JPS63147126A - Photographic lens with variable optical characteristic - Google Patents

Abstract

PURPOSE:To vary image plane characteristics optionally by composing a photographic lens of three lens groups, moving those under specific conditions for high-performance floating while aberrational variation is compensated excellently, and moving a 3rd lens group on an optical axis. CONSTITUTION:This photographic lens has three lens groups, i.e. a 1st lens group I with positive refracting power, a 2nd lens group II with positive refracting power, nd a 3rd lens group III. When focusing is changed from an infinite- distance body to a short-distance body, floating is performed by moving the 1st-3rd lens groups I-III so that two air gaps formed by both of two adjacent groups increase. Then, when the short-distance body is put in focus, only the 3rd lens group III is moved on the optical axis to vary optical characteristics. Consequently, a stopping-down quantity is reduced at the time of, specially, short-distance photography and image plane charcteristics are varied mainly and optionally.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a photographic lens with variable optical characteristics suitable for photographic cameras, video cameras, etc. A photographic lens with variable optical properties that uses floating to properly correct aberrations when focusing, and allows the optical properties, mainly the image surface properties, to be varied when focusing on objects at close range. It is related to.

(Prior Art) A photographing lens in which optical characteristics, mainly image surface characteristics, can be varied by moving some lens groups of a lens system has been proposed, for example, in Japanese Utility Model Application Publication No. 48-2823. In this publication, a floating mechanism is used in a retrofocus type wide-angle lens to manually move a predetermined lens group to vary the image surface characteristics.

In addition, Japanese Patent Laid-Open No. 52-37445 proposes a photographing lens in which the image plane characteristics are variable by moving a lens group other than the floating mechanism. In this way, various photographic lenses have been proposed in which some lens groups of the lens system are moved in order to freely control the image plane characteristics when photographing objects at normal distances.

Generally, for a close object, the photographing magnification is higher than for an object at an infinite distance, and the depth of field becomes extremely shallow. For example, when photographing flowers at high magnification, it is necessary to narrow down the aperture to clearly photograph the petals and flower core. For example, it is difficult to blur the background and make only the petals and flower core stand out. .

Furthermore, recent macro lenses designed to mainly photograph objects at close range have a large aperture ratio. However, in order to increase the depth of field, it is necessary to take pictures with the aperture narrowed down, resulting in problems such as the inability to fully utilize the performance of a macro lens having a large aperture ratio.

(Problems to be Solved by the Invention) The present invention successfully corrects aberration fluctuations when focusing on a wide range of objects, from objects at infinity to objects at short distances, and whose imaging magnification is close to 1x. To provide a photographic lens with variable optical characteristics, which uses a part of the lens group of the photographic lens that utilizes floating to reduce the amount of aperture, especially when photographing a close object, and can arbitrarily change the optical characteristics, mainly the image surface characteristics. With the goal.

(Means for solving the problem) It has three lens groups: a first lens group with positive refractive power, a second lens group also with positive refractive power, and a third lens group, in order from the object side. When focusing from a far object to a near object, the two lens groups formed by two adjacent lens groups
said first and second air spacings increase.
, when the third lens group is moved to the object side to perform floating and focused on a short distance object, the third lens group
The optical characteristics are changed by moving only the lens group on the optical axis.

(Example) FIGS. 1A and 1B and FIGS. 2A and 2B are cross-sectional views of lenses of Numerical Example 1.2 of the present invention.

In the figure, (A) shows an object at infinity, and (B) shows a case when focusing is performed on an object at a short distance. In the figure, I, rl, and III are positive, positive, and 1st. 2nd゜3rd
This is a lens group. Further, arrows indicate the moving direction of each lens group when focusing from an object at infinity to an object at a short distance.

In this embodiment, as described above, there are two first lenses with positive refractive power on the object side. A second lens group is disposed, and a third lens group having a very small positive or negative refractive power is disposed behind it, and the three lens groups constitute a photographing lens as a whole.

When focusing from an object at infinity to an object at a short distance, the three lens groups I, II, and m on the object side are adjusted so that the two air gaps formed by the two adjacent lens groups increase. So-called floating is used to move each object independently toward the object.

This further reduces aberration fluctuations caused by changes in imaging magnification, compared to when two or three lens groups are simply moved and floated, allowing a wide range of objects from infinity to close objects to be captured. This makes it possible to perform good aberration correction.

In particular, it enables excellent aberration correction for a wide range of objects that can be photographed at 1:1 magnification. “As shown in Figure 1 (B) and Figure 2 (B), when focusing on a short-distance object, by moving the third lens group, which has very small refractive power, along the optical axis, the optical characteristics, especially the image It changes the surface characteristics.

For example, the third lens group is moved toward the object side P so that the height of incidence of the light beam on the third lens group is lowered, thereby tilting the image plane characteristics toward the image plane side. This makes it possible to clearly photograph convex object surfaces such as overlapping objects or buds with a small amount of aperture. The aberration diagrams in Numerical Example 1.2 at this time are shown in Fig. 3 (D) and Fig. 4 (
Shown in D).

Conversely, the third lens group is moved in the Q direction toward the image plane so that the height of incidence of the light beam on the third lens group becomes higher, thereby tilting the image plane characteristics toward the object side.

This makes it possible to clearly photograph an object surface that is convex toward the object, from the petals to the flower core, even though the amount of aperture is small.

The aberration diagram in Numerical Example 1.2 at this time is shown in Figure 3 (
C), as shown in FIG. 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, so that changes in focal length and bit movement when the third lens group is moved can be tolerated. Moreover, it is characterized in that only the image surface characteristics are varied in a state where variations in spherical aberration, coma aberration, etc. are reduced.

