JPS62177509A - 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-3rd lens groups having positive refractive power and the 4th lens group having negative refractive power, and at the time of focusing from an infinite object to a near distance object moving the 1st-3rd lens groups to the object side so that respective air intervals are increased. CONSTITUTION:The 1st-3rd lens groups I-III having positive refractive power are arranged on the object side and the 4th lens group IV having negative refractive force is arranged on the back of the lens groups I-III to constitute the whole photographing lens of four lens groups. Especially, the arrangement of the 4th lens group IV having the negative refractive index increases the freedom of arrangement of refractive indexes of the three lens groups I-III having positive refractive index and arranged on the object side and attains excellent correction of various aberration in a reference state. At the time of focusing from the infinite object to the near distance object, so-called floating for moving the three lens groups I-III arranged on the object side respectively independently to the object side so that 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 effectively correct aberrations during focusing.

(Prior Art) Macro lenses or micro lenses (hereinafter referred to as "macro lenses") have traditionally been used as photographic lenses for photographic cameras, video cameras, etc. whose main purpose is to photograph objects at close range.

) is called.

Macro lenses are designed to provide high optical performance, especially when approaching objects at close range, compared to other photographic lenses such as standard lenses and telephoto lenses. In addition, macro lenses are often used for a wide range of objects, from objects at close range to objects at the black limit.

In general, 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 correct this well.

For example, if you try to enlarge a macro lens designed with a photographic magnification of 1/1o to a high magnification of [12], spherical aberration, field curvature, and coma aberration will occur significantly. .

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

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, JP-A-48-'+0520, JP-A-52-7723, and JP-A-57- It has been proposed in Publication No. 192916 and the like. 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 low-magnification close-range photography, but the correction effect is not necessarily sufficient in high-magnification photography. 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 satisfactorily corrects aberration fluctuations when focusing on a wide range of objects, from objects at infinity to objects at short distances, especially objects at imaging magnifications close to 1x. The objective is to provide a high-performance photographic lens that utilizes floating technology and a large aperture ratio.

(Means for solving the problem) From the object side, the first lens has a positive refractive power. 2nd, 3rd
It has four lens groups: a lens group and a fourth lens group with negative refractive power, and when focusing from an object at infinity to a near object, the three air gaps formed by two adjacent lens groups are The above-mentioned first. Second. Third
This is because the 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, r, n, and m each have a positive refractive power. Second. The third lens group (■) is a fourth lens group with negative refractive power. 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 three first lenses with positive refractive power on the object side. Second. A third lens group is disposed, and a fourth lens group having a negative refractive power is disposed behind the third lens group, and the photographing lens is constituted by the four lens groups as a whole. In particular, by arranging the fourth lens group with negative refractive power, the degree of freedom in refractive power arrangement of the three lens groups with positive refractive power placed on the object side is increased, and the standard Capture T or Jishou r 6,000. I1
, 1st r By strengthening the positive refractive power of all three lens groups, 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 a near object, the three lens groups I, n, 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, in this embodiment, in order to reduce fluctuations in aberrations due to changes in photographic magnification, it is preferable to satisfy the following conditions.

Menki 2nd. The focal length of the fourth lens group is f2° f4, 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 to satisfy the following conditions when the moving amounts of the 2nd and 3rd lens groups are respectively ml, 2, and m3.

Conditional expression <1) relates to the refractive power of the second lens group, and conditional expression (
2) relates to the refractive power of the fourth lens group, and is used to appropriately set the amount of extension 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 negative refractive power of the fourth lens group becomes too strong exceeding the upper limit of conditional expression (2), the Fi of the three lens groups on the object side will decrease.
The refractive power must be increased accordingly, and the amount of extension of each lens group during focusing will be reduced, or fluctuations in aberrations will become large, making it difficult to correct aberrations well.

Moreover, if the negative refractive power of the fourth lens group becomes weak beyond the lower limit, the technical meaning of arranging the fourth lens group decreases, and the three lens groups on the object side during focusing become less effective. This is not preferable because the amount of feed increases.

Conditional expression (3) relates to the movement ratio of the 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, both of which are related to the movement ratio of each lens group during focusing. By appropriately setting the amount of movement, 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.

By increasing the amount of change in the distance between the second lens group and the second lens group and the amount of change in the distance between the second lens group and the third lens group from an object at infinity to an object at a short distance, the off-axis light flux is By making the light incident on a higher position in the lens group and strongly refracting it, inward coma aberration is generated, and outward coma aberration, which occurs when focusing on a close object, is corrected.

On the other hand, the axial light beam diverges strongly between the first lens group and the second lens group when the object distance becomes short, so if the movement ratio of each lens group is too large, spherical aberration will be insufficiently corrected. . Therefore, in this embodiment, conditional expressions (3) and (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 third lens group and the third lens group increases too much, the focal length of the entire system will change too much to a long side, and the amount of extension of each lens group will have to be increased, which is undesirable because the overall length of the lens will become longer.

