JPH0820601B2 - Telephoto zoom lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an improvement of a compact telephoto zoom lens having a positive, negative, and positive three-group configuration on the object side.

(Prior Art) This type of telephoto zoom lens is a development of the conventional telephoto zoom lens including four groups of positive, negative, positive, and positive.
A positive third lens unit G ₃ is formed by integrating a positive third lens unit for keeping the position of the image surface constant and a positive fourth lens unit which is an image forming unit. Further, the third lens group G ₃ is moved toward the object side along the optical axis during zooming from wide (wide angle) to tele (telephoto) to give a zooming effect. Therefore, the amount of zooming by the negative second lens group G ₂ that has played the role of the conventional zooming group, that is, the first lens group G ₁ during zooming.
It was possible to make the change in magnification caused by the positional relationship between the image point and the second lens group G ₂ smaller than that in the conventional telephoto zoom lens having the four-group configuration.

(Problems to be Solved by the Invention) However, in this kind of three-group zoom lens system, if the refracting power of the first lens group G ₁ is strengthened in order to further reduce the size of the variable power system, The imaging magnification of the second lens group G ₂ becomes large, and the image point of the second lens group G ₂ , that is, the object point of the third lens group G ₃ moves to the object side significantly. Therefore, it becomes difficult to secure a sufficient distance between the second lens group G ₂ and the third lens group G ₃ at the telephoto end. Therefore, in order to eliminate this, it becomes necessary to make the third lens group G _{3 an} extreme telephoto type. If the third lens group G ₃ which is an image forming group is made to be an extreme telephoto type, there is a drawback that it becomes difficult to correct spherical aberration, particularly spherical aberration on the tele side.

The present invention solves the above-mentioned drawbacks by providing an appropriate refracting power of each lens group and an imaging magnification for zooming, and has good imaging performance over all magnifications.
The object is to provide a compact telephoto zoom lens.

(Means for Solving Problems) The first aspect of the present invention has a positive flexural force in order from the object side.
It is composed of three groups, a lens group G ₁ , a second lens group G ₂ having a negative refractive power, and a third lens G ₃ having a positive refractive power, and each lens group moves independently for zooming. , Is a telephoto zoom lens that satisfies the following conditions.

(1) 1.3 <f ₁ /fw<1.6 (2) 0.25 <| f ₂ /fw|<0.45 (3) 0.44 <f ₃ /fw<0.52 (5) 0.5 <β _2w / β _2T <0.6 (7) 0.55 <β _3w / β _3T <0.75 However, fw: focal length of the entire system at wide end (shortest focal length of the entire system) f ₁ : focal length of the first lens group G ₁ f ₂ : second lens group G ₂ of the focal length f _3: the imaging of the second lens group G ₂ telephoto end: third focal length of the lens unit G ₃ beta _2w: imaging magnification beta _2T of the second lens group G ₂ wide end Magnification β _3w : Imaging magnification at the wide end of the third lens group G ₃ β _3T : Imaging magnification at the tele end of the third lens group G ₃ (Operation) In the present invention, the refractive power of the first lens group G ₁ is compared. I made it a weak structure. As a result, the object point of the third lens group G ₃ can be moved to the image side and the imaging magnification of the second lens group G ₂ can be reduced. When the imaging magnification of the second lens group G ₂ becomes small, the load of the second lens group G ₂ is reduced for the aberration correction, the refracting power of the second lens group G _2, it is possible to enhance more. In this case, the variable power system can be made compact even though the refractive power of the first lens group G ₁ is weakened.
The object point of the lens group G ₃ can be moved toward the image side. If the refractive power of the second lens group G ₂ is increased, the third lens group
The imaging magnification of G ₃ becomes large, which leads to an increase in the size of the imaging system. However, since the object point of the third lens group G ₃ largely moves to the image side and it becomes unnecessary to make the third lens group G _{3 an} extreme telephoto type, the load of the third lens group G ₃ on the aberration correction becomes large. It is reduced, and it becomes possible to further strengthen the refractive power of the third lens group G ₃ . Therefore, the imaging system can be made compact. In this way, we succeeded in making the lens system compact without making the third lens group G _{3 an} extreme telephoto type.

The expressions (1), (2), and (3) define the range of the appropriate refractive power of each lens group. If the upper limit of equation (1) is exceeded,
The refractive power of the first lens group G ₁ becomes too weak, which makes it difficult to configure the variable power system in a small size. The Outside lower limit, the imaging magnification of the second lens group G ₂ increases further, the object point of the third lens group G ₃ is moved toward the object side, the third lens group G ₃ to the extreme telephoto type You have to
Aberration correction becomes difficult. (2) exceeds the upper limit of the expression, it becomes difficult to miniaturize the zoom system further object point of the third lens group G ₃ to the third lens group G ₃ will move to the object side to the telephoto type It is not preferable because it becomes necessary.
When the value goes below the lower limit, the Petzval sum becomes excessively negative, which makes it difficult to correct astigmatism and field curvature, and also causes the image forming magnification of the third lens group G ₃ to become excessive, resulting in a large image forming system. Will be changed. If the upper limit of expression (3) is exceeded, the imaging system will become large, and if the lower limit is exceeded, the third lens group
The refractive power of G ₃ becomes too strong, and it becomes difficult to correct spherical aberration.

