JP3106801B2 - Rear focus zoom lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear focus type zoom lens, and particularly to a zoom lens which is compact, has a high magnification, and has a short range (focal length). The present invention relates to a rear focus type zoom lens having a focus correction mechanism suitable for, for example, a 35 mm single-lens reflex camera, a video camera, an electronic still camera, etc., in which the focus movement has been corrected extremely well.

[0002]

2. Description of the Related Art Conventionally, in a zoom lens which performs focusing by moving a front lens group or a part of the front lens group on the optical axis, a focus lens for focusing on a certain object distance (object distance). The feeding amount of
It is almost constant regardless of the focal length. Therefore, focusing can be performed without requiring a complicated moving mechanism.

However, if the close-up photographing distance is set short, especially in a zoom lens including a wide angle of view in which the focal length on the short focal length side (wide angle side) is shorter than the diagonal of the screen,
In order to obtain a desired peripheral light quantity ratio, there is a problem that the diameter of the front lens becomes large. For this reason, in an autofocus camera that has become popular in recent years, a load on a driving unit for driving a focus lens increases,
There was a problem that quick auto focus could not be performed.

In order to solve this problem, various rear focus type zoom lenses which focus on a rear lens unit or a part thereof from the front lens unit have been proposed to solve this problem. .

In the case of this rear focus type zoom lens, the effective diameter of the first lens unit is smaller than that of a zoom lens which performs focusing by moving the front lens unit.
The entire lens diameter can be easily reduced in size, and close-up photography, especially very close-up photography, can be facilitated. Further, since the relatively small and lightweight lens group is moved, the driving force of the lens group is small and the focus is quick. Features such as the ability to match.

However, the rear focus type zoom lens has a problem that the amount of extension of the focus lens for focusing on a certain subject distance differs depending on the focal length.

Therefore, in order to perform zooming while maintaining the in-focus state, a focus correction mechanism for correcting the position of the focus lens in conjunction with the zooming is required.

Therefore, in a conventional rear focus type zoom lens, a typical correction method is, for example, correction by auto focus, correction by an electronic cam, correction by a mechanical cam, and the like.

[0009] Regarding, for example, JP-B-56-475
No. 33, which is proposed in, for example, Japanese Patent Application Laid-Open No. Sho 52-114321, and which is also disclosed in, for example, Japanese Patent Application Laid-Open Nos. 4-184405 and 64-33512. And so on.

In the first correction method using auto focus (Japanese Patent Publication No. 56-47533), a focus lens moved due to a change in focal length is focused on a focus lens based on information from focus detection means for auto focus. It is corrected so as not to move the focus surface from a predetermined position by driving.

In a correction method using an electronic cam (Japanese Patent Laid-Open Publication No. Sho 52-114321), the positional relationship of the variator (optical slide element) and the focus lens (optical slide element) on the optical axis during zooming is as follows. It is stored in the storage means on a matrix of the object distance and the position of the variator, and during the zoom operation after focusing, focus driving is performed based on the data read from the storage means, thereby preventing focus movement. ing.

One of the correction methods using a mechanical cam (Japanese Patent Laid-Open No. 4-184405) is a method used in an embodiment of the present invention described later. In this correction method, a focus lens at each focal length is used. A representative approximation obtained by shifting the origin so that the focus error is minimized at all focal lengths and object distances, by superimposing the focus extension curve, which is the movement trajectory for focusing from the object at infinity to the closest object. A focus zoom / cam which is a curved line is used, and its use area is moved by a zoom operation (zooming), and at the same time, the focus zoom / cam ring itself is moved in the optical axis direction to correct the focus movement.

In another correction method using a mechanical cam (JP-A-64-33512), circumferential movement of the cam represents movement of the focus lens by focusing, and movement in the radial direction is caused by zoom operation. Using a three-dimensional cam representing the movement of the focus lens, tracing the surface of the three-dimensional cam with a pin that moves in the radial direction by a zoom operation, thereby obtaining a position on the optical axis of the focus lens corresponding to the zoom position and moving the focus. Is corrected.

