JPH036508A - Five-element zoom lens - Google Patents

Abstract

PURPOSE:To realize high-accuracy automatic focusing(AF) over the entire range of zooming by moving a 2nd lens element and a 3rd lens element monotonously from the telephoto end to the wide angle end, i.e. from the image side to the object side while loci which are not parallel to each other are drawn. CONSTITUTION:The 2nd lens element II which has negative refracting power and can move forth and back on the optical axis for power variation in zooming and the 3rd lens element III which has negative refracting power and can moves forth and back on the optical axis in zooming are moved from monotonously from the telephoto end to the wide-angle end, i.e. from the image side to the object side while loci which are not parallel to each other are drawn. Consequently, high-accuracy AF which is easily controlled can be realized over the entire range of zooming and, specially, passive type AF is possible, and aberrations are compensated excellently and the lightweight, compact zoom lens which has high resolving power, high picture quality, and a high power variation rate is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a zoom lens, and more particularly to a five-component zoom lens applicable to small cameras such as video cameras having a TTL passive type AF (autofocus).

In recent years, cost reductions and miniaturization of electronic components for small cameras such as video cameras have been achieved at a considerable speed. It is difficult to say that there has been any progress in the field of camera lenses, and the proportion of lenses in the camera body is increasing year by year due to cost, weight, size, etc. Furthermore, in recent years, very high-resolution imaging devices have come into use, and the optical performance of lens systems is now required to be higher 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.

In this method of extending the lens component, the amount of lens extension for an object at a constant distance is the same throughout the entire zoom range, so there are advantages such as a simple focusing mechanism, but on the other hand, it is necessary to increase the effective diameter of the cylindrical lens component. Sufficient weight reduction cannot be achieved. In addition, the aberration fluctuations are large at close-up, and especially at the telephoto end, the spherical aberration falls to the under side and the image plane falls to the over side, making it difficult to obtain a good image.Furthermore, it is difficult to obtain a good image with a focusing lens that has an electric focusing lens mechanism. However, there are problems such as increased power consumption.

In order to solve the above problem, 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 in a rear group of a master lens system that performs image formation. For example, JP-A-55
Japanese Patent No. 40447 discloses a zoom lens that performs focusing using a compensator. However, what is shown in the above publication is a trajectory (hereinafter referred to as "tracking") when the focusing component (compensator) is made to follow (hereinafter referred to as "tracking") so that an object at a certain distance is always in focus during zooming. (hereinafter referred to as a "tracking curve") has an extreme value. Therefore, near this extreme value, the direction of movement of the compensator changes, resulting in excessive tracking or
When you stop zooming and start zooming again near this point, it becomes quite difficult to control the compensator because the direction of movement of the compensator differs depending on the direction of zooming, making it difficult to increase the accuracy of AP. be. This situation is shown in Figure 12 (a) (b) (C
). In the figure, the movement of the variator (V) is linear, but the movement of the compensator (C(F)') has an extreme value. And the compensator (C
(F) ) follows the correct tracking trajectory shown by the dotted line in the straight line portion, but at the extreme value it goes too far and deviates from the correct tracking curve, as shown by the solid line.

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 Patent Application Laid-Open No. 53-10734
Publication No. 7 discloses a zoom solution in which the magnification of a variator that changes magnification during zooming does not include 11 times 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.

In addition, as a 5-component zoom lens, the
There are those disclosed in Japanese Patent Application Laid-open No. 10, Japanese Patent Application Laid-Open No. 60-243622, and the like. However, in the former case, since focusing is performed using the first lens component, the effective diameter of the first lens component becomes large as described above, resulting in a lack of compactness in terms of weight and the like.

In the latter case, since focusing is performed using a lens closer to the image than the aperture, it cannot be used in a small camera having TTL passive type AF as described above.

Therefore, an object of the present invention is to enable the tracking curve during zooming to draw an optimal trajectory for AF in a zoom lens that performs focusing using a lens component other than the second lens component. High-precision AF throughout the zooming range
Our goal is to provide a zoom lens that can achieve this goal.

In particular, it is an object of the present invention 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 and has aberrations well corrected.

Means for Solving the Problems In order to achieve the above object, the five-component zoom lens of the present invention has, in order from the object side, a first lens component (■) which has positive refractive power and is fixed during zooming, and a negative refractive power component (■). The second lens component (■) has a strong power and can be moved back and forth on the optical axis for variable magnification during zooming, and the third lens component (■) has negative refractive power and can be moved back and forth on the optical axis during zooming. , a fourth lens component (rV) having positive refractive power and movable back and forth on the optical axis during zooming;
and a fifth lens component (V) that has positive refractive power and is fixed during zooming;
The lens component (II[) is configured to move monotonically from the image side to the object side from the telephoto end to the wide end, drawing trajectories that are not parallel to each other.

Further, it is preferable that focusing is performed by moving the third lens component (lI[) back and forth on the optical axis,
Second lens component (II) and third lens component (II[)
is preferably located closer to the object side at the wide end than at the telephoto end.

The second lens component (II) includes an imaging magnification of -1x, but by moving the fourth lens component (IV) non-linearly, the third lens component (III) is shifted from the telephoto end to the wide end. It is possible to create a solution that moves monotonically toward the object. In this case, unlike when using a solution that does not include the imaging magnification of the second lens component (II) which is a variator, it is possible to realize a power balance that can satisfactorily correct aberrations. Moreover, the amount of movement of the variator is approximately the same as that of a four-lens positive-negative-positive type zoom lens. As shown in Figure 9, the tracking curve of the third lens component (Iff) draws a trajectory without such extreme values, so that the speed of the third lens component (II[) during zooming is always in the same direction. Then,
Furthermore, since the acceleration is always in the same direction, the lens drive system can be easily controlled by AF. Accordingly, highly accurate AF can be achieved over the entire zooming range. Furthermore, since the relative positional relationship between the second lens component (II) and the fourth lens component (IV) is always fixed regardless of the position of the object point, it is similar to conventional zoom lenses that perform focusing using the lens component. Another advantage is that zooming can be controlled using a simple cam mechanism. The third lens component (I[[) is moved forward for focusing on a nearby object point than when focusing on an object point at infinity, so the third lens component (I[[) and the fourth lens component (I
Since no extra air space is required between V) and the amount of feeding is small, the overall length is short and the lunz component (1
) It is possible to realize a compact zoom lens with a small effective diameter.

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

For example, as a lens configuration, the first lens component (I) has one negative lens and two positive lenses, a total of three lenses, and the second lens component (II) has two negative lenses and one positive lens, a total of three lenses. Preferably, the third lens component (■) is composed of one negative lens component, and the fourth lens component (IV) is composed of one or two positive lens components. By adopting such a simple lens configuration, a compact and high-performance zoom lens can be obtained.

Furthermore, the fourth lens component (1) to the fourth lens component (I
V) desirably satisfies the following conditions.

2.10<19', l/ψi<6. oo, 9
), <O...■1.60<? ,/mouse<4.80
・・・・・・■0.80<%/
<2.00 -...-■ However, the refractive power of the second lens component (I) is the second lens component (n
) = refractive power of the third lens component (I[I): refractive power of the fourth lens component (IV).

Condition (2) is the first lens component (1) and the second lens component (I
It concerns the ratio of refractive power with I).

If the refractive power of the second lens component becomes strong beyond the upper limit of condition (2), the Petzval sum will become a large negative value, and the image plane will be significantly tilted toward the underside, especially at the wide end, while coma aberration will occur at the tele end. In addition, if the lower limit of condition (2) is exceeded and the refractive power of the second lens component (II) weakens, the second lens component (n) becomes The amount of movement required for this purpose increases, and the overall length of the lens becomes significantly longer, making it difficult to obtain a compact zoom lens.

Furthermore, the difference in spherical aberration between the telephoto end and the wide end becomes large, making it impossible to obtain high-performance image quality over the entire zoom range.

Condition (2) is a condition regarding the ratio of refractive power between the second lens component (I[) and the third lens component (I[l)].

