JP2004205625A - Lens system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens system with which unconfortable feeling and unnaturalness resulting from the phenomenon that the brightness of a screen is rapidly reduced in the vicinity of a telephoto end due to the original ramping characteristics of a photographing lens and from a porthole at the time of zoom operation can be reduced by simulatively generating desired ramping characteristics by controlling an iris to perform diaphragming when the focal distance is larger than the prescribed value with the iris open. <P>SOLUTION: A microcomputer 20 sets the open value of the iris I in accordance with the focal distance detected by a zoom position detector ZP when compulsive ramping is set ON and, for example, when the focal distance is altered with the iris open and the iris I is to be open wider than the open value, diaphragming is performed on the iris I till the open value. Thus, desired ramping characteristics is generated. In the ramping characteristics by the compulsive ramping, the brightness of the screen in the vicinity of the telephoto end is reduced more gently than in the original ramping characteristics of the photographing lens. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lens device, and more particularly to a lens device that reduces a problem such as a porthole caused by a problem caused by ramping and a decrease in peripheral light amount of a screen from a central portion.
[0002]
[Prior art]
In general, not only for a television camera or a television camera, a phenomenon is known in which, when the zoom is changed to the telephoto side when the taking lens is used with the aperture open, the brightness sharply decreases near the telephoto end. This phenomenon is generally called ramping. Conventionally, in aperture control, when an instruction value for the aperture is set to be brighter than the F number of the lens when the aperture is opened, the aperture is stopped down to a value that does not affect the actual brightness to improve optical performance. Such a ramping correction is known (for example, see Patent Document 1).
[0003]
In addition, in an image formed by a photographing lens, the amount of peripheral light is generally lower than that of the central portion, and the peripheral portion of the screen is generally darker than the central portion. The peripheral light amount ratio indicates a ratio of the brightness of the peripheral portion to the brightness of the central portion of the screen.
[0004]
[Patent Document 1]
JP-A-11-271835
[Problems to be solved by the invention]
It is desirable that the above-described ramping phenomenon and the phenomenon of a decrease in the amount of peripheral light do not occur. Further, the above-described ramping correction does not eliminate the ramping phenomenon itself.
[0006]
However, in the case of the ramping phenomenon, the fact that the screen is darkened more rapidly than the screen near the telephoto end is darker than the wide side is a major factor that causes unnaturalness and unnaturalness. Also, in the case of a phenomenon in which the peripheral light amount decreases, the peripheral light amount ratio greatly changes depending on the focal length when the aperture is opened, rather than the peripheral light amount being lower than the central portion. The movement (enlargement / reduction) of the circular pattern formed by the contrast with the central portion is a factor that causes an uncomfortable feeling and unnaturalness.
[0007]
Therefore, even if the ramping phenomenon and the phenomenon that the amount of peripheral light decreases cannot be eliminated, it is considered important to reduce the phenomenon that causes the unnaturalness and unnaturalness as described above.
[0008]
The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a lens device that can reduce a sharp decrease in the amount of light near the telephoto end and reduce a port hole during a zoom operation. .
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes an optical system capable of changing a focal length and a diaphragm, and when the focal length becomes longer than a predetermined value when the diaphragm is opened, the F of the optical system is changed. In a lens device having a ramping characteristic in which the number decreases, the aperture is instructed to open in a range where the focal length is shorter than the predetermined value and the focal length is longer than the narrowing start value. Aperture control means for controlling the aperture so as to reduce the upper limit aperture of the diaphragm as the focal length becomes longer and to reduce the aperture of the diaphragm so as not to exceed the upper limit aperture when the focal length is changed. It is characterized by having.
[0010]
According to a second aspect of the present invention, in the first aspect of the present invention, there is provided a switching unit for switching the control by the aperture control unit between enabled and disabled.
[0011]
A third aspect of the present invention is characterized in that, in the first aspect of the present invention, a setting means is provided for setting the upper limit opening amount with respect to a focal length to a desired value.
