JP2006243489A - Diaphragm value detecting circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the cost of an iris encoder circuit and to improve temperature-compensating properties. <P>SOLUTION: The temperature-compensating of an iris encoder is performed by using the output of a temperature sensor provided to correct the cam trajectory of a compensator lens group accompanying the expansion and contraction of a lens barrel caused by a change in temperature, in a rear focus zoom lens, so that a diode used in the conventional manner is eliminated and the cost is reduced. Further, in a temperature-compensating sensor for an RFZ cam trajectory, temperature changing properties are more linear than those of the diode and a temperature change rate can be freely changed only by changing a circuit resistance constant, so that more accurate temperature-compensating can be performed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an aperture value detection circuit.

  In a so-called video camera that obtains a standardized video signal output, such as NTSC, using an image sensor that converts an object image projected from a photographic lens into an electrical signal, the object image projected on the image sensor is supplied with an appropriate amount of light. In order to adjust the aperture mechanism, the lens is provided with a diaphragm mechanism. Generally, in the case of a home video camera, generally, a control function capable of automatically adjusting the diaphragm mechanism is provided.

  In such a video camera control unit, the aperture of the aperture mechanism is used not only for adjusting the light amount but also for automatically performing a so-called autofocus function in a system that automatically obtains the in-focus state of the subject image. It is essential to detect the value, the so-called F value.

  Conventionally, as a means for detecting the aperture value, a method is known in which a magnetic field change of a magnet inside the IG meter that drives the aperture blade is detected by a magnetic detection element.

  FIG. 3 shows an example of this system.

  In FIG. 3, 1 is a photographing lens, 2 is an aperture blade, 3 is an image sensor, 4 is a signal processing unit, 5 is a logic operation unit (hereinafter referred to as “microcomputer”), 6 is an iris drive circuit, and 7 is an IG meter. , 701 are magnets, 8 is a Hall element, and 9 is an iris encoder circuit. Note that the photographing lens 1 is generally composed of a plurality of lenses, but in the drawing, it is shown as a single lens for simplification.

  The subject image projected by the photographing lens 1 is photoelectrically converted by the image sensor 3 and converted into an electrical signal. This signal is converted into a standardized video signal such as NTSC in the signal processing unit 4 and output to the outside as a video signal.

  In this process, the microcomputer 5 reads the video signal level from the signal processing unit 4 according to the program shown in FIG. 4 and gives a control signal to the iris driving circuit 6 so that the level becomes constant, thereby driving the iris. The circuit 6 drives the IG meter 7 according to this control signal.

  By such an operation, control is performed so that the amount of light of the subject image projected onto the image sensor 3 is constant.

  Here, in the case of an aperture mechanism using an IG meter, the relationship between the rotation angle of the magnet 701 of the IG meter 7 and the aperture value formed by the aperture blades 2 interlocked therewith, that is, the F value is as shown in FIG. Is not proportional to For example, when the aperture is close to the open state, the rotation angle of the magnet 701 per aperture is larger, and conversely, the rotation angle of the magnet 701 per aperture is smaller as the aperture is smaller.

  Therefore, in order to smoothly perform the operation of driving the IG meter 7 according to the brightness of the subject and making the brightness of the subject image projected on the imaging surface of the imaging device 3 constant, the flowchart of FIG. As shown, it is necessary to change the drive level of the IG meter according to the aperture value.

  For this reason, the Hall element 8 provided inside the IG meter 7 detects a change in the lines of magnetic force of the magnet 701 accompanying the rotation of the IG meter 7, and the output of the Hall element 8 is amplified to an appropriate level by the iris encoder circuit 9. The This signal is applied to the A / D input of the microcomputer 5, and the microcomputer 5 determines the current aperture value. The microcomputer 5 drives the IG meter 7 while changing the drive level in accordance with the value, so that a smooth aperture is obtained. Control is in progress.