If the refractive power of the third lens component (III) becomes weaker by exceeding the upper limit of condition (2), the amount of movement as a compensator during zooming will increase, and the amount of aberration fluctuation from the telephoto end to the wide end will increase, resulting in cannot obtain high-performance image quality. In addition, the third condition exceeds the lower limit of condition ■.
If the refractive power of the lens component (III) 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 (2) is the fourth lens component (1) and the fourth lens component (I
V) and the refractive power ratio.

If the refractive power of the fourth lens component (IV) becomes strong beyond the upper limit of condition (2), the overall spherical aberration will be significantly tilted to the underside, making it impossible to obtain good axial performance. In addition, when the lower limit of condition (■) is exceeded and the refractive power of the fourth lens component (■) becomes weak, the amount of movement for image point correction becomes large, and the aberrations near the intermediate focal length (middle) become thick (collapsed and the entire zoom range You will not be able to obtain high-performance image quality.

Furthermore, in order to better correct various aberrations, the fifth lens component (V) is a positive lens in order from the object side.

It is desirable that the lens be composed of a negative lens, one or two positive lenses separated by a large air gap, a negative lens, and one or two positive lenses, and that the following conditions be satisfied.

-0,150<ψmouth/ψsm<0.320...
...■ However, 9'SA: The combined refractive power of the two lenses from the object side of the fifth lens component (V) ψsl: The third and subsequent lenses from the object side of the fifth lens component (V) is the composite refractive power of

Condition (2) concerns the ratio of the refractive power between the front group and the rear group of the fifth lens component (V).If the upper limit of the 0 condition (■) is exceeded and the refractive power of the front group becomes stronger, the overall spherical aberration falls to the under side.

On the other hand, if the lower limit of condition (2) is exceeded and the refractive power of the front group becomes weaker, the spherical aberration will shift to the over side.

In either case, it is difficult to realize a high-performance zoom lens.

Further, it is preferable that a prism or a mirror for splitting the optical path is inserted into the object-side end of the fifth lens component (V) in the zoom lens of the present invention. Furthermore, an aperture may be provided together with the prism or mirror, and in this case, the third lens component (I[l), which is a focusing lens group, will be placed closer to the object side than the aperture, and the third lens component (I[l), which is the focusing lens group, will be placed on the object side of the aperture. When a prism for optical path division is arranged, it becomes possible to realize a zoom lens that is optimal for a camera that performs TTL passive type AF that performs focus detection using the divided light flux.

Furthermore, in the present invention, automatic focus detection may be performed using the light beam obtained by the optical path splitting means provided in the middle of the main lens, and in this case, the third lens component is moved according to the distance measurement signal or focus signal obtained by these. It is preferable to have a system that allows FIG. 11 shows one example of this system. Prism (or mirror) (1
) The focus detection device (4) performs focus detection using the luminous flux divided by
The amount of movement in III) is calculated and the focus group drive motor (3) is driven. A part of the third lens component's ball crusher (7) is connected to a threaded shaft (8), and moves back and forth on the optical axis according to the rotation of the motor (3) transmitted through the gear. do. Note that the rotation of the motor (3) may be transmitted to the third lens component (III) only by a gear.

Examples of the five-component zoom lens according to the present invention will be described below.

However, in each example, r, ~r3□ is the radius of curvature, d
, ~dffl indicate the axial surface spacing, N1 to N12, ~v1. indicates the refractive index and Atsube number for the d-line. In each example, the flat plate placed on the object side of the fifth lens component (V) is a prism for splitting the optical path to guide the light beam to the focus detection optical system. The flat plate arranged on the image side of the fifth lens component (V) is a flat plate corresponding to a guichroic prism, a low-pass filter, or the like.