[0012]
According to the present invention, when the focal length is longer than the aperture start value when the aperture is opened, the aperture is controlled to reduce the aperture so that a desired ramping characteristic is created in a simulated manner. It is possible to reduce the phenomenon that the brightness of the screen suddenly decreases near the telephoto end due to the ramping characteristic, and the discomfort and unnaturalness due to the porthole can be reduced.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a lens device according to the present invention will be described in detail with reference to the accompanying drawings.
[0014]
FIG. 1 is a schematic configuration diagram of an optical system (photographing lens) in a lens device for a television camera to which the present invention is applied. As shown in the figure, the photographing lens includes a focus lens (group) FL, a variator lens (group) VL, a compensator lens (group) CL, a zoom lens (group) ZL, an aperture I, a relay lens (group) RL, and the like. Of optical members. The focus lens FL and the zoom lens ZL are arranged so as to be movable in the optical axis direction, and are driven by, for example, a connected motor. The aperture I is also driven by, for example, a connected motor, and the aperture amount is changed. In addition, since the variator lens VL and the compensator lens CL move with a predetermined positional relationship, these lenses are integrally formed as a zoom lens ZL. In applying the present invention, the focus lens FL and the zoom lens ZL may be driven by a manual operation force.
[0015]
The subject image formed by the photographing lens is photoelectrically converted by an image pickup device (CCD) 10 of the television camera body, and is subjected to required signal processing by a predetermined signal processing circuit 12. As a result, a video signal of a predetermined standard (for example, NTSC system) for video display is externally output from the signal processing circuit 12.
[0016]
FIG. 2 is a block diagram showing a schematic configuration of a control system in the lens device to which the present invention is applied. Note that only the components related to the present invention are shown. As shown in the figure, a microcomputer 20 is provided in the control system of the lens device, and the microcomputer 20 is provided with an iris control signal for instructing a target position to be set for the aperture I from the camera body or the like. It has become. Further, for example, the microcomputer 20 is provided with a zoom control signal for instructing a target position or a target speed to be set for a zoom (zoom lens ZL) from a zoom demand (controller) connected to the lens device by a cable or the like. Has become. In the present specification, an amount representing the state of the stop I, such as an F number or an opening amount, is expressed as “position”.
[0017]
The microcomputer 20 servo-controls the position and operation speed of the aperture I and the zoom lens ZL according to the iris control signal and the zoom control signal given from the camera body, the controller, and the like.
[0018]
As shown in the figure, the aperture I is connected to an iris drive motor IM, and the iris drive motor IM is driven at a rotation speed specified by a control signal output from the microcomputer 20 to the iris drive circuit ID. It has become. Further, an iris position signal indicating the current position of the diaphragm I is provided to the microcomputer 20 from the iris position detector IP. The microcomputer 20 drives the iris drive motor IM based on the control signal output to the iris drive circuit ID so that the current position of the aperture I matches the target position commanded by the iris control signal from the camera body or the like. For example, the iris drive motor IM is driven at a rotation speed corresponding to the difference between the current position of the aperture I and the target position. Thus, the aperture I is set to the target position commanded by the iris control signal.
[0019]
Although not described in detail, the zoom lens ZL is also connected to a zoom drive motor ZM in the same manner as the diaphragm I. The zoom drive motor ZM operates at a rotational speed indicated by a control signal output from the microcomputer 20 to the zoom drive circuit ZD. It is driven by. Further, a zoom position signal indicating the current position of the zoom lens ZL is provided to the microcomputer 20 from the zoom position detector ZP. The microcomputer 20 drives the zoom drive motor ZM based on the control signal output to the zoom drive circuit ZD so that the state of the zoom lens ZL becomes the target speed or target position commanded by the zoom control signal from the zoom demand or the like.
[0020]
A controller such as a lens device, a zoom demand, or a camera body is provided with a forced ramping ON / OFF switch 22 for an operator to select whether to turn on or off a forced ramping process, which will be described in detail later. . The on / off state selected by the forced ramping on / off switch 22 is read by the microcomputer 20 as an on / off signal. The microcomputer 20 executes the forced ramping process only when the forced ramping ON / OFF switch 22 is set to ON.
