JPH06153066A - Image pickup device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of MTF caused by diffraction. CONSTITUTION:An encoder 9 detects the position of a variater lens 1b and a relation between a machine diaphragm value and MTF corresponding to the detected position of the variater lens is read from ROM 11 by a computing element 10. Based on the read relation between the machine diaphragm value and MTF and MTF set by a minute mode switch 12, the computing element 10 calculates the limit of a machine diaphragm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus such as a video camera which performs optimum exposure by combining a mechanical diaphragm and an electronic shutter mechanism.

[0002]

2. Description of the Related Art Conventionally, an image pickup device such as a video camera controls the amount of passing light, and a mechanical diaphragm is known as a light amount control device for controlling the amount of passing light. In this mechanical diaphragm, an ND filter is attached to a part of at least one diaphragm blade of the plurality of diaphragm blades, and this ND filter is inserted in the optical path when the subject is bright. Therefore, it is possible to limit the amount of passing light without making the aperture diameter too small. Therefore, it is possible to guarantee the exposure accuracy at the time of a small aperture, eliminate the difficulty of mechanical control, and prevent the deterioration of the imaging performance due to the diffractive action of the aperture at the time of a small aperture.

[0003]

However, according to the above-mentioned conventional example, since the ND filter is attached to a part of the diaphragm blade, unevenness of image plane illuminance occurs and N
There is a problem that a diffractive action occurs at the edge of the D filter.

In recent years, in the field of broadcasting equipment, high-definition TV
(HD-TV) cameras are gradually becoming popular, and it is expected that lenses will be considerably improved in performance as compared with conventional ones. However, when the performance of a lens is improved, and particularly when a high resolution is pursued, the deterioration of the imaging performance due to diffraction becomes remarkable.

FIG. 3 generally shows the resolution with respect to the aperture value (F _NO ) of a lens in which various aberrations are well corrected. As can be seen from FIG. 3, since the actual lens has residual aberration, the aperture-to-resolution characteristic curve has a convex upward mountain shape. That is, the MTF deteriorates due to residual aberration near the aperture opening, but improves as the aperture is narrowed. Further, if the aperture is narrowed down, the MTF deteriorates due to the diffraction effect. To satisfy a certain level of resolution MTF (1) required in the lens unit,
The aperture value is within a certain range, that is, F (a) to F in FIG.
It must be held within the range of (b). However, such control is impossible even if one mechanical diaphragm is uniquely opened and closed.

An object of the present invention is to solve the above problems and to provide an image pickup apparatus capable of preventing deterioration of MTF due to diffraction.

[0007]

In order to achieve such an object, the present invention provides a setting means for setting an MTF level and a zoom position in an image pickup apparatus for controlling the speed of an electronic shutter according to a mechanical aperture value. For storing a mechanical aperture value to MTF, a detection unit for detecting a zoom position, and a mechanical aperture value-MTF relationship corresponding to the zoom position detected by the detection unit for reading from the storage unit. Means, and a calculating means for calculating the mechanical aperture range based on the relationship between the mechanical aperture value and MTF read by the reading means and the MTF set by the setting means.

[0008]

In the present invention, the zoom position is detected by the detecting means, and the relationship between the mechanical aperture value and the MTF corresponding to the zoom position detected by the detecting means is read from the storing means by the reading means and read by the reading means. Based on the relationship between the mechanical aperture value and the MTF and the MTF set by the setting means for setting the MTF level, the mechanical aperture range is calculated by the calculating means.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. This is an example of a video camera.

In FIG. 1, reference numeral 1 denotes a lens optical system, which includes a focusing lens 1a and a variator lens 1b which performs a zooming action. Reference numeral 4 denotes a CCD image pickup element, which converts an optical signal incident through the lens optical system 1 and the diaphragm 3 into an electric signal (image pickup signal). A camera signal processing circuit 5 generates a color signal and a luminance signal from the image pickup signal from the CCD image pickup element 4 and also AGC (auto gain control) to a predetermined level.
l) It controls. Reference numeral 7 denotes an integrating circuit, which integrates the luminance signal from the camera signal processing circuit 5. Reference numeral 8 denotes an arithmetic unit which compares a signal from the integrating circuit 7 with a reference value to generate a difference signal, and calculates a CCD electronic shutter speed according to a signal limiting a mechanical aperture from an iris drive controller 13 described later. To do. A CCD drive circuit 6 controls the CCD electronic shutter speed according to the difference signal from the calculator 8.

