JPH0281014A - Telephoto lens capable of short-distance photographing - Google Patents

Abstract

PURPOSE:To realize a high-performance telephoto lens system which is able to make short-distance photographing by constituting the lens system of three lens groups in such a state where the interval between the front group of the 1st lens group and 2nd lens group is expanded and one of the intervals between each adjacent lens groups is nonlinearly changed at the time of focusing. CONSTITUTION:The lens system of this telephoto lens is constituted of, from the object side, the 1st lens group G1 having positive refracting power and composed of a front group GF having positive refracting power and rear group GR having positive refracting power, 2nd lens group G2 having negative refracting power, and 3rd lens group G3 having positive refracting power. When, at the time of focusing, the interval between the front group GF and 2nd lens group G2 is expanded and, at the same time, at least one of the air intervals between each adjacent lens groups, for instance, the interval between the front and rear groups GF and GR is nonlinearly changed so that the focusing performed in the intermediate distance area can be improved. Therefore, this lens system can make short-distance photographing over a range from infinite of about 200mm in focal distance to unmagnification.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides a lens that is capable of close-range photography from infinity to life-size magnification, and that has a focal length of about 200 mm with little change in overall length due to close-range photography. [Prior Art] Conventionally, in order to take pictures up to near the same magnification, a method is known in which a close-up tool such as a bellows is used to increase the amount of extension. However, in this system, the operation is complicated, it is inconvenient to carry, and the amount of movement is extremely large, resulting in insufficient performance.

Therefore, in order to prevent the deterioration of imaging performance at short distances, macro lenses that adopt a floating method are disclosed in Japanese Patent Publication No. 62-42252, Japanese Patent Application Laid-Open No. 55-140810, and Japanese Patent Application Laid-open No. 61-132916, for example. It has been proposed in et al.

(Problem to be solved by the invention) However, Japanese Patent Publication No. 62122 filed by the same applicant as the present invention
Publication No. 52 has the advantage that the first lens group is fixed, so there is no change in overall length, the center of gravity, and vJ is extremely small, but the focal length is rather short at 162 m1, and there is a problem with astigmatism during focusing. It has problems such as large fluctuations. Furthermore, although photography is possible from infinity to the same magnification, there is a problem in that ordinary people experience aberrations around 1/2 times (middle path M region).

Furthermore, in Japanese Patent Application Laid-open No. 55-140810, the focal length is about 200 ms, but
The change in total length due to focusing is large, and the change in spherical aberration is large.
The problem is that the FJI is large.

In addition, in JP-A-61-132916, the focal length is about 200 cm, the total length at infinity is short, and aberration fluctuations are relatively small, but the change in total length due to focusing from infinity to close distance is small. Since the first lens group is large and has a large number of lens elements, it is moved out, so there is a problem in that the center of gravity moves a lot.

Therefore, the present invention has been made in view of these conventional problems, and it reduces the shift of the center of gravity of the lens while keeping the amount of change in the total length of the lens due to focusing to about 3Q+n or less.
1) Furthermore, we have improved operability by ensuring a long working distance, which is advantageous for photographing living things such as insects, and have a high focal length of approximately 200 m, which has excellent imaging performance from infinity, etc. The objective is to provide a telephoto lens that is capable of performing close-range photography.

[Means to solve problems]

In order to achieve the above object, the present invention has a front group C having a positive refractive power and a rear group G having a positive refractive power in order from the object side.
A first lens group G that includes F and has positive refractive power as a whole.
1, a second lens group G2 with negative refractive power, and a third lens group G2 with positive refractive power, and when focusing from an infinite distance to a short distance, the front group GF and the second lens group G2 so that the distance between the two groups is increased, and at least one lens group formed by two adjacent groups The air spacing is changed nonlinearly.

In the present invention, when focusing from an infinite distance to a short distance, the front group GF and the rear group GF are arranged so that the air gap formed by the front group GF and the rear group GF changes nonlinearly. G7
It is desirable to move at least one of these in a non-linear manner.

Further, in the present invention, the front group GF has at least one positive lens and one negative lens, the rear group GF has a cemented lens made of a positive lens and a negative lens, and a second
It is desirable that the lens group G2 has at least two or more negative lenses and one or more positive lenses, and that the third lens group G3 is configured to have a cemented lens of a positive lens and a negative lens.

[For production]

As mentioned above, Japanese Patent Publication No. 62-42 filed by the same applicant as the present invention
In the positive/negative type 3-group telephoto lens proposed in Publication No. 252, etc., various aberrations near infinity and near 1x can be corrected relatively well, but the imaging magnification is around 1/2 (
A large amount of aberration occurs in the intermediate distance region), resulting in a significant deterioration of imaging performance.

