JP3312129B2 - Zoom lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens used for a camera or the like.

[0002]

2. Description of the Related Art A zoom lens used in a silver halide camera or the like mainly has a field angle of about 63 ° to 84 ° at a wide angle end. A zoom lens exceeding the angle of view has a large change in the angle of view as compared with a change in the focal length, and is therefore expected to be a zoom lens having a large image forming effect even if the zoom ratio is small.

As a zoom lens satisfying this requirement, there is a lens system disclosed in Japanese Patent Application Laid-Open No. 2-296208. This lens system includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a positive refractive power. And a fourth lens group including a fourth lens having an F-number of 2.8.
Although it is a bright lens system, the number of lens groups is large and complicated, and a large-diameter aspherical lens is adopted as the lens on the most object side mainly for correction of distortion at the wide-angle end, which is difficult to manufacture. .

As a zoom lens having a simpler lens group configuration, a lens system described in Japanese Patent Application Laid-Open No. 60-130712 is known. These lens systems are, in order from the object side, a two-unit zoom lens including a first lens group having a negative refractive power and a second lens group having a positive refractive power, and the configuration of the lens system is simple. F / number changes during zooming, and F / 3.5 at the wide angle end.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lens system which is bright, has an F number of 2.8 at the wide-angle end, is small in size and has a relatively simple structure of the lens unit, and has a sufficient strength of the lens system. It is an object to provide a zoom lens.

[0006]

The wide-angle zoom lens according to the present invention comprises, in order from the object side, a first lens group having a negative refractive power as a whole, a second lens group having a negative refractive power as a whole, It is characterized by comprising a third lens group having a positive refractive power as a whole.

The wide-angle zoom lens according to the present invention has an intermediate focal length when zooming from the wide-angle end to the telephoto end.
The first lens unit and the second lens unit at the wide-angle end and the telephoto end.
In order to reduce the distance between the lens groups, the relative distance between the first lens group and the second lens group is increased once and then decreased, and the relative distance between the second lens group and the third lens group is reduced. It is characterized by doing so.

Further, the lens according to the present invention is characterized in that the first lens group is fixed during zooming from the wide-angle end to the telephoto end, and the first lens group has a focusing function.

A zoom lens for a single-lens reflex camera of a silver halide camera comprises a first lens group having a negative refractive power and a second lens group having a positive refractive power, and the relative distance between the lens groups is changed. In general, a two-group zoom that performs zooming is used.

This type of two-unit zoom lens has a negative-positive so-called retrofocus type power arrangement in order from the object side, and can provide a longer back focus than the focal length. Therefore, it is most suitable for a single-lens reflex camera. Configuration.

However, in order to secure the back focus while keeping the objective lens system compact, it is necessary to increase the negative refracting power of the first lens unit. Therefore, the first lens unit at the wide-angle end is required. , The occurrence of aberrations with respect to off-axis rays having a high ray height becomes remarkable.

Originally, a retrofocus type lens system has a negative and positive asymmetrical refractive power distribution with respect to the stop, so that it is difficult to correct off-axis aberrations. Therefore, it is not preferable that the amount of off-axis aberration generated in the negative first lens unit is large. Further, increasing the negative refracting power of the first lens group causes an increase in the amount of spherical aberration generated in the first lens group in which the fluctuation of the axial ray height is large during zooming. Becomes extremely large. Since these tendencies are more remarkable in a bright lens system having a smaller F-number, it is difficult for the two-unit zoom lens to have a bright lens system.

According to the present invention, in a two-unit zoom lens system comprising a first negative lens unit and a second positive lens unit, the first lens unit is provided in order to secure the back focus while keeping the overall length of the lens system compact. Even if the negative refracting power is increased, the aberration is satisfactorily corrected. Therefore, in the present invention, the first lens unit of the two-unit zoom lens is divided into two negative and negative lens units to provide a three-unit zoom lens.

By dispersing the negative refracting power into the two lens units in this manner, the distance between the principal points of the two lens units can be adjusted without increasing the aberration generated in the first lens unit and the second lens unit. By doing so, the combined refractive power can be increased, and the back focus and the F-number can be effectively reduced.

In particular, the zoom lens according to the present invention has the above-described configuration, and at the time of zooming from the wide-angle end to the telephoto end, the relative distance between the first lens unit and the second lens unit is increased once and then decreased. Then, the first, second, and second lens units are set so that the relative distance between the second lens unit and the third lens unit decreases.
It is preferable to move each of the third lens groups.

By moving each lens unit as described above, the combined refractive power of the first lens unit and the second lens unit increases in negative refractive power during zooming from the wide-angle end to the telephoto end. Later, it takes an extreme value near the intermediate focal length zoom position, and then weakens the negative refractive power to reach the telephoto end. Therefore, the combined refractive power of the first lens group and the second lens group at the wide-angle end and the telephoto end is relatively increased while securing the back focus by increasing the combined refractive power of the first lens group and the second lens group. It is possible to reduce the occurrence of off-axis aberrations at the wide-angle end and spherical aberrations at the telephoto end.

In the zoom lens of the present invention as described above, it is desirable to satisfy the following conditions (1) and (6). _{(1) -3.0 <f 1 /} f W <-1.0 (6) 0.85 <f 2 / f 1 <3.5 However f _1, f ₂ are respectively the first lens group and the second lens the focal length of the group, f _W is the focal length of the entire lens system at the wide-angle end.

Condition (1) defines the focal length of the first lens group. When the value goes below the lower limit of the condition (1), the refracting power of the first lens group becomes too weak, and the axial ray height on the image side becomes lower than that of the second lens group, making it difficult to secure the back focus. Further, since the entrance pupil position approaches the image plane, the outer diameter of the first lens group becomes large, which results in an increase in the filter diameter. Further, in terms of aberrations, the Petzval sum deteriorates, so that the curvature of field becomes remarkable especially at the wide-angle end. On the other hand, when the value exceeds the upper limit of the condition (1), the refractive power of the first lens unit becomes too strong, so that the on-axis ray height after the second lens unit becomes high. The next spherical aberration occurs largely in the negative direction. At the same time, at the wide-angle end, astigmatism around the screen becomes remarkable, causing image disturbance at the time of defocus.

Next, the condition (6) defines the distribution of refractive power between the first lens group and the second lens group that bears negative refractive power in the lens system. When the value goes below the lower limit of the condition (6), the negative refractive power is biased toward the second lens unit, so that the distance between the principal points between the combined lens unit of the first lens unit and the second lens unit and the third lens unit becomes small, and The refractive power of the entire system decreases. Therefore, in order to obtain a desired refractive power without increasing the overall length of the lens system, it is necessary to increase the refractive power of the third lens group, and the field curvature and spherical aberration at the telephoto end become remarkable.

The zoom lens system according to the present invention mainly performs zooming from the wide-angle end to the telephoto end by the third lens unit.
The lens group plays a role of a compensator for forming an image at a desired position while keeping the overall length of the lens system constant. However, if the upper limit of the condition (6) is exceeded, the second
The refracting power of the lens group becomes too weak, the amount of movement of the lens group becomes large in order to play the role of a compensator, and the second lens group becomes the first lens group because the first lens group is fixed.
There is a risk of colliding with the lens group or the third lens group. If the first lens group has a negative refractive power required for the lens system, the negative refractive power becomes excessive at the wide-angle end and the telephoto end, and coma and high-order field curvature at the wide-angle end also increase. Generation of spherical aberration at the telephoto end becomes remarkable.

In the two-unit zoom lens, since the first lens unit moves during zooming, the movable lens unit is further extended during focusing.
This complicates the mechanism for movement. In order to simplify the mechanism for this movement, it is desirable that the first lens group be fixed during zooming from the wide-angle end to the telephoto end.

First, with respect to the two-unit zoom lens, a condition for making the total length of the lens system coincide with the zoom position of the two focal lengths will be considered. In the zooming from the wide-angle end to the telephoto end, the first and second lens units move so that the relative distance to the image plane once decreases and then increases. It is possible to match the overall length of the lens system only for one focal length. The movement condition of the second lens group at that time is as follows: the refractive power of the first lens group is φ ₁ , the refractive power of the second lens group is φ _2, and the first lens group and the second lens group at the reference zoom position are Assuming that the distance is e ₁ , the distance between the second lens group and the image plane is e _2, and the amount of change in the distance between the first lens group and the second lens group during zooming is x, x is given by the following equation (3). Is required. x = 1 / φ ₁ − (e ₁ −e ₂ ) (3) Further, the zoom magnification ratio β from the reference position at this time is given by the following equation (4). β = (φ _s / φ ₁ ) ² (4) where φ _s is the refractive power of the lens system at the reference zoom position.

From equation (4), the zoom magnification ratio between the two zoom positions where the total length of the lens system is the same is determined by the refractive power of the entire system at the reference zoom position and the refractive power of the first lens group. It can be seen that it does not depend on the refractive power of the second lens group or the moving amount x.

In the three-unit zoom lens according to the present invention, when zooming from the wide-angle end to the telephoto end,
The relative distance between the first lens group and the second lens group increases once and then decreases, and the relative distance between the second lens group and the third lens group moves so as to decrease. It may be basically considered that the total length of the lens system coincides with the telephoto end.

At the wide angle end and the telephoto end, the first lens unit and the second lens unit
The distance between the first lens group and the second lens group at that time is equal.
Composite focal length of lens group, refractive power at wide-angle end and zoom
The zoom ratio should satisfy the expression (4), and the third lens group
Should be arranged so that the positional relationship of satisfies equation (3).
Therefore, the overall length of the lens system at the wide-angle end and
obtain. Further, during zooming, the following equation (5)
To satisfy e ₁ , E_Two By determining
The length of the lens system can be kept constant.¹C_Three =
φ e₁ -E_Two +¹A_Three/ φ = TL (5) where¹A_Three ,¹C_Three Is, for example, "Optics" Vol. 12, No. 6,
Used for paraxial analysis of zoom lenses from 484 pages to 490 pages
Using Gaussian brackets
Quantity.

¹ A ₃ = [φ ₁ , −e ₁ , φ ₂ , −e ₂ ] ¹ C ₃ = [φ ₁ , −e ₁ , φ ₂ , −e ₂ , φ ₃ ] where φ ₁ , φ 3 ₂ and φ ₃ are the refractive powers of the first, second and third lens groups, e ₁ and e ₂ are the distance between the first and second lens groups, respectively, and the second and third lens groups. Is the refractive power of the entire lens system, and TL is the total length of the lens system to be kept constant.

In the above description, β in equation (4) coincides with the zoom ratio from the wide-angle end to the telephoto end. However, it is not always necessary to match, and in order to shorten the lens system, equation (4) is used. ) Is set to be smaller than the zoom ratio from the wide-angle end to the telephoto end, and the equations (3) and (4) are used between the intermediate focal lengths.
May be used to first match the total length of the lens system. Also, assuming a zoom position that exceeds the zoom ratio from the wide-angle end to the telephoto end, that is, by increasing the value of β in equation (4) to make the entire lengths of the lens systems coincide, there is no technical problem. do not become.

By moving each lens group as described above, specifically, during zooming from the wide-angle end to the telephoto end, the first lens group is fixed and the first lens group and the second lens group are fixed. By moving the second lens group and the third lens group so as to reduce the relative distance between the second lens group and the third lens group after increasing the general distance once, and to reduce the relative distance between the second lens group and the third lens group, the zoom lens system can be zoomed. The total length can be kept constant.

[0029]

Next, embodiments of the zoom lens according to the present invention will be described. Example 1 f = 21.0-27.1-35.0, F / 2.8, 2ω = 93.8 ° -78.9 ° -64.5 ° Maximum image height = 21.6 r ₁ = 97.8441 d ₁ = 3.8000 n ₁ = 1.88300 v ₁ = 40.78 r ₂ = 215.7766 d ₂ = 0.1000 r ₃ = 50.2047 d ₃ = 1.7000 n ₂ = 1.786650 ν ₂ = 50.00 r ₄ = 19.6623 d ₄ = 7.1994 r ₅ = 46.4736 d ₅ = 1.7000 n ₃ = 1.86300 ν ₃ = 41.53 r ₆ = 24.6785 d ₆ = 2.4561 r ₇ = 23.2170 d ₇ = 3.2571 n ₄ = 1.56907 v ₄ = 71.30 r ₈ = 36.6405 d ₈ = D ₁ (variable) r ₉ = 61.9348 d ₉ = 1.7000 n ₅ = 1.69680 v ₅ = 56.49 r ₁₀ = 23.0302 _{d 10 = 3.3336 r 11 = 428.9358} d 11 = 1.7000 n 6 = 1.75500 ν 6 = 52.33 r 12 = 58.7548 d 12 = 1.9300 r 13 = 32.0759 d 13 = 4.9938 n 7 = 1.74000 ν 7 = 28.29 r 14 = 156.5435 d 14 = D ₂ (variable) r ₁₅ = (aperture) d ₁₅ = 1.0000 r ₁₆ = 106.1486 d ₁₆ = 3.1855 n ₈ = 1.65830 ν ₈ = 57.33 r ₁₇ = -62.7322 d ₁₇ = 0.1000 r ₁₈ = 22.7957 d ₁₈ = 8.1769 n ₉ = 1.58313 v ₉ = 59.36 r ₁₉ = -137.6814 d ₁₉ = 1.8502 r ₂₀ = -52.9895 d ₂₀ = 8.3404 n ₁₀ = 1.87400 v ₁₀ = 35.26 r ₂₁ = 25.4751 d ₂₁ = 1.8087 r ₂₂ = 113.1350 d ₂₂ = 3.4055 _{n 11 = 1.60300 ν 11 = 65.48} r 23 = -31.0102 d 23 = 0.1000 r 24 = 434.7946 d 24 = 4.9740 n 12 = 1.60311 ν 12 = 60.70 r 25 = -17.9517 d 25 = 1.2000 n 13 = 1.83400 ν 13 = 37.16 r ₂₆ = −38.1831 f 21.0 27.1 35.0 D ₁ 1.500 5.349 1.500 D ₂ 21.372 9.396 4.782 (back focus at the wide-angle end) = 36.94 f ₁ / f _W = -1.86, f ₂ / f ₁ = 2.57

Example 2 f = 21.1-27.1-35.0, F / 2.8, 2ω = 93.8 ° -78.8 ° -64.5 ° Maximum image height = 21.6 r₁ = 111.8232 d₁ = 3.8000 n₁ = 1.88300 ν₁ = 40.78 r_Two = 265.0478 d_Two = 0.1000 r_Three = 54.3252 d_Three = 1.7000 n_Two = 1.78650 ν_Two = 50.00 r_Four = 22.1085 d_Four = 6.0262 r_Five = 61.9112 d_Five = 1.7000 n_Three = 1.86300 ν_Three = 41.53 r₆ = 35.2817 d₆ = 0.6585 r₇ = 42.8591 d₇ = 2.9168 n_Four = 1.56907 ν_Four = 71.30 r₈ = 143.3148 d₈ = D₁ (Variable) r₉ = 69.7418 d₉ = 1.7000 n_Five = 1.69680 ν_Five = 56.49 r_Ten= 19.3825 d_Ten= 3.8734 r₁₁= 266.1766 d₁₁= 1.7000 n₆ = 1.75500 ν₆ = 52.33 r₁₂= 46.0754 d₁₂= 2.4958 r₁₃= 29.5014 d₁₃= 6.6810 n₇ = 1.74000 ν₇ = 28.29 r₁₄= 116.9584 d₁₄= D_Two (Variable) r_Fifteen= (Aperture) d_Fifteen= 1.0000 r₁₆= 191.2390 d₁₆= 3.0844 n₈ = 1.65830 ν₈ = 57.33 r₁₇= -52.9695 d₁₇= 0.1000 r₁₈= 21.2825 d₁₈= 8.4805 n₉ = 1.58313 ν₉ = 59.36 r₁₉= -85.0492 d₁₉= 1.4981 r₂₀= -43.4697 d₂₀= 7.5000 n_Ten= 1.87400 ν_Ten= 35.26 r_{twenty one}= 24.8478 d_{twenty one}= 1.9769 r_{twenty two}= 148.0842 d_{twenty two}= 3.4843 n₁₁= 1.60300 ν₁₁= 65.48 r_{twenty three}= -28.2615 d_{twenty three}= 0.1000 r_{twenty four}= 783.6786 d_{twenty four}= 4.6057 n₁₂= 1.60311 ν₁₂= 60.70 r_{twenty five}= -19.1652 d_{twenty five}= 1.2000 n₁₃= 1.83400 ν₁₃= 37.16 r₂₆= -37.8748 f 21.1 27.1 35.0 D₁ 1.500 4.057 1.500 D_Two 20.865 10.535 4.541 (back focus at wide-angle end) = 36.99 f₁/ f_W = -2.84, f_Two/ f₁ = 0.92 where r₁ , R_Two , ... are the radii of curvature of the respective surfaces of the lens, d
₁ , D_Two ,... Are the thickness of each lens and the lens interval, n
₁ , N_Two , ... is the refractive index of each lens, ν₁ , Ν _Two , ...
Is the Abbe number of each lens.

