JPH10186209A - Method and device for correcting focus of lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately maintain the best focusing position by automatically adjusting the position of a master lens at the time of zooming, at the time of switching an extender or even in the case a diaphragm is fluctuated. SOLUTION: This correcting method is provided with a focusing lens 12, a zoom lens 14, the diaphragm 16, extender lenses 18A and 18B and the master lens 20. The fluctuation amount of a focus associated with the change of at least one of the zooming position of the lens 14, the diaphragm value of the diaphragm 16 and the extender positions of the lenses 18A and 18B is obtained in advance. Then, the position of the lens 20 is controlled to cancel the fluctuation amount of the focus obtained based on the change of at least one of the zooming position of the lens 14, the diaphragm value of the diaphragm 16 and the extender positions of the lenses 18A and 18B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for correcting the focus of a lens, and more particularly to a method and an apparatus for correcting the focus of a lens for finely adjusting a position of a master lens of a lens for a television camera to maintain a best focus position.

[0002]

2. Description of the Related Art In general, a lens for a television camera has a focus lens, a zoom lens composed of a variable power system and a correction system lens, an aperture, an extender lens for switching a photographing magnification, and a master lens. The zoom lens includes a zoom lens and a correction lens. During zooming, the zoom lens and the correction lens are moved on the optical axis in a fixed relationship by rotation of the zoom cam barrel. Thus, the focal length can be changed without moving the focal position.

In the extender lens, for example, a 1 × extender lens and a 2 × extender lens are provided on a turret plate, and one of the extender lenses is placed on the optical axis by rotation of the turret plate. Be placed.

[0004]

As described above, the zoom lens changes the focal length without moving the focal position during zooming. However, the focal point does not move at all from the telephoto end to the wide end. It is difficult to configure the zoom cam barrel not to be formed because of the precision of the cam groove of the zoom cam barrel, the precision of other members involved in zooming, the assembly error of each member, and the like, and there is a problem that the zoom cam barrel needs to be remade. .

Similarly, when switching between a 1 × extender lens and a 2 × extender lens,
There is a problem that it is difficult to configure such that the focus does not move at all because of an error in assembling the extender lens to the turret plate. In particular, the permissible circle of confusion is φ0.009
The TV camera lens described below has a small depth of focus, it is difficult to keep the focus within the depth of focus at the time of zooming or switching of the extender, and the best focus position is shifted depending on the size of the aperture. is there.

The present invention has been made in view of such circumstances, and a lens focus correction method and apparatus capable of accurately maintaining the best focus position even during zooming, when switching between extenders, or when the aperture fluctuates. The purpose is to provide.

[0007]

According to the present invention, a focus lens, a zoom lens, an aperture,
In the focus correction method for a lens having an extender lens and a master lens, a zoom position of the zoom lens, an aperture value of the diaphragm, and a focus variation amount associated with a change in at least one of the extender positions of the extender lens are determined in advance. Controlling the position of the master lens so as to cancel out the obtained amount of change in focus based on at least one change among a zoom position of the zoom lens, an aperture value of the aperture, and an extender position of the extender lens. It is characterized by.

That is, according to the present invention, after assembling the lens, the amount of change of the focus associated with the change of at least one of the zoom position, the aperture value, and the extender position is determined in advance, and the lookup for reading out the amount of change is performed. A table and a calculation formula for calculating the amount of change are created in advance. Then, when the lens is used, when the zooming or the change of the extender or the aperture is changed, the amount of change of the focus is obtained from a look-up table or a calculation formula based on the change, and the position of the master lens is set so as to cancel the amount of change. I try to control.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a lens focus correction method and apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of a lens for a television camera to which the present invention is applied. The lens body 10 of this TV camera lens includes a focus lens 1
2. A zoom lens 14 including a variable power lens 14A and a correction lens 14B, an aperture 16, a 1 × extender lens 18A, and a 2 × extender lens 18B.
Optical members such as the master lens 20; drive circuits 32 to 40 and drive motors 42 to 50 for driving the respective lenses and the diaphragm 16; detectors 52 to 60 for detecting the positions of the respective lenses and the diaphragm 16; A / D converters 62 to 6
8 and a control circuit 26 for controlling each optical member. Incidentally, reference numeral 22 denotes an image sensor, and reference numeral 24 denotes a signal processing circuit, which is provided on a camera body side to which the lens for a television camera is attached.

As is well known, the zoom lens 14A constituting the zoom lens 14 changes the focal length, and the correction lens 14B corrects the focal position so that it does not fluctuate. The correction lens 14B is configured to be able to move on the optical axis in a fixed relationship by rotating the zoom cam barrel.

Also, a 1 × extender lens 18
A and the 2 × extender lens 18B are respectively disposed on a turret plate (not shown), and one of the extender lenses is disposed on the optical axis by rotating the turret plate. The photographing magnification is switched by switching the extender lens. On the other hand, the master lens 20 is provided so as to be movable along the optical axis. By moving the master lens 20 along the optical axis, the focus is corrected as described later. The movement of the master lens 20 is also controlled at the time of fine adjustment (tracking) of the lens image formation position and macro photography.