[0014]

In the above-mentioned conventional auto-focusing correction method, although there is an advantage that the mechanical structure is simplified, the focus correction largely depends on the capability of the focus detection means. In the case of a subject that is not good at the means, there has been a problem that the focus correction cannot be performed sufficiently and the focus detection tends to be delayed, so that a comfortable photographing environment cannot be obtained. Further, since an actuator (generally, a motor) as a driving means is always driven, there is a problem that a load on a power source is increased.

In the correction method using an electronic cam, unlike the above-described correction method using auto focus during the focus correction, there is an advantage that it is not affected by the capability of the focus detection means, but there is a problem that the focus drive is always performed. There are still points, and the amount of focus movement generated by the drive error of the focus driving means is large, so that precise control by the focus driving means is required. Another problem is that storage means having a relatively large storage capacity is required.

In the former correction method using a mechanical cam, unlike the correction method described above, the focus driving means is not used during the zoom operation, so that power is not consumed for focus correction. It has the merit that it can completely support manual zooming. In addition, since the system is completed within the lens barrel, there is also an advantage that the system on the camera side does not matter.

However, in the case of a power arrangement having a sharply curved focus feed-out curve, it may not be possible to approximate the focus-camera well, so that a large focus movement may occur depending on the subject distance.

Although the latter correction method using a mechanical cam has the same advantages as the former correction method, it is necessary to use pins that are sufficiently smaller than the size of the three-dimensional cam in order to obtain a correct lens position. In addition, since the three-dimensional cam cannot have a cylindrical configuration that covers the outside of the optical system, there is a problem that it is difficult to reduce the size of the lens barrel.

The present invention solves the problems of the conventional correction methods by appropriately configuring a focus correction mechanism for correcting a focus movement during zooming, and achieves a high magnification and a close distance (focal length). It is an object of the present invention to provide a rear focus type zoom lens having a relatively easy configuration as a whole system for a short and compact zoom lens.

[0020]

The rear focus type zoom lens according to the first aspect of the present invention has a zoom function, and the amount of movement of the focus lens when focusing on the same object differs depending on the zoom position. A first focus correction unit configured to maintain a predetermined focus state by a mechanical cam in conjunction with the zooming within a first subject distance range during zooming after focusing; In a second object distance range closer to the first object distance range than the first object distance range, the out-of-focus amount after the operation of the first focus correcting means exceeds the predetermined focus state. Based on the value for the amount of correction,
A second focus correction unit configured to electronically compensate for the out-of-focus amount, wherein the second focus correction unit includes:
A focus lens absolute position detecting means for detecting a position on the optical axis of the focus lens; a zoom absolute position detecting means for detecting a position of the variable power lens; Storage means for storing as a matrix composed of the divided subject distance areas; and position signals from the focus lens absolute position detection means and the zoom absolute position detection means and correction amounts for the defocus amounts stored in the storage means. And a focus lens driving means for driving the focus lens by signal processing of the value.

[0021]

[0022]

[0023]

[0024]

FIG. 1 is a main block diagram showing the system configuration of a first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a lens system, 2 denotes a camera system (camera main body), and 3 denotes an absolute focus angle detecting means, which detects a rotation angle of a focus rotation member (not shown) and detects a rotation angle of a focus lens 4b described later. The position on the optical axis is detected, and the position information is sent to the CPU 10. 4a,
4c is a lens (magnification lens group) related to the magnification operation,
Reference numeral 4b denotes a focus lens (focus lens group) for performing correction (focusing) and correction of an image plane variation accompanying zooming.

Reference numeral 5 denotes first focus correcting means which operates at least within at least one predetermined object distance range (first object distance range) and at least moves to any object point within the predetermined object distance range. On the other hand, at the time of zooming after focusing, a predetermined focusing state is mechanically maintained in conjunction with the zooming.

