JP3029177B2 - Zoom lens with flare cut aperture - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-magnification zoom lens having a zoom ratio of about 40.times. Having a flare stop suitable for a TV camera and the like. By placing a flare stop (variable diameter stop) in the lens system that shields a part of the lens, and controlling the stop diameter appropriately according to the magnification, good optical performance can be obtained over the entire zoom range. The present invention relates to a zoom lens having a flare stop.

[0002]

2. Description of the Related Art Conventionally, as a zoom lens having a high zoom ratio, a first lens unit (front lens) having a positive refractive power and performing focus adjustment in order from the object side, and a zoom lens having a negative refractive power and having a zooming function. A second unit (variator) that moves in the direction of the optical axis, and a third group that has a positive refractive power and moves in the direction of the optical axis for zooming and image plane compensation.
And a fourth group having a positive refracting power and a fixed and imaging function, and a variator and a compensator for zooming from the wide-angle end to the telephoto end. There have been proposed various so-called four-group type zoom lenses which are set so as to simultaneously have an imaging magnification of -1.

When zooming from the wide-angle end to the telephoto end, this four-group type zoom lens forms a lot of coma flare in off-axis rays from the zoom position slightly telephoto from the wide-angle end to the intermediate zoom position, resulting in image formation. There is a property that performance is reduced.

FIG. 14 is a schematic diagram showing optical elements and optical path states at the wide-angle zoom position with the aperture open, where coma flare often occurs in the aforementioned four-group type zoom lens.

In FIG. 1, ray tracing is performed on an on-axis F-number ray, an off-axis ray reaching a screen intermediate image height and a screen maximum image height. In the spaces of the second and third groups, a solid line is an on-axis F-number ray, a dotted line is an off-axis ray having an intermediate image height on the screen, and a dashed line is an off-axis ray having a maximum image height on the screen.

Now, let the center of the luminous flux of the off-axis ray be the principal ray and the lower ray be referred to as the lower ray.
It passes significantly below, and within the first and compensators (group 3), the lower ray will pass at a height above the optical axis. For this reason, it receives a strong positive refracting power and is caused to jump upward, and as a result, a lot of coma flare is generated.

A zoom lens having means for removing off-axis rays has been proposed, for example, in Japanese Patent Publication Nos. 51-21794 and 56-52291.

In Japanese Patent Publication No. 51-21794, a variable diameter stop fixed to a lens barrel between a variator and a compensator is set, and the size of the diameter is changed in accordance with zooming, so that the image is displayed at the center of the screen. Limits image height rays.

In Japanese Patent Publication No. 56-52291, a movable diaphragm having a constant diameter is provided between a variator and a compensator, and the diaphragm is moved in relation to the variator. A zoom lens in which a part of the zoom lens is limited has been proposed.

[0010]

Generally, in order to suppress fluctuations in aberrations caused by zooming, particularly fluctuations in coma flare, it is necessary to effectively remove only flare components without affecting the axial light flux.

By the way, the aforementioned Japanese Patent Publication No. 51-21794.
Japanese Patent Application Laid-Open Publication No. H11-157210 discloses that light rays having a maximum image height on a screen are not limited, and only light having an intermediate image height is limited. However,
In a zoom lens used for a TV camera or the like, only a very small zoom region near the wide-angle end can limit only a light ray having an intermediate image height on a screen. As described above, the publication does not care about the effect of coma flare caused by the lower rays of the maximum image height by the first and third lens units.
Further, in the embodiment shown in the publication, since the control of the aperture diameter is performed by a mechanical plate cam, when the aperture is determined by the aperture diameter determination aperture, or when a converter, extender, or the like is mounted. It has been difficult to freely control the aperture diameter. Further, in a high-magnification zoom lens for a TV camera, the amount of movement of a variator or compensator increases, so that there is a problem that the length of a plate cam increases and the entire zoom lens becomes heavy.

In the zoom lens proposed in Japanese Patent Publication No. 56-52929, a part of the lower light beam is restricted over the entire zoom range by the diameter-invariant moving stop as described above. There has been a problem that a useful light beam that has been well corrected may be limited. Further, since a mechanical mechanism for moving the aperture is required, there is a problem in that the mechanism becomes complicated and the weight increases.

