JPH0711628B2 - Shooting system with soft focus function - Google Patents

Description

The present invention relates to a photographing system having a soft focus function suitable for a photographic camera, a video camera, etc., and particularly to moving a part of a lens group of the photographing system. The present invention mainly relates to an image pickup system having a soft focus function in which spherical aberration is changed to produce a soft effect.

(Prior Art) Various imaging systems have been proposed in which an image having a soft effect, which is an image that feels softer than before, is obtained. The soft effect is obtained optically by intentionally generating a certain aberration, mainly a spherical aberration of a certain shape. For example, an image pickup system having a soft focus function that variously changes the spherical aberration amount to obtain an arbitrary soft effect is disclosed in JP-A-52-76921, JP-B-58-1402, and JP-A-55-52013. It is proposed in Japanese Patent Publication.

Of these, in Japanese Patent Laid-Open No. 52-76921, an air gap is provided which is sandwiched by two lens surfaces having concave surfaces facing the position where the principal ray at the time of opening intersects the optical axis, and two lens groups sandwiching this air gap are provided. The soft effect is obtained by moving the optical axis at different speeds. And focusing is performed by extending the entire lens system. This method requires an air gap that is unnecessary for maintaining normal shooting performance and a lens group for obtaining a soft effect, and the same lens group is moved at different speeds for focusing and for obtaining a soft effect. Therefore, the lens system and the lens barrel tend to have an extremely complicated structure.

In Japanese Patent Publication No. 58-1402, a soft effect is obtained by moving an optical member having a refractive power in the direction of the optical axis as the central portion is a parallel plane having no refractive power toward the peripheral portion. In this method, in order to obtain a soft effect, it is necessary to newly provide an optical member which is unnecessary for normal photographing.

In JP-A-55-52013, the soft effect is obtained by changing the distance between the front lens group having a positive refractive power and the rear lens group having a negative refractive power to obtain a soft effect, and focusing is performed by moving the entire lens system. Is going. This method tends to complicate the lens barrel structure for moving the lens group.

(Problems to be Solved by the Invention) The present invention is a lens barrel structure in which a part of lens groups in normal photographing is simply moved on the optical axis by appropriately setting a lens configuration to efficiently obtain a soft effect. The purpose of the present invention is to provide a photographing system having a soft focus function that simplifies the above.

(Means for Solving Problems) A first lens group having a positive refractive power in order from the object side, a second lens group having a meniscus lens having a convex surface facing the object side, an aperture stop, and a third lens group. And moving the second lens group on the optical axis to produce a soft effect, moving at least a part of the third lens group to perform focusing, and change the focal length of the second lens group. f2, where f is the focal length of the entire system, the condition is -0.1 <f / f2 <0.1 (1).

Besides, the features of the present invention are described in the embodiments.

(Example) FIG. 1 is a lens cross-sectional view of Numerical Example 1 of the present invention.
In the figure, L1, L2, and L3 are the first, second, and third lens groups, respectively.

In this embodiment, the second lens group is composed of a single meniscus lens A having a convex surface facing the object side, and this lens A is moved on the optical axis to obtain a soft effect. Further, the third lens group is composed of two lens groups L3-1 and L3-2 having negative and positive refracting powers, of which the lens group L3-1 having negative refracting power in the front is moved to the image plane side. Focus.

In this embodiment, the refractive power of the first lens group is positive, the total refractive power of the second lens group and the third lens group is negative, and the overall photographing system is of a telephoto type, thereby shortening the total lens length. I am trying to The so-called rear focus, which is performed by moving the compact and lightweight lens group III-1 having a negative refractive power in the third lens group, enables quick focusing. The second lens group is composed of a single meniscus lens having a convex surface directed toward the object side, thereby reducing the amount of aberration variation when the lens group L3-1 is moved to perform focusing.

Further, in this embodiment, the on-axis light flux emitted from the first lens group is in a convergent state. Therefore, to obtain the soft effect, the second
When the lens group has a negative refractive power, it is moved to the image plane side to obtain uncorrected spherical aberration, or moved to the object side to obtain overcorrected spherical aberration. When the second lens group has a positive refracting power, the movement of the second lens group causes spherical aberration in the opposite direction to that described above. Therefore, the second lens group is moved in the respective directions to obtain an arbitrary spherical aberration amount. ing.

