JP2002287031A - Zoom lens and optical equipment using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens whose viewing angle at a wide angle end is set as 105 deg., whose variable power ratio is set as 2 and whose FNo is set as 2.8 and which has excellent optical performance, and to provide optical equipment using the same. SOLUTION: This zoom lens possesses the first lens group of negative refracting power, the second lens group of positive refracting power, third lens group of the negative refracting power and the fourth lens group of the positive refracting power in order from an object side. The first lens group is moved with a projected locus to an image side at the time of variable power. At the time of the variable power from the wide angle end to a telephoto end, the second lens group is moved to the object side so as to make an interval with the first lens group smaller, and the forth lens group is moved to the object side so as to make an interval with the third lens group smaller. The interval between the third lens group and the second lens group at the telephoto end is made larger than that at the wide angle end, so that the focal distance fi of an i-th lens group is appropriately set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens and an optical apparatus using the same, and more particularly, to a film camera, a video camera, and a digital camera having an excellent optical performance including a super wide angle range and a large aperture. , SV cameras and the like.

[0002]

2. Description of the Related Art Conventionally, a so-called negative lead type zoom lens in which a lens unit having a negative refractive power precedes has a relatively short close-up distance and a relatively wide angle of view. It is often used for zoom lenses.

As a negative lead type zoom lens for a single-lens reflex camera, a zoom lens in which a lens unit having negative, positive, negative, and positive refractive power is arranged in order from the object side is known.

While this zoom type is suitable for widening the wide-angle end to a wide angle of view, the first lens unit and the second
The entire lens group constitutes a group having a positive refractive power, and the third lens group and the fourth lens group constitute a group having a negative refractive power as a whole. Since the optical system as a whole can be of a so-called telephoto type, it is bright even at the telephoto end. There is a merit that FNo (F number) is easy.

Japanese Patent Application Laid-Open Nos. 4-235515 and 10-32 disclose negative lead type zoom lenses.
Japanese Patent No. 5923 discloses a zoom lens having a field angle at the wide angle end of 100 ° or more and a zoom ratio of about 1.7.

Japanese Patent Application Laid-Open No. 10-82954 discloses a zoom lens having a field angle at the wide-angle end exceeding 100 °, a zoom ratio of about 2.0, and an FNo of about 3.5.

The applicant of the present invention has disclosed a zoom lens in Japanese Patent Application Laid-Open No. Hei 7-26084 having an angle of view at the wide-angle end of 100 ° or more, a zoom ratio of about 2.0, and an FNo of about 2.8.

[0008]

In recent years, a standard zoom lens used for a single-lens reflex camera, a video camera, a digital camera or the like has a predetermined zoom ratio, a wide angle of view, and a bright lens system. Things are desired.

The above-described zoom lens having lens units having negative, positive, negative, and positive refractive powers in order from the object side is suitable for a zoom lens for a wide angle of view, but the angle of view on the wide angle side is 100 °.
In order to provide an ultra-wide-angle zoom lens that exceeds the limit, and to ensure sufficient optical performance and zoom ratio, it is necessary to appropriately set the lens configuration.

In general, if the refractive power of each lens unit in a zoom lens is increased, the amount of movement of each lens unit to obtain a predetermined zoom ratio is reduced, so that the angle of view is increased while shortening the overall length of the lens. Becomes possible.

However, if the refractive power of each lens group is simply increased, aberration fluctuation accompanying zooming becomes large, and it is difficult to obtain good optical performance over the entire zoom range, especially when widening the angle of view. There is a problem that comes.

The present invention comprises four lens groups as a whole, and by appropriately setting the refractive power of each lens group, the lens configuration, and the moving conditions of each lens group for zooming, a wide angle of view is obtained. Further, it is an object of the present invention to provide a zoom lens having high optical performance over the entire zoom range and an optical apparatus using the same.

In addition, according to the present invention, the angle of view at the wide-angle end is about 105.
°, a zoom ratio of 2.0 or more, FNo of about 2.8, and a zoom lens having good optical performance and an optical apparatus using the same.