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate a coma flare having a maximum image height due to the influence of the first and third lens groups of a positive refractive power component, particularly for a zoom lens having a considerably high zoom ratio.

For this purpose, the present invention provides, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a flare-cut stop having a fixed and variable diameter, and a third lens unit having a positive refractive power. In a zoom lens having at least a lens group and having a flare-cut stop for performing zooming by moving the second lens group and the third lens group, the maximum off-axis light ray is not affected without affecting the axial light flux. It is characterized by comprising a control means for controlling the diameter of the flare cut stop so as to cut off the flare component of the lower light beam.

It is a further object of the present invention to find out the most desirable zoom range in which the flare cut component can be reduced, and to control the aperture diameter in at least this range.

It is a further object of the present invention to provide a zoom lens having an extremely high zoom ratio and excellent aberration correction.

It is another object of the present invention to provide an aperture drive system which is small and has good responsiveness.

[0018]

FIG. 1 is a sectional view of a zoom lens according to the present invention and a diagram showing an optical path thereof. 12 and FIG.
3 is a view showing a part of a lens cross section and an optical path at a predetermined zoom position.

In FIG. 1, F denotes a first lens unit (front lens unit) having a positive refractive power, which moves in the direction of the optical axis when focusing on a subject, and is fixed during zooming. V is a second unit (variator) having a negative refractive power, which moves in the optical axis direction during zooming due to a zooming effect. C is a third unit (compensator) having positive refracting power, which moves in the optical axis direction during zooming for zooming and image plane compensation. Arrows depict a zoom locus from the wide-angle side to the telephoto side. R forms an image in a fourth group (relay lens) having a positive refractive power. P is a 3P prism as a color separation optical system, and is shown as an optical block.

Here, B is an aperture determining aperture for determining the F number of the zoom lens, and A is a variable-diameter flare-cut aperture according to the present invention, which has at least a maximum image height in a predetermined zoom range. A part (lower side) of light is cut.

First, the optical operation of the zoom lens according to the present invention will be described. In this embodiment, a four-group type zoom lens having four lens groups as shown in FIG.
During zooming from the wide-angle end to the telephoto side in order to provide a high zoom ratio, the imaging magnifications of the second and third units are simultaneously -1.
It is moved so that it passes twice. In the variable magnification range from the wide-angle end to the telephoto end, the axial F-number light is not blocked, and especially in the middle zoom range on the wide-angle side.

[0022]

[Outside 3] In the zoom range, only the portion where the aberration of the lower light beam is increased is shielded by a variable-diameter flare stop along with the zooming operation.

Next, a more detailed description will be given with reference to FIGS.

FIG. 12 shows a zoom position on the wide-angle side when the stop B is open. Between the variator V and the compensator C, the lower ray 15b of the off-axis ray having the maximum image height is shifted on the axis F.
Since the light beam passes outside the number light beam 15a, only the lower light beam of the off-axis light beam is shielded. In the figure, the shaded portion is the portion where the lower ray is cut. In particular

[0025]

[Outside 4] In the zoom range of, light rays behave as shown in FIG. 12, so that only off-axis light rays are effectively blocked.

On the other hand, FIG. 13 shows the zoom position at the start of the F drop. Since the lower ray 15b of the off-axis ray having the maximum image height passes inside the on-axis F-number ray 15a, the off-axis ray is removed. It cannot be shaded.

However, when the aperture B is narrowed down, F
If the number increases, or if the focal length is converted over the entire zoom range by a converter or built-in extender, etc., the height of the on-axis rays and off-axis rays changes between the variator V and the compensator C. , When the lower ray of the off-axis ray passes outside the on-axis F-number ray,
Light can be blocked by the aperture A.

Particularly, in this embodiment, when the aperture diameter of the flare stop A is D at an arbitrary zoom position, and the on-axis F-number light beam diameter on the stop A surface is Da, on-axis F-number rays are shielded. In order not to do so, it is required that D ≧ Da (1) be satisfied.

