JP2001183581A - Medium telephoto lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the fluctuation of various kinds of aberration from an infinite distance to a close distance of a photographing magnification of about 0.15. SOLUTION: The lens is constituted of a 1st lens group G1 whose refractive power is positive, a 2nd lens group G2 whose refractive power is positive or negative, and a 3rd lens group G3 whose refractive power is positive in order from an object side, and at focusing, the 1st lens group G1 is fixed, and the 2nd lens group G2 and the 3rd lens group G3 are moved along an optical axis A, and the moving speed of the 3rd lens group G3 is made higher than that of the 2nd lens group G2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an F-number 2.
8. The present invention relates to a medium telephoto lens having little variation in various aberrations from infinity at an angle of view of about 26 ° to a close distance of a photographing magnification of about 0.15.

Conventionally, this kind of medium telephoto lens has a configuration based on a Gaussian lens. When focusing, the entire telephoto lens is extended, and the entire front side is extended except for the last convex lens.
Furthermore, it was common practice to float the last convex lens.

However, in recent years, since auto focus, that is, AF is the mainstream, an inner focus system or a rear focus system in which a part of a lens group inside an optical system is moved to perform focusing in order to reduce the weight of the focus lens group. Focusing methods such as a focus method have come to be used, and the above-described whole extension and a focusing method based thereon have been reduced.

That is, in the inner focus method,
For example, JP-A-5-157964 and JP-A-4-25
No. 5813, JP-A-7-199066 and JP-A-64-78208 disclose the rear focus method.
Japanese Patent Application Laid-Open Publication No. 3-200909 discloses ones as disclosed respectively.

The focusing system disclosed in JP-A-5-157964 and JP-A-4-255613 comprises three groups: positive, negative, and positive, and moves a negative lens toward the image side. This is a so-called inner focus method in which focusing is performed, and the configuration is suitable for AF since the weight of the focusing lens group can be reduced.

However, such a configuration is very close to the basic positive / negative asymmetric configuration of the telephoto lens even though it is composed of three groups, and the negative refracting power sandwiched between the positive lens groups tends to increase. Therefore, fluctuations of various aberrations including distortion become extremely large, and it becomes difficult to increase the shortest photographing magnification.

The focusing method disclosed in Japanese Patent Application Laid-Open Nos. 64-78208 and 3-200909 has a structure of two groups, positive and positive, in which the positive lens of the rear group is moved. This is a so-called rear focus system in which focusing is performed, and although the weight of the focusing unit is slightly heavier than the above-described positive, negative, and positive configurations, symmetry is improved and favorable aberration correction is possible. However, since the symmetry is lost by focusing, fluctuation of various aberrations including astigmatism becomes a problem, and the shortest photographing magnification can be achieved only up to about 0.1.

On the other hand, the focusing method disclosed in Japanese Patent Application Laid-Open No. Hei 7-199066 is basically the same as the above-described positive and positive two-group rear focusing method, but further behind it. By arranging a fixed positive lens with a low refractive power, fluctuations in astigmatism during short-distance focusing are suppressed, but this also causes aberrations in the short range from infinity to the shortest shooting magnification of about 0.1. Variations can only be corrected relatively well.

[0009]

However, when the focusing method based on the conventional rear focus method is applied to the medium telephoto lens of the present invention, the same problems as described above occur. (A) and (b) of FIG.
FIGS. 4A and 4B are explanatory diagrams showing a basic configuration of an optical system in which a configuration of a rear focus system is shown by a simple power arrangement, wherein FIG. 4A shows a case of focusing on infinity and FIG. I have.

This conventional rear focus lens has positive,
Focusing is performed from infinity to a short distance by moving the rear positive lens group on the optical axis A toward the object side. Note that, in FIG. 18, m indicates a marginal ray of the on-axis light beam, and p indicates a principal ray of the off-axis light beam.

Now, the principal ray p of the off-axis light beam passes through the intersection of the rear group, which is the focus lens group, and the optical axis A, and the incident ray of the marginal ray m of the on-axis light beam to the front group with respect to the short-distance object point. Assuming that the height h1 is the same as that at the time of focusing at infinity, the height h1 ′ of the principal ray p of the off-axis light beam incident on the front group decreases at a short distance due to focusing. growing. Further, since the symmetry is impaired, fluctuations of various aberrations such as coma, distortion, and chromatic aberration of magnification tend to increase. The present invention has been made in view of the above points, and an object of the present invention is to provide a medium telephoto lens in which various aberrations change little from infinity to a close distance of about 0.15 in magnification.