In the first embodiment, a first lens unit having a negative refractive power, a second lens unit having a negative refractive power, and a positive refractive power are arranged in order from the object side in the configuration shown in FIG. The first lens unit is fixed during zooming from the wide-angle end to the telephoto end, and the distance between the first lens unit and the second lens unit increases and decreases once. Third
The distance between the second lens group and the third lens group is reduced so that the distance between the lens groups is reduced.
Move the lens group. Further, since the first lens group is fixed, the total length from the first lens group to the image plane is constant.
By making the distance from the most object side surface of the lens system to the image plane constant, a zoom lens having a small size and a high strength can be obtained. Further, the conditions (1) and (6) are satisfied.

The first lens group includes, in order from the object side, a positive meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side. The second lens group includes, in order from the object side, a negative meniscus lens having a convex surface facing the object side, and a convex meniscus lens having a convex surface facing the object side. The third lens group includes, in order from the object side, a diaphragm, a biconvex lens, a biconvex lens, and a biconcave lens. , A biconvex lens, and a biconvex cemented lens obtained by cementing a biconvex lens and a meniscus lens.

In the first embodiment, at the wide-angle end and the telephoto end, the distance between the first lens unit and the second lens unit is made equal, the combined refractive power satisfies the expression (4), and the third lens unit The lens unit is moved so as to satisfy Expression (3) so that the entire lengths of the lens systems at the wide-angle end and the telephoto end are equal. By moving the second lens unit and the third lens unit, the total length of the lens system is kept constant at all zoom positions from the wide-angle end to the telephoto end.

The first embodiment has a wide angle of view of 93.8 ° at the wide-angle end and an F-number of 2.80 from the wide-angle end to the telephoto end due to the above configuration and movement of each lens unit.
8, the back focus is ensured, and the first lens group is fixed during zooming from the wide-angle end to the telephoto end, so that the movable mechanism is simple.

The aberrations at the wide-angle end, the intermediate focal length, and the telephoto end of this embodiment are as shown in FIGS. 3, 4, and 5, respectively, and the aberrations are well corrected.

In the second embodiment, a first lens unit having a negative refractive power, a second lens unit having a negative refractive power, and a second lens unit having a positive refractive power are arranged in order from the object side in the configuration shown in FIG. During zooming from the wide-angle end to the telephoto end, the first lens group is fixed, and the distance between the first lens group and the second lens group increases once, decreases, and then decreases. The second lens group and the third lens group move so that the distance between the lens group and the third lens group decreases. Also in the second embodiment, since the first lens group is fixed, the total length from the first lens group to the image plane is constant. By making the distance from the most object side surface of the lens system to the image plane constant, a zoom lens having a small size and a high strength can be obtained. Further, the conditions (1) and (6) are satisfied.