In particular, the aberration of the lower ray increases.

[0030]

[Outside 5] In the zoom range of, the diameter determined by the off-axis maximum image height ray on the surface of the stop A is Dm, and the stop diameter D is in the range of Dm> D (2) while satisfying the above condition (1). To effectively block the coma flare component of off-axis light rays to improve performance.

As described above, since the flare component of the off-axis light beam can be effectively shielded, high performance is achieved, and furthermore, the effect of removing the flare component is positively utilized, and the variator, compensator and compensator are used. The refractive power of the sweater can be increased, and the length of the zoom section consisting of the variator and compensator can be shortened, and at the same time, the distance between the aperture B and the front lens can be shortened, so the diameter of the front lens can be reduced. In addition, the size and weight of the zoom lens system can be reduced.

Next, the present embodiment will be described with specific numerical values.

In a numerical example to be described later, the flare cut stop A is driven by electrical control, and mainly the flare component of off-axis rays when the aperture determination stop B is open is removed. Table 1 shows parameters at each zoom position at this time.

In this embodiment, the focal length f = 256.6 m
Since the F-drop starts at the zoom position of m, the axial F-number luminous flux diameter gradually increases from Da = 28.0 mm at the wide-angle end to Da = 46.0 mm at the F-drop start point,
At the telephoto end, Da is reduced to 35.6 mm due to the F drop.

FIG. 15 shows a change in the diameter of the flare cut aperture A at each zoom position in this embodiment. The horizontal axis represents the focal length, the vertical axis represents the diameter on the flare cut aperture A surface, and in the figure, the solid line is the flare cut aperture diameter (D), the dotted line is the F number light beam diameter (Da), and the dashed line is the off-axis maximum ray. Diameter (D
m). By operating the flare-cut aperture A in a hatched area surrounded by a dotted line and a dashed line in a zoom range of f = 130 mm from the wide-angle end, only off-axis rays can be shielded. In this embodiment, particularly, the aberration of off-axis rays deteriorates. From f = 19.49 mm to f = 69.
The peripheral light amount ratio of the maximum off-axis image height is almost 50 over 78 mm
%, The diameter (D) of the flare cut aperture A is operated. At this time, when f = 19.49 mm, D = 3.
1.5mm, f = 69.78mm, D = 32.2mm
And At the wide-angle end, D = 31.5 mm, and at the F drop start point f = 256.6 mm, the F-number luminous flux diameter (D
D = 46.0 mm equivalent to a), and D> Da = at the telephoto end.
There is no limit if it is 35.6 mm, but D = 4
By controlling D to be monotonically increased from the wide-angle end to the telephoto end by setting the distance to 7.0 mm, flare is effectively removed by improving the electrical and mechanical diaphragm followability.

Next, a case where a series of processes of a control method of the aperture diameter of the aperture A will be described with reference to FIG.

In the figure, the variator V and the compensator C are supported by supporting members 18 and 19, respectively. The support members 18 and 19 are supported by the linear cam 16 and the curved cam 17, and the rotation of the curved cam 17 causes the variator V and the compensator C to move on the optical axis to change the magnification. The curved cam 17 has a zoom position detecting member 22 such as a potentiometer or an encoder.
Is connected, and sends a zoom position signal z obtained from the zoom position detecting member 22 to the control circuit 23.

The control circuit 23 controls an aperture driving member 24 such as a motor or an IG meter based on the zoom position signal z.
The rotation direction and the rotation amount are transmitted as the drive signal θ.

The driving member 24 is driven to rotate faithfully based on the driving signal θ, and is connected to the aperture mechanism 20 by gears, belts and the like.

The aperture mechanism 20 constituting the flare-cut aperture A has a structure in which the aperture is opened and closed by rotation of a rotary ring, and the aperture diameter is changed by rotation of an aperture drive member 24.

In the aperture control method shown in FIG.
A zoom position detecting member is connected to the supporting member 18 of the variator V or the supporting member 19 of the compensator C for detecting a position on the optical axis.
The zoom position signal z is sent to the control circuit 23. Subsequent processing is the same as in FIG. Note that, at this time, the variator and the compensator can be similarly moved by using an electronic cam system or the like that can be independently driven without using a mechanical member.

