JP2000039552A - Focus detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus detector whose the responsiveness is high by shortening the time required up to turning on an auxiliary light source at the time of executing focus detection for an object whose the luminance is low. SOLUTION: An arithmetic part 5 first inputs the photometric result of object luminance from a photometric circuit 12. Then, the storing time of storing operation at a first time executed by an image sensor 3 is calculated based on the photometric result. In the case that the object luminance is low and the storing time calculated is long, a first limiting time is provided for the storing time. In the case that the second and succeeding storing operations are executed by the image sensor 3, the storing time in the next storing operation is calculated based on the storing time of the previous storing operation and an output from the image sensor 3 at this time. In the case that the storing time calculated is long, a second limiting time is provided for the storing time. The first limiting time is set to be shorter than the second limiting time. Discrimination whether or not to turn on an auxiliary light source is executed based on the first time storing operation result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a camera focus detection device.

[0002]

2. Description of the Related Art A phase difference detection method is known as one of focus detection methods in an automatic focus detection device of a camera. In this phase difference detection method, a subject image formed by a photographing lens is pupil-divided and re-formed on a pair of image sensor arrays, and re-formed on each image sensor array based on an output signal of the image sensor array. The focus position of the photographing lens is calculated by calculating a relative shift amount of a subject image to be formed.

In the focus detection by the above-described phase difference detection method, the possibility of focus detection and the reliability of the detected focus position greatly depend on the contrast, which is the light luminance distribution of the subject. In other words, when calculating the relative shift amount of the subject image re-imaged on each image sensor array, it is easy to obtain a correlation if the signal output from each image sensor array has a slip.

Accordingly, the focus detection accuracy can be improved by reflecting the contrast of the object as high as possible in the signals output from the respective image sensors. For this reason, a drive controller is connected to the image sensor, and the drive controller controls the amount of incident light.

[0005] This incident light quantity control will be described. The image sensor is controlled by the drive control unit to repeatedly perform the accumulation operation and the signal output operation. At this time, the time required for the accumulation operation is also controlled. In a state where light with a constant illuminance is incident on the image sensor, the signal level output from the image sensor is increased as the accumulation time is extended, and the signal is turned off. However, if the amount of incident light is too large, the signal output from the image sensor will be saturated, and the signal will not be turned off. Conversely, if the accumulation time is short, the signal level will be low, and the signal will not turn. For this reason, the drive control unit changes the accumulation time according to the illuminance of the light incident on the image sensor. Specifically, the storage time for the next storage operation is determined based on the previous storage time and a signal output from the image sensor based on the storage operation at this time. Repeat this,
The signal output from the image sensor is converged so as to be in a state suitable for focus detection. This is the incident light amount control performed by the drive control unit.

When the luminance of the object is low, the above-mentioned accumulation time needs to be lengthened. However, if the accumulation time is too long, the focus detection operation is slowed down and the usability is reduced. Time is provided. By shortening the time limit, the focus detection operation can be hastened. However, if the time limit is short, focus detection cannot be accurately performed on a low-luminance subject, that is, the subject luminance range in which focus detection on the low-luminance side can be narrowed, and the usability of the camera decreases.

As one method for solving this problem,
There is a method of irradiating illumination light as auxiliary light for focus detection operation. This illumination light irradiation is effective when the subject brightness is low and the photographing distance is not so long. The accumulation time can be shortened by the illumination light irradiation, and an appropriate output signal can be obtained from the image sensor. .

[0008]

However, there is a problem that the time required to complete the focus detection operation becomes long even when the above-mentioned illumination light is used. Hereinafter, this will be described.

In the above-described incident light amount control, as in a state immediately after the power of the camera is turned on or a state immediately after the release button is half-pressed, the “according to the previous accumulation time and the accumulation operation at this time, Therefore, a signal output from the image sensor may not be obtained (hereinafter, this is simply referred to as a “previous accumulation result”). In such a case, the accumulation time is determined based on a signal relating to the luminance of the subject output from the photometric element, that is, the photometric output. In this case, the accumulation time determined based on the photometric output is not always optimal, and the incident light amount control based on the previous accumulation result described above may need to be repeated. This is because there is a luminance distribution in the subject, and the luminance of the area on the subject where the focus is detected by the image sensor, that is, the luminance of the focus detection area does not always match the subject luminance obtained from the photometric output.