In particular, in this embodiment, the focal length of the third lens group and the entire system is set to '!' f3. When f is 2 X 103・f < lf 3
l...-(1) should be satisfied.

If Conditional Expression (1) is not satisfied and the refractive power of the third lens group becomes too strong, the focal length and focus position of the entire system will fluctuate greatly when the third lens group is moved, and furthermore, the changes other than the image plane characteristics will occur. This is not good because the fluctuations in various aberrations will increase.

In this example, the third lens group is configured to have a negative meniscus lens with a convex surface facing the object side and a positive lens to reduce aberration fluctuations during floating, and to move the third lens group to create an image. This is preferable because it reduces fluctuations in other aberrations when changing surface characteristics.

In addition, in this embodiment, in order to properly correct various aberrations of the entire screen, the first lens group is made up of three lenses, in order from the object side: a positive lens, a meniscus-shaped positive lens, and a negative lens.
It would be good if the second lens group was composed of three lenses in two groups: a composite lens consisting of a negative lens and a positive lens, and a positive lens.

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

Numerical Example I F= 49.95 FNO= I: 2.55 2
ω=47°R+= 171.87 DI= 2
．． 31 N+=! , 72000 vl=50.2
R2= -82,41D 2= 0.16R3=
21.67 D 3= 3.00 82=1
．． 78590 ν2=44.2R4=4L91
D4=1.26R5=-2555,
39D 5 = 1.53 N 3 = 1.6034
2 C:1=38. OR6=18.07D
5= R7= (aperture) D7= :1. +5R8=
-15,64D 8= 1.85 N 4=
1.68893 ν4=31. IR9=-300,
0009=5.45 N5=1.7+300
ν5=53.8RIO=-20,540lo=
0.14R11= 396.16 011=
3.14 86=1.77250 υ6=49.
6R12= -42,76D l2= R13= 78.63 D13= 1.68
N 7 = 1.51633 Schiff = 64. lR14
= 42.65 DI4= 1.78R15=
109.14 015= 2.63 N
8=1.48749 C8=70.2R16= −
503,49 Numerical Example 2 F= 49.90 FNO= I: 2.55 2
ω=470R1= 127.75 DI=
2.31 N 1=1.72000 νI=50
．． 2R2= -118,99D 2= (1,16
R3= 21.22 03= 3.00 N
2=1.78590 ν2=44.2R4= 4
2.52 04= 1.14R5= 2597.7
1 D 5 = 1.53 N 3 = 1.60
342 ν3=38. OR[i=+7.78
06= R7= (Aperture) D7= 3.15R8=
-18,08D 8= 1.85 N 4=1
．． 6889:l ν4=3+, IR9=-20(1
, Qo D'! = 5.32 85=1.7
X300 v 5=53.8R10=-20,5
7DlO= 0.14R11= 1020.55
DI+=3.14 N5=1.77250
White = 49.6R12 = -42,64, DI2
= R13= 65.91 DI:]= 1.68
87=1.5+633 υ7=64. lR14=
42.41 D I4= 1.13R15=
101.41 D15= 2.63 88
=1.48749 C8=70.2R16=37
6.44 (Effects of the Invention) According to the present invention, the W1 shadow lens is composed of three lens groups, and by moving these three lens groups so as to satisfy the predetermined conditions as described above, it is possible to move from an object at infinity. High-performance floating that properly corrects aberration fluctuations when focusing on a wide range of objects, including objects at short distances, and by moving the third lens group along the optical axis, the image surface characteristics can be adjusted arbitrarily. It is possible to achieve a photographic lens whose optical characteristics can be changed.

[Brief explanation of the drawing]

Figures 1 (^) and (B), Figures 2 (A) and (B) are cross-sectional views of lenses of numerical example 1.2 of the present invention, and Figure 3 (
A) to (D) and FIGS. 4A to 4D are diagrams of various aberrations of Numerical Example 1.2 of the present invention, respectively. In the cross-sectional views of the lens, (A) and (B) show the cases in which focusing is performed on an object at infinity and an object at a short distance, respectively. Also, ■ and ■ are the first, second, and third lens groups, respectively, and the arrows indicate the movement direction of each lens group when focusing from an object at infinity to a close object.
In the aberration diagrams, (8) is an aberration diagram for an object at infinity, (B) is an aberration diagram when the imaging magnification is -0 and 6x, (C) and (D) are for a close object, with the third lens group on the image plane side. The aberration diagram when moving toward the object side, Y is the image height. Patent applicant Canon Co., Ltd. Kabuto 1 Figure (A) Male Page 1 (B) 111) Kusho-11 Publishing PQ Akira 3rd (A) 3rd (B) 3rd (C) Akira 3 Figure (D) also 4 times (A) Poor 4 Figure (9)

Claims (3)

[Claims] (1) From the object side, the first lens group with positive refractive power, the second lens group with positive refractive power, and the third lens group.
The first lens group has two lens groups, and when focusing from an object at infinity to an object at a short distance, the first lens group
, the second and third lens groups are moved toward the object side to perform floating, and when focusing on a close object, only the third lens group is moved on the optical axis to change the optical characteristics. A photographic lens with variable optical characteristics. (2) The focal length of the third lens group and the entire system is f_3, respectively.
, f, the photographing lens with variable optical characteristics satisfies the following condition: 2×10^3·f<|f_3|. (3) The third lens group includes two lenses, a negative meniscus lens with a convex surface facing the object side and a positive lens. Photographing with variable optical characteristics according to claim 2. lens.