JPH0281015A - Telephoto lens capable of short-distance photographing - Google Patents

Abstract

PURPOSE:To secure a relatively long working distance to the title telephoto lens so that the lens can exert extremely excellent image forming performances over the range from infinitive to unmagnification by constituting the lens system of the lens of ten pieces of lenses of two groups in a state where the lens group satisfies specific conditions. 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 2nd lens group G2 having negative refracting power and the 1st group G1 is composed of a front group GF having positive refracting power and rear group GR having positive refracting power. At the time of focusing within a range from infinitive to a short distance, both groups G1 and G2 are moved in the opposite directions so that the interval between the groups can be expanded. Moreover, this lens system is constituted so that the system can satisfy the conditions of Inequalities (1) and (2). The DELTA1 and DELTA2, DG2, and (f) of the inequalities respectively represent time moving quantities of the 1st and 2nd lens groups at the time of focusing, thickness of the 2nd lens group G2 from the most object side to the most image side on the optical axis, and focal distance of the whole system at the time of infinite focusing.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention can satisfactorily correct various aberrations over the entire photographing range from infinity to 1:1 magnification, and has an aperture ratio of about 1:4 and a focal length of about 200111R+. This invention relates to a telephoto lens capable of distance photography.

[Conventional technology]

Most conventional telephoto lenses are limited to a shooting range from infinity to about 1/1O, so close-up lenses, intermediate rings, etc. (so-called accessories for close-up photography) are used to I was taking double shots.

However, the method using a close-up accessory deviates from the normal usage conditions for a telephoto lens corrected for aberrations, resulting in insufficient performance.

On the other hand, there are some known telephoto macro lenses that can take images up to 100% magnification, but most of them are semi-telephoto lenses with a focal length of around 100 mm.

However, since the working distance (distance between the lens and the subject) that these semi-telephoto lenses have is insufficient, there are problems with illuminating the subject at close range and photographing living things such as insects. be.

Therefore, we have created a high-performance telephoto macro lens that allows for a reasonably long working distance when taking close-up shots, can produce 1M shadows up to life-size without the need for close-up accessories, and has improved operability. desired.

Therefore, a telephoto lens with a focal length of about 20,011 mm and capable of photographing from infinity to 1:1 magnification was developed in Japanese Patent Application Laid-Open No. 55-1408.
This method has been proposed in Japanese Patent Publication No. 10 and Japanese Patent Application Laid-open No. 61-132916.

[Problems to be Solved by the Invention] However, in JP-A-55-140810, it is possible to take pictures up to the same magnification, but spherical aberration, coma aberration, and astigmatism occur due to changes in the shooting distance. Since the aberrations and chromatic aberrations fluctuate greatly, it is difficult to say that this is completely satisfactory.

Furthermore, in Japanese Patent Application Laid-Open No. 61-132916, there are few variations in various aberrations due to changes in the ti shadow distance, and furthermore,
The amount of extension in the state where the 1st shadow at the same magnification is performed is relatively small compared to the entire extension method. However, since the focusing system mainly employs a focusing method in which the first lens group, which has a large number of lenses and is heavy, is extended, the center of gravity of the lens moves significantly during close-up photography, which is not preferable.

Therefore, the present invention has been made in view of these conventional problems, and has high-performance imaging performance in an imaging range from infinity to 1:1 magnification while ensuring a relatively long working distance. It is an object of the present invention to provide a telephoto lens capable of retreating and shooting images, with as little movement of the center of gravity as possible and improved operability.

[Means to solve the problem]

In order to achieve the above object, the present invention includes, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a negative refractive power. G1 has a front group GF with positive refractive power and a rear group GR with positive refractive power located at 11 from the object side, and when focusing from infinity to short distance, the first lens group G1 and the second lens group Gt
The two groups are moved in opposite directions so that the distance between the two groups is widened, and the following conditions are further satisfied.

(1) -1≦Δt/Δ1<0 (2) 0.06<Dcz<r<0.175 However, Δ1: Amount of movement of the first lens group G1 due to focusing.

Δ2: Amount of movement of the second lens group G2 due to focusing.