Numeral 6 denotes a zooming cam mechanism, and numeral 7 denotes a focus lens driving means, which drives the focus lens 4b based on a signal from the CPU 10. Numeral 8 denotes a zoom absolute position detecting means for detecting the positions of the lenses 4a and 4c on the optical axis and sending the position information to the CPU 10. Reference numeral 9 denotes a data search unit, and RO as a storage unit.
M (storage element) 11 stores information stored in CPU 1
The search is performed based on the signal from 0. Reference numeral 10 denotes a CPU of the lens system 1.

The ROM 11 stores information on the amount of correction of the out-of-focus amount. The information is composed of a matrix of a plurality of divided zoom regions and a plurality of divided subject distance regions. It is expressed using the rotation angle of the member.

Reference numerals 12 and 13 denote switches, respectively, which are CPUs.
A command signal has been sent to 10. 14 is a mirror.

Reference numeral 15 denotes an out-of-focus amount detecting means for detecting the focus state of the lens system 1. 16 is a camera C
It is a PU, and calculates and controls the amount of movement of the focus lens 4b on the optical axis using a signal from the defocus amount detection means 15.

The focus lens absolute angle detecting means 3
The elements of the zoom absolute position detection means 8, the storage means 11, and the focus lens driving means 7 constitute one element of the second focus correction means.

Next, the focusing operation of this embodiment will be described with reference to the flowchart shown in FIG.

In this embodiment, information on the focus state of the subject image guided from the lens system 1 is sent to the out-of-focus amount detecting means 15 of the camera system 2.

First, when the switch SW1 is turned on in step 201, the defocus amount def is detected by the defocus amount detecting means 15 in step 202. Next, in step 203, the defocus amount def is compared with a preset threshold value. If the defocus amount def is large, step 2 is executed.
In 04, the CPU 16 calculates the operation coefficients Sn, An, B determined by the zoom position of the lens system 1, the focus lens position, and the like.
Read Pn etc.

Next, at step 205, each operation coefficient Sn,
The movement amount x on the optical axis of the focus lens 4b is calculated from An, BPn and the defocus amount def.
At 06, the calculation result is sent to the CPU 10 of the lens system 1.

Next, in step 207, the CPU 10 sends a control command to the focus lens driving means 7 so that the movement amount of the focus lens 4b becomes x, and moves the focus lens 4b on the optical axis.

When the above operation is completed, the process returns to step 202, and the defocus amount detecting means 15 detects the defocus amount def again. Then, in step 203, the above-described operation is performed until the defocus amount def becomes smaller than the threshold value. The operation (from step 202 to step 207) is repeated.

On the other hand, in step 203, the defocus amount d
When ef becomes equal to or less than the threshold value, the CPU 16 determines that focusing has been achieved, waits for a release command from the user at step 208 in SW2, releases the shutter in step 209, and ends the focusing operation.

Incidentally, depending on the camera system, if the SW2 is turned on even when the camera is not focused, the release may be given priority.

Next, the first focus correcting means 5 according to this embodiment will be described.

FIG. 3 is an explanatory diagram for explaining the shape of the focus / zoom cam used for the first focus correcting means 5.

In the figure, the vertical axis represents the sum of a zoom parameter (hereinafter referred to as "ZP") which is a parameter for design convenience and a focus angle. This zoom parameter corresponds to the rotation angle of the manual zoom ring. Normally, a certain reference focal length state is set to 0, and the other focal length states take values proportional to the rotation angle of the zoom cam ring from the reference focal length state. In FIG. 4 described later, the wide-angle end is set to 0, and the telephoto end is set to 1.

The focus angle corresponds to the rotation angle of the manual focus ring, the origin of which is determined by the subject at infinity, but the maximum value is determined by the shape of the focus zoom cam. The focus angle will be described later in detail.

The horizontal axis represents the amount of displacement in the optical axis direction on the focus cam ring. In this embodiment, the origin is the position of the focus lens that focuses on an object at infinity at the wide angle end.

In FIG. 3, a curve 3a is a cam that is also used as a focus zoom. The focus extension curves of the curves 3b, 3c, and 3d for each focal length are set so that the focus error is minimized at all focal lengths and object distances. It is a representative curve approximated by superposition.

