JPH0416088B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a zoom lens with a soft focus function, and in particular, a zoom lens with a soft focus function that allows aberrations to be easily varied by simple operation by moving some lens groups for variable magnification. It is related to. Conventional methods for giving a soft focus 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 as proposed in Japanese Patent Publication No. 1402/1982. It can be moved within the system, and
There is a method of adding an attachment lens as proposed in the above publication. 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. Unexamined Japanese Patent Publication 1972-
No. 76921 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. The present invention provides a zoom lens that has 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. With the goal. 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 , B, the lens surface R _1R closest to the image side of lens group A and the lens surface R _2F closest to the object side of lens group B both have convex surfaces facing the object side. It consists of lenses, and aberrations are made variable by moving lens group A and lens group B at different ratios. In this way, the present invention generates aberrations, especially spherical aberrations, with a simple configuration by moving the two moving lens groups in a predetermined relationship when changing the magnification, thereby producing an arbitrary soft focus effect. It has gained. 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, 1, 2, and 3 are image points of 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 focus 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, but the incident ray 7 of the lens group 5 in Fig. 2 is at a lower position than the incident ray 6 of Fig. 1. 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. Figure 3 shows that while lens group 4 and lens group 5 are brought closer together, lens group 4 is also moved, and the image point 3 of lens group 5 is moved.
2 is a diagram in which the image point 1 is aligned with the position of the image point 1 in FIG. 1.
That is, by moving lens group 4 and lens group 5 at different ratios, spherical aberration is mainly 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 the standpoint of aberrations, 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 pupil 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. That is, since the position where the center of the light flux intersects with the central optical axis changes with each image height, a concentric lens surface no longer exists, making it difficult to obtain uniform depiction over the entire screen. Therefore, in the present invention, in order to obtain a soft focus effect, the lens surfaces corresponding to the concentric lens surfaces are the lens surface R 1R of lens group A closest to the image plane and the lens surface R _1R of lens group B closest to the object side.
By placing the diaphragm behind _{the lens surface R 2F and} changing the distance between the lens surfaces R _1R and R _2F , a good soft focus effect is obtained over the entire screen. In the present invention, particularly preferably, the radius of curvature of lens surface R _1R is RA, the refractive index of the object-side medium of lens surface R _1R is NA, the radius of curvature of lens surface R _2F is RB, and the image of lens surface R _2F is The refractive index of the medium on the surface side is
NB, lens surface that changes to make aberration variable
The maximum value of the change in air distance between R _1R and lens surface R _2F is x, and the focal length of the entire system at the telephoto end zoom position is
When f _T , 0.8<RA/RB<2.2...(1) 0.007≦|(NA-1)(NB-1)/RA×RB×x×f _T |< 0.035...(2) It is to satisfy. Next, the above-mentioned technical meaning will be explained using FIGS. 4 and 5. In FIGS. 4 and 5, 9 is the lens surface R _1R ,
10 corresponds to the lens surface R _2F , 12 and 15 are central rays of the off-axis beam, and 11, 13, 14, and 16 are marginal rays, respectively. FIG. 4 shows that by making the light ray 12 exiting the lens surface 9 substantially coincide with the normal line of the lens surface 10,
Even if the distance between the lens surfaces 9 and 10 changes, aberrations other than those corresponding to off-axis spherical aberrations are kept unchanged. 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 of the lens surface 9 is large, if the distance between the lens surfaces 9 and 10 changes, the distance between the lens surfaces 9 and 10 will change. The absolute amount and amount of change in the aberration of the light ray refracted by the surface 10 increases, and coma aberration, astigmatism, etc. change greatly, resulting in image deterioration. That is, if the radius of curvature of lens surface 9 and lens surface 10 deviates from the range of conditional expression (1),
As explained in the drawings, various aberrations other than spherical aberration are largely generated from each lens surface, deteriorating the entire image, which is not preferable. 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 satisfied, astigmatism and coma aberration occur, which significantly deteriorates the image performance around the screen, which is not preferable. 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, it is also possible to create a configuration that satisfies the conditional expression over the entire zoom range. A numerical example is shown. In the numerical examples, Ri is the radius of curvature of the i-th lens surface from the object side, Di is the thickness and air gap of the i-th lens from the object side, and Ni and νi are the i-th lens surface from the object side, respectively. are the refractive index and Atsube number of the glass.