In order to suppress performance deterioration due to the occurrence of aberrations in this intermediate distance region, at least one air gap formed by two adjacent groups must be set nonlinearly when focusing from an infinite distance to a short distance. It is necessary to improve the degree of freedom in correcting aberrations by changing the

Therefore, in the present invention, the first lens group Gl is replaced by the front group G1.
Divide into two, F and rear group G7, and create front group C7 and second lens group G! The gap between the front group GF and the rear group GR is changed so that the gap between the front group GF and the rear group GR changes non-linearly.
At least one of the forces of l is moved nonlinearly.

Then, the incident island of the light beam that enters the second lens group G2 due to focusing can be adjusted to an appropriate height, and as a result, the degree of divergence effect of the second lens group G2 can be adjusted to an optimal state. be. Therefore, deterioration of aberrations due to excessive divergence effect of the second lens group G2 in the intermediate distance region can be suppressed extremely well.

Further, in the present invention, in order to perform good aberration correction while minimizing changes in the overall length due to focusing and to make the lens system more compact, it is desirable that the lens system be configured to satisfy the following conditions.

(1) −0,7<ΔGF/Δ6□≦0(2) 1
<fca/far<3(3)-3< (A/f6
r<-1,4(,1)-5< Kukawa f(nb na) However, Δ6. : Amount of movement due to focusing of the front group GF.

Δ, 2; 2nd leg 2nd fresh 71 f　GF　j Focal length of front group GF.

f c++: rear group G. focal length.

rA = 11% point distance of the negative lens in the front group 9rb: Radius of the curvature of the cemented surface in the third lens group.

f: Focal length of the entire system.

nl: refractive index of the negative lens in the cemented lens of the third lens group.

n,: refractive index of the positive lens in the cemented lens of the third lens group.

Note that in condition (1), the moving direction in which the lens group moves toward the object side during focusing is negative, and the moving direction vj in which the lens group moves toward the image side is positive.

Below, each conditional expression of the present invention will be explained in detail.

Conditional expression (1) defines the optimal ratio of the amount of movement between the front group G and the second lens group G2 from infinity to equal magnification. However, if the upper limit of condition (1) is exceeded, not only will the change in overall length become large, but also the light rays incident on the second lens group G will become too low when photographing at around 100% magnification, making it difficult to correct spherical aberration. So I don't like it. On the contrary, if the F limit of this condition is exceeded, the amount of movement of both the front group G and the second group G2 increases, which is not preferable.

Conditional expression (2) is based on the front group GF and the rear group G. and the appropriate focal length ratio. However, condition (2)
If the upper limit of is exceeded, the refractive power of the front group G becomes strong, so that the angle at which light rays are bent in the front group G becomes steeper, making it difficult to correct spherical aberration and coma aberration. On the other hand, if the lower limit of this condition is exceeded, although it is advantageous for aberration correction, the overall length increases, which is undesirable.

Conditional expression (3) defines an appropriate focal length ratio between the negative lens in the front group G and the front group G. However, if the upper limit of condition (3) is exceeded, spherical aberration will be overcorrected, which is not preferable in terms of aberration correction. On the other hand, under this condition 1@
If the value exceeds , not only spherical aberration is insufficiently corrected, but also chromatic aberration becomes difficult to correct. Note that it is more preferable to arrange this negative lens closest to the object side in the 11;1 group.

Conditional expression (4) defines the optimum surface pressure refracting power at the cemented surface of the cemented lens in the third lens group Gel. However, if the upper limit of condition (4) is exceeded, the surface pressure refracting power of the cemented surface becomes too strong, so that the Ep surface aberration becomes less suitable for correction. In particular, it is difficult to correct spherical aberration on the near side where there is no margin for correction. Also, the angle of incidence of oblique rays increases, resulting in coma aberration,
” The fluctuation in the to-point aberration also increases. On the other hand, if the lower limit of this condition is exceeded, the surface pressure rupture force of the joint surface becomes too weak, so
This has an adverse effect on oblique rays, and in particular makes it difficult to sufficiently correct astigmatism and coma.

〔Example〕

Examples according to the present invention will be described below.

Each example has an F number of about 4.0 and a focal length of 2.
00mm. In each of the first to third embodiments, a first lens group G1 includes a front group GF having a positive refractive power and a rear group GF having a positive refractive power, and a second lens group having a negative refractive power. It consists of a lens group G2 and a third lens group G3 having positive refractive power, and has the same lens configuration as the first embodiment shown in FIG.

The specific configuration of each embodiment includes, in order from the object side, a negative meniscus lens 11 with a surface of strong curvature facing the image side, a positive lens L2 cemented to this negative meniscus lens, and a positive lens L2 cemented to the negative meniscus lens, and Positive meniscus lens L with convex surface facing
3, a rear group GR consisting of a negative meniscus lens L1 with a convex surface facing the object side, and a positive lens cemented to this negative meniscus lens L4 with a surface of strong curvature facing the object side. , a positive lens L6 with a surface of strong curvature facing the image side, and a negative lens cemented to this positive lens L6,
and a biconcave lens 17. a second lens group G2 consisting of;
The third lens group GF includes a negative lens L and a positive lens L1° cemented to the negative lens.

