JPH0250120A - Zoom lens - Google Patents

Abstract

PURPOSE:To enable high-accuracy automatic focusing over the entire range of zooming by moving a 4th lens element monotonously from an image side to an object side when the zoom lens is focused on an infinite-distance body or from the object side to the image side when the lens is focused on a short- distance body in zooming operation from the wide-angle end to the telephoto end. CONSTITUTION:When the lens is zoomed from the wide-angle end to the telephoto end, the 4th lens element IV shifts in position monotonously from the image side to the object side for the focusing on the infinite-distance body or from the body side to the image side for the focusing on the short-distance body. Namely, the focusing operation is carried out not by a 3rd lens element III as a compensator, but by a 4th lens element IV. Therefore, a tracking curve having no extremal value can be drawn. The tracking curve has no extremal value, so the speed and acceleration of the 4th lens element IV in the zooming are invariably in the same direction. Consequently, various aberrations are compensated excellently over the entire zoom range.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a zoom lens, and particularly to a zoom lens that can be applied to a small camera such as a video camera having a TTL passive type AF.

(Prior art) In recent years, electronic components for small cameras such as video cameras have been reduced in cost and made more compact at a considerable speed. It is hard to say that the technology is making any progress, and the proportion of camera bodies that are occupied by cameras is increasing year by year due to cost, weight, size, etc., and recently very high-resolution image sensors are As a result, lens systems are required to have higher optical performance than before. For this reason, there are some zoom lenses that go against the trend of becoming more compact and lightweight.

In conventional lenses, a method is often adopted in which the first lens component is extended when focusing on a nearby object. This first lens component extension method has the advantage that the focusing mechanism is simple because the lens extension for objects at a fixed distance is the same throughout the entire zoom range, but on the other hand, it is necessary to increase the effective diameter of the lower lens component. Sufficient weight reduction cannot be achieved. In addition, aberrations fluctuate greatly during zooming at close range, and especially at the telephoto end, spherical aberrations cause the image plane to fall to the under side and the image plane to the over side, making it difficult to obtain a good surface image. Those with a mechanism had problems such as increased power consumption.

In order to solve the above problems, there are known methods in which focusing is performed using a compensator that corrects image point movement due to zooming, and methods in which focusing is performed by a rear group of a master lens system that performs image formation. For example, Japanese Patent Laid-Open No. 55-40447 discloses a zoom lens that performs focusing using a compensator. However, the method disclosed in the above publication always focuses on an object at a certain distance during zooming.
The trajectory when the focusing component (compensator) is made to follow the yaw (hereinafter referred to as tracking) (hereinafter referred to as tracking)
It has an extreme value (called a tracking curve), so the direction of movement of the compensator changes around this extreme value, so tracking may go too far, or you may have to stop zooming and start zooming again around this extreme value. Sometimes, for reasons such as the movement direction of the compensator being different depending on the direction of zooming, it becomes quite difficult to control the compensator and it is difficult to improve the accuracy of AF. This situation is shown in FIG. 13.

Also, JP-A-59-28120, JP-A-59-2
Japanese Patent Application No. 8121 discloses a lens that performs focusing using the rear group of a master lens system. These examples have the advantage that the tracking curves do not have extreme values, but since focusing is performed by a lens on the image side of the aperture, a spectroscopic prism or mirror for optical path splitting is placed in front of the aperture. It was impossible to use it for a TTL passive type camera that performs AF.

Furthermore, apart from these examples, Japanese Unexamined Patent Publication No. 107-1989
No. 347 discloses a zoom solution in which the magnification of a variator that changes magnification during zooming does not include 11x so that the tracking curve does not have an extreme value. However, with such a zoom solution, the refractive coverage between each lens component deteriorates, making it difficult to properly correct various aberrations over the entire zoom range, and the amount of movement of the variator increases, making it difficult to zoom. The lens becomes larger.

(Problems to be Solved by the Invention) Therefore, an object of the present invention is to provide a zoom lens that performs focusing using a lens component other than a third lens component, which can achieve highly accurate AF over the entire zooming range. Our goal is to provide the following.

A further object of the present invention is to provide a zoom lens that enables TTL passive type AF.

A further object of the present invention is to provide a lightweight, compact, high-power zoom lens that achieves the above-mentioned objects, has aberrations well corrected, and is lightweight and compact.

(Means for Solving the Problems) In order to achieve the above object, the zoom lens of the present invention has the following features:
In order from the object side, a first lens component (1) that has positive refractive power and remains fixed during zooming, and a fifth lens component (1) that has negative refractive power and moves back and forth on the optical axis during zooming and remains fixed during zooming. When zooming from the wide-angle end to the telephoto end, the position of the fourth lens component (ff) moves monotonically from the image side to the object side when focusing on an object at infinity, and when zooming from the wide-angle end to the telephoto end, The focusing state is characterized by a monotonous movement from the object side to the image side.