【table】

【table】

【table】

【table】

【table】

【table】

[Table] Next, the relationship between the above-mentioned conditional expressions and numerical examples is shown.

[Table] In numerical example 1, R1 to R4 are lens group A,
This is a zoom lens consisting of three lens groups: R5 to R6 are lens group B, and R7 to R16 are third lens group C. During normal shooting, lens group A and lens group B are integrated when 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 lens group C fixed, the distance D4 is set from 4.34 mm to 3.0 mm, and the distance D6 is set from 0.5 mm to 4.435 mm.
This is done by changing each continuously up to . Numerical Example 2 is a zoom lens with a four-group configuration, R1 to R6 are lens group A, R7 to R8 are lens group B, R9 to R18 are third lens group C, and R19 to R20 are lens group C. 4th lens group D
During normal shooting, lens group A and lens group B move together during zooming, and the air distance between lens group B and lens group C and between lens group C and lens group D changes to change the magnification. . Lens group D is fixed during zooming. When performing soft focus photography, at the telephoto end of the zoom, the distance between lens groups C and D is fixed by D6.
from 2.16mm to 1.5mm, distance D8 from 0.26mm
Continuously change up to 2.91mm. Numerical Example 3 is a three-group zoom lens with almost the same configuration as Numerical Example 1, but the distance D4 is changed from 6.28 mm to 6.82 mm for soft focus photography.
This is an example in which aberrations are made variable by changing the distance D6 from 2.2 mm to 0.5 mm and bringing lens groups A and B closer together. Numerical Example 4 is a zoom lens with a four-group configuration, R1 to R6 are lens group A, R7 to R8 are lens group B, R9 to R18 are third lens group C,
R19 to R22 are the fourth lens group D, and all four groups move independently to perform zooming for normal shooting, and soft focus is performed at the telephoto end, during which lens group C and lens group D are fixed. has been done. In the embodiments of the present invention, focusing is performed by moving lens groups A and B together to reduce aberration fluctuations, but focusing is performed by moving lens groups A and B at different ratios. It is more preferable to perform so-called floating. It is also possible to perform focusing with the third lens group C or a lens group located further to the image plane side. 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, with a simple configuration in which some lens groups in the lens system are moved,
A zoom lens that provides a good soft focus effect over the entire screen can be achieved.

[Brief explanation of drawings]

Figures 1, 2, and 3 are explanatory diagrams of the optical system when obtaining the soft focus effect of the present invention, and Figures 4 and 5 are illustrations of the optical system when obtaining the soft focus effect of the present invention, respectively. An explanatory diagram of the lens surface, Fig. 6,
FIG. 7, FIG. 8, and FIG. 9 are lens sectional views of numerical examples 1 to 4 of the present invention, FIG. 10, FIG. 11,
Figures 12 and 13 are numerical example 1 of the present invention, respectively.
It is a diagram of various aberrations of ~4. In the figure, A, B, and C are various aberration diagrams at the wide-angle end, telephoto end, and soft focus, S is the sagittal image plane, M is the meridional image plane, d is the d-line,
g indicates the g-line, SC indicates the sine condition, and arrows in FIGS. 6 to 9 indicate the moving direction of the lens group when performing magnification change and soft focus photography.

Claims (1)

[Claims] 1. In a zoom lens having at least two lens groups, lens group A and lens group B, the lens surface R 1R of the lens group A closest to the image plane and the lens surface R _1R of the lens group B closest to the object side Both lens surfaces R _{and 2F} are composed of lenses with convex surfaces facing the object side, and the lens group A
The lens group A and the lens group B are moved at different ratios so that the image point position of the composite system of the lens group A and the lens group B becomes a constant position, and the aberration is made variable, and the radius of curvature of the lens surface _R1R is , the lens surface
The refractive power of the medium on the object side of R _1R is NA, the radius of curvature of the lens surface R _2F is RB, the refractive index of the medium on the image side of the lens surface R _2F is NB, and it is changed to make the aberration variable. The lens surface R _1R and the lens surface R _2F
When x is the maximum value of the _change in the air spacing of )/RA×RB×x×f _T | < 0.035 A zoom lens having a soft focus function is characterized by satisfying the following condition. 2 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. Place the power lens group C,
2. A zoom lens having a soft focus function according to claim 1, wherein the lens group C is moved together with the lens groups A and B during zooming.