JP2000180722A - Rear focusing type zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a small-sized zoom lens, even though the lens has five lens groups as a whole and high power variation ratio range from 24 to 30. SOLUTION: This lens has the five lens groups of a first group L1, having positive refractive power, a second group L2 having negative refracting power, a third group L3 having positive refracting power, a fourth group L4 having negative refracting power, and a fifth group L5 having positive refracting power in order from an object side, variable power from a wide angle end to a telephoto end is performed by the moving of the group L2 to an image surface side and the moving of the group L4 to an object side in a recessed state, focusing is performed by the moving of the group L4, the group L1 is constituted of one negative lens and two positive lenses, the group L2 is constituted of two negative lenses, one positive lens, and one negative lens, and the group L5 is constituted of one negative lens and one positive lens. If the focal distance of the group L2 is defined as F2, and the focal distance of the negative lens on a side nearest to an image surface in the group L2 is denoted as f2n3, the condition 2.2<f2n3/F2<4.6 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens of an inner focus or rear focus type (hereinafter collectively referred to as "rear focus type"). The present invention relates to a small, rear-focus type zoom lens having a large angle but a small front lens diameter and a long back focus.

[0002]

2. Description of the Related Art In recent years, as home video cameras and the like have become smaller and lighter, remarkable progress has been made in miniaturization of zoom lenses for image pickup. Emphasis is placed on simplification.

As one means for achieving these objects, there is known a so-called rear focus type zoom lens which performs focusing by moving a lens group other than the first group on the object side.

In general, a rear focus type zoom lens has a smaller effective diameter of the first group than a zoom lens which moves and focuses the first group, so that the entire lens system can be easily miniaturized, and close-up photography can be performed. In particular, extremely close-up photography is facilitated, and since the relatively small and lightweight lens group is moved, the driving force of the lens group is small, and there are advantages such as quick focusing.

A zoom lens having a relatively high zoom ratio and comprising five lens groups as a whole has been proposed, for example, in Japanese Patent Application Laid-Open No. H5-221567. According to the publication, a first lens group having a positive refractive power in order from the object side,
A second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power, and a fifth lens group having a positive refractive power. A rear-focus type zoom lens that performs zooming by moving a lens group and performs focusing by moving a third to a fifth lens group is disclosed.

On the other hand, the applicant of the present invention has disclosed a first lens unit having a positive refractive power and a second lens unit having a negative refractive power in order from the object side in JP-A-8-5913 and JP-A-8-190051. A lens group, a third lens group having a positive refractive power,
A fourth lens group having a negative refractive power, and a fifth lens group having a positive refractive power, wherein the second lens group and the fourth lens group are moved to perform zooming, and the fourth lens group is moved. A rear focus type zoom lens characterized by performing focusing by moving a group is disclosed.

[0007]

Generally, when a rear focus system is adopted in a zoom lens, the overall lens system is reduced in size as described above, quick focusing becomes possible, and close-up photographing becomes easier. can get.

On the other hand, in recent zoom lenses, it is desired to make the entire lens system compact and at the same time to increase the zoom ratio. In order to increase the zoom ratio of a zoom lens, the number of lens units contributing to zooming is increased, or the refractive power of the lens unit contributing to zooming is increased to increase the zooming effect, or What is necessary is just to increase the amount of movement of the lens group that contributes to the magnification.

However, simply increasing the refractive power of the lens unit for zooming or increasing the amount of movement of the lens unit for zooming increases the occurrence of various aberrations and improves image quality over the entire zooming range. It becomes difficult to obtain the image, and the entire lens system becomes larger.

According to the present invention, in a five-unit zoom lens, a magnification ratio of about 24 to 30 is mainly set by appropriately setting a moving condition of each lens group accompanying zooming, a lens configuration of each lens group, and the like. It is an object of the present invention to provide a rear focus type zoom lens having high optical performance over the entire zoom range and over the entire screen.

[0011]

According to the present invention, there is provided a rear focus type zoom lens comprising: (1-1) a first unit having a positive refractive power, a second unit having a negative refractive power, and a positive refraction in order from the object side. A third group of power, a fourth group of negative refractive power,
The zoom lens has five lens units, a fifth lens unit having a positive refractive power, and when zooming from the wide-angle end to the telephoto end, the second unit is moved to the image plane side, and the fourth unit is concave toward the object side. Move to
Focusing is performed by moving the fourth group, and the first group is moved by 1
The second group is composed of two negative lenses and two positive lenses.
The fifth group includes one negative lens, one positive lens, and one negative lens, and the fifth group includes one negative lens and one positive lens. The focal length of the second group is F2. When the focal length of the negative lens closest to the image plane in the second group is f2n3, the following condition is satisfied: 2.2 <f2n3 / F2 <4.6 (1)