[0014]

According to a first aspect of the present invention, there is provided a zoom lens having a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a second lens unit having a negative refractive power. The zoom lens has three lens units and a fourth lens unit having a positive refractive power. During zooming, the first lens unit moves with a part of a locus convex toward the image side, and moves from the wide-angle end to the telephoto end. When changing the magnification of the second
The lens group moves toward the object side so that the distance from the first lens group decreases, and the fourth lens group moves toward the object side so as to reduce the distance from the third lens group. On the other hand, the distance between the third lens group and the second lens at the telephoto end increases, and the focal length of the i-th lens group is set to fi,
When the focal length of the entire optical system at the wide-angle end is fw and the focal length of the entire optical system at the telephoto end is ft, 0.9 <| f1 / fw | <1.70.6 <f2 / ft <1.2. 1.9 <| f3 / fw | <4.51.4 <f4 / (fw × ft) ^0.5 <2.5

According to a second aspect of the present invention, in the first aspect, the first lens group has two or more aspheric surfaces.

According to a third aspect of the present invention, in the second aspect, the first lens group includes an aspheric surface having a positive refractive power increasing from the optical axis toward the periphery of the lens, and a negative surface extending from the optical axis toward the periphery of the lens. Is characterized by having an aspherical surface having a high refractive power.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the fourth lens group has an aspheric surface having a negative refractive power increasing from the optical axis toward the periphery of the lens. Features.

According to a fifth aspect of the present invention, in the first aspect of the present invention, the fourth lens group has two or more cemented lenses each composed of a positive lens and a negative lens.

According to a sixth aspect of the present invention, in the invention of the fifth aspect, the Abbe number of the material of the positive lens of at least one cemented lens among the cemented lenses of the fourth lens group is ν4p
It is characterized by satisfying the condition of 80 <ν4p.

According to a seventh aspect of the present invention, in the invention of the fifth aspect, an arbitrary Abbe number among the Abbe numbers of the material of the positive lens of at least two cemented lenses of the fourth lens group is set to ν4
When pp is satisfied, a condition of 80 <ν4pp is satisfied.

According to an eighth aspect of the present invention, in the invention of any one of the first to seventh aspects, the lens closest to the image in the fourth lens group has a stronger negative refractive power from the optical axis toward the periphery of the lens. It is characterized by having an aspherical surface.

According to a ninth aspect of the present invention, there is provided an optical apparatus including the zoom lens according to any one of the first to eighth aspects.

[0023]

1 is a sectional view of a zoom lens according to a first numerical embodiment at a wide-angle end, FIG. 2 is an aberration diagram at a wide-angle end of the zoom lens according to the first numerical embodiment, and FIG. FIG. 4 is an aberration diagram at the telephoto end of the zoom lens according to Numerical Example 1 at an intermediate zoom position of the zoom lens.

FIG. 5 is a sectional view of the zoom lens according to the second embodiment at the wide-angle end, FIG. 6 is an aberration diagram at the wide-angle end of the zoom lens according to the second embodiment, and FIG. 8 is an aberration diagram at a telephoto end of the zoom lens according to Numerical Example 2. FIG.

FIG. 9 is a sectional view of the zoom lens of Numerical Embodiment 3 at the wide-angle end, FIG. 10 is an aberration diagram of the zoom lens of Numerical Embodiment 3 at the wide-angle end, and FIG. FIG. 12 is an aberration diagram at the telephoto end of the zoom lens according to Numerical Example 3. FIG.

FIG. 13 is a sectional view of the zoom lens of Numerical Embodiment 4 at the wide-angle end, FIG. 14 is an aberration diagram of the zoom lens of Numerical Embodiment 4 at the wide-angle end, and FIG. 16 is an aberration diagram at the telephoto end of the zoom lens of Numerical Example 4. FIG.