Numerical examples to be described later disclose that spherical aberration is changed in both an undercorrection direction and an overcorrection direction.

In this embodiment, the lens A of the second lens group has a meniscus shape with a convex surface facing the object side, and an aperture stop is arranged behind the second lens group so that the spherical center of the lens A faces the aperture stop side. There is. As a result, the on-axis light beam is largely refracted and the off-axis light beam is not refracted so much that the lens A is moved by utilizing the difference in height from the optical axis of the on-axis light beam to obtain a soft effect. The amount of various aberrations other than the aberration is reduced.

As described above, in this embodiment, in order to obtain the soft effect, the special lens group is not arranged and a part of the lens groups in the normal photographing is moved to obtain the soft effect. Then, the focusing lens group and the lens group for obtaining the soft effect are separated to prevent the lens barrel structure from becoming complicated.

Then, the focal length of the second lens group is made to satisfy the conditional expression (1), whereby the soft effect is efficiently obtained.

Conditional expression (1) is for reducing fluctuations of aberrations other than spherical aberrations when moving the second lens group on the optical axis, and favorably correcting fluctuations of aberrations when rear focus is adopted. If the refractive power of the second lens group deviates from the conditional expression (1) and becomes too strong or too weak, astigmatism, coma aberration, distortion other than spherical aberration when moving the second lens group to obtain a soft effect, and distortion. This is not preferable because the amount of fluctuation of various aberrations such as the above becomes large.

In the present embodiment, at least one lens surface in the second lens group is preferably provided with an aspherical surface having a shape in which the refractive power gradually becomes stronger or weaker toward the lens peripheral portion. According to this, it is possible to extremely easily obtain an arbitrary soft effect that largely affects only spherical aberration and hardly affects other various aberrations.

In this embodiment, the refractive power of the second lens group is expressed by the conditional expression (1).
If it satisfies, it may be positive or negative, but in the numerical examples described later, it has a negative refracting power, and in particular, it is set within the range of -0.1 <f / f2 <0 to obtain a soft effect efficiently with a small moving amount. ing.

In the present embodiment, in order to satisfactorily correct various aberrations of the entire screen and further satisfactorily correct aberration fluctuations during focusing, the first lens group is composed of two lenses whose both lens surfaces are convex and both lens surfaces are concave. 3 lenses of the lens of
It is preferable that the lens unit L3-1 of the lens unit be composed of a cemented lens in which positive and negative lenses are cemented together.

The second lens group may be composed of a plurality of lenses including a positive lens or a negative lens. At this time, the first lens surface and the final lens surface of this group have a convex shape on the object side. Just go.

Next, numerical examples of the present invention will be shown. Ri in the numerical examples
Is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air gap from the object side, Ni and νi
Are the refractive index and Abbe number of the glass of the i-th lens in order from the object side.

(Effects of the Invention) According to the present invention, by appropriately specifying the lens configuration, it is possible to efficiently obtain a soft effect by moving a part of the lens groups in normal shooting without disposing a special lens group. By configuring it separately from the focusing lens group, it is possible to achieve a photographic system having a soft focus function that simplifies the lens barrel structure.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of Numerical Embodiment 1 of the present invention, FIG. 2 is a diagram showing various aberrations of Numerical Embodiment 1 of the present invention during normal shooting, and FIG.
The figure is a diagram showing various types of aberration during soft focusing in Numerical Example 1 of the present invention. In the figure, L1, L2, and L3 are respectively the first, second, and third lens groups, arrow SF is the moving direction during soft focus, and arrow F is the moving direction during focus during normal shooting.

Claims (1)

[Claims] 1. A first lens group having a positive refractive power in order from the object side, a second lens group having a meniscus lens having a convex surface facing the object side, an aperture stop and a third lens group, A soft effect is generated by moving the two lens groups on the optical axis, and at least a part of the third lens group is moved for focusing, and the focal length of the second lens group is f2, An imaging system with a soft focus function, which satisfies the condition of -0.1 <f / f2 <0.1, where f is the focal length.