[0012]

FIG. 1 is a sectional view of a wide-angle end lens according to a first numerical embodiment of the present invention. 2 and 3 are aberration diagrams at the wide-angle end and at the telephoto end according to Numerical Embodiment 1 of the present invention. FIG. 4 is a lens cross-sectional view at a wide angle end according to Numerical Example 2 of the present invention. 5 and 6 are aberration diagrams at the wide-angle end and at the telephoto end in Numerical Embodiment 2 of the present invention. FIG. 7 is a lens sectional view at the wide-angle end according to Numerical Example 3 of the present invention. 8 and 9 show a third embodiment of the present invention.
3 is an aberration diagram at a wide-angle end and a telephoto end of FIG. FIG. 10 is a sectional view of a lens at a wide angle end according to Numerical Example 4 of the present invention. FIGS. 11 and 12 are aberration diagrams at the wide-angle end and at the telephoto end according to Numerical Embodiment 4 of the present invention.

In the drawing, L1 is a first lens unit having a positive refractive power, L2 is a second lens unit having a negative refractive power, L3 is a third lens unit having a positive refractive power, and L4 is a positive lens.
Denotes a fourth unit having a negative refractive power, L5 denotes a fifth unit having a positive refractive power, and
P denotes an aperture, which is provided in front of the third lens group. IP is an image plane. G is a glass block such as a face plate and a filter.

In this embodiment, when zooming from the wide-angle end to the telephoto end, the second lens unit is moved to the image plane side as indicated by an arrow, and the image plane fluctuation due to zooming is reduced by moving the fourth lens unit to a concave shape toward the object side. The movement is corrected while having a locus.

Also, a rear focus system is employed in which the fourth unit is moved on the optical axis to perform focusing. A solid line curve 4a and a dotted line curve 4b of the fourth lens group shown in the same figure show the image plane fluctuation caused by zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at a short distance, respectively. The movement locus for correction is shown. The first and fifth units are fixed during zooming and focusing.

In this embodiment, for example, when focusing from an object at infinity to an object at a short distance at the telephoto end, the fourth unit is moved backward as indicated by a straight line 4c in FIG.

In the present embodiment, a rear focus system in which the fourth lens unit is moved and focused is used instead of the general conventional front focus system in which the first lens unit is moved out to perform focusing. The focus is shortened and focusing on a short-distance object is facilitated.

In addition, a high zoom ratio can be obtained by moving the second lens unit of the zoom lens according to the present embodiment from the wide-angle end to the telephoto end so that the lateral magnification β2 exceeds the unity magnification (β2 = −1). On the other hand, as described above, by moving the fourth unit so as to draw a concave locus on the object side, the space efficiency is increased, and the effective diameter of the first unit is shortened. While trying, a high zoom ratio is obtained.

At this time, in order to simplify the lens barrel structure, it is desirable to fix the third lens unit. However, the third lens unit may be moved so that zooming is shared between the third lens unit. By doing so, it becomes easy to give a high zoom ratio while achieving further miniaturization.

In this embodiment, the first group is composed of one negative lens and two positive lenses, the second group is composed of three negative lenses and one positive lens, and the fifth group is composed of one lens. Negative lens and 1
A zoom that is made compact while providing a high zoom ratio by setting the focal length of the second group and the focal length of the negative lens closest to the image plane in the second group as described above. The lens has achieved.

Next, the technical meaning of the conditional expression (1) will be described.

Conditional expression (1) relates to the refracting power of the negative lens closest to the image plane in the second lens unit, and is intended to reduce the fluctuation of aberration due to high magnification while achieving compactness. . When the focal length of the negative lens becomes shorter than the lower limit of the conditional expression (1) and the power becomes strong, the principal point position of the second lens unit becomes closer to the image plane. And it becomes difficult to reduce the diameter of the front lens. Conversely, if the value exceeds the upper limit, it becomes difficult to satisfactorily correct chromatic aberration fluctuation and the like.

In this embodiment, it is more preferable to set the numerical range of the conditional expression (1) as follows: 2.4 <f2n3 / F2 <4.3 (1a).

In the present invention, in order to obtain a compact rear focus type zoom lens which has good optical performance from the wide angle end to the telephoto end and has good optical performance over the entire object distance, the following conditions must be satisfied. It is better to satisfy at least one of the following.

(A-1) The fifth lens group has at least one aspherical surface.

(A-2) An aperture is arranged closest to the object side of the third lens unit.