In FIG. 1, (A) shows the wide-angle end, (B) shows the intermediate zoom position, and (C) shows the telephoto end. In each lens cross-sectional view, L1 is a first group (first lens group) having a negative refractive power, L2 is a second group (second lens group) having a positive refractive power, L
Reference numeral 3 denotes a third group having a negative refractive power (third lens group), and L4 denotes a fourth group having a positive refractive power (fourth lens group). SP is an aperture stop, FC is a fixed flare cut stop, and IP is an image plane. SSP is an open FNo aperture that regulates the open F number.

The arrows indicate the movement trajectories of the respective lens units when zooming from the wide-angle end to the telephoto end. Note that at the wide-angle end and the telephoto end, the zoom positions are defined when the zooming lens group is located at both ends of a range that is mechanically movable on the optical axis.

In the present embodiment, upon zooming from the wide-angle end to the telephoto end, the first lens unit L1 is moved while having a part of a convex locus on the image plane side to reduce the image plane fluctuation accompanying the zooming. Correction is performed, and zooming is performed by moving the second, third, and fourth lens units to the object side.

At this time, the second lens unit L2 is moved so that the distance between the second lens unit and the first lens unit is reduced, and the third lens unit L3 is moved to the third lens unit.
Move the distance between the group and the second group so as to increase the distance.
The group L4 is moved so that the distance between the fourth group and the third group is reduced.

In the zoom lens of this embodiment, the focal length of the ith lens group is fi, the focal length of the entire optical system at the wide-angle end is fw, and the focal length of the entire optical system at the telephoto end is ft.
0.9 <| f1 / fw | <1.7 (1) 0.6 <f2 / ft <1.2 (2) 1.9 <| f3 / fw | <4 ... (3) 1.4 <f4 / (fw × ft) ^0.5 <2.5 (4)

When designing an ultra-wide-angle zoom lens, it is important not only to satisfy good optical performance and specifications, but also to suppress the size of the optical system, particularly the enlargement of the front lens diameter. .

The zoom lens of the present invention uses a zoom type in which a lens unit having a negative refractive power precedes, a so-called negative lead type. In this zoom lens, increasing the refractive power of the first lens unit having a negative refractive power is advantageous in reducing the diameter of the front lens. However, if the refractive power of the first lens unit having a negative refractive power is excessively increased, it becomes difficult to satisfactorily correct distortion, coma, and curvature of field particularly at the wide-angle end, and a telephoto type at the telephoto end. Since it is difficult to arrange the refractive power, it is difficult to secure a bright F-number at the telephoto end.

Conditional expression (1) is set in view of the above-mentioned reason, and is for appropriately setting the focal length of the first lens unit.

If the value exceeds the upper limit of conditional expression (1), it becomes difficult to reduce the diameter of the front lens. If the value exceeds the lower limit, it becomes difficult to correct distortion, coma and field curvature at the wide-angle end. At the telephoto end, it becomes difficult to arrange the refractive power of the telephoto type.
It becomes difficult to secure numbers.

In the zoom lens of the present invention, at the telephoto end, the first lens unit having a negative refractive power and the second lens unit having a positive refractive power have a positive refractive power as a whole.

That is, in the zoom type according to the present invention, at the telephoto end, the first lens group and the second lens group have a positive refractive power group as a whole, and the third lens group and the fourth lens group have a negative refractive power group as a whole. And the optical system as a whole is a so-called telephoto type. At this time, in the first lens group and the second lens group which are groups of positive refractive power as a whole, the first lens group having negative refractive power diverges the incident light beam, so that the second lens group has a large diameter FNo. A light beam will be incident. In particular, since a large FNo light beam is incident on a large-aperture zoom lens like the present invention, a large amount of spherical aberration is likely to occur at the telephoto end in the second lens group.

Conditional expression (2) is a condition for appropriately setting the focal length of the second lens group based on the above.

When the value exceeds the upper limit of conditional expression (2), it becomes difficult to secure a large zoom ratio, and it becomes difficult to arrange the refractive power of the telephoto type at the telephoto end. It is difficult to secure a bright F-number at the end. If the lower limit value is exceeded, it becomes difficult to satisfactorily correct spherical aberration particularly at the telephoto end.