As described above, in this embodiment, since the aperture diameter is electrically controlled, the weight can be further reduced.
Since the rate of change of the aperture diameter with respect to the zoom position can be easily and optimally converted by changing the control circuit, it is possible to more accurately shield the flare component of off-axis light rays.

Next, a case where a series of processes of another control method of the aperture diameter of the aperture A will be described with reference to FIG.

In the figure, the zoom mechanism is the same as that of the embodiment of FIG. 2, and the curved cam 17 is connected to a zoom position detecting member 22 such as a potentiometer and an encoder. The zoom position signal z obtained from 22 is sent to the arithmetic circuit 27.

The arithmetic circuit 27 calculates an amount φ ′ related to the aperture diameter.
Is calculated based on a fixed relational expression φ ′ = f (z) using the zoom position signal z as a parameter, and is sent to the control circuit 23 as an aperture diameter signal φ.

The control circuit 23 sends a signal to an aperture driving member 24 such as a motor or an IG meter based on the aperture diameter signal φ.
The rotation direction and the rotation amount are transmitted as a drive signal θ.

The aperture drive member 24 is driven to rotate faithfully based on the drive signal θ, and is connected to the aperture mechanism 20 by gears, belts, and the like.

The aperture mechanism 20 constituting the flare cut aperture A has a structure in which the aperture is opened and closed by rotation.
The aperture diameter is changed by rotation of the aperture drive member 24.

The same processing can be performed by connecting the zoom position detecting member to the supporting member 18 of the variator V or the supporting member 19 of the compensator C as shown in FIG. The same can be applied to the case where an electronic cam system or the like that can independently drive the movement of the compensator without using a mechanical member is used.

As described above, in this embodiment, since the aperture diameter is electrically controlled, the weight can be further reduced.
Since the rate of change of the aperture diameter with respect to the zoom position can be easily and optimally converted by changing the relational expression of the arithmetic circuit, the flare component of off-axis rays can be more accurately shielded.

Next, a case where a series of processes of another control method of the aperture diameter of the aperture A will be described with reference to FIG.

In this figure, the zoom mechanism is the same as that of the embodiment shown in FIG. 2, and the curved cam 17 is connected to a zoom position detecting member 22 such as a potentiometer and an encoder. The zoom position signal z obtained from 22 is sent to the arithmetic circuit 27.

On the other hand, in a storage circuit 28 composed of a ROM, a RAM, and the like, the relationship between the amount φ ′ relating to the aperture diameter and the zoom position information z ′ is stored in association with each other.

The arithmetic circuit 27 determines the amount related to the aperture diameter by comparing and referring to the zoom position information in the storage circuit 28 based on the zoom position signal z, and sends it to the control circuit 23 as the aperture diameter signal φ.

The control circuit 23 sends a signal to a diaphragm driving member 24 such as a motor or an IG meter based on the diaphragm diameter signal φ.
The rotation direction and the rotation amount are transmitted as a drive signal θ.

The aperture driving member 24 is driven to rotate faithfully based on the drive signal θ, and is connected to the aperture mechanism 20 by gears, belts, and the like.

The diaphragm mechanism 20 constituting the flare cut diaphragm A has a structure in which the diaphragm is opened and closed by rotation.
The aperture diameter is changed by rotation of the aperture drive member 24.

The same processing can be performed by connecting the zoom position detecting member to the supporting member 18 of the variator V or the supporting member 19 of the compensator C as shown in FIG. The same can be applied to the case where an electronic cam system or the like that can independently drive the movement of the compensator without using a mechanical member is used.

As described above, in this embodiment, since the aperture diameter is electrically controlled, the weight can be further reduced.
Since the rate of change of the aperture diameter with respect to the zoom position can be easily and optimally converted by rewriting the information in the storage circuit, the flare component of off-axis rays can be more accurately shielded.

Next, a case where a series of processes of a method of controlling the aperture diameter of the aperture A will be described with reference to FIG.

