JPH0511176A - Focus detector - Google Patents

Abstract

PURPOSE:To always perform focus detection with high precision even though any optical system is used and under any applied environment. CONSTITUTION:This detector is provided with a means SW to perform weighting to the amplitude of a photoelectric conversion output signal in accordance with the respective positions of the respective elements of a senser to make the same light quantity distribution by omitting the difference of the light quantity distribution generated between two sensers against the uniform brightness surface of an object and means 8, 9 and 10 changing transiently weighting information in accordance with the respective positions of the respective elements of the senser by the means to perform weighting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a so-called shift type focus detection device used in a camera or the like and utilizing secondary image formation.

[0002]

2. Description of the Related Art FIG. 5 is a view for explaining the structure of a shift type focus detection optical system using a secondary imaging optical system, in which 21 is a subject, 22 is a photographing lens, 23 is a field lens,
Reference numerals 24a and 24b are secondary imaging lenses, and 25a and 25b are sensors.

The image of the subject 21 passes through the photographing lens 22 to form a primary image, and then the field lens 23 and the secondary image forming lenses 24a and 24b form sensors 25a and 25b.
A secondary image is formed on top.

In the shift type focus detecting apparatus using such a secondary image forming optical system, the sensors 25a, 2 have been conventionally used.
As a method of removing the non-uniformity of the light amount distribution on 5b, that is, shading, the photoelectric conversion signal of the sensor array is usually weighted according to the position of the sensor element.

[0005]

However, in the conventional focus detection apparatus, the nonuniformity of the light quantity due to the individual photographing lenses and the environment where the color temperature is different (natural light, strobe light, tungsten light in the room, etc.). It is not possible to eliminate non-uniformity of the light amount due to the difference in color temperature depending on each photographing), and the two sensors 25a and 25b.
This has been a cause of lowering the detection accuracy of the displacement amount of the above two images.

An object of the present invention is to solve the problems found in such a conventional focus detecting device and to provide a focus detecting device capable of always performing highly accurate focus detection.

[0007]

According to the present invention, in order to eliminate the difference in the light amount distribution between two sensors with respect to the uniform luminance surface of an object to obtain the same light amount distribution, each of the sensors is arranged. Means for weighting the amplitude of the photoelectric conversion output signal corresponding to each position of the element, and means for temporarily changing weighting information according to each position of each element of the sensor by the weighting means Therefore, the weighting information according to the position of each element of the sensor is temporarily changed according to the intention of the photographer according to the optical system used and the color temperature.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory diagram of a sensor used in a focus detection apparatus which is an embodiment of the present invention and which is composed of a large number of photoelectric conversion element arrays.

A charge-coupled device (hereinafter referred to as CCD) 2 (2a, 2b, 2c) is used as a transfer means of photoelectric conversion signals (sensor signals) of the sensors 1a, 1b, and a driving pulse is applied from the CCD 2c side. When the signal φ is input, the sensor signal VS of each element of the sensors 1a and 1b becomes C
It is adapted to be serially output from the CD 2a.
The coordinates X on the sensors 1a and 1b are set as shown in FIG. 1, and the central coordinates of the two sensors 1a and 1b are defined as XN.

FIG. 2 is a diagram showing a coordinate distribution of a sensor signal, its correction signal, and a correction coefficient for generating the correction signal. Shading as shown in FIG. 2 (a) obtained from the sensors 1a and 1b. The sensor signal VS with
In order to convert to the uniform correction signal V0 as shown in (b), the weighting coefficient W as shown in FIG. 2 (c) should be multiplied on the sensor signal VS at each coordinate position. That is,
VS (X), where VS, VO, and W are time series representations,
Expressing VO (X) and W (X), W (X) is determined so that VO (X) = VS (X) .multidot.W (X) .......... (1) do it. Here, W (X) is a correction coefficient that can be obtained in advance by the configuration of the optical system.

Hereinafter, the signal processing such as the equation (1) will be called shading correction, and W (X) will be called a shading correction coefficient.

FIG. 3 is a circuit block diagram for realizing shading correction, which is an embodiment of the present invention.

Reference numeral 3 denotes the above-mentioned sensors 1a and 1b and CCD.
2 is an image pickup device and is driven and controlled by the CCD drive circuit 4. The CCD drive circuit 4 receives three signals S when the clock pulse CLK of the clock oscillator 5 is input.
Outputs H, φ, N. The signal SH is a clear signal for the sensors 1a and 1b and the CCD 2, and clears the charge in the CCD 2 at a high potential (hereinafter referred to as H level), and at the same time transfers the charge in the sensors 1a and 1b to the CCD 2. The signal φ is a CCD drive pulse signal, and one pulse of the signal φ causes CC
One charge in D2 moves to the next. Further, the signal N is a signal indicating the discrimination between the sensors 1a and 1b, and when the potential is low (hereinafter referred to as L level), the sensor signal VS of the sensor 1a
Is output from the image pickup device, and when it is at the H level, the sensor signal VS of the sensor 1b is output.