For example, a curve 3b shows the extension of the focus lens when focusing from an object at infinity to a close object at the wide angle end.

FIG. 4 is an explanatory diagram showing an operation for obtaining a focus extension amount for focusing on an arbitrary focal length and an arbitrary subject distance using the focus zoom cam.

The focus and zoom cam moves in the direction of the vertical axis represented by the zoom parameter by the zoom operation. In this figure, the rotation of the focus and zoom cam ring that is linked with the rotation of the zoom cam ring is developed in a plane. It is shown in FIG.

As will be described later, the focus / cam ring itself moves in the optical axis direction by the zoom operation.
I do not show that. Therefore, FIG. 2 shows only the focus extension amount, not the position on the optical axis of the focus lens.

In this embodiment, the area of the focus and zoom cam used for focusing is a portion surrounded by the straight lines 4e and 4f in the figure, and moves by the zoom operation as shown in the figure. I do.

That is, at the wide-angle end, the upper end of the focus and zoom cam moves downward as it moves toward the telephoto side, and becomes the lowest end region at the telephoto end. By rotating a cam follower interlocking with the focus lens in the moved area, a desired focus extension amount is obtained.

Further, as described above, by specifying the shape of the focus / zoom cam, the zoom operation can be performed with the focus angle (rotation angle) fixed at a value corresponding to a certain focal length and a certain subject distance. , A focus extension amount corresponding to the focal length after zooming can be approximately obtained.

Incidentally, wmod, mmod, tmod in the figure
Indicates the amount of focus extension at the wide-angle end, the middle, and the telephoto end at the closest subject distance, respectively.

Further, it is shown that focusing can be performed from an object at infinity to an object at a close distance at the same focus angle regardless of the zoom position.

By the way, there is a lens system power arrangement in which both the movement path of the focus lens by the zoom operation and the movement path of the focus lens by the focusing operation can be expressed by almost one curve. Is limited and the degree of freedom is not preferable.

Therefore, in the present embodiment, the focus and zoom cam ring itself is configured to be movable in the optical axis direction in conjunction with the zoom operation, so that the amount of rotation of the focus angle for focusing with respect to the zoom rotation angle is obtained. And the direction of rotation can be set freely.

FIG. 5 is an explanatory diagram showing, as an example, the locus of zoom movement of the focus lens with respect to the closest subject. As shown in the figure, the focus lens position (the position on the optical axis of the focus lens) includes the amount of movement of the focus zoom cam ring in the direction of the optical axis (in FIG. Curve a by the sum of
It is changing like.

Here, the focus angle will be described.

As described above, the focus extension amount for focusing of the focus lens is obtained by rotating the cam follower in conjunction with the focus lens and inscribed in the focus zoom cam along with the cam by the focus rotation member. . The rotation angle for focusing of the focus rotation member is the focus angle described above. By setting the focus angle to the above-described configuration, when focusing on the same subject, a change in focus movement due to the focal length can be reduced.

FIG. 6 shows a change in the focus angle due to the zoom operation when a focus zoom / cam which is considered to be optimal is designed for a zoom lens having a zoom ratio of about 4 times.

As a result, when zooming from the telephoto end to the wide-angle side, for example, as shown in the figure, even if the focus angle at the telephoto end is fixed, the focus angle is the focus angle at another focal length during zooming. Is small, the amount of focus movement that occurs is small, and object points within the subject distance range excluding a part on the close subject side can be kept within the depth of field.

That is, once the focusing operation is performed at the telephoto end to obtain the focus angle, it is not necessary to perform the focus driving again, and the in-focus state can be maintained at all the focal lengths.

FIG. 7 shows the change of the focus angle due to the zooming operation when a focus and zoom cam is designed for a zoom lens with a zoom ratio increased to about 7 times while reducing the size and the close distance. .

In this case, as shown in the figure, the focus angle is determined at the telephoto end with respect to an object point within the subject distance range from the subject at infinity to the subject distance of about 2.2 m (first subject distance range). The amount of focus movement after zooming is ±
It can be 0.3 mm or less. This is within the allowable range.