Reference numeral 16 is an encoder for detecting the opening amount of the diaphragm 3. Reference numeral 17 denotes a buffer amplifier which amplifies the level of the signal from the encoder 16 to a predetermined level. A multiplier 18 corrects the difference signal from the calculator 8 according to the aperture amount of the diaphragm 3. An iris drive controller 13 outputs either an aperture drive signal from the multiplier 18 or a mechanical aperture limit signal from the calculator 10. A driver 14 drives the diaphragm 3 via an actuator in response to a signal from the iris drive controller 13.

Reference numeral 11 denotes a ROM, which is a diaphragm pair MTF (mod) for each position (zoom position) of the variator lens 1b.
repetition transfer functio
The relationship of n) is stored. Reference numeral 12 denotes a fine mode switch for determining how much MTF is required. An encoder 9 reads the position of the variator lens 1b. Reference numeral 10 denotes an arithmetic unit, which reads from the ROM 11 the relationship between the aperture pair MTF corresponding to the position of the variator lens 1b read by the encoder 9, and uses the read relationship between the aperture pair MTF and the fine mode switching unit 12 to determine the mechanical The limit range of the aperture is determined. 20 is an LED switching device, which is an encoder 16
Aperture value based on the signal from the LED 19 in the viewfinder
Is to be displayed.

FIG. 2 is a flow chart showing the control procedure.

In step S1, the fine mode switch 12
When the definition (MTF) is input from, the zoom position is read by the encoder 9 in step S2,
In step S3, the relationship between the aperture value and the MTF corresponding to the read zoom position is read from the ROM 11. Then, in step S4, the computing unit 10 calculates the mechanical aperture range based on the relation between the aperture value and the MTF that has been read and the MTF input from the fine mode switching unit 12. The relationship between the read aperture value and MTF is as shown in the graph of FIG. 3, and when the MTF input from the fine mode switch 12 is MTF (1), the mechanical aperture range is from F (a) to It becomes F (b).

Next, in step S5, the exposure signal from the CCD image pickup device 4 is processed by the camera signal processing circuit 5, the signal from the camera signal processing circuit 5 is integrated by the integrating circuit 7, and in step S6, the machine The arithmetic unit 8 determines whether or not dimming is possible only with the diaphragm.

If the result of the determination is affirmative, then the flow shifts to step S7, and in step S7 exposure control is performed only by the mechanical aperture. On the other hand, if the result of the determination as to whether or not dimming is possible only with the mechanical aperture is negative, the process moves to step S8, and in step S8, the mechanical aperture takes the maximum value of the aperture specified in step S4. Then, the drive of the CCD electronic shutter is controlled so as to obtain an appropriate exposure value. Then, the opening amount of the mechanical diaphragm 3 is detected by the encoder 9, and based on the detected opening amount, it is determined whether or not the maximum value defined in step S4, that is, the maximum value of the diaphragm is taken. As a result of the determination, if the determination is affirmative, the LED 19 is turned on to notify the switching of the fine mode, and then the process returns to step S1. On the other hand, if the determination is negative, the process ends.

[0018]

As described above, according to the present invention,
Since it is configured as described above, there is an effect that it is possible to prevent deterioration of the MTF due to diffraction.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart showing an example of a control procedure.

FIG. 3 is a diagram showing an example of a relationship between aperture value and MTF.

[Explanation of symbols]

 1 Lens Optical System 1a Focusing Lens 1b Variator Lens 3 Mechanical Aperture 4 CCD Imaging Device 5 Camera Signal Processing Circuit 6 CCD Drive Circuit 7 Integration Circuit 8, 10 Operator 9, 16 Encoder 11 ROM 12 Fine Mode Switch 13 Iris Drive Controller 14 Driver 15 Actuator 17 Buffer Amplifier 18 Multiplier 19 LED 20 LED Switch

Claims (1)

[Claims] 1. An image pickup apparatus for controlling a speed of an electronic shutter according to a mechanical aperture value, setting means for setting an MTF level, storage means for storing a relationship between a mechanical aperture value and MTF with respect to a zoom position, and a zoom position. Detecting means for detecting the relation between the mechanical aperture value and the MTF corresponding to the zoom position detected by the detecting means from the storage means, and the mechanical aperture value pair MTF read by the reading means.
And a calculation unit that calculates the mechanical aperture range based on the MTF set by the setting unit.