FIG. 4 is a timing chart of the three output signals of the CCD drive circuit 4. In FIG. 4, the sensors 1a, 1 are first detected by the H level of the signal SH at the time point r.
b is cleared. Then, after the storage time s determined by a photometric circuit (not shown), the charges of the sensors 1a and 1b are transferred to the CCD 2 by the H level of the signal SH at the time point t. After that, the sensor signal VS of the sensors 1a and 1b is output from the image pickup device 3 in time series by the CCD drive pulse signal of the signal φ in the period u.

At the time v when the signal VS changes from the sensor 1a to the sensor 1b, the signal N changes from L level to H level.
Switch to level. This time point v is the central coordinate XN in FIG.
It corresponds to. When the output of all the sensor signals is completed, the signal SH becomes H level again at the time point r ′, the sensors 1a and 1b are cleared, and the next accumulation is started.
And the CCD drive circuit 4 repeats the above series of operations.

Returning again to FIG. 3, the counter 6 receives the clock pulse CLK of the clock oscillator 5, the reset signal RESET receives the signal SH from the CCD drive circuit 4, and the up / down switching signal U / D. The signal N is input from the CCD drive circuit 4. Therefore, the counter 6 operates in synchronization with the CCD drive circuit 4,
When the signal of the sensor 1a is output (when the L-level signal N is input) until time v during the output period u of the sensor signal VS shown in FIG.
When the signal is output (when the H-level signal N is input), down counting is performed. Outputs of counter 6 Q0, Q1, ...
, Qn are connected to address inputs A0, A1, ..., An of the ROM (read only memory) 7 and the RAM (random access memory) 8, respectively.

The ROM 7 stores correction information based on the shading correction coefficient W that is predetermined by the configuration of the target imaging optical system, and the RAM 8 includes the switch SW of the camera body. By the operation, new correction information based on the shading correction coefficient W is temporarily stored.

In these cases, since the address value corresponds to the coordinate X of the sensors 1a and 1b, the count value,
That is, the correction information at the coordinate X is output as a digital signal from the data outputs D0, D1, ..., Dn of the ROM 7 or RAM 8. The digital signals D0, D1, ..., Dn are input B of the D / A conversion circuit 9.
1, B2, ..., Bn connected to the D / A conversion circuit 9
Is converted from digital to analog, and the analog output VA is output. Therefore, the signal VA is obtained by converting the shading correction coefficient into an analog voltage.

Reference numeral 10 is a well-known multiplication circuit, which comprises differential amplifiers 11 and 12, field effect transistors 13 and 14, and resistors R1, R2, ..., R6.

The output V0 of the multiplication circuit 10 is expressed as follows by the sensor signal VS through the buffer amplifier 15, the output VA of the D / A conversion circuit 9 and the reference potential VR.

V0 = (VS * VA) / VR (2) However, the above expression (2) is satisfied when the characteristics of the field effect transistors 13 and 14 are equal and the resistance R1 is = R
2 = R3 = R4, R5 = R6. (2)
The formula is expressed as the following formula (3) by a time series expression.

V0 (X) = VS (X) .VA (X) / VR (3) From the above equation (1) and the above equation (3), W (X) = VA (X) / VR VA (X) = VR.multidot.W (X) .................... (4) is obtained. That is, VA is obtained as the product of the reference potential VR and the shading correction coefficient W.

Since the shading correction coefficient W (X) can be determined in advance from the characteristics of the image pickup optical system used,
The correction information Va (X) at the coordinate X on the sensors 1a and 1b is obtained from this W (X) and the equation (4), and this correction information may be digitally converted and stored in the ROM 7.

Next, the operation of the ROM 7 using the shading correction coefficient W will be described with reference to the circuit block diagram of FIG.

The signal SH at the time t when the accumulation of the sensors 1a, 1b of the image pickup device 3 is completed after the accumulation time s from the time r in FIG. 4 is at the H level, and the charges in the sensors 1a, 1b are transferred to the CCD 2. At the same time, the counter 6 causes the signal SH to
Is reset by. The sensor signal VS of the sensor 1a is output by the subsequent pulse of the signal φ. Sensor 1
The sensor signal VS (X1) at the coordinate X1 of a is the image pickup device 3
, The counter 6 has been up-counted X1 times since it was reset at this point, and its outputs Q0, Q1, ..., Qn are directly input as the addresses of the ROM 7. Therefore, the data outputs D0, D1, ..., Dn of the ROM 7 are bit inputs B0.
, B1, ..., Bn, the output Va of the D / A conversion circuit 9 is the address of the ROM 7 at that time, that is, the shading correction information Va at the coordinate X1.
(X1).

The corrected output V0 (X1) is obtained by the above-mentioned multiplication circuit 10
By the above operation, from the expressions (3) and (4), VO (X1) = VS (X1) .multidot.W (X1) ... (5) When the coordinate subsequently becomes X1 + 1, similarly, VO (X1 + 1) = VS (X1 + 1) · W (X1 + 1) …………………… (6), and so on. The sensor signal VS of the sensor 1a is corrected to VO.

When the output of the signal from the sensor 1a is completed and the center coordinate XN at the time point v in FIG. 4 is reached, N becomes H level,
After that, the counter 6 counts down. This is because the shading correction coefficient W is symmetrical between the sensors 1a and 1b as shown in FIG. 2C, so that the same information in the ROM 7 is used.

That is, the shading correction coefficient W (X) in this case is W (X) = W (2XN -X) (7), and the ROM 7 stores the coordinates up to the central coordinate XN. It is sufficient if the correction information is stored. Therefore, assuming that the sensor signal VS (X2) at the coordinate X2 of the sensor 1b is now being output, the counter 6 at this point will change from XN to (X2--
Since it is counting down XN times, its output is (2
XN-X2). In this way, the sensor signal VS is corrected as follows.

VO (X2) = VS (X2) W (2XN-X2) (8) This operation is repeated thereafter, and the sensor signal VS of the sensors 1a and 1b is (b) in FIG. ) Is corrected to a uniform signal (correction output V0).

Next, the operation using the shading correction coefficient by the RAM 8 will be described.

In this case, new shading correction information according to the image pickup optical system and color temperature used is input (created) on the spot by the switch SW and temporarily stored in the RAM 8. Then, when the shading correction information is stored in the RAM 8, the shading correction information in the above operation is extracted from the RAM 8 instead of the ROM 7 and the shading correction is performed. The shading correction information in the RAM 8 is canceled by replacing the lens, pressing the switch again, or turning off the power of the camera body.

According to the present embodiment, the weighting information (depending on the position of each element of the sensor for removing the nonuniformity of the light amount due to the nonuniformity of the light amount and the difference in color temperature for each imaging optical system used ( Since the shading correction information) can be freely set based on the will of the photographer, no matter what kind of imaging optical system is used and under what kind of shooting environment (different color temperature) ), It is possible to always detect a highly accurate focus state.

(Modification) In this embodiment, new shading correction information corresponding to the image pickup optical system used by the switch SW provided in the camera body is input, but the ROM 7 is compatible with various interchangeable lenses in advance. The shading correction information may be stored and the shading correction information may be automatically or manually transferred to the RAM 8 when the lens is replaced to perform the shading correction. Similarly, the shading correction information of the color temperature may be stored in the ROM 7 in advance, and the shading correction information may be manually transferred to the RAM 8 according to the usage environment to perform the shading correction.

[0034]

As described above, according to the present invention,
A photoelectric conversion output signal corresponding to each position of each element of the sensor in order to remove the difference in the light amount distribution generated between the two sensors with respect to the uniform luminance surface of the object to obtain the same light amount distribution. Means for weighting the amplitude of, and means for temporarily changing weighting information according to the respective positions of the respective elements of the sensor by the weighting means,
Therefore, weighting information according to the position of each element of the sensor,
Depending on the optical system used and the color temperature, the photographer's intention is to change it temporarily. Therefore, it is possible to always perform highly accurate focus detection regardless of what kind of optical system is used and under any usage environment (color temperature is different).

[Brief description of drawings]

FIG. 1 is a configuration diagram of a sensor used in a focus detection device that is an embodiment of the present invention.

FIG. 2 is a diagram illustrating a coordinate distribution of an output signal of the sensor of FIG. 1, its correction signal, and its correction coefficient.

FIG. 3 is a circuit block diagram of a focus detection apparatus that is an embodiment of the present invention.

4 is a timing chart of output signals of the CCD drive circuit of FIG.

FIG. 5 is a diagram illustrating a configuration of a focus detection optical system by a shift method using this type of secondary imaging optical system.

[Explanation of symbols]

 1a, 1b Sensor 2, 2a, 2b, 2c Charge coupled device (CCD) 3 Imaging device 4 CCD drive circuit 7 Read only memory (ROM) 8 Random access memory (RAM) 10 Multiplier circuit VA, VA (X ) Analog output VO, VO (X) correction signal VR, reference potential VS, VS (X) sensor signal W, W (X) correction coefficient

Claims (1)

Claim: What is claimed is: 1. A plurality of object images formed by dividing a pupil of a primary imaging and photographing optical system for performing focus detection, and forming light fluxes emitted from respective optical regions of the divided pupils. The amount of movement of
In a focus detection apparatus of a shift type in which two sensors having a large number of photoelectric conversion element arrays are electrically detected to detect a focus state, a light quantity distribution generated between the sensors with respect to a uniform luminance plane of an object is detected. Means for weighting the amplitude of the photoelectric conversion output signal for each position of each element of the sensor, and each element of the sensor by the means for weighting, in order to eliminate the difference and obtain the same light amount distribution And a means for temporarily changing the weighting information according to each position of the focus detection device.