JPH036510A - Five-element zoom lens - Google Patents

Abstract

PURPOSE:To realize high-accuracy automatic focusing(AF) over the entire range of zooming by allowing 2nd - 4th lens elements to draw mutually inparallel movement curves. CONSTITUTION:The 3rd lens element (III) which has negative refracting power and can moves forth and back on the optical axis in zooming and the 4th lens element (IV) which has positive refracting power and can moves forth and back on the optical axis in zooming are extended out in zooming toward the object side monotonously from the telephoto end to the wide-angle end and the 2nd lens element (II) which has negative refracting power and moves forth and back on the optical axis for power variation in zooming and the 3rd and 4th lens elements III and IV draw mutually inparallel movement curves. Consequently, the high-accuracy AF is realized over the entire range of zooming.

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 that can be applied to small cameras such as video cameras having TTL basiv type AF (autofocus).

Conventional techniques ■Technology In recent years, electronic components have been reduced in cost and made more compact in small cameras such as video cameras at a considerable speed. It is hard to say that the technology is making any progress, and the ratio of lenses to the camera body is increasing year by year due to factors such as cost, weight, and size. 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 fixed 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 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 11 (a) (b) (C
), in which 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 as shown by the solid line and deviates from the correct tracking curve.

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.

The purpose of the present invention is to provide a zoom lens that performs focusing using a lens component other than the second lens component, so that the tracking curve during zooming can draw an optimal trajectory for AF. High precision AF over the entire range of
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.

In order to achieve the above object, the five-component zoom lens of the present invention consists of a second lens component (■) which has positive refractive power and is fixed during zooming, a negative lens component (■), and A second lens component (■) which has a refractive power and is movable back and forth on the optical axis for variable magnification during zooming, and a third lens component (■) which has negative refractive power and is movable back and forth on the optical axis during zooming. ■) The fourth lens component (IV) has positive refractive power and can move 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, and the third lens component (■) and fourth lens component (IV) have a positive refractive power from the telephoto end to the wide end. The second
lens component (■), third lens component (I[[) and fourth
The lens components (IV) are configured to draw movement curves that are not parallel to each other.

In addition, the third lens component (III) and the fourth lens component (
rV), preferably at least one lens component performs focusing.

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 addition, by appropriately adjusting the amount of movement of the third lens component (III), the fourth lens component (TV)
In addition, it is possible to create a solution that moves monotonically toward the object from the telephoto end to the wide end. For this purpose, it is desirable to satisfy the conditional expression shown below.

ffi engineering 1 >0.0127 ・・・・・・■
3 However, 6m14:f14=fT-f″3rd at 19:00
Amount Z of the lens component extending from the telephoto end: Zoom ratio (= fy / fw) rT = Focal length of the entire system at the telephoto end f: Focal length of the entire system at the wide end Focal length of the third lens component (III) f, 4
If the amount of protrusion from the telephoto end in is smaller than the amount specified by this second, the fourth lens component (■)
moves in a convex trajectory toward the image side from the telephoto end to the wide end. Therefore, it is necessary to provide a sufficiently large distance between the fourth lens component (■) and the fifth lens component (V), which is undesirable because the total length of the lens becomes significantly large. Furthermore, since the entrance pupil position is also set back in the image plane direction, the front lens diameter also becomes large. In this case, the second lens component (■
), unlike when using a solution that does not include an imaging magnification of 11x, it is possible to achieve a power balance that satisfactorily corrects aberrations, and moreover, the amount of movement of the hariniku is 4
This is almost the same as a component positive/negative/negative type zoom lens. As shown in FIG. 7, the third lens component (1) and the fourth lens component (1)
Since the tracking curve of the lens component (IV) draws a trajectory that does not have such an extreme value, focusing can be performed with either the third lens component (m) or the fourth lens component (IV). During zooming, the speeds of the third lens component (I [[) and the fourth lens component (■)] are always in the same direction, and the accelerations are also always in the same direction, making it easy to control the lens drive system by AF. . Accordingly, highly accurate AF can be achieved over the entire zooming range. In addition, the third lens component (III)
There is also an advantage that focusing may be performed using both the lens component (1) and the fourth lens component (■), and that it is also possible to selectively use auto and manual, macro range and normal range, etc.

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

For example, as a lens configuration, the first lens component (I) has a total of three lenses, one negative lens and two positive lenses, and the second lens component (n) 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 (summer) to the fourth lens component (r
V) desirably satisfies the following conditions.

2.10<l/'/'r<6.00.
Beg 0 ・・・・・・■1.60<9', /to<4
．． 80 ・・・・・・■0.80<
Width/width<2.00 ・・・・・・■
However, ψII: refractive power of the second lens component (1) ψII: refractive power of the second lens component (II) ψIII: refractive power of the third lens component (I[[) Light: refraction of the fourth lens component (IV) It is power.

The condition (2) is the second lens component CI) and the second lens component (CI).
II).

If the refractive power of the second lens component (II) becomes strong beyond the upper limit of condition (2), the Petzval sum will become a large negative value, and the image plane will be greatly tilted to the underside, especially at the wide end.
On the other hand, coma aberration occurs at the telephoto end, making it impossible to obtain high-performance image quality over the entire screen. Also,
When the refractive power of the second lens component (II) becomes weaker than the lower limit of condition (2), the amount of movement of the second lens component (It) required for zooming increases, and the total length of the lens becomes significantly longer. This makes 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) relates to the ratio of refractive powers between the second lens component (ff) and the third lens component (I[[).

