JPS62177510A - Photographing lens utilizing floating - Google Patents

Abstract

PURPOSE:To attain correction excellent in the variation of aberrations by constituting the titled photographing lens of the 1st and 2nd lens groups having positive refractive power, the 3rd lens group having negative refractive power and the 4th lens group having positive refractive power, and at the time of focusing from an infinite object to a near distance object, moving the 1st-3rd lens groups so that respective air intervals are increased. CONSTITUTION:The 1st and 2nd lens groups I, II having positive refractive force are arranged on the object side and the 3rd lens group III having negative power and the 4th lens group IV having positive refractive power are arranged on the back of the lens groups I, II to constitute the photographing lens of four lens groups as a whole. Especially, the arrangement of the 3rd lens group having negative refractive power increases the freedom of arrangement of the refractive power of two lens groups I, II having positive refractive power and attains excellent correction of various aberrations in a reference state. At the time of focusing from the infinite object to the near distance object, so-called floating for moving the lens groups I-III on the object side respectively independently to the object side so that all of three air intervals formed by two adjacent lens groups are increased is utilized. Consequently, excellent correction of aberrations can be attained.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a photographic lens using floating, suitable for photographic cameras, video cameras, etc., and particularly for a wide range of objects ranging from objects at infinity to objects at short distances. The present invention relates to a high-performance photographing lens that uses a floating mechanism to properly correct aberrations during focusing.

(Prior Art) Conventionally, photographic lenses used in photographic cameras, video cameras, etc. whose main purpose is to photograph objects at close range are called macro lenses or micro lenses (hereinafter referred to as "macro lenses").

Macro lenses are designed to provide high optical performance, especially for close objects, compared to other photographic lenses such as standard lenses and telephoto lenses. It is also used for a wide range of objects, from Ichikenwa 14, end h) to objects at infinity.

Generally, when the photographing magnification range of a macro lens is expanded, especially toward higher magnifications, aberration fluctuations occur frequently as the photographing magnification changes, and it becomes difficult to properly correct this.

For example, the imaging magnification is 1/. A macro lens designed based on the image magnification of 115 is expanded towards higher magnification to produce 4K.
If you try to use j++2, spherical aberration, field curvature, and coma aberration will occur significantly.

In addition, if the effective F number of the macro lens is made brighter in order to make focusing easier, aberration fluctuations due to changes in photographic magnification will occur in proportion to the brightness, making it difficult to properly correct for this. .

Methods for correcting aberration fluctuations due to changes in imaging magnification when photographing from an object at infinity to a close object are disclosed in, for example, Japanese Patent Laid-Open No. 48-90520, Japanese Patent Laid-Open No. 7723-1972, and Japanese Patent Laid-open No. 192916-1982. It has been proposed in the Publication No. All of these proposed photographic lenses utilize so-called floating, in which at least two lens groups are moved independently during focusing. however,
In all of these proposed photographic lenses, aberrations are corrected relatively well in close-range MWt shadows with low magnification, but the correction effect is not necessarily sufficient in WL3E with high magnification. For example, at low magnifications, coma aberration is relatively well corrected, but at high magnifications, distortion, chromatic aberration, etc. tend to occur frequently.

(Problems to be Solved by the Invention) The present invention improves aberration fluctuations when focusing on a wide range of objects, from objects at infinity to objects at short distances, especially objects whose J1 shadow magnification is close to equal magnification. The objective is to provide a photographic lens that utilizes high-performance floating with a corrected large aperture ratio.

(Means for solving the problem) In order from the object side, a first lens group with positive refractive power, a second lens group also with positive refractive power, a third lens group with negative refractive power, and a third lens group with positive refractive power. It has four lens groups of a fourth lens group,
When focusing from an object at infinity to an object at a short distance, the first. Second. This is because the third lens group is moved toward the object side.

Other features of the invention are described in the Examples.

(Example) FIGS. 1 and 2 are cross-sectional views of a lens according to a numerical example 1°3 of the present invention. In the figure, I, H, and III indicate positive, positive, and negative refractive powers in order. Second. This is the third lens group, and the fourth lens group has the same 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 third 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 three lens groups I, II, and III on the object side are adjusted so that the three air gaps formed by the two adjacent lens groups increase. So-called floating is used to move each object independently toward the object.

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.

Furthermore, in this embodiment, in order to reduce fluctuations in aberrations due to changes in photographic magnification, it is preferable to satisfy the following conditions.

Said 2nd. The focal length of the third lens group is f2° f3, the focal length of the entire system is f, and the first lens group when focusing from an object at infinity to a close object. It is necessary to satisfy the following conditions when the moving amounts of the 2nd and 3rd lens groups are ffl+, m2, and m3, respectively.

Conditional expression (1) relates to the refractive power of the second lens group, and conditional expression (
2) relates to the refractive power of the third lens group, and is used to appropriately set the amount of edge protrusion of the lens group during focusing.

If the upper limit of conditional expression (1) is exceeded and the refractive power of the second lens group becomes weak, the amount of extension during focusing will increase too much, and if the lower limit is exceeded and the refractive power becomes too strong. Although the amount of extension decreases, fluctuations in aberrations, especially spherical aberrations, increase as the photographic magnification changes.

If the upper limit of conditional expression (2) is exceeded and the negative refractive power of the third lens group becomes too strong, the refractive power of the two lens groups on the object side must be strengthened accordingly, resulting in poor focusing. Although the amount of extension of each lens group at this time is reduced, aberration fluctuations become larger and it becomes difficult to achieve good aberration correction. or,
When the negative refractive power of the third lens group becomes weaker beyond the lower limit, the technical meaning of arranging the third lens group decreases, and the amount of extension of the two lens groups on the object side during focusing becomes smaller. This is not desirable as it increases the number of

Conditional expression (3) relates to the movement ratio of the first lens group to the second lens group, and conditional expression (4) relates to the movement ratio of the second lens group to the third lens group. By appropriately setting the amount of movement of the lens, it is possible to satisfactorily correct aberration fluctuations caused by changes in imaging magnification.

In particular, fluctuations in spherical aberration and extroverted coma that occur with changes in imaging magnification are well corrected.

The first lens group and the second
By increasing the amount of change in the distance between the lens group and the distance between the second and third lens groups, the off-axis light beam enters a higher position in the second lens group and is strongly refracted, thereby redirecting it inward. It corrects the outward coma aberration that occurs when focusing on a close object.

On the other hand, the glaze light flux diverges strongly between the first and second lens groups when the object distance becomes short, so if the movement ratio of each lens group is too large, spherical aberration will be insufficiently corrected. come. Therefore, in this embodiment, conditional expression (3), (
By setting as in 4), comatic aberration and spherical aberration are corrected in a well-balanced manner.

If the distance between the first lens group and the second lens group increases too much beyond the upper limit of conditional expression (3), the extroverted coma is well corrected, but the spherical aberration becomes insufficiently corrected. Further, unless the lower limit is exceeded and the distance between the first lens group and the second lens group is increased by a certain amount or more, the correction of extroverted coma becomes insufficient.

If the upper limit of conditional expression (4) is exceeded and the distance between the second lens group and the third lens group is not increased by a certain amount or more, the correction of coma aberration will be insufficient, and if the lower limit is exceeded and the distance between the second lens group If the distance between the lens group and the third lens group increases too much, the focal length of the entire system will change to a shorter one, and the amount of extension of each lens group will become smaller, or it will be difficult to correct aberrations, which will further shorten the shooting distance, which is preferable. do not have.

In this example, the diaphragm is placed between the first lens group and the second lens group, and by moving it together with the second lens group, the height of incidence of the light beam on the glaze into the fourth lens group can be adjusted to infinity. It is preferable to make large changes for distant objects and close objects in order to reduce aberration fluctuations caused by changes in imaging magnification.

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.
The second lens group is a composite lens of a negative lens and a positive lens, and the positive lens is a two-group three-element lens, the third lens group is a meniscus-shaped negative lens, and the fourth lens group is at least one
It is best to use 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 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 ν! are the refractive index and Atsube number of the first glass from the object side, respectively.