In the first and second embodiments of the present invention, focusing from infinity to the same magnification is achieved by moving the front lens group so that the distance between the front group GF and the second lens group G2 increases, as shown in FIGS. 1 and 2. J! While fcr moves to the object side and the second lens group G2 moves to the image side, the front group G
The rear group GF moves nonlinearly in a convex manner toward the image side so that the air distance between F and the rear group G@ changes nonlinearly.

In addition, the third embodiment employs an internal focusing system, and focusing from infinity to the same magnification in the third embodiment is achieved by using the front group GF and the second lens group G2, as shown in FIG. While the second lens group G2 moves toward the image side so that the group spacing of 3r linear movement.

In Tables 1 to 3 below, which list the values of the specifications of the first to third embodiments, the leftmost number represents the order from the object side, r is the radius of curvature of the lens surface, and d is the lens The interplanar spacing, refractive index n, and number ν are values for the d-line (λ = 587.6 nm), 2ω is the angle of view, β is the imaging magnification, and no is the distance from the object to the vertex of the first lens surface. It is.

Topsoil ffLJ'N round f = 200.0, F number: 4. O12ω-12,3
3' front Uni-U rainbow mark and f = 200.0, F number: 4.0, 2 b)
= 12. ．． 33゜530.768 (variable) 290.493 (variable) 73.248 (variable) 71.861 (B f ) B f 120.1500 120.1bUIJ lZIJ, Ll)υυ feces-IA-th J-fusei ML! - f = 200.0, F 7c: 4.0.2 ω = 1
2.33 ``In Table 4, list the values corresponding to the conditions in each embodiment of the present invention.

However, 2. P = f(n, -n force) From the values of the specifications shown in Tables 1 to 3 above, the amount of change in the total length due to focusing in the first and second embodiments is 27.
11.7+nm, 15.001mm, and the third
In this embodiment, since it is an internal focusing type, the overall length does not change and remains constant. Therefore, it can be seen that the amount of change in the overall length due to focusing from infinity to the same magnification and the movement of the center of gravity of the lens are extremely small, and the operability is improved.

Various aberration diagrams in the first to third embodiments of the present invention are shown in FIGS. 4 to 6 at around i, respectively. (B) is a diagram of various aberrations in the intermediate distance shooting state (β--0,
5x), (C) is the closest shooting condition B
(β−1.0 times) various aberration diagrams are shown.

Comparison of each aberration diagram shows that the aberrations that have traditionally been a problem in intermediate distance shooting conditions have been well corrected, and the camera has extremely excellent imaging performance from infinity to close distances (at 1:1 magnification). I know that there is.

In addition, in the present invention, when focusing from an infinite distance to a short distance, only the front group is moved nonlinearly, and the air distance between the M'J group and the rear group is changed nonlinearly. is also possible.

〔Effect of the invention〕

According to the present invention, the movement of the center of gravity of the lens system is minimized while suppressing changes in the overall length of the lens system due to close-up photography, and a relatively long working distance is ensured to improve operability. From 1 addition (equal size) to F
), it is possible to achieve a telephoto lens with extremely excellent imaging performance.

[Brief explanation of the drawing]

Figures 1 to 3 are lens configuration diagrams in the first to third embodiments of the present invention, and Figures 4 (A) to 6 (Δ), respectively.
4(B) to 6(B) are diagrams of various aberrations in the infinite distance photographing state of the first to third embodiments of the present invention, respectively.
) are various aberration diagrams in the intermediate distance photographing state (β-0.5 times) of the first to third embodiments of the present invention, and Fig. 4 (
C) to FIG. 6(C) are the first to third embodiments of the present invention, respectively.
Various aberration diagrams in the closest distance photographing state (β-1,0 times) of the embodiment are shown. [Explanation of main parts]

Claims (1)

[Claims] 1) A first lens group G_1 having a positive refractive power as a whole, including, in order from the object side, a front group G_F having a positive refractive power and a rear group G_R having a positive refractive power; The second with negative refractive power
Lens group G_2 and third lens group G_ with positive refractive power
3, and when focusing from an infinite distance to a short distance, the distance between the front group G_F and the second lens group G_2 is changed so that the distance between the two groups is expanded, and A telephoto lens capable of photographing at close range, characterized in that at least one air gap formed by two adjacent groups is changed nonlinearly so as to improve focusing performance in a distance range. 2) When focusing from an infinite distance to a short distance, the front group G
The front group G_F and the rear group G_R are arranged so that the air gap formed by the rear group G_R changes non-linearly.
A telephoto lens capable of close-range photography according to claim 1, characterized in that at least one of R and R is moved nonlinearly. 3) The front group G_F has at least one positive lens and one negative lens, the rear group G_R has a cemented lens made of a positive lens and a negative lens, and the second lens group G_2 has Claim 2, characterized in that the third lens group G_3 has at least two or more negative lenses and one or more positive lenses, and the third lens group G_3 has a cemented lens of a positive lens and a negative lens. A telephoto lens that can take close-up shots.