JPH07140389A - Zoom lens - Google Patents

Abstract

PURPOSE:To provide a zoom lens which is compact because the diameter of a front lens is small and by which focusing can be performed to an extremely close object point with small moving amount. CONSTITUTION:This zoom lens is constituted of plural lens groups where a lens group having positive refractive power is arranged on a side closest to an image side. The lens group having the positive refractive power arranged on the side closest to the image side is divided into two, and focusing is performed by moving the lens group on the side closest to an object side simultaneously with moving one of the lens groups. When it is assumed that the focal distance of the lens group on the side closest to the object side is (f), the focal distance of an entire system at the telephoto end is f1, and the magnification of the moving lens group out of the lens groups on the side closest to the image side is beta, the lens system satisfies a next condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact zoom lens having a small front lens diameter, and more particularly to a zoom lens characterized by a focusing method.

[0002]

2. Description of the Related Art In zoom lenses, a front-lens focusing method is widely used in which a front lens is moved forward when focusing at a short distance.

In focusing by feeding the front lens, the diameter of the front lens must be made extremely large so that the peripheral light amount does not decrease even at the wide-angle end where the angle of view is widest.

In particular, recently, zoom lenses also tend to have a large aperture ratio, and therefore the front lens diameter tends to be large. Therefore, when the focusing method of feeding the front lens is adopted, the diameter of the front lens is further increased, which is not preferable. That is, when the diameter of the front lens becomes large, the entire lens system becomes large, and the weight also increases, which makes the handling inconvenient. Especially when weight is applied to the front,
When mounted on a camera, the balance is poor and the mobility of the zoom lens is poor.

From the above, it is desirable that the zoom lens be as compact as possible, and for that purpose it is necessary to prevent the front lens diameter from increasing.

Regarding focusing of a conventional zoom lens, JP-A-56-48607 and JP-A-56-5031 are used.
No. 1 is known. In the devices described in these publications, focusing is performed by moving the first lens group, but in the case of this example, the diameter of the first lens group must be increased in order to secure the peripheral light amount. The size of the diameter is proportional to the moving amount of the first lens unit during focusing.
Generally, the relationship between the movement of an object point and the image point is Δ
Letting Z be the amount of movement of the image point be ΔZ ′, and β be the magnification of the lens that moves for focusing, then βZ ′ = β ² ΔZ. Therefore, the amount of movement can be reduced by focusing at a large β ² . However, in the above-mentioned conventional example, since the magnification of the first group is not so large, the moving amount is also relatively large, and therefore the front lens diameter is also large.

As described above, the larger the angle of view at the wide-angle end, the larger the front lens diameter as compared with the rear lens group, and it is extremely important to reduce the front lens diameter in order to make the entire system compact. Therefore, the focusing method as described above is not preferable for a wide-angle zoom lens.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to obtain a zoom lens having a small front lens diameter, a compact size, a small amount of movement, and focusing to an extremely close object point. A zoom lens in which a lens unit having a positive refracting power is arranged closest to the image side, and the lens unit closest to the image side is divided into two and one of them is moved to perform focusing. It provides a focusing method of.

[0009]

That is, the zoom lens according to the present invention comprises a plurality of lens groups in which a lens group having a positive refractive power is arranged closest to the image plane, The lens group having a positive refracting power arranged in 2 is divided into two lens groups, and one of the lens groups is moved for focusing, and the lens group divided into two as described above. At the same time as the movement of one of the lens groups, the lens group arranged closest to the object side is moved to perform focusing to the closest object point.

Further, in the present invention, when the focal length of the lens unit arranged closest to the object in the lens system is f ₁ and the magnification of the lens unit that moves during focusing is β, the following relationship is satisfied. To do.

| F _T / f ₁ | <β where f _T is the focal length of the entire system at the telephoto end.

FIG. 1 shows an embodiment of the present invention in which the focusing system used in the present invention is applied to a zoom lens composed of four lens groups. It is a zoom lens that performs zooming by moving each group as shown in the drawing. This zoom lens has the positive refractive power, which is the closest to the image side. Focusing from the distance object to the closest object.

As described above, the larger the magnification of the moving lens unit, the smaller the amount of movement for focusing. Therefore, the moving lens group (in the case of the example shown in FIG. Subsequent magnification _{| f T / f 1 | (} f 1 is the composite focal length of the first group, f _T is the focal length of the entire system at the telephoto end) greatly the amount of movement than the conventional method by the larger than It can be made very small. And by this, the front lens diameter can be further reduced. That is, by satisfying the above conditions, the front lens diameter can be reduced,
The lens system can be made extremely compact.

If this condition is not satisfied, the front lens diameter becomes large, which is not preferable.

Further, the first group is also provided with a focusing function, and one of the lens groups obtained by dividing the lens group closest to the image side is moved, and at the same time, the first group is also moved so as to focus up to the closest object point. You can In addition, a compact lens system with a small lens diameter can be designed as a zoom lens capable of focusing up to an extremely close object point.

For example, in the zoom lens having the basic structure shown in FIG. 1, as shown in FIG. A possible zoom lens is obtained.

Next, an embodiment of the zoom lens according to the present invention having the above basic structure will be described. FIG. 3 is a sectional view of an embodiment of the present invention, and the data of this lens system are as follows.