<Example 1> F, -1,865 to 1.486 to 1.485 to 1.4
80F=66.3~32.0~19.0~8.7536 Σd=121.355~121.355~121.3
55 <Example 2> F No = 1.866 ~ 1.529 ~ 1.526 ~
1.480F=66.3~32.0~19.0~8.7
5d+ 1.800 N+ 1.84tjbti ν, za, hz Z4 -J4. jU9 r3゜Σd =124.224~124.224~124.2
24-124.224 <Example 3> F,, = 1.829-1.413-1.409-1.4
40F=66.3-32.0-19.0-8.751l -5UU, 188 <Example 4> FNO=1.870-1.471-1.466-1.4
60F = 66.3~32.0~19.0~8.751
9:3'/,'108Σd=119.160~119.160~119.1
60Σd = 117.122~117.122~117
．． 122 Next, FIGS. 1 to 4 show schematic configurations at the telephoto end of Examples 1 to 4. Fifth lens component (V
) A prism (or mirror) (1) and a diaphragm (10) are shown on the object side, and a flat plate (11) corresponding to a guichroic prism, a low-pass filter, etc. is shown on the image side.

FIGS. 5 to 8 are diagrams corresponding to each of Examples 1 to 4,
<L> represents the aberration at the telephoto end, <old> and M2> represent the intermediate focal length (middle), and <S> represents the aberration at the wide end. In addition, the solid line (d) is the aberration for the d-line, and the dashed line (g
) represents the aberration for the g-line, the two-dot chain line (c) represents the aberration for the g-line, and the dotted line (SC) represents the sine condition. Furthermore, the dotted line (DM) and the solid line (DS> represent astigmatism on the meridional plane and sagittal plane, respectively).

Figure 9 shows the second to fourth lens components (II) (I[[)
(rV) from the tele end <T> to the wide end <W>, and FIG. 10 shows the infinity object focusing state of the third lens component (III) and the closest object (S1= 1.5m) Schematically shows the movement from the telephoto end <T> to the wide end <W> in the focusing state. Note that the third lens component (In) moves toward the object side as shown by the arrow when approaching.

FIG. 11 is a schematic diagram showing an embodiment of a system to which the zoom lens of the present invention is applied.

Figure 12 shows the telephoto end of the conventional variator (V) and compensator (C (F)) that performs focusing.
> to the wide end <W>, the solid line shows actual tracking, and the dotted line shows correct trunking.

According to the present invention, highly accurate and easily controllable AF can be realized over the entire zooming range, and in particular, TTL passive type AF can be achieved. Furthermore, aberrations are well corrected, high resolution, high image quality, and a lightweight and compact high-power zoom lens can be realized.

[Brief explanation of drawings]

Fig. 1, Fig. 5, Fig. 2, Fig. 3, and Fig. 4 are lens configuration diagrams corresponding to each embodiment of the present invention, and Fig. 5, Fig. 6, Fig. 7, and Fig. 8 are their aberration diagrams. , FIG. 9 is a schematic diagram showing the movement of the second to fourth lens components (■) (III) (TV) in the present invention from the tele end to the wide end, and FIG. 10 is a schematic diagram showing the movement of the third lens component (I) in the present invention. [[] is a schematic diagram showing the movement from the tele end to the wide end, and the 11th
This figure is a schematic diagram showing an embodiment of a system to which the zoom lens of the present invention is applied, and FIG. 12 is a schematic diagram showing the movement of a conventional variator and compensator from a telephoto end to a wide end.

Claims (1)

[Claims] (1) In order from the object side, the first lens component has a positive refractive power and is fixed during zooming, and the first lens component has a negative refractive power and moves back and forth on the optical axis for variable magnification during zooming. A movable second lens component, a third lens component that has negative refractive power and is movable back and forth on the optical axis during zooming.
a fourth lens component that has a positive refractive power and is movable back and forth on the optical axis during zooming; and a fifth lens component that has a positive refractive power and is fixed during zooming; A zoom lens characterized in that the three lens components move monotonically from the image side to the object side from the telephoto end to the wide end, drawing trajectories that are not parallel to each other. (2) The zoom lens according to claim 1, wherein the third lens component is movable back and forth on the optical axis for focusing. (3) The zoom lens according to claim 1 or claim 2, wherein the first to fourth lens components satisfy the following conditions; 2.10<|ψ_II|/ψ_I <6.00, ψ_II<
01.60<ψ_II/ψ_III<4.80 0.80<ψ_IV/ψ_ I <2.00 However, ψ_ I: Refractive power of the first lens component ψ_II: Refractive power of the second lens component ψ_III: Third lens component refractive power ψ_IV: refractive power of the fourth lens component.