A command signal is applied to the control circuit 26 from operating means such as a focus demand (focus ring), zoom ring, aperture knob, extender changeover switch, and flange back adjustment knob (not shown). The circuit 26 controls each lens based on the input command signal. The image pickup device 22 converts the subject image formed on the light receiving surface via each optical member of the lens body 10 into an electric signal and outputs this to a signal processing circuit 24, and the signal processing circuit 2 receives the input signal from the image pickup device 22. The signal to be processed is sampled and subjected to signal processing such as white balance adjustment and gamma correction to generate a television signal. This television signal is output to the viewfinder VF for reproduction and output to an output terminal.

Next, a correction method for correcting the focal point shift accompanying the switching of the extender lens will be described with reference to FIG. In the figure, correction signals for a 1 × extender lens 18A and a correction signal for a 2 × extender lens 18B are set in advance in the correction signal generators 70 and 72, as will be described later. Is output to the changeover switch 74. The extender position detector 58 is a 1 × extender lens 18.
This is for detecting whether A is located on the optical axis or the extender lens 18B for double magnification is located on the optical axis. The changeover switch 74 is switched based on the detected position. That is, when the 1 × extender lens 18A is located on the optical axis, the 1 × correction signal is output from the correction signal generator 70 to the adder 76 via the changeover switch 74, and the 2 × Extender lens 18B
Is located on the optical axis, the correction signal generator 72
Is output to the adder 76 via the changeover switch 74.

A position signal for controlling the position of the master lens 20 from the flange back adjustment knob 70 is added to the other input of the adder 76, and the adder 72 adds these input signals and compares them. Output to the device 79. A signal indicating the current position of the master lens 20 is added from the position detector 60 to another input of the comparator 79, and the comparator 79 drives a control signal so that the deviation of these input signals becomes zero. Output to the drive motor 50 via the circuit 40.

That is, the master lens 20 is provided with an adder 76.
Is subjected to position feedback control using the position signal output from the controller as a target value. Next, the correction signals set in the correction signal generators 70 and 72 will be described. Now, with reference to the 1 × extender lens 18A, the extender lens 18A is positioned on the optical axis, and the correction signal in the correction signal generator 70 is set to 0. Here, the flange back adjustment knob 70 is operated, and the position of the master lens 20 is adjusted so that the image forming position of the lens becomes the best focus position (on the light receiving surface of the image sensor 22) at the wide end and the tele end of the zoom lens 14. To adjust.

Subsequently, an extender lens 1 for double magnification
Switch to 8B. 1x extender lens 18
When the mutual positional relationship between A and the 2 × extender lens 18B is accurately positioned, the focal point does not move from the best focus position, but the focal point shifts due to a positional shift between the extender lenses. When moving from the best focus position, the flange back adjustment knob 70 is operated again to move the position of the master lens 20 so that the image forming position of the lens becomes the best focus position. Then, the amount of change in the position signal associated with the operation of the flange back adjustment knob 70 at this time is set as a correction signal for the double extender lens 18B.

In this way, the amount of change in the focus due to the switching of the extender lens is obtained in advance, and when the extender lens is switched, the position of the master lens 20 is controlled so as to cancel the amount of the change. , The best focus position can be maintained. FIG. 3 is a diagram illustrating an example of spherical aberration. As shown in the figure, the imaging position moves in the optical axis direction depending on the height at which the light beam enters the lens. Now, assuming that the incident height when the diaphragm is fully opened is A, the center position Pa of the fluctuation width of the imaging position is the best focus position. On the other hand, when the stop is stopped down, the central position of the fluctuation range of the image forming position when the incident height is B is Pb, and the best focus position is shifted by L.

In the present invention, the deviation of the best focus position due to the aperture value of the aperture 16 is also corrected. That is, the amount of deviation of the best focus position based on the aperture value of the aperture 16 is determined in advance, and when the aperture 16 is changed, the master lens 2 is adjusted so as to cancel the deviation of the best focus position.
0 position is controlled. FIG. 4 is a diagram showing an example of a shift of the best focus position when the zoom lens 14 is zoomed from the telephoto end (T) to the wide end (W). This deviation of the best focus position indicates that the focus position has not been perfectly corrected by the correction system lens 14B.

In the present invention, the deviation of the best focus position due to the zoom position of the zoom lens 14 is corrected. That is, the shift amount of the best focus position based on the zoom position as shown in FIG. 4 is obtained in advance, and when zooming is performed, the position of the master lens 20 is controlled so as to cancel the shift of the best focus position. I do.