In this embodiment, the diaphragm is placed between the lens group and the i2 lens group, and by moving it together with the second lens group, the height of incidence of the axial light beam on 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 the narrowing aberration 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-like positive lens, and a negative lens, and the second lens group is made of a negative lens. It is preferable to configure a bonded lens of a lens and a positive lens, two groups of three lenses of positive lenses, a third lens group of at least one positive lens, and a fourth lens group of a meniscus-shaped negative 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 υi are the refractive index of the i-th glass from the object side, respectively.

] Numerical Example I F= 5], 6 FNO= 1 : 2.55 2ω
= 45.5゜Rl= -531,25D l=
2.23 N I=1.72000 ν1=50
．． 2R2= -61,75D 2= 0.15R3
= 22.00 D 3= 3.04 N
2=1.78590 υ2=44.2R4= 7
8.06 D4= 1.05R5= -137
,25D 5= 1.19 N 3=1.603
42 ν3=38. OR6= 19.00D
6= (Variable) R7: (Aperture) D 7=
4.05R8=-16,21D8=1.
62 N 4=1.69895 ν4=30. I
RQ=-85,24D 9=3.71N
5=1.77250 5=49.6R1O=
−19,66DlO= 0.15R11= −139
,17D11=2.52 N6=1.772
50 C6 work 49.6R12= -40,93D1
2= (variable) R13= 346.13 D13
= 2.53 N 7 = 1.48749 υ7
=70.2R14= -120,56D14= (variable) R15= 58.1:l D15= 1.8
2 N 8=1.51633 C8=64. lR
16=40.90 Numerical Example 2 F=50.4FNO=2.552ω=46.50Rl
= -325,25D I = 2.20N
l =1.72000 υ1=50.2R2=
-59,14D2=0.15R3=21.27
D3=3.24 N2=1.77250
C2=49.6R4=77.63 D4=
0.97R5=-133,47D5=1.
50 N3=1.60562 C3=43.7
R6= 18.75 D 6= (variable) R7=
(Aperture) D7= 3.80R8=
-16,41D 8= 1.67 N 4=1.
75520 Shi4=27.5R9--59,43D9
= 3.65 N5=1.77250 υ5=
49.6R1O=-19,40D 10=0.
15R11=-258, 63D11=2.40
N 6 = 1.77250 White = 49.6R12
= -40,59DI2=(variable)R13=15
0.63 D13= 1.90 N 7=1
．． 65844 Schiff = 50.9R14 = -899,
48DI4= (variable) R15= 82.71
D15=1.75 N8=1.62299
C8=58.2R16=43.02 Numerical Example 3 F=51.61 FNO=1 : 2.55 2
ω= 45.5°RI= 65.20 DI=
2.80 N 1=1.78590 ν1=
44.2R2=-646,44D2=0.15
R3=20.20 D3=2.97
N2=1.80610 υ2=40.9R4=
44.49 D4=0.70R5=8
4.16 D 5 = 2.07 83 = 1.6
9895 ν3=30. IR6=15.86
D 6= (variable) R7= (aperture) D
7=5.00R8=-13,84D8=1
．． 97 N4=1.72825 ν4=28.5
R9=-40,00D 9=2.86N
5=1.78590 ν5=44.2R1O=
−17,840lo= 0.15all= −117
,46D11=2.410 N6=1.77
250 Shiro = 49.6R12 = -31,52D
I2= (variable) R13= -75,60D13=
2.50 N7=1.48749 Schiff=70
．． 2R14= -44, 81D14= (variable) R1
5=-64,38D15=1.60 N8
=1.53172 shi8=48.9R16= -1
17, 76 (Effects of the Invention) According to the present invention, the photographic lens is composed of four lens groups, and by moving the three lens groups of the object/jill so as to satisfy the predetermined conditions as described above, ,
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 close 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. I, IT, Ill, and ■ on the right side of the lens cross-sectional view are 1st. Second. Third. The 4th 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, (8) is an object at infinity, and (B) is an image with a magnification of 11x. , and Y is the image height. Figure 1 Figure 84 CB)

Claims (1)

[Claims] (1) First and second lenses each having positive refractive power in order from the object side.
, has four lens groups: a third lens group and a fourth lens group with negative refractive power, and when focusing from an object at infinity to a near object, the three lens groups formed by two adjacent lens groups
the first and second air intervals are increased
, a photographic lens utilizing floating, characterized in that the third lens group is moved toward the object side. (2) The focal lengths of the second and fourth lens groups are f_2, f
_4. 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.1. The following conditions must be satisfied: 1<f_2/f<1.25 -6.0<f_4/f<-3.9 1.1<m_1/m_2<1.18 0.5≦m_3/m_2<0.8 A photographic lens utilizing floating according to claim 1, characterized in that: