JPH0271214A - Focal length correcting device for auto-focus zoom lens - Google Patents

Abstract

PURPOSE:To obtain a clear image even for an object moving in the direction of the optical axis by driving a power varying lens group toward the short focus side to increase the depth of field as the whole of a lens system at the time when a focusing lens group cannot follow up movement of the object in the direction of the optical axis. CONSTITUTION:A focal length correction extent table 15 is provided where focal length correction extent data where the difference between the extent of movement of the object and the extent of following-up of a focusing lens group 2c corresponds to the difference between a focal length included in the depth of field and the present focal length has the focal length, the subject distance, and the object speed divided by the aperture value and is stored. A focal length present value signal indicating the present value of the focal length, a subject distance signal indicating the subject distance, an object speed signal indicating the object speed, and an aperture value signal indicating the aperture value are used as the address to read out focal length correction extent data from the focal length correction extent table 15, and a power varying lens group 2b is driven toward the short focus side in accordance with this data. Thus, a clear image is obtained.

Description

[Detailed description of the invention] [Industrial application field]

The present invention is an autofocus zoom lens that has a variable power lens group and a focus lens group, and each lens group is driven by an independent actuator. When taking pictures, if the moving speed of the subject exceeds the tracking speed of the focusing lens group, the variable magnification lens group is driven in a direction that expands the depth of field to obtain a clear image. The present invention relates to a focal length correction device for an autofocus zoom lens.

[Conventional technology]

An autofocus zoom lens used in a video camera or the like includes at least a variable power lens group for continuously changing the focal length and a focusing lens group for focusing an image on a focal plane. The position of the focus lens group is controlled by the output of the object distance detection section to form a subject image on the focal plane, and the position of the variable power lens group is controlled by the output of the variable power input section connected to the 5-operation switch. This is done so that a desired focal length can be obtained.

[Problems to be solved by the invention]

An autofocus zoom lens like the one above basically responds to the movement of the subject in the optical axis direction by moving the focusing lens group, but the moving speed of the subject can follow the focusing lens group. If the speed is faster than the subject's movement, the focus lens group will not be able to respond to the movement of the subject, and the subject may become invisible, especially if the variable magnification lens group is set to the long focal length side with a shallow depth of field. There is a problem in that a clear image may not be obtained because the depth of field is out of range.

[Means to solve the problem]

The present invention has been made to solve these problems, and is designed to provide a clear image even when the moving speed of the subject in the optical axis direction exceeds the tracking speed of the focusing lens group. An object of the present invention is to provide a focal length correction device for an autofocus zoom lens. In summary, the autofocus zoom lens focal length correction device of the present invention includes: a focus system lens group that is driven in response to a subject distance signal indicating a subject distance to focus a subject image on a focal plane; and a focal length correction device that commands a focal length. This assumes an autofocus zoom lens that has a variable magnification lens group that is driven in response to a focal length command signal to obtain the desired focal length: the difference between the amount of movement of the subject and the amount of tracking by the focusing lens group. Equipped with a focal length correction amount table that stores focal length correction amount data corresponding to the difference between the focal length included in the depth of field and the current focal length, categorized by focal length, subject distance, subject speed, and aperture value. : The focal length current value signal indicating the current value of the focal length, the subject distance signal indicating the subject distance, the subject velocity signal indicating the subject speed, and the aperture value signal indicating the aperture value are used as addresses to calculate the focal length from the focal length correction amount table. Reading correction amount data: The variable power lens group is driven to the short focus side in accordance with the read focal length correction amount data. In addition, the focal length correction device for an autofocus zoom lens according to the present invention has a modified aspect: a focal length that includes the difference between the moving amount of the subject and the tracking amount of the focusing system lens group within the depth of field, and the current focal length. The camera is equipped with a focal length correction amount table that stores focal length correction amount data corresponding to the difference between the object distance and the object speed, divided by the combination step of the object distance and the object speed, and the focal length: an object distance signal indicating the object distance and an object distance signal indicating the object speed. The focal length correction amount data is read out from the focal length correction amount table using the combination step with the object speed signal and the current focal length signal indicating the current value of the focal length as an address.

[Effect]

That is, according to the present invention, even if the focusing lens group cannot follow the movement of the photographing lens in the optical axis direction, the depth of field on the difference plate between the amount of movement of the subject and the amount of tracking by the focusing lens group The variable magnification lens group is driven until it reaches a focal length of . Even if the focusing lens group cannot follow the movement of the subject, a clear image can be obtained due to the depth of field of the lens.

【Example】

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.However, prior to a specific embodiment, the basic principle of the present invention will first be explained with reference to FIG. In FIG. 1, 1 is a camera, and A and A' are objects. Now, a subject A existing at a point P1, which is a subject distance L1 away from the camera 1, moves in the direction of the camera 1 at a speed ■,
When the subject distance reaches L2 after a certain period of time has elapsed, the automatic focus adjustment mechanism of the camera 1 continues to track the subject A. As long as the tracking speed of the automatic focus adjustment mechanism can follow the moving speed V of the subject A, there will be no out-of-focus problem, but if the tracking speed of the automatic focus adjustment mechanism cannot follow the moving speed Focus issues occur. For example, while the subject moves from A to A'' as described above, the focus position by the automatic focus adjustment mechanism changes from Pl to P.
If tracking is possible only up to 2, it means that the tracking speed of the object by the automatic focus adjustment mechanism does not follow the moving speed of the object A. If the depth of field when the automatic focus adjustment mechanism focuses on point P2 is Dl, then the subject A will be photographed by an amount corresponding to the positional difference OUT between the near point of the depth of field D1 and the subject A. ° becomes ara I focus. Now, it is well known that the near point and far point of the depth of field are expressed by (Equation-1) and (Equation-2), and the shorter the focal length f of the photographic lens of the camera 1, the more the depth of field is expressed. The depth of field becomes deeper. Depth of field near point - (HFD x D) + (HFD
+ D) (Formula-1) Depth of field near point = (IIFD
X D) + (HFD-11) (Formula-2) HFD=
f2÷δF (Formula-3) However, HFD:
Hyperfocal distance f: Focal length δ: Allowable blur F: F number D = Shooting distance Therefore, in the case of Fig. 1 above, the near point of the depth of field should reach the position of the subject A after movement. By correcting the focal length of the photographic lens of the camera 1, it is possible to obtain a clear image even of a moving subject. As is clear from (2-1) and (Equation-2), the focal length correction amount is the current focal length and subject distance. It varies depending on the subject speed, F number, etc. Therefore, in Raikou/Mei, we prepare in advance a focal length correction amount table in which focal length correction amount data indicating the focal length correction amount is accumulated, and this focal length correction amount table is used for the current focal length, subject distance, and subject. The speed, F number, etc. are read out as an address, and the focal length correction amount data read out is used to operate the variable magnification mechanism of the zoom lens so that the moving subject is kept within the depth of field. The near point and far point of the depth of field are determined by (Equation-1) and (Equation-2) above, so it is necessary as long as it can tolerate the increase in memory capacity that makes up the focal length correction amount table. To perform the minimum focal length correction, the current focal length and subject distance. It is desirable to construct a focal length correction amount table using the subject speed and F-number as independent four-dimensional addresses, and such an embodiment is shown in FIG. In FIG. 2, 2 is a photographing lens having a front lens group 2a, a variable power lens group 2b, and a focus lens group 2C, and 3 is a focal plane, which allows the variable power lens group 2b to be moved along the optical axis 4. By moving the focus system lens group 2C along the optical axis 4, images of objects having different object distances are focused on the focal plane 3. 5 is a step motor for rotating the driving cam ring of the focus system lens group 2c, and 6 is a subject distance detection device that measures the subject distance by, for example, a triangulation method or other known method and generates a subject distance signal. Part, 7
1 and 2 respectively show an automatic focus control section that controls the amount of rotation of the step motor 5 in response to a subject distance signal generated by the subject distance detection section 7; By controlling the amount of rotation of the step motor 5 by the automatic focus control section 7, the focus system lens group 2C is positioned, and the subject image is focused on the focal plane 3. Next, 8 is a step motor for rotating the driving cam ring of the variable power lens group 2b, and 9 is a focal length command value signal f indicating a desired focal length command value. 10 is a focal length command value signal f generated by the variable magnification input section 9. Each shows a variable magnification control section that controls the amount of rotation of the step motor 5 correspondingly, and a focal length command value signal f generated by a variable magnification input section 9. The variable power control unit 10 controls the amount of rotation of the step motor 8 in response to this, thereby positioning the variable power lens group 2b and determining the focal length of the photographic lens 2. The specific configuration of the variable magnification input section 9 can take various forms, but for example, the variable magnification input section 9 is equipped with an amplifier down counter, and a switch PB1 for changing to the long focus side and a short focus side. The focal length command value signal f is amplified down by the output of the switch PB2 to change the focal length command value signal f. Output. In the above configuration, the basic operation is for the photographer to switch F.
A focal length command value signal f generated by the variable magnification input section 9 by pressing BI or PB2. The magnification control unit 10 corresponds to
By controlling the step motor 8, the variable magnification lens group 2b is driven to obtain the focal length desired by the photographer, and automatic focusing is performed in response to the subject distance signal generated by the subject distance detection section 6. When the control unit 7 controls the step motor 5, the focus system lens group 2c is driven and a subject image is formed on the focal plane 3. However, in the case of a subject moving in the direction of the optical axis 4, there is a possibility that the subject image will be out of focus, as explained with reference to FIG. 1 above. In order to obtain a clear image even for such a subject moving in the optical axis direction, this embodiment has the following configuration. First, reference numeral 11 indicates the position of the variable magnification lens group 2b (i.e., the actual focal length) by, for example, detecting the position of the step motor 8.
12 is a subject speed signal that differentiates the subject distance signal generated by the subject distance detector 6 with respect to time and indicates the amount of change in subject distance (subject speed). A speed detection unit that generates V, 13
indicates an aperture detection unit that detects the aperture value adjusted by aperture blades (not shown) and outputs an aperture value signal F, and one output of each of these detection units is sent to the central processing unit along with the output of the subject distance detection unit 6. 14. Next, reference numeral 15 is a focal length correction amount table for storing focal length correction amount data indicating the amount of focal length correction. Each address in the focal length correction amount table 15 contains a numerical value corresponding to the difference between the current focal length and the focal length that includes the difference between the amount of movement of the subject and the tracking amount of the focusing lens group within the depth of field. Focal length correction amount data is stored, and each address of the focal length correction amount table 15 is w-x-y.
- Specified by the 4-dimensional address of z. More specifically, the W-direction component of the address in the focal length correction amount table 15 corresponds to the subject distance signal output from the subject distance detection unit 6, and the shorter the subject distance signal indicates, the more the focal length is corrected. The data in the focal length correction amount table 15 is configured such that the amount increases. Similarly, the X-direction component of the address corresponds to the subject speed signal ■ output by the speed detection unit 12, and the focal length correction amount table is set such that the faster the absolute value of the subject speed signal ■ is, the larger the focal length correction amount is. The data within 15 is configured. Note that even if the absolute values of the subject velocity signals V are equal, the signs are positive (
The data in the focal length correction amount table 15 is configured such that the focal length correction amount is larger when the sign is negative (when the object is moving away) than when the sign is negative (when the object is moving away). Similarly, the X-direction component of the address corresponds to the focal length current value signal f outputted by the focal length detection unit 11, and the focal length current value signal f1 indicates a longer focal length, so that the focal length correction amount increases. The data in the distance correction amount table 15 is configured. Furthermore, the X-direction component of the address corresponds to the aperture value signal F outputted by the aperture detection section 13, and is set in the focal length correction amount table 15 so that the larger the aperture value signal F indicates, the larger the focal length correction amount is. Data is configured. Then, the central processing unit 14 specifies the W direction component of the address of the focal length correction amount table 15 based on the subject distance signal output from the subject distance detection unit 6, and
The X-direction component of the address of the focal length correction amount table 15 is specified by the subject speed signal V outputted by the object speed signal V outputted by the lens 2, and the Specify the direction component and specify the X direction component of the address of the focal length correction amount table 15 using the aperture value signal F output by the aperture detection unit 13, and obtain the focal length correction amount data f2 from the focal length correction amount table 15. The focal length of the photographing lens 2 is read out and given to the variable magnification control unit 10 as focal length correction amount data f.
Corresponding to 2, the correction is made to the short focus side. Next, the operation of the embodiment shown in FIG. 2 will be explained with reference to flowcharts 1 to 3 in FIG. First, the basic operation of the embodiment shown in FIG. The lens group 2b is driven to obtain the focal length desired by the photographer, and the automatic focus control section 7 controls the step motor 5 in response to the subject distance signal generated by the subject distance detection section 6. As described above, the focus system lens group 2C is driven to form a subject image on the focal plane 3. In the process of performing the basic operation of 1, the central processing unit 1
4 designates the address W\no-acid component of the focal length correction amount table 15 according to the object distance signal outputted by the object distance detection section 6, and specifies the focal length correction amount table 15 according to the object speed signal ■ outputted from the speed detection section 12. The X-direction component of the address of the focal length correction amount table 15 is designated by the focal length current value signal f1 outputted by the focal length detection section 11, and the 1-aperture detection section 13