[0021]
Here, the forced ramping will be described. The forced ramping is a process of forcibly stopping down the aperture I when the focal length of the photographing lens becomes longer than a predetermined value. In the original optical characteristics of the taking lens, the relationship between the focal length and the F-number when the aperture is fully opened (open F-number) is represented as a graph in FIG. According to this, when the focal length is set to a value smaller than the predetermined value P (for example, about 100 mm) close to the telephoto end, the open F number indicates a constant value Fnomax (for example, about 1.7). On the other hand, when the focal length is longer than the predetermined value P, the incident light flux is restricted by other factors even when the aperture I is open, and as the focal length becomes longer, the open F-number increases as shown by the inclined portion (1) of the graph. Will increase. The characteristic indicated by the inclined portion {circle around (1)} is called a ramping characteristic.
[0022]
On the other hand, in the forced ramping process, the aperture I is controlled as if the ramping characteristic is shown as a sloped portion (2) in the graph of FIG. That is, even when an instruction value for opening the aperture I is given by an iris control signal from the camera body or the like, if the focal length becomes longer than the predetermined value FzDropPoint, the F-number of the inclined portion (2) is indicated. Then, the opening amount of the stop I is limited to a value (upper limit opening value) smaller than when the stop is opened. In other words, assuming that the value indicating the aperture position at the time of opening the aperture is called an aperture value, when the focal length is shorter than the predetermined value FzDropPoint, the aperture value is set to a constant value Fnomax, and when the focal length is longer than the predetermined value FzDropPoint, The aperture value is changed according to the focal length so as to indicate the F-number of the inclined portion (2). The open value means a value at the time of opening of the aperture, which cannot be further changed in the direction in which the aperture position is opened in control (a value of the aperture position at an upper limit aperture which indicates a limit to which the aperture can be changed). However, if the aperture position becomes a position that is more open than the open value, the aperture is controlled by the aperture control of the microcomputer 20 until the aperture position reaches the open value. Therefore, by changing the aperture value according to the focal length as described above and controlling the aperture position according to the aperture value, a photographic lens having the ramping characteristic shown in the inclined portion (2) can be obtained. . As a result, a ramping characteristic in which the F number changes more slowly than the original ramping characteristic can be obtained. When a value indicating the aperture position is associated with an F number (an F number when the ramping characteristic is not considered), a value FnoDropmax shown in FIG. 4 indicates an open value when the focal length reaches a maximum value.
[0023]
The following effects are obtained by such forced ramping. First, in the case of the original ramping characteristic of the photographing lens shown in the inclined portion (1) in FIGS. 3 and 4, if the zoom operation is performed with the aperture open and the focal length is changed from the wide side to the telephoto end, abruptly. The open F number increases. For this reason, the sense of strangeness and unnaturalness that the brightness of the screen suddenly becomes dark is conspicuous. On the other hand, when the ramping characteristic is changed to the ramping characteristic shown in the inclined portion (2) of FIG. 4 by performing the forced ramping process, the zoom operation is performed with the aperture open, and the focal length is changed from the wide side to the telephoto end. Even so, since the open F-number changes slowly, the brightness of the screen does not suddenly decrease, and the unnaturalness and unnaturalness caused by the original ramping characteristics of the photographing lens are reduced.
[0024]
In addition, there is a different effect of porthole reduction. The porthole is caused by the fact that the ratio of the amount of light in the peripheral portion to the central portion of the screen (peripheral light amount ratio) greatly changes due to a change in the focal length. FIGS. 5 and 6 show graphs in which the light amount ratio at the peripheral portion of the screen is expressed as a percentage with the light amount at the central portion being 100% when the focal length is set to the wide side and the tele side, respectively. As can be seen from these graphs, when the aperture is opened (when the aperture is originally opened), the characteristics of the peripheral light amount ratio greatly differ between the wide side and the tele side as shown by the solid line curves on the respective graph surfaces. . For this reason, a porthole appears remarkably on the screen. On the other hand, when the aperture is stopped down, the difference between the light amount at the center and the light amount at the peripheral portion is reduced as indicated by the dashed line on each graph surface. The difference in characteristics is reduced.