F = 36 to 101, F / 4 r ₁ = 336.568 d ₁ = 2.5 n ₁ = 1.75520 ν ₁ = 27.51 r ₂ = 51.2875 d ₂ = 1.5 r ₃ = 52.8538 d ₃ = 7.8 n ₂ = 1.69350 ν ₂ = 53.23 r ₄ = -257.2847 d ₄ = 0.1 r ₅ = 44.5048 d ₅ = 4.7 n ₃ = 1.58913 ν ₃ = 60.97 r ₆ = 168.3003 d ₆ = D ₁ (variable) r ₇ = 152.7245 d ₇ = 1.5 n ₄ = 1.77250 ν ₄ = 49.66 r ₈ = 19.3909 d ₈ = 2.9 r ₉ = 46.1614 d ₉ = 3.5 n ₅ = 1.76182 v ₅ = 26.55 r ₁₀ = -34.35 d ₁₀ = 1.2 n ₆ = 1.78590 v ₆ = 44.18 r ₁₁ = 75.0166 d ₁₁ = 1.6 r ₁₂ = -34.7288 d ₁₂ = 1.2 n ₇ = 1.69350 ν ₇ = 53.23 r ₁₃ = 16.2332 d ₁₃ = 3.5 n ₈ = 1.83400 ν ₈ = 37.16 r ₁₄ = 72.3062 d ₁₄ = D ₂ (variable) r ₁₅ = ∞ _{(stop) d 15 = 1.5 r 16 =} 32.3180 d 16 = 4.1 n 9 = 1.57250 ν 9 = 57.76 r 17 = -52.2151 d 17 = 0.11 r 18 = 60.1866 d 18 = 2.4 n 10 = 1.6910 ν 10 = _{54.84 r 19 = -147.8576 d 19 =} 1.6 r 20 _{-34.8713 d 20 = 1.2 n 11 =} 1.78472 ν 11 = 25.68 r 21 = 1241.5930 d 21 = D 3 ( _{variable) r 22 = 44.5951 d 22 =} 3.4 n 12 = 1.69680 ν 12 = 55.52 r 23 = -59.0046 d 23 = D ₄ (variable) r ₂₄ = -29.1382 d ₂₄ = 1.2 n ₁₃ = 1.80610 ν ₁₃ = 40.95 r ₂₅ = 42.7114 d ₂₅ = 1.8 r ₂₆ = -124.4920 d ₂₆ = 3.17 n ₁₄ = 1.65830 ν ₁₄ = 57.33 r ₂₇ = -27.9011 d ₂₇ = 0.1 r ₂₈ = 272.8908 d ₂₈ = 2.95 n ₁₅ = 1.65830 ν ₁₅ = 57.33 r ₂₉ = -57.0148 f ₁ = 73.335, f ₂ = -17.412, f ₃ = 41.370, f ₄ = 59.807 where f is The focal length of the entire system, r ₁ , r ₂ , ... R ₂₉ are the radii of curvature of each lens surface, d ₁ , d ₂ , ... D ₂₈ are the wall thickness and air gap of each lens, and n ₁ , n ₂ , ... n ₁₅
Is the refractive index of each lens, ν ₁ , ν ₂ , ... ν ₁₅ is the Abbe of each lens The combined focal length.

In the zoom lens having the above-mentioned structure, each group is moved for zooming as shown in FIG. The intervals D ₁ , D ₂ , D ₃ , and D ₄ during this zooming are as follows for wide (f = 36.22), standard (f = 60.588), and tele (f = 101.35).

D ₁ D ₂ D ₃ D ₄ Wide 0.821 14.339 9.512 4.442 Standard 12.357 7.413 4.901 4.442 Tele 22.449 1.429 0.794 4.442 Moreover, in the zoom lens of the above data, (1) the front lens which is conventionally performed The distances D ₁ , D ₄ and the first in each case
The chief ray heights are as follows. However, the object distance is 1.5m
At the wide end.

D ₁ D ₄ First surface chief ray height (1) 4.951 4.442 22.32 (2) 0.821 5.072 18.35 (3) 1.821 4.922 19.31 The value of the ratio β at the tele end is as follows.

F _T / f ₁ = 1.38, β = 3, β / │
f _T / f ₁ | = 2.17 As is clear from this data, in any case of the method of the present invention, the movement amount is smaller than that of the conventional front lens feeding method. Moreover, the height of the chief ray on the first surface is small, and the diameter of the front lens can be reduced by 10% or more.

[0023]

The zoom lens of the present invention is a lens system which has a small front lens diameter, is compact, and has a small amount of movement of the lens during focusing, and is capable of focusing to an extremely close object point.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a basic configuration of a zoom lens of the present invention.

FIG. 2 is a diagram showing a moving state of lens groups during focusing of the zoom lens.

FIG. 3 is a sectional view of an embodiment of the zoom lens according to the present invention.

Claims (2)

[Claims] 1. A zoom lens comprising a plurality of lens groups in which a lens group having a positive refracting power is disposed closest to the image side, and the lens group disposed closest to the image side is divided into two lens groups. A zoom lens that performs focusing by moving either one of the lens groups and the lens group disposed closest to the object side in the lens system, and further satisfies the following conditions. | F _T / f ₁ | <β where f ₁ is the focal length of the lens unit closest to the object side, and f
_T is the focal length of the entire system at the telephoto end, and β is the magnification of the lens unit that moves for focusing within the lens unit having the positive refractive power closest to the image side. 2. The most image-side lens group is divided into two lens groups, a positive lens group and a negative lens group, and the negative lens group among them is moved to the image side, and the most object-side lens group is moved to the object side. The zoom lens according to claim 1, wherein focusing is performed to a short distance by moving the zoom lens.