Reciprocal of the magnification of the second lens group G ₂ illustrates a distance between the image point and the second lens group G ₂ of the first lens group G _1. Therefore, equations (4) and (5) define the amount of zooming that the second lens group G ₂ bears, based on the difference and ratio of the distance between the image point of the first lens group G ₁ and the second lens group G ₂ due to zooming. To do.
If the upper limits of the expressions (4) and (5) are exceeded, the amount of zooming that the second lens group G ₂ bears becomes large. Therefore, fluctuations due to zooming of aberrations caused by the zooming action of the second lens group G ₂ also become
It becomes larger, and it becomes difficult to correct aberrations by the second lens group G ₂ . To eliminate this, the second lens group G ₂
Therefore, the refracting power of the second lens group G ₂ cannot be increased, which makes it difficult to make the lens system compact. If the value goes below the lower limit, the amount of zooming that the second lens group G ₂ bears becomes too small, and it becomes impossible to secure a sufficient zoom ratio. Therefore, the amount of zooming that the third lens group G ₃ bears becomes too large, and in terms of aberration correction. Not preferable.

The reciprocal of the imaging magnification of the third lens group G ₃ is determined by the second lens group G ₂
3 shows the distance between the image point of and the third lens group G ₃ . Therefore, the equations (6) and (7) define the amount of magnification variation of the third lens group G ₃ based on the difference and ratio of the distance between the image point of the second lens group G ₂ and the third lens group G ₃ due to zooming. It is a thing.
If the upper limits of the expressions (6) and (7) are exceeded, the amount of magnification variation of the third lens group G ₃ will be too large, which is not preferable for aberration correction. If the value goes below the lower limit, the amount of zooming that the third lens group G ₃ bears becomes too small, so the amount of zooming that the second lens group G ₂ bears must be too large, which is not preferable.

In the present invention as described above, it is desirable that the third lens group G ₃ has the following structure. Third lens group G ₃
Is divided into a front positive lens group G _3F and a rear negative lens group G _{3R in} order from the object side. Further, the front positive lens group G _3F has a positive refractive power as a composite by bonding a positive lens L ₃₁ , a positive lens L _32, and a negative lens L ₃₃ with a good strong curvature toward the object side in order from the object side. cemented lens consists of three positive lens component of a positive meniscus lens L ₃₄ with its surface convex toward the object side, satisfy the following respective conditions.

(8) 0.6 <f _3F / f ₃ <1.3 (9) 1.5 <| f _3R / f ₃ | <8.5 (10) 0.35 <f _3F / f ₃₁ <0.65 where f _3F : in front of the third lens group Focal length of positive lens group G _3F f _3R : focal length of rear negative lens group G _3R in third lens group f ₃₁ : first lens L _{31 in} front positive lens group of third lens group
The focal lengths of Eqs. (8), (9) and (10) define the structure of the third lens group G ₃ .

If the upper limit of expression (8) is exceeded, it becomes difficult to make the third lens group G ₃ compact. On the other hand, if the value goes below the lower limit, the aperture ratio of the third lens group G ₃ becomes large, and it becomes difficult to correct spherical aberration.

When the value exceeds the upper limit of the expression (9), the total length of the third lens group G ₃ becomes long, which makes it difficult to make it compact. If the lower limit is exceeded, the Petzval sum becomes excessively negative, making it difficult to correct astigmatism and field curvature.

If the value exceeds the upper limit of the expression (10), outward coma is generated, and further spherical aberration, particularly spherical aberration on the wide side becomes negative, and the variation of spherical aberration due to zooming becomes excessive, which is not preferable. On the other hand, if the value goes below the lower limit, inward coma is generated, and further spherical aberration, particularly spherical aberration on the wide side, becomes positive, and fluctuation of spherical aberration due to zooming becomes excessive, which is not preferable.

Example 1 As shown in FIG. 1, the configuration and shape of the lens of Example 1 according to the present invention will be specifically described.