Next, a description will be given of a correction method for correcting switching of the extender lens, a change in the aperture, and a focal point shift accompanying zooming of the zoom lens, with reference to FIGS. In FIG. 5, the same parts as those shown in FIG. 1 are denoted by the same reference numerals. As shown in FIG. 5, zoom position data and aperture position data are added to the control circuit 26 from the zoom position detector 54 and the aperture position detector 56 via A / D converters 64 and 66.
The extender lens 18A for 1 × and the extender lens 1 for 2 × from the extender position detector 58
Extender position data indicating which of 8B is located on the optical axis is added to the control circuit 26. The position data of the master lens 20 when the tracking adjustment is performed from the flange back adjustment knob 78 via the A / D converter 80 from the flange back adjustment knob 78 is added to the control circuit 26, and the position data indicating the position of the master lens 20 is further added. It is added from the master lens position detector 60 via the A / D converter 68.

The control circuit 26 outputs a control signal for controlling the position of the master lens 20 based on these input data as described below. That is, the control circuit 26 first inputs each position data indicating the zoom position, the aperture position, and the extender position (step S1).
0). Then, an appropriate correction amount of the focal position is obtained based on the position data (step S12). That is, the control circuit 26 has the correction information of each optical member as a look-up table or a calculation formula as previously described with reference to FIGS. 2 to 4, and based on the position data input in step S10, the focal position. Is determined.

Then, the position of the master lens 20 is controlled based on the appropriate correction amount thus obtained (step S14). That is, the control circuit 26 outputs a control signal obtained by adding the above-described appropriate correction amount to the position data of the master lens 20 at the time of performing the tracking adjustment (FIG. 5). This control signal is applied to the drive motor 50 via the D / A converter 69 and the drive circuit 40. Thereby, the drive motor 50 is driven, and the master lens 20 is moved along the optical axis by the drive force. The position of the master lens 20 is detected by the master lens position detector 60, and is added to the control circuit 26 as position data (position feedback signal) indicating the current position of the master lens 20 via the A / D converter 68.

As described above, the control circuit 26 controls the position of the master lens 20, and controls the zoom lens 14, the diaphragm 1
6. The master lens 20 offsets the amount of change in the focal position due to each position of the extender lens. Thereafter, it is determined whether or not any of the zoom lens 14, the aperture 16, and the extender lens has changed (step S16). If any of them has changed, the process returns to step S10, and the processes of steps S10 to S14 are executed. Then, the position of the master lens 20 is controlled again. As a result, the focal position of the lens is maintained at the best focus position.

It should be noted that the present invention relates to a change in focus during zooming,
The present invention can be applied not only to the case where one of the focus fluctuation at the time of switching the extender and the focus fluctuation due to the size of the aperture is corrected, but also to the case where two or more fluctuations are simultaneously corrected.

[0025]

As described above, according to the present invention, the focal point fluctuates during zooming due to the accuracy of members involved in zooming, assembling errors, etc., and the extender due to errors in assembling the extender lens. Even if the focus fluctuates at the time of switching, and even if the focus fluctuates due to the size of the aperture, these fluctuation amounts of the focus are offset by controlling the master lens, so that the best focus position can be accurately maintained. it can. In addition, there is a margin in the accuracy and assembly error of each optical member, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a lens for a television camera to which the present invention is applied.

FIG. 2 is a diagram used for explaining a correction method for correcting a focal point shift accompanying switching of an extender lens.

FIG. 3 is a diagram used to explain a correction method for correcting a focus shift accompanying a change in a diaphragm.

FIG. 4 is a diagram used to explain a correction method for correcting a focal point shift accompanying zooming of a zoom lens.

FIG. 5 is a block diagram of a main part of a lens focus correction apparatus according to the present invention.

FIG. 6 is a flowchart used to explain a focus correction method for a lens according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Lens body 12 ... Focus lens 14 ... Zoom lens 16 ... Aperture 18A ... 1x extender lens 18B ... 2x extender lens 20 ... Master lens 22 ... Image sensor 24 ... Signal processing circuit 26 ... Control circuit 42, 44, 46, 68, 50: drive motors 52, 54, 56, 58, 60: position detectors

Claims (2)

[Claims] 1. A focus correction method for a lens having a focus lens, a zoom lens, an aperture, an extender lens, and a master lens, wherein at least one of a zoom position of the zoom lens, an aperture value of the aperture, and an extender position of the extender lens. The amount of change of the focus associated with one change is obtained in advance, and the amount of change of the obtained focus is determined based on at least one change among the zoom position of the zoom lens, the aperture value of the aperture, and the extender position of the extender lens. A focus correction method for a lens, wherein the position of the master lens is controlled so as to cancel each other. 2. A focus correcting apparatus for a lens having a focus lens, a zoom lens, a diaphragm, an extender lens, and a master lens, wherein at least one of a zoom position of the zoom lens, a diaphragm value of the diaphragm, and an extender position of the extender lens. A detecting means for detecting one of them; a look-up table or a look-up table for previously obtaining an amount of change of a focal point accompanying a change in at least one of a zoom position of the zoom lens, an aperture value of the aperture, and an extender position of the extender lens. Means for calculating the focus variation from the look-up table or calculation formula based on the value detected by the detection means, and the master lens so as to cancel the calculated focus variation. Control means for controlling the position, Focus correction system of lenses, wherein the door.