Conditional expression (3) is to set the focal length of the third lens group appropriately and secure a bright F-number at the telephoto end.
This is for favorably correcting aberration.

When the value exceeds the upper limit of conditional expression (3), it becomes difficult to make the combined refractive power of the third lens unit and the fourth lens unit sufficiently negative at the telephoto end. This makes it difficult to secure a bright F-number at the telephoto end, because the force arrangement becomes difficult. On the other hand, if the lower limit is exceeded, good correction of coma and distortion in particular over the entire focal length range becomes difficult.

Conditional expression (4) is for appropriately setting the focal length of the fourth lens unit and favorably correcting spherical aberration at the telephoto end while mainly ensuring a long back focus.

When the value exceeds the upper limit of conditional expression (4), it becomes difficult to correct spherical aberration, particularly at the telephoto end, to secure a back focus at the wide-angle end, and to achieve a sufficient zoom ratio, and to exceed the lower limit. This makes it difficult to correct negative distortion at the wide-angle end.

In this embodiment, more preferably, the numerical ranges of the conditional expressions (1), (2), (3) and (4) are set as follows.

1.1 <| f1 / fw | <1.4 (1a) 0.75 <f2 / ft <1.0 (2a) 2.3 <| f3 / fw | <3 ... (3a) 1.6 <f4 / (fw × ft) ^0.5 <2.3 (4a) The initial objective zoom lens of the present invention is achieved by the above configuration. In order to obtain higher optical performance, it is preferable to satisfy at least one of the following conditions.

The first lens group has two or more aspherical surfaces.

If at least two aspherical surfaces are arranged in the first lens group, it becomes easy to satisfactorily correct negative distortion at the wide-angle end, which is a problem when forming an ultra-wide-angle zoom lens. .

The first lens group has an aspheric surface whose positive refractive power increases from the optical axis toward the periphery of the lens and an aspheric surface whose negative refractive power increases from the optical axis toward the periphery of the lens. That is.

The negative distortion generated by the ultra-wide-angle zoom lens tends to be a so-called jinkasa-shaped distortion in which the distortion at the periphery of the screen is generally smaller than the distortion at the intermediate angle of view. Therefore, if the first lens group is provided with an aspheric surface having a positive refractive power increasing from the optical axis toward the periphery of the lens and an aspheric surface having a negative refractive power increasing from the optical axis toward the periphery of the lens, the first lens group has This is preferable because it is easy to prevent the distortion from being excessively smaller than the distortion at the intermediate angle of view.

The fourth lens group has an aspherical surface whose negative refractive power increases from the optical axis toward the periphery of the lens.

It is preferable to dispose an aspherical surface having a negative refractive power from the optical axis toward the periphery of the lens in the fourth lens group because negative distortion at the wide-angle end can be easily corrected satisfactorily.

The fourth lens group has two or more cemented lenses composed of a positive lens and a negative lens.

If two or more cemented lenses each composed of a positive lens and a negative lens are arranged in the fourth lens group, it becomes easy to satisfactorily correct negative lateral chromatic aberration at the wide-angle end and axial chromatic aberration at the telephoto end. When the Abbe number of the material of the positive lens of at least one cemented lens among the cemented lenses in the fourth lens group is ν4p, the condition of 80 <ν4p (5) is satisfied.

Conditional expression (5) is a condition for defining the Abbe number of the material of the positive lens of the cemented lens of the four lens group, and at least one of the two or more cemented lenses of the fourth lens group. If the positive lens satisfies conditional expression (5), it becomes easy to favorably correct negative lateral chromatic aberration at the wide-angle end and axial chromatic aberration at the telephoto end. The smaller Abbe number among the Abbe numbers of the materials of the positive lenses of at least two cemented lenses in the fourth lens group is ν
When it is 4pp, it satisfies the condition of 80 <ν4pp (6).