That is, the focus movement amount can be corrected by the first focus correction means. However, from the object distance of 2.2 m to 0.5 m (the second object distance range), the focus movement amount cannot be corrected at the same focus angle, and is out of the allowable range. In this embodiment, at this time, the focus movement amount is corrected by the second focus correction unit.

Next, the overall focus correction operation in this embodiment will be described with reference to the flowchart of FIG.

First, when the switch SW1 is turned on in step 801, the focusing operation is started in step 802 based on the flowchart shown in FIG.
Then, the CPU 10 in the lens system 1 reads the focus angle information FPo from the absolute focus angle detecting means 3 and reads the zoom position information ZPo from the absolute zoom position detecting means 8. This focus angle information FPo is represented using the rotation angle of the focus rotation member.

The ROM 11 as the storage means stores a zoom position / zoom area representative value correspondence table in which the zoom position is divided into a plurality of areas and each zoom area is represented using a representative value. The CPU 10 uses the correspondence table in the ROM 11 via the data search means 9,
The representative value Z of the zoom area corresponding to the zoom position information ZPo
Po ′ is obtained, and at the same time, the representative value ZP
Let o 'be an initial value ZPtump'.

Next, at step 806, the representative value ZP on the matrix relating to the correction amount of the defocus amount in the ROM 11 is obtained.
The data stored in the row o 'is searched to find a value FPo' closest to the focus angle information FPo.

Next, in step 807, the number of the column on the matrix to which the value FPo 'belongs is recognized, whereby
A subject distance area S corresponding to the subject is obtained.

Next, at step 808, the subject distance area S
Is determined to be an area where focus correction is performed only by the above-described first focus correction unit or an area where focus correction is performed by the second focus correction unit described later. As a result, if the subject distance area S is an area in which only the first focus correction means is used, the CPU ends the processing, and if not, the operation of the second focus correction means from step 809 is performed.

In step 809, the CPU 10 reads the zoom position information ZP again.
The representative value ZP ′ of the zoom area to which the zoom position information ZP belongs is obtained using the correspondence table in the OM 11.

Next, at step 811, the representative value ZP 'of the zoom area is compared with the initial value ZPtump', and if it is determined that these values are different values and that it is necessary to perform correction driving during zooming, step 812 is executed. To read the value of the data FP 'of the representative value ZP' row of the zoom area in the column of the subject distance area S on the matrix relating to the correction amount of the defocus amount.

Next, in step 813, the control pulse Pk of the focus lens driving means 7 is obtained by the following equation: Pk = (FP'-FPo ') / B (B is a conversion coefficient). Pk is sent, and the focus lens 4b is driven in step 815.

Then, at step 816, the representative value ZP 'is set as a new initial value ZPtump' and FP 'is set as a new FPo.
And returns to step 809 to read the value of the zoom position information ZP again, obtain the representative value ZP 'of the zoom area to which the zoom position information ZP belongs using the correspondence table in the ROM 11, and obtain the representative value ZP. 'And the initial value ZPtum
The operation described above (from step 809 to step 816) is repeated each time both values are different from each other, and correction driving of the focus position is performed.

On the other hand, in step 811 the representative value ZP '
Is determined to be equal to the initial value ZPtump ', the CPU 10 determines that the zoom is not being performed or that it is not necessary to perform the correction drive.
The state of W1 (ON / OFF) is determined, and SW1 is OFF
In this case, the CPU terminates the processing. Otherwise, the CPU returns to step 809 to execute the operation described above (step 80).
9 to step 816) are repeated.

In this embodiment, by performing the focus correction according to the above-described procedure, the focus lens can be driven to an appropriate focus angle even during the zoom operation. Is kept small, and the in-focus state is favorably maintained.

In any of the above operations, when the user turns on the switch SW2, the focusing operation is performed or the shutter is released without performing the focusing operation.