[0025]
For this reason, when the forced ramping process is performed, even when the aperture is opened, the aperture is narrowed down to a certain extent over a wide range of the focal length, so that the porthole is reduced to such an extent that the porthole is not recognized on the screen.
[0026]
By the way, the data necessary for the forced ramping process, that is, the data necessary for obtaining the open value corresponding to the focal length in the forced ramping process, is stored in advance in the memory 24 shown in FIG. 20 reads the data from the memory 24 and executes the forced ramping process. For example, as data necessary to obtain an aperture value corresponding to the focal length, there are a focal length value FzDropPoint at which to start narrowing down and an aperture value FnoDropmax at the maximum focal length as shown in FIG. The aperture value corresponding to the focal length can be obtained by storing them in the memory 24 and reading them out. Instead of the data of the open value FnoDropmax at the maximum focal length, for example, data indicating the ratio of narrowing the aperture I from the true open value to the open value FnoDropmax at the maximum focal length may be stored in the memory 24. The data to be stored in the memory 24 may be other than the above data as long as the data can be used to determine an open value according to the above. Further, the ramping characteristic by the forced ramping may be a curve instead of a straight line as shown by the inclined portion (2) in FIG. 4, and when a relational expression other than a straight line is allowed as the ramping characteristic, data on the relational expression is also stored in the memory. 24 may be stored. However, in the present embodiment, it is assumed that the ramping characteristic is represented only by a straight line, and that data relating to the relational expression of the ramping characteristic is not referred to from the memory 24.
[0027]
Also, as shown in FIG. 2, the lens device is provided with an interface 26 (RS-232C, USB, etc.) with an external device such as a personal computer. The data can be transmitted to the microcomputer 20 through the interface 26 and stored in the memory 24. As a result, the user can arbitrarily change the setting of the effectiveness of the ramping characteristics due to the forced ramping.
[0028]
The data of the forced ramping exhibiting a plurality of different ramping characteristics is stored in the memory 24. When a desired ramping characteristic is selected by a predetermined selecting means, data relating to the selected ramping characteristic is read from the memory 24. Alternatively, the forced ramping process may be executed.
[0029]
Next, the processing procedure of the aperture control of the microcomputer 20 will be described with reference to the flowcharts of FIGS. First, in the aperture control main process of FIG. 7, the microcomputer 20 performs iris control signal processing to set a value ICamCtrl indicating a target aperture position (step S10). Details of the iris control signal processing will be described later with reference to the flowchart of FIG.
[0030]
Subsequently, the microcomputer 20 reads the value IPosiData of the iris position signal indicating the current position of the aperture I from the iris position detector IP (Step S12). Next, assuming that a command value indicating the rotation speed of the iris drive motor IM is IDataOut,
[0031]
(Equation 1)
IDataOut = IPosiData-ICamCtrl
Is calculated (step S14). Further, a value obtained by multiplying this by a predetermined gain Gain, that is,
[0032]
(Equation 2)
IDataOut = IDataOut * Gain
Is calculated (step S16). Then, the command value IDataOut obtained in step S16 is output to the iris drive circuit ID as the value of the control signal (step S18). By repeating the above processing, the aperture I is set to the target position obtained in step S10.
[0033]
Next, the iris control signal processing in step S10 will be described with reference to the flowchart in FIG. The microcomputer 20 first reads the value of the iris control signal given from the camera body or the like, and sets the value as a value ICamCtrl indicating the target position of the aperture I (step S20). Subsequently, the data FzDropPoint and FnoDropmax related to the forced ramping stored in 24 are read (step S22). Note that, as shown in FIG. 4, FzDropPoint indicates the value of the focal length at which aperture stop starts, and FnoDropmax indicates the open value of the aperture I at the maximum focal length.