Conditional expression (6) defines the Abbe number of the material of the positive lens of at least two cemented lenses in the fourth lens group. If conditional expression (6) is satisfied, the negative value at the wide-angle end is further reduced. Chromatic aberration of magnification and axial chromatic aberration at the telephoto end can be favorably corrected.

The lens closest to the image in the fourth lens group has an aspheric surface whose negative refractive power increases from the optical axis toward the periphery of the lens.

In the zoom lens of the present invention, the lens closest to the image in the fourth lens group has a relatively off-axis light beam passing through a position far from the optical axis at the wide-angle end. By disposing an aspherical surface having a negative refractive power increasing toward the periphery of the lens, it becomes easier to correct negative distortion at the wide-angle end.

In the aspherical surface used in the present embodiment, if the aspherical surface is arranged other than the surface closest to the object and the surface closest to the image, an aspherical layer made of resin or the like is formed on the surface of the spherical lens. May be.

Focusing from an object at infinity to an object at a short distance is performed by moving the first lens unit toward the object side. However, the first lens unit is divided into two negative lens units, and the lens unit on the image side is used. May be moved to the object side. According to this, the diameter of the front lens can be easily reduced.

In Numerical Examples 1 to 4, in order from the object side, the first lens unit L1 has a meniscus-shaped negative lens having a convex surface facing the object side, a negative lens having both lens surfaces concave, and a convex surface facing the object side. It consists of a positive lens.

The second lens unit L2 is composed of a positive cemented lens of a negative lens and a positive lens, and a cemented lens of a positive lens whose both lens surfaces are convex.

The third lens unit L3 comprises a negative lens, a cemented lens of a negative lens having both concave surfaces and a positive lens having both convex surfaces.

The fourth lens unit L4 comprises a positive cemented lens of a positive lens and a negative lens, a positive cemented lens of a negative lens and a positive lens, and a positive lens.

Next, an embodiment of a single-lens reflex camera system using the zoom lens of the present invention will be described with reference to FIG. In FIG. 17, reference numeral 10 denotes a single-lens reflex camera body, 1
1 is an interchangeable lens equipped with a zoom lens according to the present invention,
Reference numeral 12 denotes recording means such as a film or an image sensor for recording a subject image obtained through the interchangeable lens 11, reference numeral 13 denotes a finder optical system for observing a subject image from the interchangeable lens 11, and reference numeral 14 denotes a means for recording a subject image from the interchangeable lens 11. 1
This is a rotating quick return mirror for switching and transmitting between the finder optical system 2 and the finder optical system 13. When observing the subject image with the viewfinder, the subject image formed on the focus plate 15 via the quick return mirror 14 is turned into an erect image by the pentaprism 16, and then enlarged and observed by the eyepiece optical system 17. At the time of photographing, the quick return mirror 14 rotates in the direction of the arrow, and the subject image is formed on the recording means 12 and recorded.

As described above, by applying the zoom lens of the present invention to an optical device such as a single-lens reflex camera interchangeable lens, an optical device having high optical performance can be realized.

The present invention can be similarly applied to an SLR (Single lens Reflex) camera without a quick return mirror.

Next, numerical examples of the present invention will be described. In the numerical examples, i indicates the order of the surfaces from the object side, Ri is the radius of curvature of each surface, Di is the i-th and i + 1-th optical member thickness or air gap, and Ni and νi are the i-th optical members. The refractive index and the Abbe number for the d-line of the member.

In the aspherical shape, the radius of curvature at the center of the surface is R, and the displacement in the optical axis direction (light traveling direction) at a height Y from the optical axis is X with respect to the surface vertex. , A, B, C,
When D and E are aspheric coefficients respectively

[0069]

(Equation 1)

It is assumed that Note that “ ^ex ” represents “× 10 ^−x ”. Table 1 shows the relationship between some of the above-described conditional expressions and various numerical values in the numerical examples.