In this embodiment, as described above, the subject distance range using only the first focus correction means and the
The correction of the focus movement during zooming is performed by dividing into the object distance range to which the electronic correction controlled by U is applied, but the electronic correction may be applied to the entire object distance range. The focus state can be maintained satisfactorily by further reducing the focus movement amount in the entire subject distance range.

The present invention can be applied to a rear focus type zoom lens other than the lens configuration shown in FIG. 1 in the same manner as in the above-described embodiment.

[0081]

According to the present invention, as described above, the focus driving means is provided by incorporating the first focus correcting means constituted by the cam mechanism, while having a relatively simple structure completed within the lens system. The focus movement amount is small with respect to the drive error, and manual zoom is also possible at the main subject distance. Since the focus drive means is not driven at all times, there is no burden on the power supply. Since the area is obtained and the correction drive is performed, the storage capacity can be reduced. Further, the focus angle is directly converted into data, so that the CPU does not perform complicated and highly accurate calculations, so that all focal lengths and object distances can be obtained. To achieve a rear-focus type zoom lens that can satisfactorily correct focus movement due to zooming over Door can be.

[Brief description of the drawings]

FIG. 1 is a main block diagram illustrating a system configuration according to a first embodiment of the present invention.

FIG. 2 is a flowchart illustrating a focusing operation according to the first embodiment of the present invention.

FIG. 3 is an explanatory view showing the shape of a cam combined with a focus zoom.

FIG. 4 is an explanatory diagram showing a principle for obtaining a feed-out amount using a focus zoom / cam.

FIG. 5 is an explanatory diagram showing a locus of zoom movement of a focus lens with respect to a close subject.

FIG. 6 is an explanatory diagram showing a change in focus angle due to zooming when the first focus correction unit is applied to a zoom lens having a zoom ratio of about 4 times;

FIG. 7 is an explanatory diagram showing a change in focus angle due to zooming when the first focus correction unit is applied to a zoom lens having a zoom ratio of about 7 times;

FIG. 8 is a flowchart illustrating a focus correction operation according to the first embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lens system 2 Camera system 3 Focus lens absolute angle detection means 4a Lens group 4b Focus lens group 4c Lens group 5 First focus correction means 6 Zooming cam mechanism 7 Focus lens drive means 8 Zoom absolute position detection means 9 Data search means 10 CPU 11 Storage means (ROM) 12 SW1 13 SW2 14 Mirror 15 Defocus amount detection means 16 CPU

Continuation of front page (56) References JP-A-52-114321 (JP, A) JP-A-64-33512 (JP, A) JP-A-4-184405 (JP, A) JP-A-4-268523 (JP) JP-A-4-367810 (JP, A) JP-A-5-5822 (JP, A) JP-A-5-113533 (JP, A) JP-A-5-210039 (JP, A) 50-92127 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B ⁷ /02-7/105

Claims (1)

(57) [Claims] 1. A rear focus type zoom lens having a zoom function and a moving amount of a focus lens which is different depending on a zoom position when focusing on the same object, the zoom distance after focusing is within a first object distance range. Then, the mechanical cam is used in conjunction with the zooming .
A first focus correction unit configured to maintain a predetermined focus state, and a first object distance range in which an out-of-focus amount after operation of the first focus correction unit exceeds the predetermined focus state.
In a second object distance range from circumference of closest distance side, the's
A second focus correction unit configured to electronically compensate for the out-of-focus amount based on a value related to the correction amount of the out-of-focus amount in conjunction with the zooming ; The focus correction means divides the focus lens absolute position detection means for detecting the position of the focus lens on the optical axis, the zoom absolute position detection means for detecting the position of the variable power lens, and the correction amount of the out-of-focus amount into a plurality. Storage means for storing as a matrix composed of a zoom area and a plurality of divided subject distance areas; position signals from the focus lens absolute position detection means and the zoom absolute position detection means; and defocus stored in the storage means and signal processing and a value related to the correction amount of the amount, characterized in that it has a focus lens driving means for driving said focus lens rear Four Scan type of the zoom lens.