(A-3) The aperture diameter of the stop varies with the position of the second and fourth units in the optical axis direction.

(A-4) The focal lengths of the entire system at the wide-angle end and the telephoto end are Fw and Ft, respectively, the focal length of the i-th group is Fi, and the fourth and fifth groups of an infinite object at the wide-angle end are When the lens interval of the group is D45w∞,

[0029]

(Equation 2) Satisfying the following conditions.

Conditional expression (2) defines the range of movement of the fourth lens unit which performs correction of the image plane fluctuation due to zooming and performs the focusing action. If the lower limit is exceeded, it becomes difficult to perform focusing on a sufficiently close object. If the upper limit value is exceeded, focusing can be performed relatively easily, but the entire lens becomes undesirably large.

Conditional expression (3) relates to the focal lengths of the first and second lens units. In order to maintain compactness while maintaining high zoom ratio and maintain good optical performance with a long back focus. belongs to. If the focal length of the second lens unit is longer than the lower limit of conditional expression (3) and the focal length of the first lens unit is short, the amount of movement of the second lens unit is increased, and it is difficult to reduce the overall length or the front lens diameter. become. In addition, there is also a problem that the amount of movement of the fourth lens unit near the telephoto end becomes large, and the fluctuation of aberration during zooming becomes large. Conversely, if the upper limit is exceeded, it becomes difficult to satisfactorily correct various aberrations such as distortion.

Conditional expression (4) relates to the focal length of the second lens unit. If the focal length of the second lens unit becomes shorter than the lower limit of conditional expression (4), the Petzval sum becomes negative and large, and it becomes difficult to correct aberrations such as image plane tilt. Conversely, if the focal length of the second lens unit becomes longer than the lower limit, the amount of movement of the second lens unit increases, and the diameter of the front lens becomes too large.

The conditional expression (5) is an expression relating to the focal length of the fourth lens unit. The exit pupil position of the present zoom lens is set so as not to be too short, and the oblique light beam from the object side has a small angle to the entrance pupil. This is a condition for contributing to miniaturization of the front lens diameter. If the upper limit of conditional expression (5) is exceeded, the oblique luminous flux cannot be set at a shallow angle, causing an increase in the front lens diameter. If the lower limit is exceeded, the exit pupil becomes too short on the plus side, and solid-state imaging is performed. It is not possible to secure a telecentric light flux for the element, and the aberration variation is large with respect to zoom and focus, which is not appropriate. If it is in this range, it will not be a large movement for distance adjustment (focusing), contributing to miniaturization. Conversely, if it is out of the range, the front lens diameter will be large and the whole system will be large, and furthermore, the image sensor On the other hand, it becomes impossible to set an appropriate injection angle.

As described above, by setting the conditional expressions (2) to (5), it is possible to achieve a high zoom ratio. However, even with a high zoom ratio, a small size and good aberration correction are achieved. It is preferable to set the numerical ranges of the conditional expressions (2) to (5) as follows.

[0035]

(Equation 3) (A-5) The Abbe numbers of the materials of the positive lens and the negative lens constituting the fourth unit are ν4p and ν4n, respectively, and the focal length of the i-th unit is Fi.
Ν4n−ν4p> 26.3 (6) −1.27 <F4 / F5 <−0.90 (7)

Conditional expression (6) relates to the Abbe number of the glass material of the lens constituting the fourth lens unit. If the value deviates from this range, it becomes difficult to suppress fluctuations in aberrations caused by focusing, especially fluctuations in chromatic aberrations. At this time, the positive lens and the negative lens are preferably bonded together.

Conditional expression (7) relates to the ratio of the focal lengths of the fourth and fifth lens units, and relates to the position of the exit pupil. When the value exceeds the upper limit, the refractive power of the fourth lens unit becomes strong, and the fluctuation of focusing distance becomes large, which is not appropriate. On the other hand, if the lower limit value is exceeded, the moving amount of focusing becomes large and the size becomes large, which is not suitable. In addition, the refractive power of the fifth group, which is a fixed imaging lens, becomes strong and the exit pupil becomes short, which is not suitable.

In the present embodiment, it is more preferable to set the numerical ranges of the conditional expressions (6) and (7) as follows.

Ν4n−ν4p> 27.8 (6a) −1.20 <F4 / F5 <−0.95 (7a) (A-6) The first group has the convex surface facing the object side. A negative lens having a meniscus shape, a positive lens having both lens surfaces convex, and a positive lens having a convex surface facing the object side.