The first lens group G ₁ is composed of, in order from the object side, a negative meniscus lens L ₁₁ having a convex surface directed toward the object side, a biconvex positive lens L ₁₂ and a biconvex positive lens L ₁₃ , which are cemented to the negative meniscus lens L ₁₁ . The second lens group G ₂ includes, in order from the object side, a negative lens L ₂₁ having a surface having a stronger curvature toward the image side, a positive meniscus lens L ₂₂ cemented to this, which has a convex surface facing the object side, and a lens having a stronger curvature toward the object side. The front lens group G _3F of the third lens group is composed of a negative lens L ₂₃ with a surface facing the positive lens L ₃₁ having a stronger curvature toward the image side, a biconvex positive lens L _32, and the positive lens L ₃₂ cemented to this, to the image side. A negative meniscus lens L ₃₃ with a convex surface facing the positive meniscus lens L ₃₄ with a convex surface facing the object side, and a rear lens group G 3 of the third lens group.
_{The 3R} is composed of a negative lens L ₃₅ having a stronger curvature toward the image side and a biconvex positive lens L ₃₆ .

Further, FIG. 1 shows the movement loci of the respective lens groups when zooming from the wide-angle side to the telephoto side. The first lens group moves linearly toward the object side, the second lens group moves toward the image side along a convex non-linear trajectory, and the third lens group moves nonlinearly toward the object side.

The specifications of the embodiment of the present invention are shown below. However, in each table,
The leftmost number represents the order from the object side, f represents the focal length of the entire system, and Bf represents the back focus. (The same applies to the specifications table below) f ₁ /fw＝1.566 | f ₂ /fw|＝0.373 f ₃ /fw＝0.483 β _2w / β _2T = 0.505 β _3w / β _3T = 0.690 f _3F / f ₃ = 0.757 | f _3R / f ₃ | = 1.963 f _3F / f ₃₁ = 0.459 The above values satisfy the conditional expressions (1) to (10).

Example 2 As shown in FIG. 3, the configuration and shape of the lens of Example 2 according to the present invention will be specifically described.

The first lens group G ₁ includes, in order from the object side, a positive lens L ₁₁ having a surface having a stronger curvature toward the object side, a negative meniscus lens L ₁₂ having a convex surface facing the object side, and a cemented lens having a stronger curvature toward the object side. The positive lens L ₁₃ having a convex surface and the second lens group G ₂ are, in order from the object side, a negative lens L ₂₁ having a surface having a stronger curvature toward the image side, and a positive meniscus having a convex surface facing the object side, which is joined to the negative lens L _21. A lens L ₂₂ and a negative lens L ₂₃ with a surface having a stronger curvature facing the object side, and the front lens group G _3F of the third lens group is a positive lens L ₃₁ with a stronger convex surface facing the image side from the object side.
A biconvex positive lens L ₃₂ , a negative lens L ₃₃ cemented to this, which has a surface having a stronger curvature toward the object side, and a positive meniscus lens L ₃₄ having a convex surface directed toward the object side. G _3R is a negative meniscus lens L with a convex surface facing the image side
₃₅ and a positive lens L ₃₆ with a surface having a stronger curvature facing the image side.

Further, FIG. 3 shows the movement loci of the respective lens groups when zooming from the wide-angle side to the telephoto side. The first lens group moves linearly toward the object side, the second lens group moves toward the image side along a convex non-linear trajectory, and the third lens group moves nonlinearly toward the object side. Hereinafter, the specifications of the second embodiment of the present invention will be shown.

f ₁ /fw＝1.567 | f ₂ /fw|＝0.373 f ₃ /fw＝0.483 β _2w / β _2T = 0.513 β _3w / β _3T = 0.680 f _3F / f ₃ = 0.989 | f _3R / f ₃ | = 8.028 f _3F / f ₃₁ = 0.607 The above values satisfy the conditional expressions (1) to (10).

Example 3 As shown in FIG. 5, the configuration and shape of the lens of Example 3 according to the present invention will be specifically described.

The first lens group G ₁ includes, in order from the object side, a positive lens L ₁₁ having a surface having a stronger curvature toward the object side, a negative meniscus lens L ₁₂ having a convex surface facing to the object side, and a cemented lens having a stronger curvature toward the object side. Positive lens L _{13 with} convex surface facing, second lens group G ₂
Is a negative lens L ₂₁ with a stronger curvature surface facing the image side, a positive meniscus lens L _{22 with} a convex surface facing the object side cemented to this, and a negative lens with a stronger curvature surface facing the object side. L ₂₃ and the front lens group G _3F of the third lens group G _3F is a positive lens L with a surface having a stronger curvature facing the image side from the object side.
₃₁ , a biconvex positive lens L ₃₂ , a negative lens L ₃₃ joined to this, which has a surface with a stronger curvature facing the object side, and a positive meniscus lens L ₃₄ having a convex surface facing the object side. The rear group G _3R is a negative meniscus lens L ₃₅ with a convex surface facing the image side, and a positive lens L ₃₆ with a surface with a stronger curvature facing the image side.
Made of.