[0012]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides, in order from the object side, a first lens having a positive refractive power.
A lens group, a second lens group having a positive or negative refractive power, and a third lens group having a positive refractive power,
During focusing, the first lens group is fixed, the second lens group and the third lens group move at different speeds along the optical axis, and a medium telephoto lens satisfying the following conditional expression. To provide. (1) 1.6 <f1 / f <2.2 (2) −0.63 <f / f2 <0.53 (3) 0.64 <f3 / f <1.9 (4) 0.5 < X2 / X3 <1 where f: focal length of the entire system when focused on infinity f1: focal length of the first lens group f2: focal length of the second lens group f3: focal length of the third lens group X2: infinity The second when focusing from a distance to the shortest shooting distance
Movement amount of lens group X3: Second lens when focused from infinity to shortest shooting distance
Movement amount of lens group

In the above-mentioned medium telephoto lens,
The first lens group includes at least two positive lens components and one negative lens component from the object side, and the second lens group includes a positive lens component, a negative lens component, and a negative lens component and a positive lens component from the object side. It is preferable that the third lens group has a positive lens component.

Further, in the above-mentioned medium telephoto lens, it is possible to further improve the performance by satisfying the following conditional expressions. (5) 1.35 <D1 / D2 <5.9, where D1: the distance between the first lens group and the first lens group in the infinity in-focus state D2: the second lens group and the second lens group in the infinity in-focus state Distance from three lens groups

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments and examples of the present invention will be specifically described below with reference to the drawings. 1 to 8
FIGS. 9 to 16 are configuration diagrams of Embodiments 1 to 8 of the present invention.
9 is an aberration curve diagram of Examples 1 to 8. FIG.

A middle telephoto lens according to the present invention comprises, as shown in FIG. 1, for example, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive or negative refractive power in order from the object side. A third lens group G3 having a positive refractive power. During focusing, the first lens group G1 is fixed, and the second lens group G2 and the third lens group G3 are arranged along the optical axis A. Move at different speeds.

F is the focal length of the entire system when focused on infinity, and f1 and f2 are the first and second lens groups G1 and G, respectively.
When the focal length is 2, (1) 1.6 <f1 / f <2.2 (2) −0.63 <f / f2 <0.53 (3) 0.64 <f3 / f <1. 9 to determine the focal length of each group.

The second and third lens groups G when X2 and X3 are respectively focused from infinity to the shortest photographing distance.
(4) The moving amounts of the second and third lens groups G2 and G3 during focusing are set such that 0.5 <X2 / X3 <1.

The first lens group G1 includes, from the object side, at least two positive lens components, first and second lenses L1 and L2, and one negative lens component, a third lens L3.
The second lens group G2 includes, from the object side, a fourth lens L4 that is a positive lens component, a fifth lens L5 that is a negative lens component with an aperture stop S interposed therebetween, and a sixth lens L6 that is a negative lens component. The third lens group G3 includes an eighth lens L8, which is a positive lens component.

Further, when D1 and D2 are set at infinity, the distance between the first and second lens groups G1 and G2,
When the distance between the third lens groups G2 and G3 is satisfied, the following conditional expression is satisfied: (5) 1.35 <D1 / D2 <5.9.

According to such a configuration, the symmetry of the entire optical system is maintained, and fluctuations of various aberrations such as coma, distortion, and chromatic aberration of magnification can be suppressed. Less than,
The reason will be described with reference to FIG. (A) of FIG.
(B) is an explanatory view showing a basic configuration of an optical system according to the present invention, (a) shows a focusing state at infinity, and (b) shows a focusing state at a short distance, which is the same as FIG. 18 described above. Where m is the marginal ray of the on-axis light beam, and p is the principal ray of the off-axis light beam.

The first lens group G1 has a positive refractive power as a whole, the second lens group G2 has a positive or negative relatively weak refractive power, and the third lens group G3 has a positive refractive power. In focusing, the third lens group G3 is moved in the same direction on the optical axis X at a higher speed than the second lens group G2. At this time, the third factor that is greatly related to zooming is
The second lens group G2 has a role of maintaining the symmetry of the entire optical system.

Now, the principal ray p of the off-axis light beam passes through the intersection of the second lens group G2 and the optical axis A, and the marginal ray m of the on-axis light beam incident on the short-distance object point enters the first lens group G1. Assuming that the ray height h1 is the same as the incident ray height h1 at the time of focusing on infinity, the movement amount of the second lens group G2 is smaller than the movement amount of the third lens group G3. The rate of change of the ray height h1 'of p passing through the first lens group G1 can be made smaller than in the case of FIG.