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 to correct image plane movement during zooming will increase, resulting in aberrations from the telephoto end to the wide end. The amount of variation becomes large, making it impossible to obtain high-performance image quality over the entire zoom range. Also,
If the refractive power of the third lens component (III) becomes strong beyond the lower limit of condition (2), 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 aberrations near the intermediate focal length (middle) are greatly degraded and become high throughout the entire zoom range. In addition, when focusing is performed using the fourth lens component, the amount of movement for focusing becomes large, and the performance at close range also deteriorates.

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<ψsA/ψs+<0.320 ・
Old... ■However, ψsA: The combined refractive power of the two lenses from the object side of the fifth lens component (V)? 58: Combined refractive power of the third and subsequent lenses from the object side of the fifth lens component (V).

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, at least one component of the third lens component (Ill) and the fourth lens component (IV), which are the focusing lens group, is located closer to the object than the aperture. In addition, if a prism for optical path splitting is placed on the object side of the diaphragm, a TTL passive type A that performs focus detection using the split light beam.
It becomes possible to realize a zoom lens that is optimal for a camera that performs F.

Further, 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 (I [I) or the fourth
Preferably, it has a system for moving the lens component (■). FIG. 10 shows one example of this system. A focus detection device (4) performs focus detection using the light beam split by the prism (or mirror) (1),
Based on the detected signal, the calculation and control circuit (5) selects the third lens component (II[) or the fourth lens component according to the defocus amount.
The amount of movement of the lens component (■) (the third lens component (■) in FIG. 10, the same applies hereinafter) is calculated, and the focus group drive motor (3) is driven. Third lens component ([
[) or a part of the ball crusher (7) of the fourth lens component (IV) is connected to a threaded shaft (8), and the light is emitted according to the rotation of the motor (3) transmitted through the gear. Move back and forth on the axis.

Note that the rotation of the motor (3) may be transmitted to the third lens component (Iff) or the fourth lens component (IV) only by gears.

Embodiments of the five-component zoom lens according to the present invention will be shown below.

However, in each example, r1 to r3□ are the radius of curvature, d
+-d3+ indicates the distance between the upper surfaces of the shaft, N1 to N18. ν1
~ν, 6 indicates the refractive index and Abbe number for the d-line. still,
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 that guides the light beam to the focus detection optical system, and is placed on the image side of the fifth lens component (V). The flat plate shown is a flat plate equivalent to a dichroic prism, a low-pass filter, etc.

<Example 1> F,, = 1.865-1.483-1.481-1.4
80F = 66.3~32.0~19.0~8.75d
ze 1.000 t9 22.00O N blind 5 ■. 80500 ν 40.97 7 1Z, '14U Σd = 124.365 ~ 124.365 ~ 124.3
65 <Example 2> FNO=1.820-1.452-1.448-1.4
40F=66.3~32.0~19.0~8.75Σd
=119.214~119.214~119.214
<Example 3> Fso=1.870-1.455-1.449-1.4
60F = 66.3~32.0~19.0~8.75d
.

1.80O 1 1,84666 S1 23.82 Σd =117.194~117.194~117.1
94 Next, FIGS. 1 to 3 show schematic configurations at the telephoto end of Examples 1 to 3. On the object side of the fifth lens component (V), there is a prism (or mirror) (1) and an aperture (1).
0) is shown, and a flat plate (11) corresponding to a guichroic prism, a low-pass filter, etc. is shown on the image side.

4 to 6 are aberration diagrams corresponding to each of Examples 1 to 3,
<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 C-line, and the dotted line (SC) represents the sine condition. Further, the dotted line (DM) and the solid line (DS) represent astigmatism on the meridional plane and the sagittal plane, respectively.

Figure 7 shows the second to fourth lens components (II) ([[)
(IV) schematically shows the movement from the telephoto end <T> to the wide end <W>, and FIGS. 8 and 9 show the third lens component (I[[) and the fourth lens component ( IV
) and the closest object (S
L=1.5m) Tele end <T in focusing state
> to the wide end <W> is schematically shown. In addition, the third lens component (■) and the fourth lens component (
IV) moves toward the object side and the image side as shown by the arrows when approaching, and when focusing with the third lens component (III), the fourth lens component (rV) becomes 51=
The fourth lens component (
When focusing on TV), the third lens component (
1) moves along the trajectory of 51=ω (Fig. 8).

FIG. 10 is a schematic diagram showing an embodiment of a system to which the zoom lens of the present invention is applied.

Figure 11 shows a conventional variator (V) and a compensator (C (F)) that performs focusing at the telephoto end <T.
> to the wide end <W>, the solid line shows actual tracking, and the dotted line shows correct tracking.

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 the drawing]

FIGS. 1, 2, and 3 are lens configuration diagrams corresponding to each embodiment of the present invention, FIGS. 4, 5, and 6 are aberration diagrams thereof, and FIG. 7 is a lens configuration diagram corresponding to each embodiment of the present invention. A schematic diagram showing the movement of the second to fourth lens components (I[) (III) (TV) from the telephoto end to the wide end, and FIGS. 8 and 9 are respectively the third lens component (III) and FIG. 10 is a schematic diagram showing the movement of the fourth lens component (TV) from the telephoto end to the wide end; FIG. 10 is a schematic diagram showing an embodiment of a system to which the zoom lens of the present invention is applied; FIG. 1 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; During zooming, the four lens components move monotonically toward the object side from the telephoto end to the wide end.
A zoom lens characterized in that the second lens component, the third lens component, and the fourth lens component draw movement curves that are not parallel to each other. (2) Of the third lens component and the fourth lens component,
Zoom lens according to claim 1, characterized in that at least one lens component performs 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 ＜ψ_II＜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 of lens component: This is the refractive power of the fourth lens component.