In the figure, the zoom mechanism is the same as that of the embodiment of FIG. 2, and the curved cam 17 is connected to a zoom position detecting member 22 such as a potentiometer and an encoder. The zoom position signal z obtained from 22 is sent to the arithmetic circuit 27.

A diaphragm mechanism 2 constituting an aperture diameter determining diaphragm B
Reference numeral 1 denotes a structure in which the aperture is opened and closed by rotation.

The F-number detecting member 29 may be a potentiometer, an encoder, or the like connected to the diaphragm mechanism 21, an auto iris signal (not shown) from the camera side, or a device for driving the diaphragm mechanism 21. The F-number signal F is sent to the arithmetic circuit 27.

The focal length conversion detecting member 30 determines whether or not a device for converting the focal length over the entire zoom range, such as a converter or a built-in extender (IE), is used, and sends it to the arithmetic circuit 27 as a focal length conversion signal IE. are doing.

On the other hand, in the storage circuit 28 composed of a ROM, a RAM and the like, the amount φ ′ relating to the aperture diameter is associated with the zoom position information z ′, the F number information F ′, and the focal length conversion information IE ′. It is remembered.

In the arithmetic circuit 27, based on the output signals z, F, and IE from the three detection members, the three pieces of information z ', F', and IE 'in the storage circuit 28 are compared and referred to, and the aperture diameter is determined. The control unit 23 determines the amount of the stop signal and sends it to the control circuit 23 as the stop diameter signal φ.

The control circuit 23 sends a signal to an aperture driving member 24 such as a motor or an IG meter based on the aperture diameter signal φ.
The rotation direction and the rotation amount are transmitted as a drive signal θ.

The aperture drive member 24 is driven to rotate faithfully based on the drive signal θ, and is connected to the aperture mechanism 20 by gears, belts and the like.

The diaphragm mechanism 20 constituting the flare cut diaphragm A has a structure in which the diaphragm is opened and closed by rotation.
The aperture diameter is changed by rotation of the aperture drive member 24.

The same processing can be performed by connecting the zoom position detecting member to the supporting member 18 of the variator V or the supporting member 19 of the compensator C as shown in FIG. The same can be applied to the case where an electronic cam system or the like that can independently drive the movement of the compensator without using a mechanical member is used.

As described above, in this embodiment, since the aperture diameter is electrically controlled, the weight can be further reduced.
In addition, the change rate of the aperture diameter with respect to the zoom position, the F-number, and the presence or absence of the focal length conversion can be easily and optimally converted by rewriting the information in the storage circuit. It is possible to shield light.

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 spacing from the object side, and Ni and νi are the i-th lens surfaces in order from the object side. These are the refractive index and Abbe number for d-line of glass.

R1-r8 are a front lens group F having a positive refractive power
Therefore, the lens moves in the optical axis direction when focusing on the subject, and is fixed during zooming. Reference characters r9 to r15 denote a variator V having a negative refractive power, which moves in the optical axis direction during zooming in order to perform a variable power operation. Reference numeral r16 denotes a flare cut stop A having a variable diameter, and r17 to r26 denote compensators C having a positive refractive power, which move in the optical axis direction during zooming in order to perform a zooming operation and image plane compensation. r27 denotes a stop B for determining the F number of the zoom lens, and r28-r43 form an image by a relay lens R having a positive refractive power. r44-r45 is a dummy glass P such as a prism.

Table 1 shows the relationship between the F-number, the focal length f, and the variable interval in the numerical examples, and the parameters of the present invention.

FIG. 7 (f = 10.0 mm) and FIG. 8 (f = 1
9.49 mm), FIG. 9 (f = 69.78 mm), FIG.
(F = 256.6 mm), FIG. 11 (f = 440.0 m
m).

In the aberration diagram, the left side from the shaded portion t is a light-shielded portion, f = 19.49 mm, 69.78.
It can be seen that the effect of removing the flare component of the lower light beam is the largest in the vicinity of mm.