[0034]
Next, the microcomputer 20 reads an ON / OFF signal indicating the ON / OFF state of the forced ramping ON / OFF switch 22 (Step S24). Then, it is determined whether or not the forced ramping ON / OFF switch 22 is set to ON, that is, whether or not to turn on the forced ramping is determined (step S26). If the determination is NO, the aperture value IMaxPoint indicating the aperture position at the time of opening the aperture where the aperture position cannot be further changed to the opening direction is fixed to a constant value (Fnomax) (step S28). This constant value is a true open value of the aperture I. On the other hand, if NO is determined, the open value at the current focal length is determined based on the FzDropPoint and FnoDropmax obtained in step S22 and the current focal length data obtained from the zoom position signal from the zoom position detector ZP. IMaxPoint is obtained (step S30). It should be noted that the open value IMaxPoint obtained in step S30 is a value for restricting the aperture position in control, and a value showing a ramping characteristic like the inclined portion (2) in FIG. 4 is obtained.
[0035]
After setting the opening value IMaxPoint by the processing of step S28 or step S30, the microcomputer 20 determines whether the target position ICamCtrl of the aperture read in step S20 is on the opening side from the opening value IMaxPoint (step S32). When the determination is NO, the value of the target aperture position ICamCtrl is not changed, and when the determination is YES, the target aperture ICamCtrl is set to the open value IMaxPoint (step S34).
[0036]
After setting the aperture target position ICamCtrl as described above, the process returns to the flowchart of FIG.
[0037]
In the above embodiment, the case where the present invention is applied to a lens device for a television camera has been described. However, the present invention can be applied to a lens device used for applications other than the television camera.
[0038]
【The invention's effect】
As described above, according to the lens device of the present invention, when the aperture is opened, when the focal length is longer than the aperture start value, the aperture is controlled to narrow down the aperture, thereby creating a desired ramping characteristic in a pseudo manner. At the time of the zoom operation, it is possible to reduce the phenomenon that the brightness of the screen rapidly decreases near the telephoto end due to the inherent ramping characteristic of the photographing lens, and the discomfort and unnaturalness due to the porthole.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an optical system (photographing lens) in a lens device for a television camera to which the present invention is applied.
FIG. 2 is a block diagram showing a schematic configuration of a control system in a lens device to which the present invention is applied.
FIG. 3 is a diagram exemplifying a relationship between a focal length and an F-number in an original optical characteristic of a photographing lens.
FIG. 4 is a diagram illustrating an example of a relationship between a focal length and an F-number when a forced ramping process is performed;
FIG. 5 is an explanatory diagram used for describing a port hole.
FIG. 6 is an explanatory diagram used for describing a port hole.
FIG. 7 is a flowchart illustrating a main processing procedure relating to aperture control of a microcomputer;
FIG. 8 is a flowchart illustrating a processing procedure of the iris control signal processing of FIG. 7;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Image sensor, 12 ... Signal processing circuit, 20 ... Microcomputer, 22 ... Forced ramping ON / OFF switch, 24 ... Memory, 26 ... Interface, FL ... Focus lens, ZL ... Zoom lens, I ... Aperture, RL ... Relay lens , IM: iris drive motor, ID: iris drive circuit, IP: iris position detector, ZM: zoom drive motor, ZD: zoom drive circuit, ZP: zoom position detector

Claims (3)

A lens device having an optical system capable of changing a focal length and an aperture, and having a ramping characteristic in which the F-number of the optical system decreases when the focal length becomes longer than a predetermined value when the aperture is opened,
In a range in which the focal length is shorter than the narrowing start value with a value in a range in which the focal length is shorter than the predetermined value, the upper limit opening amount of the diaphragm when the opening of the diaphragm is instructed is set as the focal length. A lens device comprising: aperture control means for reducing the aperture as the length increases and controlling the aperture so that the aperture of the aperture does not exceed the upper limit aperture when the focal length is changed. 2. The lens apparatus according to claim 1, further comprising a switching unit that switches between the control by the aperture control unit and the control unit. 2. The lens apparatus according to claim 1, further comprising a setting unit that sets the upper limit aperture amount with respect to a focal length to a desired value.

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