(A-7) The second group is composed of a meniscus negative lens having a convex surface facing the object side, a negative lens having both lens surfaces concave, a positive lens having both lens surfaces convex, and a concave surface having a concave surface on the object side. Is constituted by a negative lens directed to

(A-8) The third unit is composed of a positive lens having a convex surface facing the image surface side, a positive lens and a negative lens having both convex lens surfaces, or a cemented lens in which these are joined. .

(A-9) The fourth unit is composed of a meniscus positive lens having a convex surface facing the image surface side, a negative lens having both lens surfaces concave,
Or, it is composed of a laminated lens in which they are joined.

(A-10) The fifth unit includes a meniscus negative lens having a convex surface facing the object side, a positive lens having both lens surfaces convex,
Or, it is composed of a laminated lens in which they are joined.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air gap from the object side, and Ni and νi are the glass of the i-th lens from the object side. Refractive index and Abbe number.

In the numerical examples, the last two lens surfaces indicate an optical filter, a face plate, and the like.
These can be omitted as necessary.

The aspherical shape has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis, a positive direction of light propagation, R represents a paraxial radius of curvature, and B, C, D, and E represent aspherical coefficients. And when

[0047]

(Equation 4) It is represented by the following expression. " ^EX " means "10-X".

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples.

[0049]

[Outside 1]

[0050]

[Outside 2]

[0051]

[Outside 3]

[0052]

[Outside 4]

[0053]

[Table 1]

[0054]

According to the present invention, as described above, in the five-unit zoom lens, by appropriately setting the moving conditions of each lens unit mainly due to zooming, the lens configuration of each lens unit, and the like, It is possible to achieve a rear-focusing zoom lens having a high optical performance over the entire zoom range of a zoom ratio of about 24 to 30 times and over the entire screen.

In particular, according to the present invention, by setting the refractive power of each lens unit as described above, the front lens diameter is small, the angle of view is wide, and the zoom ratio is reduced from 24 while the size of the entire lens system is reduced. The rear focus type has a large aperture ratio that achieves good aberration correction over the entire zoom range, has a small variation in aberration during focusing, and has a sufficiently long back focus ratio, while having a high zoom ratio of about 30 times. A zoom lens 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 a telephoto end in Numerical Example 1 of the present invention;

FIG. 4 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 5 is an aberration diagram at a wide angle end according to Numerical Example 2 of the present invention.

FIG. 6 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention;

FIG. 7 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 8 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 9 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

FIG. 10 is a sectional view of a lens according to a numerical example 4 of the present invention.

FIG. 11 is an aberration diagram at a wide angle end according to Numerical Embodiment 4 of the present invention.

FIG. 12 is an aberration diagram at a telephoto end in Numerical Example 4 of the present invention.

[Explanation of symbols]

 L1 First group L2 Second group L3 Third group L4 Fourth group L5 Fifth group SP Aperture d d-line g g-line ΔM Meridional image plane ΔS Sagittal image plane

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H087 KA03 MA15 PA11 PA20 PB14 QA02 QA07 QA17 QA21 QA25 QA34 QA42 QA46 RA05 RA12 RA13 RA32 RA42 RA43 SA43 SA47 SA49 SA53 SA55 SA63 SA64 SA65 SA72 SA74 SA76 SB04 SB15 SB24 SB33 SB43

Claims (5)

[Claims] 1. A first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a negative refractive power, and a positive refractive power in order from the object side. The fifth group has five lens groups. When zooming from the wide-angle end to the telephoto end, the second group is moved to the image plane side, and the fourth group is concavely moved to the object side. Focusing is performed by moving the fourth group, the first group is composed of one negative lens and two positive lenses, the second group is composed of two negative lenses and one positive lens, and The fifth group is composed of one negative lens and one positive lens, the focal length of the second group is F2, and the second group is
A rear-focusing zoom lens that satisfies the following condition: 2.2 <f2n3 / F2 <4.6, where the focal length of the negative lens closest to the image plane in the group is f2n3. 2. The rear focus type zoom lens according to claim 1, wherein said fifth group has at least one aspherical surface. 3. The rear focus type zoom lens according to claim 1, wherein an aperture is arranged closest to the object side of said third lens unit. 4. The rear focus type zoom lens according to claim 1, wherein an opening diameter of the stop changes depending on a position of the second group and the fourth group in the optical axis direction. 5. The focal lengths of the entire system at the wide-angle end and the telephoto end are Fw and Ft, respectively, the focal length of the i-th group is Fi, and the fourth and fifth lens groups at infinity at the wide-angle end. When the interval is D45w∞, 4. The method according to claim 1, wherein the following condition is satisfied.
Or a rear focus type zoom lens of 4.