In other words, the focusing operation is not performed by the third lens component (Il+), which is a compensator, but by a separate fourth lens component.
By using the lens component (ff), it is possible to draw a tracking curve that does not have extreme values.Because the tracking curve does not have extreme values,
The velocity and acceleration of the fourth lens component during zooming are always in the same direction.

Generally, when focusing is performed using a lens component other than the first lens component (1), the amount of focusing extension for the same photographing distance is larger at the telephoto end and smaller at the wide-angle end. Figure 12 shows the object distance (Sl) of the focusing lens component (fourth lens component (■)) during zooming.
) shows the movement axis traces when the object is at infinity and when it is closest to the object. As shown in Figure 12 (b), the position of the focusing lens component relative to the object at infinity remains constant regardless of the zooming state. (In other words, the tracking curve for the infinite relic object is almost stationary.) For example, if you zoom to the telephoto end while focusing on the closest object at the wide-angle end,
The amount of movement of the focusing component near the telephoto end rapidly increases. In other words, the slope of the tracking curve with respect to the closest object suddenly increases near the telephoto end.

Conversely, as shown in FIG. 12(C), the position of the focusing lens component relative to the nearest object remains constant regardless of the zooming state (that is, the tracking curve relative to the nearest object remains almost stationary). If this is done, the slope of the tracking curve for an object at infinity will suddenly increase near the telephoto end.

On the other hand, as in the zoom lens of the present invention, the position (M) corresponds to the midpoint of the amount of extension of the focusing lens component from the infinite relic object to the nearest object at the telephoto end.
If we use a solution in which the tracking curve for an object located in Tracking curves for the infinitely distant object and the closest object are obtained as shown.

Fourth lens component (ff) which is a focusing lens component
However, by drawing a tracking curve as shown in Fig. 12(a), the fourth lens component (f
The amount of movement near the telephoto end in f) is equally distributed to the object at infinity and the closest object. Therefore, the movement amount and velocity of the fourth lens component = e(ff) during zooming are small compared to those shown in FIG. 12(b) (or (C)), so the lens Control of the drive system becomes easy, and highly accurate AF can be achieved over the entire zoom range.

Further, the zoom lens of the present invention has the fourth lens component (
ff) and the fifth lens component (ma) are provided with a prism or mirror for optical path division, and a diaphragm in order from the object side. Therefore, the fourth lens l1il12'1 (ff), which is a focusing lens group, is placed closer to the object side than the aperture, and a prism for the optical path source side is placed on the image side of the fourth lens component (ff). Therefore, TTL performs focus detection using the divided luminous flux.
It becomes possible to realize a zoom lens that is optimal for cameras that perform passive type AF.

Further, in the zoom lens of the present invention, when zooming from the wide-angle end to the telephoto end, the second lens component (■) moves from the image side to the object side, and the third lens component ([1) moves from the image side to the object side. It is characterized by moving in a convex trajectory. In other words, the second lens component ([+) and the third lens component ([f
Since the relative positional relationship with f) is always fixed regardless of the object position, it has the advantage of being able to perform zoom reversal compared to the conventional method of focusing with the first lens component (1).

IC display. The second lens component (0
) moves non-linearly during zooming from the wide-angle end to the wide-angle end as shown in FIG. 11(b), so that the second lens component (b)
), the fourth lens component (ff
) can be made sufficiently small. By making the movement locus of the second lens component (11) non-linear in this way, AF control becomes easier and stable performance can be improved.

Furthermore, in order to obtain a lightweight and compact zoom lens with well-corrected aberrations, it is desirable that the first lens component (1) to the fourth lens component (IV) be configured as follows.

That is, the first lens component (I) is one negative lens and two positive lenses, the second lens component (n) is two negative lenses and one positive lens, and the third lens l1lW
The component (1) is one negative lens component, and the fourth lens component is one or two positive lens components.

As shown in FIG. 11, in the present invention, the fourth lens component (ff) moves closer to the image side when focusing on a nearby object than when focusing on an object at infinity. Sufficient air space is required on the image side. However, @Luns component (1) to 4th lens component (
ff) with the simple configuration described above,
Even if a sufficient air gap is provided between the fourth lens component (lv) and the fifth lens component (ma), it is possible to obtain a lightweight and compact zoom lens.

Furthermore, the first lens component (I) to $44 lens component (I
V) desirably satisfies the following conditions.