Dcm: Axial thickness from the vertex closest to the object side of the second lens group G2 to the vertex closest to the image side of the second lens group G2.

f: Focal path # of the entire system in the infinity focus state.

Note that the movement amount of each group in condition (1) also takes into account the movement direction, with the movement direction moving toward the object side being negative, and the movement direction moving toward the image side being positive.

[For production]

In order to reduce the amount of extension of the first lens group G1 using a focusing method in which the first lens group G1 is extended in the positive and negative two-group lens type of the present invention, the refractive power of the first lens group GF must be strengthened. However, if the refractive power of the first lens group G1 is increased (then, not only will it be difficult to ensure the brightness of the first lens group GF, but also a large amount of spherical aberration will occur. Since the magnification of group G2 increases,
In particular, it becomes difficult to correct distortion aberration.

Therefore, in the present invention, in order to minimize the amount of extension of the first lens group GF and the movement of the center of gravity of the lens system due to focusing from infinity to a short distance, the second lens group is moved down toward the image side and operated. We aim to significantly improve sexual performance.

Each conditional expression in the present invention will be explained in detail below.

Condition (1) defines the optimal ratio of the amount of movement of each group in a focusing method in which the first lens group G1 is advanced while the second lens group G2 is moved down. If the upper limit of this condition (1) is exceeded, the incident height of the off-axis light beam entering the second lens group GF will become too high, which is not preferable because fluctuations in astigmatism and coma aberration will become significant. On the other hand, exceeding the lower limit of this condition is not preferable because it not only increases the amount of extension of the first lens group G1 but also causes an increase in the movement of the center of gravity as the lens moves. Note that the lower limit of this condition (1) is 0.15
It is more preferable that

Conditional expression (2) defines the optimal axial thickness of the second lens group G2. If the upper limit of condition (2) is exceeded, the total length of the second lens group G2 becomes long, and unless the lens diameter at the rear end of the second lens group G2 is made large, principal ray breakage will occur when the second lens group G2 is moved down. Occur. Moreover, in the case of a negative-eye reflex camera, it is difficult to make the lens diameter match the inner diameter of a predetermined mount. On the contrary, if the lower limit of this condition is exceeded, it becomes difficult for the second lens group GF to cancel out the positive distortion generated in the first lens group G1, and the positive distortion increases as a whole, which is not preferable.

As mentioned above, the specific lens configuration of the present invention is that the front group GF includes a positive lens L, a positive lens L2 with a surface of stronger curvature facing the object side, and a positive meniscus lens with a convex surface facing the object side. 3, a negative lens L4 having a concave surface with a stronger curvature facing the image side, and a negative lens L having a rear group GF having a concave surface having a stronger curvature facing the object side, a positive lens L,
and a biconvex lens 14. The second lens group Gt has
It is desirable to configure the lens to include a positive lens L8, a biconcave lens, and a positive meniscus lens LIO with a convex surface facing the object side.

Further, in the present invention, by configuring the device so as to satisfy the following conditions, it becomes more advantageous in terms of high performance.

(3) 0.07<DGII/f<0.12(4
) 0.5 < (GW/f < 1f (n,
-1) (5) -4<<-2,5 However, Dc*: On-axis thickness from the vertex closest to the object side of the rear group GF to the vertex closest to the image side of the rear group GL.

r　GF　I Focal length of front group GF.

r: Negative lens with concave surface facing the object side in the rear group GF,
Radius of curvature of the side of the object.

nl: Negative lens L with a concave surface facing the object side in the rear group G
, the refractive index of .

Conditional expression (3) is the rear group G of the first lens group G1. Exceeding the upper limit of the zero condition (3), which defines the optimum axial thickness of the lens, is advantageous in terms of aberration correction, but is not preferable because the overall length increases. On the other hand, if the lower limit of this condition is exceeded, the total length will be shortened, but the refracting surfaces will come closer together and the optical path length in the rear group will be shortened. As a result, rays from infinity (land rays) that are parallel to the optical axis and pass through the front group are not sufficiently affected by the divergence effect of the concave surface located closest to the object in the rear group, and are positioned behind this concave surface. Since it is subject to the convergence effect of the positive lens, it becomes difficult to correct spherical aberration. Especially when shooting at close range, there is not enough room to correct spherical aberration, so the swell of spherical aberration becomes large. Therefore, in the close-up 1st shadow, which is often used with the aperture closed down, the movement of the image plane becomes large when the aperture is stopped down, which is not preferable.