At this time, the ray height h3 'when the principal ray p of the off-axis light beam passes through the third lens group G3 also changes.
This is because, by appropriately setting the amount of relative movement of the third lens group G3 with respect to the second lens group G2, it is possible to suppress a change in the ray height to be small. This makes it possible to reduce the fluctuation force of the ray heights h1 'and h3' when the principal ray p of the off-axis light beam passes through the first and third lens groups G1 and G3. The marginal ray m of the upper luminous flux passes through the third lens group G3, and the ray height h3 increases on the short distance side, and the fluctuations in the ray heights h1 'and h3' are canceled out by the aberration coefficient. It is possible to reduce the fluctuation of aberration.

Further, the movement of the second and third lens groups G2 and G3 causes the ray heights h1 'and h3' to have different signs, and the ray heights h1 'and h3' increase or decrease in absolute value due to focusing. Change in the same direction, the symmetry of the optical system is maintained, and fluctuations such as coma, distortion, and chromatic aberration of magnification are reduced.

Next, the reasons for the conditional expressions (1) to (5) will be described. Conditional expressions (1) to (3) define the refractive power of the first, second, and third lens groups G1, G2, and G3. If the value of conditional expression (1) exceeds the upper limit, the first
The refractive power of the lens group G1 becomes weak, and the total length increases,
Below the lower limit, the overall length is relatively short, but the refractive power of the first lens group G1 becomes too strong, and the fluctuation of spherical aberration at the time of focusing increases.

Conditional expression (2) is a condition for setting the refracting power of the second lens group G2 as weak as possible. If the value deviates from the upper and lower limits, the axis of the second lens group G2 at the time of focusing is set. Fluctuations in the ray height of the marginal ray m of the upper light beam become large, which greatly affects fluctuations in various aberrations. That is, conditional expression (2)
Deviates from the positive side to the positive side, the fluctuation of the spherical aberration at the time of focusing becomes large.

If the value of conditional expression (3) exceeds the upper limit, the refracting power of the third lens group G3 becomes too weak to obtain the required shortest photographing magnification. The refracting power of the third lens group G3 becomes too strong, and the symmetry of the entire system is broken, and various aberrations such as spherical aberration, coma, astigmatism, field curvature, distortion, and chromatic aberration of magnification upon focusing are reduced. Fluctuations increase.

Conditional expression (4) satisfies the first to third lens groups G1
After setting the refractive powers of G1 to G3 as in the conditional expressions (1) to (3), fluctuations of various aberrations during focusing are suppressed. If the value exceeds the upper limit, the third lens group G
3 is smaller than the movement of the second lens group G2, the second lens group G2 must be obtained before the required minimum photographing magnification is obtained.
May interfere with the first lens group G1.

On the other hand, when the value goes below the lower limit of conditional expression (4), the amount of movement of the second lens group G2 relative to the amount of movement of the third lens group G3 is too small, and in particular, fluctuations of various aberrations including astigmatism. Can not be suppressed enough. By satisfying the following condition: 0.6 <X2 / X3 <0.84, a further effect can be obtained. By satisfying these conditional expressions (1) to (4), it becomes possible to perform favorable aberration correction for the middle telephoto lens according to the present invention.

In the above-described medium telephoto lens, the first
By controlling the generation of spherical aberration, coma, and astigmatism while converging a light beam, the lens group G1 includes at least two positive lens components and one negative lens component from the object side. Can be.

The second lens group G2 is of a so-called tesser type comprising a positive lens component, a negative lens component, and a cemented lens of a negative lens component and a positive lens component from the object side.
The relay from the first lens group G1 to the third lens group G3 is performed while suppressing fluctuations of various aberrations such as coma and astigmatism during focusing.

Further, on the front side of the second lens group G2,
Alternatively, the aperture stop S may be located between the positive lens component and the negative lens component or between the negative lens component and the cemented lens.
And moving it integrally with the second lens group G2, it is possible to further enhance the effect of correcting aberration fluctuations during focusing. The third lens group G3 has a positive lens component, and suppresses the fluctuation of coma aberration with respect to the off-axis light beam while performing the main focusing action.

Finally, the conditional expression (5) is for appropriately setting the distance between the respective lens groups at the time of focusing. When the value exceeds the upper limit, the second and third lens groups G2 , G3 become too small and interfere with the second and third lens groups G2 and G3 before the required shortest photographing magnification is obtained. If the distance falls below the lower limit, the distance from the first surface to the last surface of the optical system is reduced. Becomes longer, which causes insufficient peripheral light quantity at the time of focusing on infinity.