  However, the number of magnetic lines of the Hall element 8 and the magnet 701 in the IG meter 7 varies depending on the temperature, and both have negative characteristics with respect to the temperature. That is, as the temperature rises, the number of lines of magnetic force of the magnet 701 decreases and the output level of the Hall element 8 itself also decreases, so that the overall output level of the Hall element 7 decreases. Conversely, the lower the temperature, the larger it becomes. In order to cope with this, a current compensation circuit using a temperature change of the forward voltage of the diode is provided in the iris encoder circuit.

  FIG. 6 shows an example of the iris encoder circuit.

  In FIG. 6, 8 is a Hall element, 901 and 902 are OP amplifiers, 903, 904, 905, 906, 907, 908, and 909 are resistors, 810 is a diode, and 811 and 812 are reference voltages.

  A fixed current is supplied to IN + and IN−, which are input terminals of the Hall element, by a constant current circuit including an OP amplifier 901, a resistor 903, a resistor 904, a diode 811, and a reference voltage 812, and this is the Hall element. Bias current. A voltage corresponding to the magnetic force of the magnet inside the IG meter 7 is output from the output elements OUT + and OUT−, which are Hall element outputs, and a differential amplifier composed of an OP amplifier 902 and a resistor 905, a resistor 906, a resistor 907, and a resistor 908. Amplified to an appropriate level and added to the A / D input of the microcomputer 5.

  The Hall element output level between OUT + and OUT− is proportional to the bias current value of the Hall element. However, as described above, the number of lines of magnetic force between the Hall element and the magnet has a negative temperature characteristic. This is compensated by the temperature characteristic of the diode 811 inserted between the resistor 903 and the resistor 903.

  On the other hand, a so-called rear focus zoom system is used for the optical system of the video camera. Since this optical system can make a lens with a large zoom ratio relatively small, most of the recent home video cameras employ this rear focus zoom system.

  FIG. 7 shows an example of the configuration of the rear focus zoom. 101 is a front lens group, 102 is a variator / lens group that changes the focal length of the lens by moving its relative position with respect to the front lens group 101, and 103 is a moving surface of the subject image. In addition, a compensator lens group for correcting a change in focal plane due to movement of the variator lens group 102, a zoom motor 104 for driving the variator lens group 102 back and forth in the optical axis direction, and 105 a compensator lens It is a focus motor that drives the group 103 back and forth in the optical axis direction.

  When the variator / lens group 102 is moved back and forth with respect to the front lens group 101 fixed to the lens barrel by the zoom motor 104, the focal length of the entire lens changes.

  That is, when the variator / lens group 102 moves away from the front lens group 101 side, the focal length of the entire lens becomes longer, which is generally called the tele side. Further, when the variator / lens group 102 moves in the direction toward the front lens group 101, the focal length of the entire lens is shortened, which is generally called the wide side.

  However, with the movement of the variator / lens group 102 on the tele side / wide side, the image plane of the subject image projected on the imaging surface of the image sensor 3 moves.

  Therefore, it is necessary to correct the movement of the imaging plane by moving the compensator / lens group 103 in accordance with the change in focal length, that is, the zooming operation.

  The positional relationship of the variator / lens group 102 and the compensator / lens group 103 by zooming is shown in FIGS.

  The movement of the variator / lens group 102 in each of the tele-side, middle- and wide-side states has a simple proportional relationship with the zoom amount, that is, the focal length of the optical system. The movement of the compensator / lens group 103 for correction so as not to move does not have a simple relationship as shown in FIG. The compensator / lens group 103 that is close to the imaging surface on the tele side moves toward the subject side in the middle state, and returns to the imaging surface again on the wide side. Furthermore, the degree of this movement varies depending on the subject distance.

  FIG. 9 is a graph showing the relationship between the tele-wide position of the variator / lens group 102 and the position of the compensator / lens group 103 for each subject distance.

  As shown in FIG. 9, the movement of the compensator lens group 103 for correcting the imaging plane to move with respect to the tele-wide movement of the variator lens group 102 exhibits a fairly complicated curve. Yes.

  Therefore, in order to drive the focus motor 105 for the compensator / lens group 103 along such a curve, a table as shown in FIG. 9 is generally provided in the memory of the microcomputer 5, and the focus is set based on the microcomputer 5 program. The motor 105 is driven.

  However, in recent years, video camera bodies have become smaller and lighter, and accordingly, the image pickup surface size of the image sensor has been reduced year by year from 1/2 inch to 1/3 inch and 1/4 inch. At the same time, the optical system is getting smaller. Furthermore, as a recent trend, the zoom ratio of the zoom lens tends to be relatively large, such as 10 to 20 times.

  In such a rear focus zoom system that can obtain a large zoom ratio with a small optical system of ¼ inch or less, it is far more problematic that the conventional rear focus zoom system can be ignored. Become.

  One of them is the expansion and contraction of the lens barrel due to temperature. The lens barrel expands and contracts due to the ambient temperature or temperature changes due to the heat generated by the video camera body, etc. Therefore, a compensator for correcting the image plane to not move due to the movement of the variator / lens group 102 shown in FIG. The curve of the locus of the lens group 103 changes slightly. For this reason, as described in JP-A-8-94910, a temperature sensor is provided in the lens barrel, the output of this temperature sensor is input to the microcomputer, and the change curve due to this temperature is corrected in the program in the microcomputer. ing.

As a conventional example, for example, Patent Document 1 can be cited.
Japanese Patent Laid-Open No. 11-21974

  In the above configuration, the temperature compensation diode of the iris encoder is preferably arranged in the vicinity of the magnet and the Hall element in the IG meter because the compensation targets are the magnet and the Hall element in the IG meter. However, since the IG meter is very miniaturized and it is difficult to dispose the compensation diode in the space in terms of space, it has been conventionally placed on the iris encoder circuit board.

  Here, since the power consumed inside the IG meter and the power consumed on the circuit board side are generally different, there is a difference in heat generation during operation, so the temperature of the Hall element / magnet itself, It does not necessarily match the temperature on the circuit board.

  As shown in FIG. 10, the output temperature change characteristic of the Hall element including the temperature change of the number of lines of magnetic force of the magnet is almost linear, but that of the diode is non-linear. For this reason, it is difficult to accurately compensate the temperature along the temperature change curve of the magnet and the Hall element.

  Thus, the conventional iris encoder circuit has not been sufficiently temperature compensated. In particular, when the aperture state is a small aperture state such as F11 or F16, the F value changes greatly with respect to the rotation angle of the IG meter, and it is difficult to obtain accurate aperture information.

  Therefore, the aperture control may vary depending on the ambient temperature, and the aperture control may not be performed smoothly.

  According to the present invention, the temperature compensation temperature sensor output of the rear focus zoom system attached to the lens barrel of the photographing lens is also used for temperature compensation of the iris encoder at the same time. An iris encoder system that can obtain aperture information can be obtained.

  Further, the temperature compensation diode conventionally used in the iris encoder circuit is not required, and the manufacturing cost can be reduced.

  As described above, the temperature sensor output for temperature compensation of the rear focus zoom system attached to the lens barrel of the taking lens is also used for temperature compensation of the iris encoder at the same time. An iris encoder system from which information can be obtained can be obtained.

  Further, the temperature compensation diode conventionally used in the iris encoder circuit is not required, and the manufacturing cost can be reduced.

  An embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 shows the configuration of aperture control of a video camera using the present invention. In FIG. 1, the elements 1 to 8 and 701 are the same as those in the conventional example shown in FIG. 3, and 10 is a temperature sensor.

  As in the conventional example shown in FIG. 5, the subject image projected by the photographing lens 1 is photoelectrically converted by the image sensor 3 and converted into an electrical signal.