Conditional expression (4) defines the optimum focal length ratio between the front group GF of the 1121st group and the entire system.

If the upper limit of this condition is exceeded, the refractive power of the front group GF becomes weaker, which is advantageous in terms of aberration correction. This is undesirable because it forces the refractive power to be reduced, resulting in an increase in the size of the lens system. Conversely, if the lower limit of this condition is exceeded, it is advantageous for downsizing, but large chromatic aberrations and spherical aberrations occur in the front group GF of the 1121st group, and this front group G
.

It becomes difficult to cancel out these aberrations with a lens system placed behind the lens.

Conditional expression (5) defines an appropriate surface layer refracting power at the object side of the negative lens L in the rear group GF, which has a concave surface facing the object side. If the upper limit of this condition (5) is exceeded, the negative surface pressure refracting power becomes weaker and spherical aberration becomes insufficiently corrected, and conversely, if the lower limit of this condition is exceeded, the negative surface pressure refractive power becomes stronger and spherical aberration becomes excessive. This is not preferable because it is a correction.

〔Example〕

Examples according to the present invention will be described below.

Each of the embodiments is a telephoto lens with an F number of about 4.0, W, and a point distance of about 200 mm, which allows close-range ↑ maximum shadow.

The first and second embodiments both consist of a first lens group G1, which is made up of a front group GF and a rear group Gll, and has a positive refractive power, and a second lens group G2, which has a negative refractive power. It has a lens configuration similar to that of the first embodiment shown in .

The specific lens configuration in each embodiment of the present invention is a positive lens L+ and a positive lens L! with a surface of stronger curvature facing the object side. and a positive meniscus lens I5 with the convex surface facing the object side. , a front group GF consisting of a negative lens L4 with a concave surface with a stronger curvature facing the image side, a negative lens L with a concave surface with a stronger curvature facing the object side, a positive lens L, and a biconvex lens L7. It consists of a rear group GR, a positive lens L8, a biconcave lens L, and a second lens group G2 consisting of a positive meniscus lens L1° with a convex surface facing the object side. The aperture S is arranged between the 11th power group GF and the rear group G8.

Focusing from infinity to a short distance is achieved by moving the first lens group G toward the object side and moving the second lens group GF toward the image side.

Tables 1 and 2 below list the values of the specifications of the first and second embodiments. In the table, the leftmost number represents the order from the object side.
r is the radius of curvature of the lens surface, d is the distance between the lens surfaces, and the refractive index n
The number ν is a value for dim (λ-587.6 nm), 2ω is the angle of view, β is the imaging magnification, and Do is the distance from the object to the apex of the first lens surface.

1 juice L f = 200.0, F number: 4.0, 2ω: '12
．． 33゜153.456 1202.508 57.677 2232.993 41.228 81.122 147.800 34.745 46゜402 176.213 56.323 147.0B1 147.141 201.022 51.944 38.089 46.429 81.698 f =199.9979 2.0038 96.0478 5゜00 0.40 8.00 0.40 6.70 2.50 5.00 12.00 54.0 82.6 82.6 45.4 2.00 38.0 10.00 60.1 0.20 9.00 45.9 (Variable) 5.00 33.9 4.00 45.0 15.00 4.00 46.4 (Bf ) β--0,5000 479,1689 31,4918 91,1331 1,61720 1,49782 1,49782 1,79668 1,60342 1,62041 1,54814 1,80384 1,74400 1,58267 β--1 ,0000 278,9999 62,2837 86,0011 Table 1 - Friendship rule - f = 200.0, F number 137.573 2471.254 58.107 266.097 35.149 89.766 82.922 28.392 :4.0.2ω: 12.33' 5.00 54.6 1.514540.40 8.00 82.6 1.497820.40 6.70 82.6 1.497822.20 5.00 45.4 1.7966814.00 46.81? 5.00 37.9 1.72
342209.747 10.00 60.3 1
．． 5183547.512 0.40 567.655 -99.366 118.725 36.004 47.843 102.975 f・199.9973 3.4707 87.6036 4.40 1.70 15.00 4.40 (Br ) 28.6 45.4 45.4 β,, -0,5000 454,8821 38,1937 70,2421 1,79504 1,79668 1,79668 β・-1°ooo.