Further, FIG. 5 shows the movement loci of the respective lens groups when zooming from the wide-angle side to the telephoto side. The first lens group moves linearly toward the object side, the second lens group moves toward the image side along a convex non-linear trajectory, and the third lens group moves nonlinearly toward the object side. The specifications of the third embodiment of the present invention are shown below.

f ₁ /fw＝1.567 | f ₂ /fw|＝0.373 f ₃ /fw＝0.483 β _2w / β _2T = 0.513 β _3w / β _3T = 0.679 f _3F / f ₃ = 0.989 | f _3R / f ₃ | = 7.957 f _3F / f ₃₁ = 0.608 The above values satisfy the conditional expressions (1) to (10).

A sectional view of the first embodiment is shown in FIG. As shown in the figure, in the third lens group G ₃ , a diaphragm is arranged between the front positive lens group G _3F and the rear negative lens group G _3R . FIG. 2 shows the aberration diagrams at the focal lengths of the entire system f = 71.500 mm, 115.000 mm, 205.000 mm.

A sectional view of the second embodiment is shown in FIG. As shown in the figure,
In the third lens group G _3, it is arranged aperture between the front positive lens group G _3F and the rear negative lens group G _3R. Focal length f of the whole system
Aberration diagrams at = 71.500 mm, 115.000 mm, and 205.000 mm are shown in FIG.

A sectional view of the third embodiment is shown in FIG. As shown in the figure,
In the third lens group G _3, it is arranged aperture between the front positive lens group G _3F and the rear negative lens group G _3R. Focal length f of the front system
Aberration diagrams at = 71.500 mm, 135.000 mm, and 205.000 mm are shown in FIG.

It is clear from each aberration diagram that any of the examples maintains excellent imaging performance in the entire zoom range.

(Effects of the Invention) As described above, according to the present invention, a telephoto zoom lens that is compact and has excellent imaging performance over the entire zoom range can be achieved.

[Brief description of drawings]

FIGS. 1, 3, and 5 are lens configuration diagrams of the first, second, and third embodiments according to the present invention. Second
FIGS. 4, 4 and 6 show a first embodiment according to the present invention,
It is each aberration figure of a 2nd example and a 3rd example. (Explanation of symbols of main parts) G ₁ ...... First lens group, G ₂ ...... Second lens group G ₃ ...... Third lens group G _3F ...... Front positive lens group G _{3R in} the third lens group …… Rear negative lens group L _{31 in} the 3rd lens group …… 1st lens in front positive lens group of the 3rd lens group L ₃₂ …… 2nd lens in front positive lens group of the 3rd lens group L ₃₃ ...... The third lens in the front positive lens group of the 3rd lens group L ₃₄ ...... The 4th lens in the front positive lens group of the 3rd lens group

Claims (2)

[Claims] 1. A first lens having a positive refractive power in order from the object side.
A lens group G ₁ and a second lens group G ₂ having a negative refractive power,
And a third lens group G ₃ having a positive refractive power,
Each lens group moves independently during zooming,
A telephoto zoom lens characterized by satisfying the following conditions. (1) 1.3 <f ₁ /fw<1.6 (2) 0.25 <| f ₂ /fw|<0.45 (3) 0.44 <f ₃ /fw<0.52 (5) 0.5 <β _2w / β _2T <0.6 (7) 0.55 <β _3w / β _3T <0.75 where fw: focal length of the entire system at wide end f ₁ : focal length of first lens group G ₁ f ₂ : focal length of second lens group G ₂ f ₃ : Focal length of the third lens group G ₃ β _2w : Imaging magnification β _{2T of} the second lens group G _{2 at} the wide end β _2w : Imaging magnification β _{3w of} the second lens group G _{2 at} the tele end β _3w : Third lens Imaging magnification at wide end of group G ₃ β _3T : Imaging magnification at tele end of third lens group G ₃ Wherein said third lens group G ₃ front in order from the object side positive lens group G _3F, consists of a rear negative lens group G _3R, said front positive lens group G _3F in order from the object side, positive lens L ₃₁ with its surface with a stronger curvature the image side, a biconvex positive lens L _32, is joined to the positive lens L ₃₂ of the both convex, negative lens having a surface with a stronger curvature the object side L _33. The telephoto zoom lens according to claim 1, comprising a positive meniscus lens L ₃₄ having a convex surface directed toward the object side and satisfying the following conditions. <F _3F / f ₃ <1.3 (9) 1.5 <| f _3R / f ₃ | <8.5 (10) 0.35 <f _3F / f ₃₁ <0.65 where f _3F : Front positive lens group G in the third lens group Focal length of _3F f _3R : Focal length of rear negative lens group G _3R in the third lens group f ₃₁ : First lens L ₃₁ of front positive lens group of the 3rd lens group
Focal length