(1) 2.1 <lψnl/ψI <6.0(2
) 1.6 <9 mouths 79m <4.8 (3) o
, s < ψIf/ψI < 2.0 However, ψI! 1st
Refractive power ψII of lens component (I): second lens component (1
1) refractive power ψIU: refractive power ψ■ of i3 lens component (III): refractive power of fourth lens component (ff).

Condition (1) defines the refractive power of the lower two lens components (■) with respect to the first lens component (r).

If the refractive power of the second lens component (b) becomes strong beyond the upper limit of condition (1), the Petzval sum will become a large negative value, and the image plane will be greatly tilted to the underside, especially at the wide-angle end, and on the other hand, At the telephoto end, coma aberration occurs, making it impossible to obtain high-performance image quality over the entire screen. Conversely, if the lower limit of condition (1) is exceeded and the refractive power of the second lens component (I+) becomes weaker, the amount of movement required for the second lens component (b) to change magnification increases. , the total length of the lens becomes significantly longer, making it difficult to obtain a compact zoom lens. Furthermore, the difference in spherical aberration between the wide-angle end and the telephoto end increases, making it impossible to obtain high-performance image quality over the entire zoom range.

Condition (2) appropriately defines the relationship between the refractive powers of the second lens component ([+) and the third lens component ([[I)]. The third lens component (111) exceeds the upper limit of condition C).
When the refractive power of the lens becomes weaker, the amount of movement as a compensator increases during zooming, and aberration fluctuations2 from the wide-angle end to the telephoto end become larger, making it impossible to obtain high-performance image quality over the entire zoom range. . Additionally, if the lower limit of condition (2) is exceeded and the refractive power of the third lens component (Ill) becomes strong, the image plane at the telephoto end will be significantly tilted to the underside, making it impossible to obtain high-performance image quality over the entire screen. .

Condition (3) defines the refractive power of the fourth lens component (ff) with respect to the second lens component (I). Condition (3
) If the refractive power of the fourth lens component (If) becomes stronger than the upper limit of ), the spherical aberration will be large over the entire screen and will fall to the underside, making it impossible to obtain good axial performance. on the other hand,
If the lower limit of condition (3) is exceeded and the refractive power of the fourth lens component (ff) becomes weak, the amount of focusing movement with respect to a close object increases, and aberrations at close range become extremely bad.

Furthermore, in order to properly correct various aberrations, the fifth lens component (ma) must be arranged in order from the object side: a positive lens, a negative lens, and a
1 or 2 positive lenses, 1 or 2 negative lenses
It is desirable that the lens be composed of two positive lenses and that the following conditions be satisfied.

(4) -0,15<ψ5A/ψ5B (0,32, ψ5A: composite refractive power of two lenses from the object side of the fifth lens component (Ma), ψ5B: object of the fifth lens component (Ma) The composite refractive power of the third and subsequent lenses from the side is:

Condition (4) appropriately defines the relationship between the refractive powers of the front group and the rear group of the fifth lens component (ma). If the upper limit of condition (4) is exceeded and the refractive power of the front group becomes strong, spherical aberration will be large over the entire screen and the lens will fall to the under side. On the other hand, the condition (
4) When the refractive power of the front group becomes negative beyond the lower limit,
Spherical aberration tends to be excessive, making it difficult to obtain a high-performance zoom lens in either case.

(Example) The configuration of a zoom lens to which the present invention is applied when focusing on an object at infinity is shown below. In each example, rt is a surface number indicating the first lens surface from the object side, and Nd and νd indicate that the zoom component (ff) moves on the optical axis toward the image side. The object distance at which the fourth lens component (IV) does not move due to zooming is 5I=1.35 m in each example.

(Left below) It is a flat plate equivalent to a sufilter, etc. In addition, in each example, from the infinite object focusing state to the nearest object (5I = 0.7 m, however, in Example 2, 5I = Q, 5 m
) The fourth lens component O required to focus on
Table 1 shows the amount of extension in 1) for each focal length.

However, the negative Shugo is 4th Len Example 1 <L><Ml><M2><S> f=66.3
~32.0~19.0~8.75ri Curvature radius axis upper surface distance d νd Example 2 <L><Ml><M2><S>f=6a3~3
2.0~19.0~8.75ri Radius of curvature Axial surface spacing d νd SUMT=118.409~118.409~118.
409~118.409SUMT=113.484~1
13.484-113.484-113.4.84 Example 3 <Ml><M2><S>f=66
．． 3-32.0-19.0-875ri Radius of curvature Axial surface spacing d νd Example 4 <L><Ml><M2><S> E=66.3-32.0-190-8.75ri
Radius of curvature Axial surface distance d νd UMT 122.284~122.284~122.284~1
22.284SUMT=118.895~118.89
5~118.895~118.895 Example 5 <L><Ml><M2><S>f=66.3~
32.0~19.0~875ri Radius of curvature Shaft top surface spacing S UMT= 116.874~116.874~11
6.874-116.874

