JPH07115580A - Automatic focus device - Google Patents

Abstract

PURPOSE:To enhance automatic focus performance pleasant at all times independently of an object by defining the out-of focus amount from a focal point due to an aperture with number of inverted pulses so as to make the out-of focus amount due to override of a focus lens just before focusing constant. CONSTITUTION:The sensitivity is unchanged and a blur circle diameter (d) is expressed as F.k in he rear focus type being a main stream at present, that is, a system for automatic focusing using a high frequency component of a video signal, where F is an F number, and k is a constant. Thus, the out-of focus amount deltap per one pulse is expressed as deltap=F.k/p, where p is a pulse number. The amount of out-of focus due to overshoot from a focal point is always made constant with the F number and the optical design value of a lens 1 in use. That is, the out-of focus amount due to overshoot from the focal point is converted into an inverted pulse number 3 from the focal point with an inverted blur circle diameter of 45mum with an F number where the amount of out-of focus per pulse is 15mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus device which uses a high frequency component of a video signal and drives a focus lens by a pulse motor to perform a focusing operation.

[0002]

2. Description of the Related Art Conventionally, as an autofocus device used in video equipment such as a video camera, a high frequency component in a video signal obtained from an image pickup device such as a CCD is extracted,
A so-called hill-climbing control system is known in which a focus lens is driven so as to maximize the high-frequency component to perform focusing.

Such an auto-focusing device does not require a special optical member for focus adjustment, and has an advantage that accurate focusing can be performed regardless of the distance of the subject, and it is one of the current cameras. This method is most often used for body video cameras.

More specifically, when the focus lens is moved at a high speed in the large blur state and the focus evaluation signal becomes large, the focus lens is continuously moved in the same direction, and when the focus evaluation signal becomes small, The focus lens is moved in the direction opposite to that until then, and the focus lens is always moved in the direction in which the focus evaluation signal is increased.
Then, the hill-climbing control operation is performed until the focus evaluation signal drops to a certain level, and the focus motor is controlled to reversely rotate and stop until the focus evaluation signal reaches the maximum.

In such an autofocus device in the hill climbing control system, since the value of the focus evaluation signal differs depending on the subject, it is impossible to judge whether or not the focus is achieved unless the focus is blurred once. If the amount of blurring from the focus is too large, blurring will be noticeable to the photographer. Conversely, if the amount of blurring from the focus is too small, blurring will stop and it will be difficult to determine the focus reversal threshold that determines when to reverse. There was a problem to say.

Conventionally, in order to solve such a problem,
The focus reversal threshold was changed according to the aperture value.

[0007]

However, even if the focus reversal threshold of the focus evaluation value is changed according to the aperture value as in the prior art, the increase / decrease state of the focus evaluation signal is not constant depending on the subject, so that the focus evaluation signal is constantly constant. There is a problem in that the image cannot be reversed due to the diameter of the circle of confusion, and depending on the subject, the blur from the point of focus passing to the point of reversal is conspicuous, which gives the photographer a feeling of strangeness.

The present invention has been made in view of the above circumstances, in which the amount of blurring due to overshooting of the focus lens immediately before focusing is made constant, and comfortable autofocus performance can always be exhibited without depending on the subject. An object of the present invention is to provide a focusing device.

[0009]

In an autofocus device which performs a focusing operation by using a high frequency component of a video signal and driving a focusing lens by a pulse motor, the focusing operation is performed and the driving amount of the focusing lens is adjusted. Definable focus adjusting means, position detecting means for detecting an absolute position of the focus adjusting means, signal processing means for extracting a high frequency component of a video signal to generate a focus evaluation signal,
Focusing control means for controlling a focusing operation in accordance with the output of the signal processing means, the focusing control means driving the focus adjusting means and adjusting the peak point of the focusing evaluation signal. When detected, the blur amount on the focal plane for the unit drive amount of the pulse motor is calculated from the current aperture value, and the pulse motor of the pulse motor corresponding to the overshoot amount of the focus lens with respect to the peak point is calculated based on the calculated value. It is characterized in that the number of pulses is variable.

[0010]

The focus reversal threshold when the focus is exceeded is defined as the number of pulses from the focus to the reversal operation by using the blur amount per pulse calculated from the aperture value at that time. Makes the amount of blurring due to overshooting of the focus lens just before focusing constant.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the structure of a video camera equipped with an autofocus device according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a focus lens for focusing and a variable magnification. An optical system (focus adjusting means) including a zoom lens, 2 is a diaphragm for adjusting the light amount, 3 is an image pickup device such as a CCD, which converts the light passing through the optical system 1 and the diaphragm 2 into an electric signal and outputs it as a video signal. It is what is output.

Reference numeral 4 is a signal processing circuit (CDS) for sampling and holding the video signal output from the image pickup device 9, 5 is a signal processing circuit (AGC) for controlling the gain of the video signal output from the signal processing circuit 4, and 6 Is an A / D converter for converting an analog video signal output from the signal processing circuit 5 into a digital signal, and 7 is a signal for extracting a specific frequency component from the video signal output from the A / D converter 6. A bandpass filter (BPF) 8 as a processing means is a gate (GATE) circuit for extracting a signal of a specific portion from the video signal output from the bandpass filter 7.

