JPH0750243B2 - Shooting lens with variable optical characteristics - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photographic lens with variable optical characteristics suitable for a photographic camera, a video camera, etc., and particularly for a wide range of objects from infinity objects to short-distance objects. Taking a lens with variable optical characteristics that makes it possible to change the optical characteristics when focusing on a short-distance object, mainly the image plane characteristics, by using the floating that has performed good aberration correction during focusing It is about.

(Prior Art) Conventionally, for example, Japanese Utility Model Application Laid-Open No. 48-2823 proposes a photographing lens in which a part of lens groups of a lens system is moved to change optical characteristics, mainly image plane characteristics. In the publication, in a retrofocus wide-angle lens, a floating mechanism is used to manually move a predetermined lens group to make the image plane characteristic variable.

In addition, Japanese Patent Application Laid-Open No. 52-37445 proposes a photographing lens in which a lens group different from the floating mechanism is moved to make the image plane characteristic variable. As described above, various photographing lenses have been proposed in which a part of the lens group of the lens system is moved in order to freely control the image plane characteristic in photographing a normal distance object.

Generally, a short-distance object has a higher photographing magnification than an infinite object, and the depth of field becomes extremely shallow. For example, when shooting a flower at a high magnification, it is necessary to narrow down the aperture in order to clearly capture the petals and cores. For example, it is difficult to shoot with the background blurred and only the petals and cores stand out. .

Further, a macro lens designed to mainly shoot a short-distance object recently has a large aperture ratio. However, in order to increase the depth of field, there is a problem in that the aperture must be narrowed to take a picture, and the performance of a macro lens having a large aperture ratio cannot be fully exhibited.

(Problems to be Solved by the Invention) The present invention satisfactorily corrects aberration fluctuations when focusing is performed on a wide range of objects from infinity objects to short-distance objects and shooting magnifications near unity magnification. Providing a photographic lens with variable optical characteristics that uses a part of the lens group of the photographic lens that uses floating and can reduce the amount of narrowing down especially when shooting a short-distance object, and can arbitrarily change the optical characteristics, mainly the image plane characteristics With the goal.

(Means for Solving the Problems) The first lens group having a positive refractive power, the second lens group having a positive refractive power, and the third lens group having a positive refractive power are arranged in this order from the object side. When focusing from a distant object to a near object, it is formed by two adjacent lens groups.
When the first, second, and third lens groups are moved toward the object side so as to increase the distance between the two airs to float, and when focusing on a short-distance object, only the third lens group is illuminated. When the optical characteristics are changed by axial movement and the focal lengths of the third lens group and the whole system are f ₃ and f, respectively, 2 × 10 ³ · f <| f ₃ | Is to be satisfied.

(Example) FIGS. 1 (A) and (B) and FIGS. 2 (A) and (B) are lens cross-sectional views of Numerical Examples 1 and 2 of the present invention, respectively. In the figure, (A) is an object at infinity, and (B) is an object at a short distance. In the figure, I, II, and III are the first, second, and third lens groups having positive, positive, and positive or negative refractive power in order. Further, the arrows indicate the moving directions of the respective lens groups when focusing from an object at infinity to a near object.

In this embodiment, as described above, the two first and second lens groups having positive refracting power are arranged on the object side, and the third lens group having very small positive or negative refracting power is arranged behind them. 3 as a whole
A shooting lens is composed of three lens groups.

When focusing from an object at infinity to a near object, the three lens groups I, II, and III on the object side are set so that the two air spaces formed by the two adjacent lens groups both increase. So-called floating, which moves independently to the object side, is used.

As a result, compared with the case where two lens groups or three lens groups are simply moved to perform floating, aberration fluctuations due to changes in shooting magnification are further reduced, and a wide range of objects from infinity objects to short-distance objects are obtained. On the other hand, good aberration correction is possible.

In particular, it is possible to perform good aberration correction on a wide range of objects up to the same-size shooting.

Then, as shown in FIGS. 1 (B) and 2 (B), by moving the third lens group, which has a very small refractive power when focusing on a short-distance object, on the optical axis, especially the optical characteristics The characteristics are changing.