[0035]

Next, preferred embodiments of the medium telephoto lens according to the present invention will be described. In the following examples, f: focal length of the entire system Fn: F number 2ω: angle of view I: surface number

The following Tables 1 to 8 show Examples 1 to 8
Are shown.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

[Table 4]

[0041]

[Table 5]

[0042]

[Table 6]

[0043]

[Table 7]

[0044]

[Table 8]

[0045]

As described above, in the middle telephoto lens according to the present invention, the invention according to claim 1 has various aberrations, particularly astigmatism, when focusing, compared to the conventional rear focus method.
Fluctuations such as coma, distortion, and chromatic aberration of magnification can be suppressed to a small extent, and good performance can be obtained from infinity to a short distance at a photographing magnification of about 0.15.

According to the second aspect of the present invention, the effect of correcting aberration fluctuation at the time of focusing is further improved.
It becomes possible to suppress the fluctuation of the coma aberration with respect to the off-axis light beam. Further, according to the third aspect of the invention, in addition to the above effects, it becomes easy to obtain a required minimum photographing magnification,
In addition, it is possible to prevent a peripheral light quantity shortage at the time of focusing on infinity.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a third embodiment of the present invention.

FIG. 4 is a configuration diagram of a fourth embodiment of the present invention.

FIG. 5 is a configuration diagram of a fifth embodiment of the present invention.

FIG. 6 is a configuration diagram of a sixth embodiment of the present invention.

FIG. 7 is a configuration diagram of a seventh embodiment of the present invention.

FIG. 8 is a configuration diagram of Embodiment 8 of the present invention.

FIG. 9 is an aberration curve diagram according to the first embodiment of the present invention.

FIG. 10 is an aberration curve diagram according to the second embodiment of the present invention.

FIG. 11 is an aberration curve diagram according to the third embodiment of the present invention.

FIG. 12 is an aberration curve diagram according to the fourth embodiment of the present invention.

FIG. 13 is an aberration curve diagram according to the fifth embodiment of the present invention.

FIG. 14 is an aberration curve diagram according to the sixth embodiment of the present invention.

FIG. 15 is an aberration curve diagram according to the seventh embodiment of the present invention.

FIG. 16 is an aberration curve diagram of the eighth embodiment of the present invention.

FIG. 17 is an explanatory diagram showing a basic configuration of an optical system of a middle telephoto lens according to the present invention.

FIG. 18 is an explanatory diagram showing a basic configuration of an optical system of a conventional middle telephoto lens.

[Explanation of symbols]

 G1 to G3: first to third lens groups L1 to L9: first to ninth lenses r1 to r18: radii of curvature of first to eighteenth surfaces d1 to d17: surface intervals of each lens m: axis Peripheral ray of upper beam p: principal ray of off-axis beam S: aperture stop A: optical axis ω: half angle of view ΔM: meridional ΔS: sagittal

Claims (3)

[Claims] 1. A first lens having a positive refractive power in order from the object side.
A lens group, a second lens group having a positive or negative refractive power, and a third lens group having a positive refractive power,
In focusing, the first lens group is fixed, the second lens group and the third lens group move at different speeds along the optical axis, and satisfy the following conditional expressions. Medium telephoto lens. (1) 1.6 <f1 / f <2.2 (2) −0.63 <f / f2 <0.53 (3) 0.64 <f3 / f <1.9 (4) 0.5 < X2 / X3 <1 where f: focal length of the entire system when focused on infinity f1: focal length of the first lens group f2: focal length of the second lens group f3: focal length of the third lens group X2: infinity The second when focusing from a distance to the shortest shooting distance
Movement amount of lens group X3: 3rd when focused from infinity to shortest shooting distance
Movement amount of lens group 2. The first lens group includes at least two lenses from the object side.
The second lens group includes one positive lens component and one negative lens component, and the second lens group includes a positive lens component, a negative lens component, and a cemented lens of a negative lens component and a positive lens component from the object side, and the third lens group. 2. The mid-telephoto lens according to claim 1, further comprising a positive lens component. 3. The middle telephoto lens according to claim 1, wherein the following conditional expression is satisfied. (5) 1.35 <D1 / D2 <5.9, where D1: the distance between the first lens group and the second lens group in the infinity in-focus state D2: the second lens group and the second lens group in the infinity in-focus state Distance from three lens groups