Reference numeral 9 denotes an autofocus (AF) control device (focus control means, position detection means) which drives a focus ring (not shown) toward the magnitude of the high frequency component of the video signal, and the value of the high frequency component. According to the above, the focus ring is modulated to perform autofocus control. A motor driver 10 drives a pulse motor 11, and the pulse motor 11 drives a focus lens in the optical axis direction.

Next, the operation of the autofocus device according to this embodiment will be described with reference to FIGS. 2 is shown in FIG.
FIG. 3 is a diagram showing an increase / decrease state of the focus evaluation signal when the focus lens is driven at an appropriate speed in the video camera of FIG. 3, and FIG. 3 shows an F number and a pulse per pulse when the confusion circle diameter is 45 μm. It is a figure which shows the relationship between the amount of blurs and the number of pulses.

In the rear-focusing method, which is currently the mainstream, that is, in the method of performing the auto-focusing operation by using the high frequency component of the video signal, the sensitivity does not change depending on the focal length.
The diameter of the circle of confusion d is expressed by the following equation (1).

D = F · k (1) where F is an F number and k is a constant. Above (1)
As can be seen from the equation, the diameter of the circle of confusion, that is, the amount of blur is inversely proportional to the value of the F number.

The blur amount δp per pulse is p
Is represented by the following equation (2).

Δp = d / p = F · k / p (2) As can be seen from the above equation (2), the blur amount δp per pulse is inversely proportional to the value of the F number.

From this, if the F number value and the optical design value (sensitivity) of the lens used are known, the blur amount due to overshoot from the in-focus point can be constantly made constant. That is, the amount of blurring due to overshoot from the in-focus point can be accurately converted into the number of inversion pulses from the in-focus point by calculation.

Here, if the blur amount for focusing reversal is defined as 45 μm, the focusing reversal pulse can be calculated as shown in FIG. The value in the middle row of FIG. 3 is the blur per pulse when the F number of a certain lens is F1.4 and the blur amount per pulse is 15 μm. It shows how much the quantity δp changes.

The value at the bottom of FIG. 3 is the number of pulses which indicates how many pulses from the peak point at each F-number the transition to the inversion operation takes when the diameter of the circle of confusion is 45 μm.

For example, when performing the focusing operation using this focusing reversal pulse, first, the increase / decrease state of the focusing evaluation signal as shown in A and B of FIG. 2 is monitored to increase the focusing evaluation signal. If so, the focus lens is driven in the same direction as before, and if the focus evaluation signal decreases, the focus lens is driven in the opposite direction. Then, the apex of the focus evaluation signal, that is, the peak point (point P in FIG. 2) is searched for. The focus evaluation signal decreases from the pulse position where the peak is held for the number of inversion pulses shown in FIG. Only when the peak point is detected, the inversion operation is started.

Further, since the increase / decrease state of the focus evaluation signal may not be smooth due to the influence of noise components and the like, it is desirable that the focus evaluation signal to be monitored is sufficiently averaged. Further, when the focus evaluation signal is averaged in this way, a signal delay occurs,
It is necessary to calculate the inversion pulse number in consideration of them.

As described above, the AF controller 9 may perform the calculation each time the value of the F-number changes, but the optical design value of the lens does not change except in the case of the interchangeable lens system. ROM for calculated data
You may make it write in storage means, such as (read only memory).

Further, by defining a circle of confusion such that the blur cannot be recognized by the photographer, a good autofocus operation can always be realized.

The advantage of the present invention is that unlike the case where the focus evaluation signal inversion threshold value is changed according to the value of the F number, the focus inversion pulse number is calculated according to the value of the F number. It means not to receive.

[0028]

As described above in detail, according to the autofocus device of the present invention, the blur amount from the in-focus point is defined by the number of inversion pulses by the aperture value, so that the autofocus is always comfortable regardless of the subject. It can exert its performance.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a video camera equipped with an autofocus device according to an embodiment of the present invention.

FIG. 2 is a diagram showing how the focus evaluation signal increases and decreases when the focus lens is driven at an appropriate speed in the video camera of FIG.

3 is a diagram showing the relationship between the F number, the blur amount per pulse, and the number of pulses in the video camera of FIG. 1 when the diameter of the circle of confusion is 45 μm.

[Description of Reference Signs] 1 optical system (focus adjusting means) 7 bandpass filter (signal processing means) 9 autofocus control device (position detection means, focus control means) 10 motor driver (focus lens drive means) 11 pulse motor ( Focus lens driving means)

Claims (1)

[Claims] 1. An autofocus device that uses a high-frequency component of a video signal and drives a focus lens by a pulse motor to perform a focus operation. A focus that can perform a focus operation and define a drive amount of the focus lens. Adjusting means, position detecting means for detecting the absolute position of the focus adjusting means, signal processing means for extracting a high-frequency component of a video signal to generate a focus evaluation signal, and combining means according to the output of the signal processing means. Focusing control means for controlling a focusing operation, the focusing control means driving the focus adjusting means and detecting the peak point of the focusing evaluation signal from the current aperture value. A blur amount on the focal plane is calculated for a unit drive amount of the pulse motor, and the pulse mode corresponding to the overshoot amount of the focus lens with respect to the peak point is calculated based on the calculated value. An autofocus device characterized by changing the number of pulses of the data.