For example, the image plane characteristic is tilted toward the image plane side by moving the third lens group in the object side P direction so that the incident height of the light flux on the third lens group becomes low. This makes it possible to clearly capture a convex object surface such as a snail or a bud as the object to be photographed with a small amount of aperture. Aberration diagrams in Numerical Examples 1 and 2 at this time are shown in FIGS. 3 (D) and 4 (D).

On the contrary, the third lens group is moved in the Q direction on the image plane side so that the height of incidence of the light beam on the third lens group becomes high, so that the image plane characteristic is tilted toward the object side.

This makes it possible to clearly capture an image of a convex object surface on the object side, for example, from the flower petals to the flower core, despite the small amount of narrowing down.

Aberration diagrams in Numerical Examples 1 and 2 at this time are shown in FIGS. 3 (C) and 4 (C).

Further, in the present invention, the absolute value of the refractive power of the third lens group is configured to be as small as possible, whereby the change of the focal length and the change of the bit movement when the third lens group is moved are allowed, Moreover, it is characterized in that only the image plane characteristic is changed in a state in which changes in spherical aberration and coma are reduced.

In particular, in the present invention, the focal lengths of the third lens group and the entire system are made to satisfy the above-mentioned conditional expression (1). | F ₃ | / corresponding to conditional expression (1) in Numerical Examples 1 and 2 described later
f is 10982 and 68429, respectively.

If conditional expression (1) is exceeded and the refractive power of the third lens group becomes too strong, fluctuations in the focal length and the bin position of the entire system when the third lens group is moved become large, and other than the image surface characteristics. This is not good because the fluctuations in various aberrations will increase.

In the present embodiment, the third lens group is configured to have a negative meniscus lens having a convex surface directed toward the object side and a positive lens to reduce aberration fluctuation during floating and to move the third lens group to form an image. This is preferable because variations of other aberrations when changing the surface characteristics are reduced.

In order to satisfactorily correct various aberrations of the entire screen in the present embodiment, the first lens group is composed of three lenses, a positive lens, a meniscus-shaped positive lens and a negative lens, in order from the object side.
It is preferable that the second lens unit is composed of a cemented lens of a negative lens and a positive lens, and a positive lens with two lenses and three lenses.

Next, numerical examples of the present invention will be shown. In the numerical example, Ri is the radius of curvature of the i-th lens surface 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 from the object side, respectively.

(Effect of the Invention) According to the present invention, the taking lens is composed of three lens groups, and these three lens groups are moved so as to satisfy the predetermined condition as described above, thereby changing from an infinite object to a short-distance object. Image plane characteristics can be arbitrarily changed by performing high-performance floating with excellent correction of aberration fluctuations when focusing on a wide range of objects, and further by moving the third lens group on the optical axis. A photographic lens with variable optical characteristics can be achieved.

[Brief description of drawings]

FIGS. 1 (A) and (B), FIGS. 2 (A) and (B) are lens cross-sectional views of Numerical Embodiments 1 and 2 of the present invention, and FIG. 3 (A), respectively.
(D) and FIGS. 4 (A) to (D) are aberration diagrams of Numerical Examples 1 and 2 of the present invention, respectively. In the lens cross-sectional views, (A) and (B) show the case where focusing is performed on an object at infinity and an object at a short distance, respectively. I, II, and III are the first and
The second and third lens groups, arrows indicate the moving directions of the respective lens groups when focusing from an object at infinity to a near object, and in the aberration diagrams, (A) shows an object at infinity, and (B) shows a photographing magnification of −. 0.
Aberration diagrams (C) and (D) at 6 × are aberration diagrams when the third lens group is moved to the image plane side and the object side in a short-distance object, respectively, and Y is an image height.

Claims (1)

[Claims] 1. A first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power in order from the object side. When focusing on an object, the first, second, and third lens groups are moved toward the object side to float so that the distance between two air formed by two adjacent lens groups increases. And when focusing on a short-distance object, only the third lens group is moved along the optical axis to change the optical characteristics, and the focal lengths of the third lens group and the entire system are f ₃ and f, respectively. , 2 × 10 ³ · f <| f ₃ |, which is a photographic lens with variable optical characteristics.