[0077]

[Outside 4]

[0078]

[Table 1]

[0079]

As described above, it is possible to remove the flare having the maximum image height by providing the stop whose diameter changes at a specific position. Further, by changing the aperture diameter in a specific zoom range, it becomes easy to obtain good optical performance. In addition, by providing an arithmetic circuit and a storage circuit, the responsiveness is good, the number of mechanical parts is reduced, and the size can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view of a zoom lens according to the present invention;
FIG.

FIG. 2 is a diagram illustrating control of a flare stop according to the present invention.

FIG. 3 is a diagram showing control of a flare stop according to the present invention.

FIG. 4 is a diagram showing control of a flare stop according to the present invention.

FIG. 5 is a diagram showing control of a flare stop according to the present invention.

FIG. 6 is a diagram showing control of a flare stop according to the present invention.

FIG. 7 is a diagram illustrating various aberrations at a wide-angle end according to a numerical example of the present invention.

FIG. 8 shows an intermediate value (focal length 19.4) of a numerical example of the present invention.
9 mm).

FIG. 9 shows an intermediate example (focal length 69.7) of a numerical example of the present invention.
8mm).

FIG. 10 is a diagram illustrating various aberrations at an F drop start point in a numerical example of the present invention.

FIG. 11 is a diagram showing various aberrations at the telephoto end in a numerical example of the present invention.

FIG. 12 is a lens cross-sectional view on the wide-angle side for illustrating the optical function of the present invention.

FIG. 13 is a sectional view of a lens at an F drop starting point for illustrating an optical function of the present invention.

FIG. 14 is a sectional view of a general zoom lens.

FIG. 15 is a diagram illustrating a flare cut aperture A at each zoom position.
FIG.

[Explanation of symbols]

F First group V Second group C Third group R Fourth group IE Focal length conversion lens such as IE converter, built-in extender, etc. P Prism block A Flare cut aperture B Aperture aperture diameter aperture (F number aperture aperture)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-186477 (JP, A) JP-A-49-58825 (JP, A) JP-A-3-243928 (JP, A) JP-A-63-1988 70218 (JP, A) JP-A-60-150019 (JP, A) JP-A-60-117209 (JP, A) JP-A-60-191219 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) G02B 9/00-19/00

Claims (7)

(57) [Claims] A first lens group having a positive refractive power, a second lens group having a negative refractive power, a flare-cut diaphragm having a fixed diameter and a variable diameter, and a third lens group having a positive refractive power. In a zoom lens having a flare cut stop for performing zooming by moving the second lens group and the third lens group, a flare component of a lower ray of a maximum off-axis ray is not affected without affecting an axial ray flux. A zoom lens having a flare cut stop, comprising a control unit for controlling the diameter of the flare cut stop. 2. The control means according to claim 1, wherein said zoom ratio is z. 2. A zoom lens having a flare cut stop according to claim 1, wherein the diameter of the stop is controlled so as to cut the lower light beam in the range of. 3. A zoom lens having a flare-cut aperture according to claim 1, wherein said second lens group and said third lens group simultaneously pass −1 times each imaging magnification from a wide-angle end to a telephoto end. 4. A zoom lens having a flare cut aperture according to claim 1, further comprising an aperture for determining an f-number behind said third lens group. 5. The zoom lens having a flare cut aperture according to claim 1, wherein said control means controls said flare cut aperture diameter based on a detection signal of a zoom position detection means. 6. A zoom position detecting means, and storage means for storing information corresponding to a diameter of the flare-cut stop corresponding to each zoom position, wherein the zoom position detecting means and information stored in the storage means are also stored. 2. A zoom lens having a flare cut aperture according to claim 1, wherein said control means controls said flare cut aperture diameter. 7. The flare-cut aperture diameter is determined by D, the luminous flux diameter determined by an on-axis F-number ray on the flare-cut aperture surface is determined by Da, and the off-axis maximum image height ray is determined on the flare-cut aperture surface. Where Dm is the diameter
Satisfies D ≧ Da throughout the zoom range. 2. The zoom lens having a flare-cut aperture according to claim 1, wherein the control means controls the aperture so as to satisfy Dm> D in a zoom range (z: zoom ratio) up to the range.