For the same reason, the determination as to whether to use the illumination light is not made based on the photometric output. First, the first accumulation operation is performed without using the illumination light. The above determination has been made based on the output signal from the image sensor. Thereby, the illumination light is used only when the luminance of the portion corresponding to the focus detection area of the subject is so low that it is not really suitable for focus detection.

Here, consider the case where the above-described focus detection is performed on a subject under low luminance. In this case, the first accumulation time calculated based on the photometric output becomes longer, and the accumulation operation may be performed at the full time limit. At this time, furthermore, due to the low brightness of the subject, a sufficient output may not be obtained from the image sensor even by the accumulation operation for the full time limit.

When the output from the image sensor obtained in the first accumulation operation is not sufficient as described above, illumination light is used in the second and subsequent accumulation operations. But,
The first accumulation operation is, so to speak, "wasteful". In such a case, it takes time for the photographer to operate the release button, emit the illumination light, and complete the focus adjustment,
It is inevitable that the operability is reduced.

The present invention provides a highly responsive focus detection apparatus that suppresses a long time required for lighting of illumination light even when focus detection is performed on a low-luminance subject. The purpose is to:

[0014]

FIG. 1 shows an embodiment of the present invention.
The present invention will be described with reference to FIG. (1) The invention according to claim 1 is a focus detection optical system 2 that forms an image of a light beam from a subject; and a photoelectric output device that outputs a signal corresponding to the light intensity of the subject image formed by the focus detection optical system 2. A conversion unit 3; and a photoelectric conversion unit 3 that is repeatedly performed after the focus detection operation is started when the light emitting unit 10 that emits illumination light toward the subject can emit illumination light.
In the accumulation operation of the above, the first time limit provided for the accumulation time in the first accumulation operation is shorter than the second time limit provided for the accumulation time in the second and subsequent accumulation operations, whereby Achieve the objectives. (2) The invention according to claim 2 further includes a determination unit 5 for determining whether or not the light emitting unit 10 emits light; the determination unit 5 causes the light emitting unit 10 to emit light for the first time limit. The storage time is substantially equal to the accumulation time such that an output suitable for focus detection can be obtained from the photoelectric conversion means 3 under the brightness serving as a determination boundary when the determination is made.

In the section of the means for solving the above-mentioned problems, which explains the configuration of the present invention, the drawings of the embodiments of the present invention are used for easy understanding of the present invention. However, the present invention is not limited to this.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment-Configuration of Focus Detection Device-FIG. 1 showing a configuration of a camera 100 in which a focus detection device 30 according to a first embodiment of the present invention is incorporated. Light beams from positions corresponding to a plurality of focus detection areas in the object field pass through the objective lens 1, pass through the focus detection optical system 2, and form an image on the image sensor 3. In the present embodiment,
The focus detection unit 20 including the focus detection optical system 2 and the image sensor 3 is of a phase difference detection type. The configuration of the focus detection unit 20 and the principle of focus detection by the focus detection unit 20 will be described later.

The focus detecting device 30 includes the focus detecting unit 2
0, A / D conversion unit 4, arithmetic unit 5, and sensor control unit 11
Etc. The A / D converter 4 converts signals (analog signals) sequentially output from the image sensor 3 into digital signals and inputs the digital signals to the arithmetic unit 5. The arithmetic unit 5 calculates A
The focus detection calculation is performed based on the output signal of the image sensor 3 that has been A / D converted by the / D conversion unit 4, and the defocus amount is calculated.