The first lens group includes, in order from the object side, a positive meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side. The second lens group includes, in order from the object side, a negative meniscus lens having a convex surface facing the object side, and a positive meniscus lens having a convex surface facing the object side. The third lens group includes, in order from the object side, a diaphragm, a biconvex lens, a biconvex lens, a biconcave lens, and a negative meniscus lens having a convex surface facing the object side. It is composed of a biconvex lens, and a biconvex cemented lens in which a biconvex lens and a meniscus lens are cemented.

In this embodiment, the distance between the first lens unit and the second lens unit is made equal at the wide-angle end and the telephoto end, and the combined refractive power is set so as to satisfy the expression (4). By moving the lens units so as to satisfy the expression (3), the total length of the lens system at the wide-angle end and the telephoto end is made equal, and at the focal length position therebetween, the expression (5) is satisfied. By moving the second lens unit and the third lens unit, the total length of the lens system is kept constant at all zoom positions from the wide-angle end to the telephoto end.

The second embodiment is different from the first embodiment in that the first
The negative refracting power of the lens group is weakened, and the negative refracting power of the second lens group is increased, so that the rear principal point position of the combined lens group of the first lens group and the second lens group is brought out to the image side. Further, the total length of the lens system is shortened by setting the rear principal point position of the third lens unit to the image side, thereby providing the lens system having the shortest overall length in the examples.

With the above-described configuration and the movement of the lens groups, the F-number from the wide-angle end to the telephoto end is 2.8, which is bright, while the angle of view at the wide-angle end is 93.8 °.
The back focus was secured, and the first lens group was fixed during zooming from the wide-angle end to the telephoto end, so that the movable mechanism could be a simple zoom lens.

The aberrations at the wide-angle end, the intermediate focal length, and the telephoto end of this embodiment are satisfactorily corrected as shown in FIGS. 6, 7, and 8.

[0042]

According to the present invention, the F-number at the wide-angle end is 2.8, which is bright, the back focus is sufficiently ensured, and the lens group is relatively simple and compact. A zoom lens having extremely high intensity can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is an aberration curve diagram at the wide angle end according to the first embodiment of the present invention.

FIG. 4 is an aberration curve diagram at an intermediate focal length according to the first embodiment of the present invention.

FIG. 5 is an aberration curve diagram at the telephoto end according to the first embodiment of the present invention.

FIG. 6 is an aberration curve diagram at the wide-angle end according to a second embodiment of the present invention.

FIG. 7 is an aberration curve diagram at an intermediate focal length according to the second embodiment of the present invention.

FIG. 8 is an aberration curve diagram at a telephoto end according to a second embodiment of the present invention.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 15/20

Claims (5)

(57) [Claims] 1. A first lens group having a negative refractive power as a whole and a second lens group having a negative refractive power as a whole in order from an object side.
The zoom lens includes a lens group and a third lens group having a positive refractive power as a whole. In zooming from the wide-angle end to the telephoto end, the third lens group is located at the wide-angle end and the telephoto end rather than in the intermediate focal length state.
The distance between the first lens group and the second lens group is reduced.
The zoom movement is configured so that the relative distance between the first lens group and the second lens group is increased once and then decreased, and the relative distance between the second lens group and the third lens group is reduced, Further, the first lens group is fixed in the entire zoom range from the wide-angle end to the telephoto end, and the second lens group is moved to the third lens group once and then moved to the first lens group. A zoom lens characterized in that: 2. The lens system according to claim 1, wherein the entire length of the lens system from the first lens group to the image plane at all zoom positions from the wide-angle end to the telephoto end is kept constant. 1 zoom lens. 3. The zoom lens according to claim 1, wherein the third lens group moves toward the second lens group when zooming from the wide-angle end to the telephoto end. 4. The zoom lens according to claim 1, wherein the conditions (1) and (6) are satisfied. _{(1) -3.0 <f 1 /} f W <-1.0 (6) 0.85 <f 2 / f 1 <3.5 However f _1, f ₂ are respectively the first lens group and the second lens the focal length of the group, f _W is the focal length of the entire lens system at the wide-angle end. 5. The zoom lens according to claim 2, wherein the condition (6) is satisfied. _{(6) 0.85 <f 2 /} f 1 <3.5 However f _1, f ₂ is the focal length of the respective first lens group and the second lens group.