The two-way content of the address of the focal length correction amount table 15 is designated by the aperture value signal F outputted by the focal length correction amount table 15, and the focal length correction amount data f2 is read out from the focal length correction amount table 15. The focal length correction amount data f2 read from the focal length correction amount table 15 is given to the zoom control unit 10, and the zoom control unit 10 applies a pulse to the step motor 8 in response to the focal length correction amount data f2. and moves the variable power lens group 2b to the short focus side. By converting the focal length to the short focal length side in this way, the depth of field of the photographing lens 2 becomes deeper, and the object after moving is included within the depth of field, even if it is not in focus. Depth of field allows you to obtain clear images. Now, as in the embodiment shown in FIG. 2 described above, focal length correction is stored in a focal length correction amount table that has four-dimensional addresses each independently specified by the current value of focal length, subject distance, subject speed, and aperture value. If the amount data is stored, it is possible to perform the minimum necessary focal length correction, but the address structure of the focal length correction amount table becomes complicated.
The memory capacity configuring the focal length correction amount table increases. FIG. 4 shows an embodiment in which the memory capacity constituting the focal length correction amount table is compressed. The embodiment shown in FIG. 4 differs from the embodiment shown in FIG. 2 in the address structure of the focal length correction amount table 16. The focal length correction amount table 16 has two-dimensional addresses in the X direction and the X direction. Further, in the embodiment shown in FIG. 4, the focal length correction is always performed assuming the open aperture for one aperture value. The larger the aperture value, the shallower the depth of field, so if you perform focal length correction assuming a wide aperture, sufficient focal length correction will always be made even for small apertures, and the memory of the focal length correction amount table 16 will be corrected. Capacity is compressed. Furthermore, in the embodiment shown in FIG. 4, the X-direction component of the address of the focal length correction amount table 16 is specified by the focal length current value signal f output by the focal length detection section 11, and
The focal length is corrected by specifying the X-direction component of the address in the focal length correction amount table 16 through arithmetic processing based on the subject distance signal ■- output by the subject distance detection section 6 and the subject speed signal ■ outputted by the speed detection section 12. The 'memory capacity of the quantity table 16 is further compressed. The specific content of the calculation is appropriately determined by the number of stages of the object distance signal or object speed signal, or the tracking speed of the focus system lens group 2c. Weighting is carried out in stages, and weighting of the subject speed signal (2) is carried out in six stages according to its absolute value.The X component of the address in the focal length correction amount table 16 is specified in steps according to the sum of the two. Table 1 shows an example of calculation for stepping the X-direction address of the focal length correction amount table 16 using the subject distance signal 1 and the subject velocity signal 2. Table 1 As shown above, when the object distance is stepped in six steps, for example, so that the weighting increases as the distance becomes shorter, and the object speed is stepped, for example, in six steps, so that the weighting increases as the speed increases. There are 36 combinations of the subject distance signal 1 and the subject speed signal 2, but as shown in Table 1 above, the value obtained by adding 9 of the two is added to the address X of the focal length correction amount table 16.
When used as directional components, there are essentially 11 combinations. In addition, considering that the depth of field is shallow in the foreground and deep in the background, if the sign of the object velocity signal V is negative, a predetermined value is subtracted from the added value in Table 1 above, or The added value in Table 1 may be divided by a predetermined value. Next, the operation of the embodiment shown in FIG. 4 will be explained with reference to the flowchart shown in FIG. The basic operation of the embodiment shown in FIG. 4 is the same as that of the embodiment shown in FIG. and the subject speed signal V output by the speed detection unit 12
The calculations shown in Table 1 are performed to specify the X-direction component of the address in the focal length correction amount table 16. Subsequently, the X-direction component of the address of the focal length correction amount table 16 is designated by the focal length current value signal f output by the focal length detection section 11, and the focal length correction amount data f2 is read from the table 16. The focal length correction amount data f2 read from the table 16 is given to the variable power control section 10, and the variable power control section 10 applies a pulse to the step motor 8 in accordance with the focal length correction amount data f2. The system lens group 2b is moved to the short focus side. By converting the focal length to the short focus side in this way, the depth of field of the photographing lens 2 becomes deeper, and the object after moving is included within the depth of field and is not in focus. Depth of field also allows you to obtain clear images. In the embodiment shown in FIG. 4, the X-direction component of the address in the focal length correction amount table 16 is specified by the focal length current value signal f. An example in which the X-direction component of the address of the focal path Ul [correction amount table 16 is specified by arithmetic processing based on the subject distance signal outputted by the subject distance detection section 6 and the subject velocity signal ■ outputted from the velocity detection section 12 However, the Y-direction component of the address of the focal length correction amount table 16 can be specified in steps by arithmetic processing based on the current focal length value signal r and the aperture value signal F. Furthermore, although the above example shows an example in which the present invention is applied to a focal length correction device for an autofocus zoom lens for a video camera, even in an autofocus zoom lens for a still camera, the variable magnification lens group is driven by a motor. The present invention can be applied as long as the

【effect】

As explained above, according to the present invention, when the focusing lens group among the lens groups constituting an autofocus zoom lens cannot follow the movement of the subject in the optical axis direction, the variable power lens group is used as a short-focus lens group. Since the lens is driven to the side and deepens the depth of field of the lens system as a whole, it is possible to obtain a clear image even of a subject moving in the optical axis direction. Furthermore, when the present invention is applied, the focal length of a subject moving in the optical axis direction is usually corrected for the subject moving toward the camera, but 3, the present invention corrects the focal length of the subject moving toward the camera. This essentially has the effect of canceling out the increase in photographing magnification caused by the movement of the lens by shortening the focal length, and also prevents a subject moving toward the camera from moving out of the photographic field of view.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the basic principle of the present invention, FIG. 2 is a block diagram showing one embodiment of the present invention, FIG. 3 is a flowchart of the embodiment shown in FIG. 2, and FIG. 4 is a diagram showing other embodiments of the present invention. FIG. 5 is a flowchart of the embodiment shown in FIG. 4. 1...Camera 2...Photographing lens 2a・
...Front lens group 2b...Variable power lens group 2C...
... Focus system lens group 3 ... Focal plane 5 ... Step motor 6
...Subject distance detection section 7.Automatic focus control section 8.
・Step motor 9... Change (r input part 10・
...Magnification control section 11...Focal length detection section 12.
...Speed detection section 13..."1 diameter detection section 14...
・Central processing unit 15, 16... Focal length correction amount table

Claims (2)

[Claims] (1) A focus system lens group that is driven in response to a subject distance signal that indicates the subject distance to focus the subject image on a focal plane, and a focus system lens group that is driven in response to a focal length command signal that commands the focal length to set the desired focal length. In an autofocus zoom lens that has a variable magnification lens group that obtains Equipped with a focal length correction amount table that stores focal length correction amount data classified by focal length, subject distance, subject speed, and aperture value, and a focal length current value signal that indicates the current value of the focal length and a subject distance that indicates the subject distance. The focal length correction amount data is read from the focal length correction amount table using the signal, the object speed signal indicating the object speed, and the aperture value signal indicating the aperture value as addresses, and is changed in accordance with the read focal length correction amount data. A focal length correction device for an autofocus zoom lens, characterized in that a magnification lens group is driven to the short focus side. (2) A focus system lens group that is driven in response to a subject distance signal that indicates the subject distance to focus the subject image on a focal plane, and a focus system lens group that is driven in response to a focal length command signal that commands the focal length to set the desired focal length. In an autofocus zoom lens that has a variable magnification lens group that obtains It is equipped with a focal length correction amount table in which focal length correction amount data is classified and stored according to the combination step of object distance and object speed and focal length, and the object distance signal indicating the object distance and the object speed signal indicating the object speed are combined. The focal length correction amount data is read from the focal length correction amount table using the combination step and the focal length current value signal indicating the current value of the focal length as an address, and the zooming system is adjusted in accordance with the read focal length correction amount data. A focal length correction device for an autofocus zoom lens characterized by driving a lens group toward a short focus side.