  Similarly to the conventional example, the microcomputer 5 detects the opening / closing state of the diaphragm based on the information from the iris encoder circuit 9 according to the program shown in FIG. A control signal is given to the iris drive circuit 6 so that the amount of light is constant, and the iris drive circuit 6 drives the IG meter 7 in accordance with this control signal. A temperature sensor 10 for temperature compensation of the rear focus zoom system is attached to the lens barrel of the lens 1.

  FIG. 2 shows an example of an iris encoder circuit using the present invention.

  In FIG. 2, elements 8 and 901 to 812 are the same as those in the conventional example shown in FIG. 6, and 813 is a resistor.

  Similar to the conventional example shown in FIG. 6, the bias current of the Hall element is supplied by a constant current circuit including an OP amplifier 901, a resistor 903, a resistor 904, and a reference voltage 812.

  The Hall element output is amplified to an appropriate level by an operational amplifier 902 and a differential amplifier composed of a resistor 905, a resistor 906, a resistor 907, and a resistor 908, and added to the A / D input of the microcomputer 5.

  Here, the output of the temperature sensor 10 provided for temperature compensation of the rear focus zoom system shown in FIG. 1 is input to the + side of the OP amplifier 902 via the resistor 813.

  The output voltage of the temperature sensor 10 increases when the temperature is high, and decreases when the temperature is low. This relationship is almost linear.

  On the other hand, the number of lines of magnetic force of the magnet 701 of the IG meter 7 and the output of the Hall element 8 both have negative temperature characteristics as described above, and the output level of the Hall element 8 including these has a high temperature. Although it becomes low and becomes high when it is low, this is corrected by the output of the temperature sensor 10 via the resistor 813.

  For example, when the temperature rises, the output of the temperature sensor 10 via the resistor 813 raises the reference potential of the constant current circuit configured by the OP amplifier 901 and the like, and the bias current of the Hall element 8 increases. Conversely, when the temperature is lowered, the reference potential of the constant current circuit is lowered, and the bias current of the Hall element 8 is reduced.

  As described above, since the output of the Hall element 8 is proportional to the bias current flowing through the Hall element 8, fluctuations in the output level due to temperature are compensated.

  The input impedance of the reference potential of the constant current circuit configured by the OP amplifier 901 and the like is determined by the resistor 908 and the resistor 909. By changing the value of the resistor 813, the temperature change output of the temperature sensor 10 is obtained. The level and the output temperature change of the Hall element 8 including the temperature change of the number of lines of magnetic force of the magnet 701 can be matched to each other, and the temperature change characteristics are both linear. Can be almost completely matched in all states from the end to the end.

The figure which shows the structure of the aperture_diaphragm | restriction control system to which this invention is applied. The figure which shows an example of the iris encoder circuit to which this invention is applied. The figure which shows an example of a structure of the conventional aperture_diaphragm | restriction control system. The flowchart which shows an example of the program of the microcomputer of the conventional aperture control system. The graph which shows the relationship between the magnet rotation angle of an IG meter, and the F value of a diaphragm. The figure which shows an example of the conventional iris encoder circuit. The figure which shows the structure of a rear focus zoom system. The figure which shows each zoom state of a rear focus zoom system. The figure which shows the relationship between the variator lens group position of a rear focus zoom system, and a compensator lens group position. The figure which shows the temperature change curve of the forward voltage of a diode, and the temperature change curve of a Hall element.

Claims (1)

  In a diaphragm mechanism in a photographic lens, a mechanism that detects a magnetic field change of a magnet inside an IG meter that drives a diaphragm blade by a magnetic detection element and obtains an aperture value based on an output thereof, and is attached to a lens barrel of the photographic lens An aperture value detection circuit which corrects a change in magnetic lines of force of the magnet of the IG meter and an output fluctuation of the magnetic detection element by using a temperature sensor output.

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