[Brief explanation of the drawing]

1 to 5 are cross-sectional views showing the lens arrangement at the telephoto end <L> of the zoom lenses shown in Embodiments 1 to 5 of the present invention, respectively, and FIGS. FIG. 11 is an aberration diagram showing various aberrations for an object at infinity at the telephoto end <L>, intermediate focal lengths <Ml>, <M2>, and wide-angle end <S> of the zoom lenses of Example 5. A diagram showing the movement curves of the second to fourth lens components due to lens zooming, FIG. 12 is a diagram showing the tracking curve of the fourth lens component, and FIG. 13 is a diagram of a conventional zoom lens in which focusing is performed using a compensator. It is a figure which shows the movement curve of a variator and a compensator. Applicant Minolta Camera Co., Ltd. WIj Figure 3 Figure 2 Figure 4 Figure 6 (δ) Spherical aberration Sine condition Astigmatism Distortion 0/. Spherical aberration Sine condition Astigmatism Distortion "l. Figure (a) Spherical aberration Bodhisattva sine condition - o, i o, i Non-7 point IIK difference - 5,05,0 Distortion 010 FNO1,473 Y; 4 pieces Y2 4.1 Royal plane aberration sine line Fubut 7 white, aberration distortion 0IO 9th Figure FNO1494 Y stem 41 Y; 41 β-plane aberration sine condition Ihara aberration distortion 0/. I8 Figure Cb) FNO1,472 Y 4.1 Y241 FNOl, 440 Y; 41 Y; 2nd string Ig point convergence distortion 67° Fig. 9 (b) FNO1491 Y': 41 Y': 41 -0.1 01 Spherical aberration Sine string I ↑ -0, 10, 1 # Point aberration -5, 050 Distortion 0mmFNO1,440 Y;4.1 Y;41 Spherical aberration sinusoidal distortion, fort, aberration distortion 6/. (II) 4〉S...Ingredients (■) 3rd L-, S...10,000℃ 7 minutes ([I) Sl:OQ
51=4shi1st publicationshi<L> -206= (c)

Claims (1)

[Claims] (1) In order from the object side, a first lens component has a positive refractive power and is fixed during zooming, and a first lens component has a negative refractive power and moves back and forth on the optical axis during zooming to change the magnification. a second lens component that has a negative refractive power and moves back and forth on the optical axis during zooming to correct image point movement; and a fourth lens component that has a positive refractive power and performs focusing. component, and a fifth lens component that has positive refractive power and is fixed during zooming,
When zooming from the wide-angle end to the telephoto end, the position of the fourth lens component moves monotonically from the image side to the object side when focusing on an object at infinity, and moves monotonically from the object side to the image side when focusing on a nearby object. A zoom lens that is characterized by: (2) The zoom lens according to claim 1, further comprising a prism or a mirror for optical path division, and a diaphragm, arranged in order from the object side between the fourth lens component and the fifth lens component. (3) When zooming from the wide-angle end to the telephoto end, the second lens component moves from the image side to the object side, and the third lens component moves while drawing a convex axis trace toward the object side. The zoom lens according to claim (1). (4) The first lens component consists of one negative lens and two positive lenses, the second lens component consists of two negative lenses and one positive lens, and the third lens component consists of one negative lens and one positive lens. Consists of a negative lens component, and the fourth lens component is one or two.
Claim (3) characterized in that it consists of positive lens components
) Zoom lenses listed. (5) The zoom lens according to claim (4), characterized in that it satisfies the following conditions in addition to the above conditions: 2.1<|＾ψII|/＾ψ I <6.0 1.6< ＾ψII／＾ψIII＜4.8 0.8＜＾ψIV／＾ψ I＜2.0 However, ＾ψ I: Refractive power of the first lens component ＾ψII: Refractive power of the second lens component ﾈψIII: th Refractive power of the three lens components ^ψIV: This is the refractive power of the fourth lens component. (6) The fifth lens component is, in order from the object side, a positive lens,
Negative lens, 1 or 2 positive lenses, negative lens, 1
The zoom lens according to claim (5), characterized in that it is composed of one or two positive lenses and satisfies the following conditions: 0.15<^ψ5A/^ψ5B<0.32 However,^ ψ5A: Combined refractive power of two lenses from the object side of the fifth lens component ^ψ5B: Combined refractive power of the third and subsequent lenses from the object side of the fifth lens component.