Numerical Example I F251. OFNO=I: 2.55 2ω=4
6.0°Rl= 246.54 DI= 2
．． 20 N ]=1.72000 υ1=50.
2R2= -81,01D 2= 0.15R3=
22.17 D 3= 2.85 N
2=1.711590 ν2=44.2R4=5
8.52 D4= 0.99R5= -602
, 47D 5 = 1.46 N 3 = 1.60
342 ν3=313. OR6=18.25
D 6= (variable) R7= (aperture) D
7=3.00R8=-15,:IIID
8 = 2.52 N 4 = 1.68893
υ4=:l], IR9= −139,71D 9=
3.50 N 5=1.71300 υ5=53
．． 8RIO=-19,65DIO=0.15R
11=3:IO,52D11=2.98
N 6=1.77250 Shiro=49.6R12=
-39,86D12= (variable) RI3= 47.
67 013 = 1.60 N 7 = 1.51
633 Schiff=64. lR14=32. +10
DI4= (variable) R15= 325.73
DI5=1.80 N8=1.48749
Z/8=70.2R16=-768,13 Numerical Example 2 F= 51.6 FNO= l: 2.55 2ω
= 45.50RI= 25:1.43 DI=
2.20 N1=1.72000 vl=5
0.2R2=-82,08D 2=0.15R
3= 22.17 D3= 2.85 N
2=1.78590 ν2=44.2R4= 59
．． 58 D4=0.99R5=-612
,18D 5=1.4fi N3=1.60
342 v 3=38. OR6=18.19
D 6= (variable) R7= (aperture) D
7= 3.00RIO= -19,620IO=
0.15RI+= 352.18 Dll=
2.98 N6-1.77250 Shiro=49
．． 6R12= -39,98DI2= (Variable) Numerical Example 3 F= 51. OFNO=I: 2.55 2ω=
46.0°Rl= 210.99 DI=
2.20 N 1=1.72000 ν1=50
．． 2R2= -old, 05 D 2= 0.15
R3= 22.26 03= 2.85 N
2=1.78590 ν2=44.2R4=6
4.33 D4= 0.99R5= -365
,00D 5= 1.46 N 3=1.603
42 ν3=38.0R6= 17.73 D
6= (Variable) R7= (Aperture) D 7=
:1.00R8=-15,38D8=2.
52 N4=1.68893 υ4=31. IR
9=-192.63 D9= 3.50 N
5=1.71300 ν5=53.8R10= −
19,80D lo= 0.15R11= 230
．． 27 D11=2.98 N6=1.
77250 Shiro=49.6RI2=-38,9
1DI2= (variable) R13= 98.76 D
I3=1.60 N7=1.516:13
Schiff = 64. IRI4= 33.67 DI4
= (variable) R15= 57.93 DI5=
2.50 N 8=1.48749 C8=7
0.2R16=197.10 (Effects of the Invention) According to the present invention, the photographing lens is composed of four lens groups, and among these, the three lens groups on the object side are moved so as to satisfy the predetermined conditions as described above. By doing so, it is possible to achieve a high-performance photographing lens using floating that satisfactorily corrects aberration fluctuations when focusing on a wide range of objects, from objects at infinity to objects at short distances.

[Brief explanation of drawings]

FIGS. 1 and 2 are cross-sectional views of the lens of Numerical Example 1.3 of the present invention, and FIG. 3. 4th. FIG. 5 is a diagram showing various aberrations of numerical examples 1, 2.3 of the present invention, respectively. In the cross-sectional view of the lens, 1. Second. Third. The fourth lens group, the arrows indicate the movement direction of each lens group when focusing from an object at infinity to a close object, and in the aberration diagram, (A) is for an object at infinity, and (B) is for an object at an imaging magnification of 11x. , and Y is the image height. Heart 10 Aya 2 Figure Ball Tooth Kuizaka Non, White, Shuki Zeng Shiura 4 Li Rinshami Throwing Barley 4th Figure

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 third lens group has a positive refractive power. The first lens has four lens groups, and when focusing from an object at infinity to an object at a close distance, the three air intervals formed by two adjacent lens groups increase. , a photographic lens utilizing floating, characterized in that the second and third lens groups are moved toward the object side. (2) The focal lengths of the second and third lens groups are f_2, f
_3. When the focal length of the entire system is f, and the amounts of movement of the first, second, and third lens groups when focusing from an object at infinity to a near object are m_1, m_2, and m_3, respectively, 0. 8<f_2/f<0.9 -4.2<f_3/f<-1.8 1.03<m_1/m_2<1.1 0.2≦m_3/m_2<0.55 Satisfy the following conditions. A photographic lens utilizing floating according to claim 1, characterized in that: