-40.914- 1
8.53 D 4-5.78R5-212,8505
-1,28N 3-1.80400 ν 3-46
．． 6R6-35,68D 6-variable R7-28,29D 7-3.49 N 4-180
518 ν 4-25.4R8-108,51D 8
-Variable R9=69.68 D 9-2.65 N S-1
60311v 5-60.7110--63.73 D
lo-1,46R12-66,75Dl5-4.07 113--51.14 DI413.8 N
7-1.84666 ν 7-23.9R14-20
,34Dl5-124 R15-2204,17Dl6-1.67 N B
-1,62004ν 8-56.5R16--76,9
5Dl7-0.2 117 114-31 Dl8-2.72 N 9
-1. +52004 ν 9-36.3118--2
2.68 Dl9-variable R19-43,03D20-
1.5 N10-1.48749 C10-70
．． lR20-53,57 Normal zoom D 6-2.16 D 8-2
8.85-0.26D19-118-22.4 For soft focus photography D 6-15 D 8-2.91
Numerical Example 6 f-36, 0-679 7NO-4, 1R1-40,
58D I-2,6N 1-169350 y 1-
53.2R2-2555D2-6.9 R3-412, 23D 3-17 N 2-16.
6672 ν Su-48,2R4-! i4.53
D 4-variable R5-34,49D 5-3.6 N 3-1.75
520 M 5-27.516- 67.31
D 6-variable R7-34,69D 7-4.1 N 4-1.62
299 C4-58.518--19185 D8
-0.1 R9-28,69D 9-3.3 N 5-160
311 ν 5-60.7R10-65,67Dlo
-1,7 Aperture Dll-12 R11-26,48Dl2-5.1 N 6-1.5
6384 Jiro 60.7112- 43.06 D
l3-1.5R13-416, 37Dl4-2.3
N 7-1.80518 v 7-25.4114-
19.60 Dl5-5.6R15-107,49D
l6-2.9 N 8-1.6200498-36.
SR1,5--34,11 Normal Nosu Ar Ha D 4-6.28 D 6-33.
0-2.2 Soft focus photography D 4-6.82
D 6-0.5 Numerical Example 4 f 55.57~55.31~7926R1-54,3
3D I-1,92N 1-180400 ν
1-46.612- 22.51 D 2-6.15
R3-357,45D 3-3.55 N 2-1
．． 65636 M 2-55.4R4--70,0
3D 4-2.43 R10--239, 151110-0, 13R11-2
6,90Dll-3,37N 6-1.77250
Jiro 49.6R15-25, 67Dl4-2.78
N 7-1.65160 v 7-58.6R1
4-50,42Dl5-1.29 R15-475,33Dl(S-2,15N 8-1.
84666 ν 8-23.9116- 17.28
Dl7-2.64R19--77,25D20-3
．． 22 N10-180610 ulo-40,9
With normal zoom D6-2.486~2.611~2
．． 986D8-29.279-11. +554~0.7
79D19-5.072~5.634~10.710 Punk 7 Orcasus 38.59~54.04~62.95
For soft focus photography D 6-2.4865 D B-2
, 0267 In numerical example 1, R1 to R4 are lens group A.
, R5 to R6 are lens group B, and SR7 to R16 are lens group C, which is a zoom lens consisting of six lens groups. During normal shooting, lens group A and lens group B are integrated during zooming. By moving the lens and further changing the air distance between lens groups B and C, magnification is changed. When performing soft focus photography, at the telephoto end of the zoom lens, with the lens group O fixed, the interval D4 is set from 4.341111 to 3.0 dew, and D6 is set to 0.
．． The distance is changed continuously from 5 m to 4.4351111.

Numerical Example 2 is a zoom lens with a four-group configuration, and R1-
Up to R6 is lens group A, and from R7 to R8 is lens group B.
, R9-R18 are the third lens group 0XR19-R
20 is the fourth lens group, and during normal shooting, lens group A and lens group B move together during zooming, and the air between lens group B and lens group C, and between lens group C and lens group The interval changes to perform magnification. The lens group remains fixed during zooming. When performing soft focus photography, at the telephoto end of the zoom, the distance D6 is set to 2.16111 with lens group C and lens group fixed.
From 11 to 1.5 kana, the interval D8 is from 0.26 to 2.
It is performed by continuously changing up to 91 w#sL.

Numerical Example 6 is a 6-group zoom lens with almost the same configuration as Numerical Example 1, but the interval D4 is changed from 6.28- to 6.821111, and the interval D is changed during soft focus photography.
This is an example in which aberrations are made variable by changing the lens 6 from 2.211@ to Q, 5111L, and bringing the lens detail closer to lens group B.

Numerical Example 4 is a zoom lens with a four-group configuration, and R1-
Up to R6 are lens groups ASR7 to R8 are lens groups B1R9
~118 is the third lens group, and 0XR19~R22 is the fourth lens group. All four lenses move independently to perform zooming for normal shooting, and soft focus is performed at the telephoto end. , C and the lens group are fixed.

In the embodiment of the present invention, focusing is performed in lens group A.
It is better to move lens group B and lens group B together to reduce aberration fluctuations, but it is more preferable to perform focusing by moving lens group M and lens group B at different ratios, so-called floating. It is also possible to perform 7 focusing with the third lens group O or a lens group located further toward the image plane.

The above description describes the case where the present invention is applied to a type of zoom lens in which three lens groups move when changing the magnification, but it is also applicable to a so-called two-group zoom lens in which two lens groups move when changing the magnification. The present invention can also be applied to.

Although the mechanism is somewhat complicated, the present invention can also be applied to a zoom lens in which lens group A or lens group B is fixed, or both lens groups are fixed, and the magnification is changed using another lens group. I can do it.

As described above, according to the present invention, a zoom lens that can obtain a good soft focus effect over the entire screen can be achieved with a simple configuration in which some lens groups in the lens system are moved.

[Brief explanation of drawings]

Figures 1, 2, and 3 are explanatory diagrams of the optical system used to obtain the soft 7 orcus effect of the present invention, and Figures 4 and 5 are illustrations of the optical system used to obtain the soft focus effect of the present invention, respectively. FIG. 3 is an explanatory diagram of the lens surface. Figures 7, 8, and 9 are numerical examples 1 to 1 of the present invention, respectively.
4, FIG. 10, and FIG. 11. 12 and 13 are aberration diagrams of numerical examples 1 to 4 of the present invention, respectively. In the figure, (A), (average, (Q are various aberration diagrams when performing wide-angle end, telephoto end, and soft focus, respectively, S is the sagittal image plane, K is the meridional image plane, d is the d-line, and g is the g@, S
o indicates a sine condition, and arrows in FIGS. 3 to 9 indicate the moving direction of the lens group when performing magnification change and soft focus photography.

Claims (1)

Scope of Claims: (1) A zoom lens that has at least two lens groups, lens group M and lens group B, in order from the object side, and that changes magnification by moving at least the two lens groups A and B. In, the lens surface R_1_R of the lens group A closest to the image plane and the lens surface B closest to the object side of the lens group B
Both _2_F are composed of lenses with convex surfaces facing the object side,
A zoom lens having a soft focus function, characterized in that aberrations are made variable by moving the lens group A and the lens group B at different ratios. (2) A patent characterized in that the aberration is made variable by moving the lens group A and the lens group B so that the image point position of the composite system of the lens group A and the lens group B becomes a constant position. A zoom lens having a soft focus function according to claim 1. (3) The radius of curvature of the lens surface R_1_R is RA, the refractive power of the medium on the object side of the lens surface R_1_R is NA, the radius of curvature of the lens surface R_2_F is RB, and the refraction of the medium on the image side of the lens surface R_2_F NB, the maximum amount of change in the air distance between the lens surface R_1_R and the lens surface R_2_F that is changed to make the aberration variable is x, and the focal length of the entire system at the telephoto end zoom position is f_T. When, 0.8<(RA)/(RB)<2.2 | [(NA-1)(NB-1)]/(RA×RB)×x
A zoom lens having a soft focus function according to claim 2, which satisfies the condition xf_T|<0.035. (4) The lens group A has a negative refractive power, the lens group B has a positive refractive power, and the combined refractive power of both lens groups is negative, and the lens group B has a positive refractive power on the image plane side. A lens group C having a refractive power of
, B. A zoom lens having a soft focus function according to claim 3, wherein the lens group C is moved together with the lens group C.