251.6147 81.2176 48.7302 Below, in Table 3, the amount of movement and change in total length of each lens group due to focusing in each example is shown, and as a comparative example, in Table 4, the amount of change in the first lens of each example is shown. The amount of movement and the amount of change in overall length of each lens group due to focusing when the group is extended is shown. In each table, the amount of movement of the first lens group GF is shown as Δ1, the amount of movement of the second lens group G2 is shown as Δ2, and the amount of change in the overall length is shown as ΔL.

Furthermore, if the entire extension focusing method is adopted, an extension amount equivalent to the focal length of the lens system is required. That is, if the lens with a focal length of 200 shown in each of the above embodiments employs the entire extension focusing method, an extension amount of approximately 200 is required.

As described above, in the present invention, by adopting a focusing method in which the first lens group G1 is integrally extended toward the object side and the second lens group G2 is integrally lowered toward the image side, the center of gravity of the lens can be relatively moved. It can be seen that this is very advantageous because it is not only possible to improve the operability by being smaller, but also to suppress the amount of change in the overall length to a small value.

Table 5 below shows the condition corresponding values in each example of the present invention.

2 and 4 show various aberration diagrams in the present invention,
(A) is a diagram of various aberrations when focused at infinity, (B) is t
Various aberration diagrams when the i-shadow magnification β is -0,5, (C)
shows various aberration diagrams in a state where the imaging magnification β is -1, 0 (equal magnification).

Comparison of each aberration diagram shows that the lens maintains a compact shape and maintains brightness at an F number of about 4.0, while providing excellent imaging performance from infinity to life-size.

〔Effect of the invention〕

According to the present invention, it is possible to improve operability by ensuring a relatively long working distance while suppressing the amount of change in overall length and movement of the center of gravity due to focusing, and also to achieve extremely good imaging performance from infinity to life-size. A telephoto lens capable of close-range photography can be achieved.

[Brief explanation of the drawing]

1 and 3 are lens configuration diagrams in a first embodiment and a second embodiment of the present invention, respectively, and FIG. 2(A),
FIG. 4(A) shows the first embodiment and the second embodiment of the present invention, respectively.
FIG. 2(B) and FIG. 4(B) are diagrams of various aberrations in the infinity focused state in the embodiment, and FIG. 2(B) and FIG. 4(B) are respectively
FIGS. 2(C) and 4(C) are diagrams showing various aberrations in the state where the photographing magnification β is -0 and 5 in the embodiment and the second embodiment, respectively. FIG. 7 is a diagram showing various aberrations in a state where the photographing magnification β is 1.0 (equal magnification) in the second embodiment. [Description of main parts] Second lens group

Claims (1)

[Claims] In order from the object side, the first lens group G_1 having positive refractive power;
and a second lens group G_2 with negative refractive power, and the first lens group G_1 has a front group G_F with positive refractive power.
and a rear group G_R having positive refractive power, so that the distance between the first lens group G_1 and the second lens group G_2 is expanded when focusing from infinity to a short distance. A telephoto lens capable of close-range photography, characterized in that both groups are moved in opposite directions along the optical axis, and the following conditions are satisfied. (1) -1≦Δ_2/Δ_1<0 (2) 0.06<D_G_2<f<0.175 However, Δ_1: Movement amount due to focusing of the first lens group G_1. Δ_2: Movement amount of the second lens group G_2 due to focusing. D_G_2: Axial thickness from the vertex closest to the object side of the second lens group G_2 to the vertex closest to the image side of the second lens group G_2. f: Focal length of the entire system when focused at infinity.