[0071]

[Outside 1]

[0072]

[Outside 2]

[0073]

[Outside 3]

[0074]

[Outside 4]

[0075]

[Table 1]

[0076]

According to the present invention, as described above, the lens unit is composed of four lens units as a whole, and the refracting power of each lens unit, the lens configuration, and the moving conditions of each lens unit during zooming are appropriately set. By doing so, it is possible to achieve a zoom lens having a wide angle of view and high optical performance over the entire zoom range, and an optical apparatus using the same.

According to the present invention, the angle of view at the wide-angle end is about 10
A zoom lens having 5 °, a magnification ratio of 2.0 or more, an FNo of about 2.8, and excellent optical performance, and an optical apparatus using the same can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is an aberration diagram at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 3 is an aberration diagram at an intermediate zoom position in Numerical Embodiment 1 of the present invention.

FIG. 4 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention;

FIG. 5 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 6 is an aberration diagram at a wide angle end according to Numerical Example 2 of the present invention.

FIG. 7 is an aberration diagram at an intermediate zoom position in Numerical Example 2 of the present invention.

FIG. 8 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention.

FIG. 9 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 10 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 11 is an aberration diagram at a middle zoom position in Numerical Example 3 of the present invention.

FIG. 12 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

FIG. 13 is a sectional view of a lens according to a numerical example 4 of the present invention.

FIG. 14 is an aberration diagram at a wide angle end according to Numerical Example 4 of the present invention.

FIG. 15 is an aberration diagram at an intermediate zoom position in Numerical Example 4 of the present invention.

FIG. 16 is an aberration diagram at a telephoto end in Numerical Example 4 of the present invention.

FIG. 17 is a schematic view of a main part of the optical apparatus of the present invention.

[Explanation of Symbols] L1 First group L2 Second group L3 Third group L4 Fourth group SP stop FC flare cut stop SSP open FNo stop IP image plane d d-line g g-line ΔS sagittal image plane ΔM meridional image plane

Claims (9)

[Claims] 1. 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 fourth lens group having a positive refractive power are arranged in order from the object side. During zooming, the first lens group moves with a part of a locus convex toward the image side, and moves during zooming from the wide-angle end to the telephoto end.
The lens group moves toward the object side so that the distance from the first lens group decreases, and the fourth lens group moves toward the object side so as to reduce the distance from the third lens group. On the other hand, the distance between the third lens group and the second lens at the telephoto end increases, the focal length of the i-th lens group is fi, the focal length of the entire optical system at the wide-angle end is fw, and the entire optical system at the telephoto end is 0.9 <| f1 / fw | <1.70.6 <f2 / ft <1.21.9 <| f3 / fw | <4.51.4 <f4 A zoom lens characterized by satisfying a condition of / (fw × ft) ^0.5 <2.5. 2. The zoom lens according to claim 1, wherein the first lens group has two or more aspheric surfaces. 3. The first lens group includes an aspheric surface having a positive refractive power from the optical axis toward the lens periphery and an aspheric surface having a negative refractive power from the optical axis toward the lens periphery. The zoom lens according to claim 2, further comprising: 4. The zoom according to claim 1, wherein the fourth lens group has an aspheric surface whose negative refractive power increases from the optical axis toward the periphery of the lens. lens. 5. The zoom lens according to claim 1, wherein the fourth lens group includes two or more cemented lenses each including a positive lens and a negative lens. 6. The cemented lens of the fourth lens group,
The zoom lens according to claim 5, wherein a condition of 80 <ν4p is satisfied when the Abbe number of the material of the positive lens of at least one cemented lens is ν4p. 7. The condition that 80 <ν4pp is satisfied, wherein the smaller Abbe number among the Abbe numbers of the materials of the positive lenses of at least two cemented lenses of the fourth lens group is ν4pp. Item 6. The zoom lens according to Item 5. 8. The lens according to claim 1, wherein the lens closest to the image in the fourth lens group has an aspheric surface whose negative refractive power increases from the optical axis toward the periphery of the lens. Item 2. The zoom lens according to item 1. 9. An optical apparatus comprising the zoom lens according to claim 1. Description: