JPS63147125A - Photographic lens with variable optical characteristic - Google Patents

Abstract

PURPOSE:To enable image plane characteristics to be varied optionally by moving three lens groups on an object side among four groups 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 four lens groups, i.e. a 1st lens group I with positive refracting power, a 2nd lens group II with positive refracting power, a 3rd lens group III with negative refracting power, and a 4th lens group IV with positive refracting power in order from the object side. When focusing is changed from an infinite-distance body to a short-distance body, floating is performed by moving the 1st-4th lens groups I-IV so that three air gaps formed by the 1st-4th lens groups I-IV all 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 characteristics are varied mainly and optionally.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a three-lens lens with variable optical properties suitable for photographic cameras, video cameras, etc. On the other hand, there is a variable optical characteristic 1 that uses floating, which performs good aberration correction when focusing, and can also change the optical characteristics, mainly the image plane characteristics, when focusing on a close object. This relates to the darkest lens.

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

In addition, Japanese Patent Application Laid-Open No. 137445/1983 proposes a photographic lens whose 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, making it difficult to blur the background and make only the petals and flower core stand out. It's coming.

Recently, macro lenses designed to mainly photograph close objects have a large aperture ratio.

However, if the aperture is narrowed down, the performance of a macro lens with a large aperture ratio cannot be fully demonstrated.

(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) In order from the object side, the first lens group has a positive refractive power, the second lens group also has a positive refractive power, the third lens group has a negative refractive power, and the third lens group has a positive refractive power. It has four lens groups, and when focusing from an object at infinity to an object at a short distance, the second,
The first, second, and third lens groups are moved toward the object side so as to increase the two air gaps formed by the third and fourth lens groups, and are focused on a close object. When the lenses are aligned, only the third lens group is moved along the optical axis to change the optical characteristics.

Other features of the invention are described in the Examples.

(Example) FIGS. 1A and 1B are cross-sectional views of a lens according to Numerical Example 1 of the present invention. In the figure (A) is an object at infinity, (B)
is when focusing on a close object. I in the diagram
, n, m are positive, positive and negative refractive powers in order. Second.
The third lens group (■) is a fourth lens group with positive refractive power.

Further, the arrows indicate the direction of movement 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 arranged, and behind it a third lens group with a negative refractive power and a fourth lens group with a positive refractive power are arranged, and the photographing lens is composed of four lens groups as a whole. In particular, by arranging the 'fJ3 lens group with negative refractive power, the degree of freedom in refractive power arrangement of the two lens groups with positive refractive power placed on the object side is increased, and various aberrations can be corrected effectively in the standard state. I'm going to Furthermore, by increasing the positive refractive power of the two lens groups as a whole, the overall amount of movement of the three lens groups during focusing is reduced, and the overall length of the lens is shortened.

When focusing from an object at infinity to an object at a short distance, the 2nd, 3rd and 4th lens groups form +129+-1
It uses so-called floating, which moves the three lens groups r, n, and m on the knitting body side independently toward the object side.

As a result, compared to the case where two or three lens groups are simply moved and floated, aberration fluctuations due to changes in imaging magnification can be further reduced, and it can be used for a wide range of objects from infinity to close objects. On the other hand, it is 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.

Furthermore, by providing the fourth lens group with positive refractive power, the first lens group. Second. The degree of freedom in the refractive power of the third lens group is increased, and the third
The refractive power of the lens group is strengthened, the amount of extension of the lens group is reduced, and fluctuations in chromatic aberration of magnification caused by movement of the third lens group are reduced.

Then, as shown in FIG. 1(B), when focusing on a short distance object, the third lens group with negative refractive power is moved along the optical axis using the air gap obtained by floating, thereby improving optical characteristics. In particular, the image plane characteristics can be easily changed.

For example, by moving the third lens group toward the object side P so that the height of incidence of the light beam on the third lens group is lowered, the image plane characteristics are shifted to the image plane (lit). It is possible to clearly photograph a convex object surface such as a bud with a small aperture amount.The aberration diagrams in Numerical Example 1.2 at this time are shown in Fig. 2 (C) and Fig. 3 (C). Shown below.

On the other hand, the third lens group is moved in the direction of the image plane flIQ 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 concave object surfaces, from the petals to the core of a flower, even though the amount of aperture is small.

The aberration diagram in Numerical Example 1.2 at this time is shown in Figure 2 (
D), as shown in FIG. 3(D).

In this embodiment, the diaphragm is placed between the zi lens group and the second lens group, and by moving it together with the second lens group, the height of incidence of the axial light flux into the fourth lens group is adjusted to the point at which the axial light beam enters the fourth lens group. It is preferable to make a large change for close objects in order to reduce fluctuations in aberrations caused by changes in imaging magnification.

In addition, in order to properly correct various aberrations of the entire screen in this embodiment, in order from the object side, the first lens group is made up of three lenses: a positive lens, a meniscus-shaped positive lens, and a negative lens, and the second lens group is made of a negative lens. A bonded lens of a lens and a positive lens, two groups of three elements of positive lenses, a third lens group consisting of a negative meniscus lens with a convex surface facing the object side, and a fourth lens group consisting of at least one positive lens. It's good.

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

Numerical Example I F=51. OFNO= 1 : 2.55 2ω=
46.0°RI= 210.99 DI=
2.20 N 1=1.72000 ν1=
50.2R2=-81,05D2=0.15
R3=22.28 D3=2.85
N2=1.78590 ν2=44.2R4=
64.33 D4=0.99R5=-:
165.00 D 5= 1.46 N 3
=1.60342 ν3=38. OR6=17.
7:l D 6= (variable) R7= (aperture)
D7=3.00R8=-15,38D
8 = 2.52 N 4 = 1.68893
ν4=31. IRQ=-192,63D 9=3
．． 50 N 5=1.7+300 ν5=53.
8RIQ=-19,80DI(1=I),+5
R11= 230.27 D11= 2.98
86=1.77250 Shiro=49.6R+2=
-38,91DI2= (variable) R13=98
．． 78 DI3=1.60, N7=1
．． 5+δ33 Schiff=64. IRI4=33.6
7 DI4= (variable) R15= 57.93
D15=2.50 NO=1.4874
9 ShiB=70.2R16=197.10 Numerical Example 2 F=51. li FNO= l : 2.5 2
ω= 46.0°Rl= -288,51D I=
2.50 N I=1.77250
υ 1=49.6R2= -74,54D2=
0.15R3= 18.34 D3= 3
．． 00 N 2 = 1.78590 ν2 = 44.
2R4=57.45D4=0.47R
5= 98.65 D 5= 1.60
N 3=1.63636 υ3=35.4R6=
15.16 D 6= (Variable) R7= (Aperture) D7= 5.00R8= -13,42D
8= 2.50 N4=1.68893 υ4
=31. IRQ=-78, 13D9=3.50
N5=1.77500 υ5=52.3R11
)= −17,46DIO= 0.15RIl=
313.32 D11= 3.00 N
S=1.77250 υ6=49.6RI2= −
53,890] 2= (variable) R13= 84.50
D13=1.60 N7=1.516
:l:] υ7=64. IRI4=39.34
DI4= (variable) RI5= 137.63
DI5=3.00 N8=1.48749
B=70.2R16=-190,90 (Effects of the Invention) According to the present invention, the JHfly lens is composed of four lens groups, of which the three lens groups on the object side satisfy the predetermined conditions as described above. By moving it so that By moving the lens along the optical axis, it is possible to achieve a photographing lens with variable optical characteristics that can arbitrarily change the image plane characteristics.

[Brief explanation of the drawing]

Figures 1 (A) and (B) are cross-sectional views of the lens of Numerical Example 1 of the present invention, Figures 2 (A) to (O), and Figures 3 (A) to (D).
are various aberration diagrams of Numerical Examples 1.2 of the present invention, respectively. In the cross-sectional views of the lens, (A) and (B) show when focusing on an object at infinity and an object at a short distance, respectively. Matako,
■, ■, ■ are the first, second, third, and fourth 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 diagram (A) is an object at infinity, and (B) is an aberration diagram when the wL shadow magnification is 11x.
(C) and (D) are aberration diagrams when the third lens group is moved toward the object side and the image plane side, respectively, for a close object, and Y is the image height. Patent Applicant: Canon Co., Ltd. Higashi 1 Sono (A'1 7-Dai- 2 times (C) Ishi 3 Kuchi (A) Ryo 3 side ([11) 3rd time (C) Kabuto 3 times (D) Procedure City official letter (spontaneous) July 9, 1988 Commissioner of the Patent Office Mr. 2 Name of the invention Photographic lens with variable optical characteristics 3 Relationship to the case of person making corrections Patent applicant address 3-30 Shimomaruko, Ota-ku, Tokyo -2 name (+00
) Canon Co., Ltd. Representative Kaku Nshi 3 Division 4, Agent Address 301 Helheim Jiyugaoka, 2-17-3 Okusawa, Setagaya-ku, Tokyo 158 (Telephone: 8-5614) (2)
(() From line 8 to line 9 on page 4 of the specification)
"Two formed by the second, third, and fourth lens groups" is corrected to "three formed by the 1st, 2nd, 3rd, and 7B4 lens groups." (b) From the 19th line to the 20th line of page 5 of Specification V, "two formed by the 2.3.4 lens group" is replaced with "the 1st degree formed by the 2.3.4 lens group". The three
and correct it. Claims (1) In order from the object side, a lens group with positive refractive power, a second lens group with positive refractive power, a third lens group with negative refractive power, and a fourth lens group with positive refractive power. It has four lens groups, and when focusing from an object at infinity to a close object,
1st. Second. The first... Second.
A patent shadow characterized in that the third lens group is moved toward the object side to perform floating, and when focusing is not performed on a close object, only the third lens group is moved on the optical axis to change the optical characteristics. lens.

Claims (1)

[Claims] (1) In order from the object side, the first lens group has a positive refractive power, the second lens group also has a positive refractive power, the third lens group has a negative refractive power, and the fourth lens group has a positive refractive power. The first and second lens groups have a lens group, and when focusing from an object at infinity to an object at a close distance, the first and second lens groups are arranged such that two air gaps formed by the second, third, and fourth lens groups all increase. 2. 3rd
Floating is performed by moving the lens group toward the object side.
A photographing lens with variable optical characteristics, characterized in that when focusing on a close object, only the third lens group is moved on the optical axis to change the optical characteristics.