The auxiliary light source unit 4 is
0, a drive control unit 13, a photometric circuit 12, and the like.
The auxiliary light source unit 40 includes the auxiliary light control unit 9 and the auxiliary light source 10, and emits illumination light in synchronization with the accumulation operation of the image sensor 3, as described later, when the luminance of the subject is low. The auxiliary light source unit 40 is built in the camera 100. The arithmetic unit 5 determines whether the auxiliary light source 10 needs to emit light based on the accumulation time of the image sensor 3 and the output signal, and when it determines that the auxiliary light source 10 emits light, the auxiliary light control unit 9 of the auxiliary light source unit 40 Issues a control signal. The auxiliary light controller 9 causes the auxiliary light source 10 to emit light in response to a control signal output from the calculator 5. The sensor control unit 11
The drive of the image sensor 3 is controlled based on the output from the arithmetic unit 5. The lens drive control unit 13 drives the motor 14 based on the control signal output from the calculation unit 5 to drive the objective lens 1 to focus. The photometry circuit 12 measures the luminance of the subject, and outputs subject luminance information based on the measurement result to the arithmetic unit 5.

-Principle of Operation of Focus Detection by Focus Detection Unit-The configuration of the focus detection unit 20 and the principle of focus detection operation by the focus detection unit 20 will be described with reference to FIG.

The focus detection unit 20 includes an infrared light cut filter 700, a field mask 200, and a field lens 3.
00, aperture mask 400, re-imaging lenses 501 and 5
02, and the image sensor 3.

An area 100 is an exit pupil of the objective lens 1 (FIG. 1). Further, the regions 101 and 102 are formed in the opening mask 4.
00 is an area where an image obtained by back-projecting the apertures 401 and 402 formed on the area 100 onto the area 100 by the field lens 300 is present. The position of the infrared light cut filter 700 may be on the right side or the left side of the field mask 200.

The light beam incident through the regions 101 and 102 is focused on the film equivalent surface 600, and thereafter, the infrared light cut filter 700, the field mask 200, the field lens 300, the openings 401 and 402, Image sensor arrays 3a, 3b passing through image lenses 501, 502
Re-image on top.

The pair of subject images formed on the image sensor arrays 3a and 3b approach each other in a so-called front focus state in which the objective lens 1 forms a sharp image of the subject before the film equivalent surface 600 (subject side). On the contrary, in the so-called rear focus state in which a sharp image of the subject is formed after the film equivalent surface 600, they move away from each other. Then, when the subject images formed on the image sensor arrays 3a and 3b are at a predetermined interval, the sharp image of the subject becomes a film equivalent plane 600.
Located on top. Therefore, the pair of subject images are photoelectrically converted by the image sensor arrays 3a and 3b and converted into electric signals,
By calculating these signals and calculating the relative distance between the pair of subject images, the focus adjustment state of the objective lens 1, that is, the position at which a sharp image is formed by the objective lens 1 is determined with respect to the film equivalent surface 600. How far apart in the direction, that is, the amount of deviation is obtained. Hereinafter, this deviation amount is referred to as “defocus amount” in this specification. In FIG. 3, the focus detection areas are the image sensor arrays 3a and 3a.
b is back-projected by the re-imaging lenses 501 and 502 and corresponds to a portion overlapping near the film equivalent surface 600.

Next, an arithmetic processing method for obtaining the defocus amount output from the image sensor arrays 3a and 3b will be described. Each of the image sensor arrays 3a and 3b includes a plurality of photoelectric conversion elements.
As shown in (b), a plurality of data strings a1, a2,.
, b1, b2,..., bn are output. Then, the correlation operation is performed while relatively shifting each data string by a predetermined data amount L. Specifically, the correlation amount C (L) is calculated by equation (1).

(Equation 1) ji = L, L = -lmax, ...,-2, -1,0,1,2, ..., lmax

Here, L is an integer corresponding to the shift amount of the data string as described above, and the first term k and the last term r are the shift amount L
May be changed depending on In the shift amount giving the minimum correlation value among the correlation amounts C (L) thus obtained, the numerical values of the optical system including the field lens 300 and the re-imaging lenses 501 and 502 shown in FIG. The defocus amount is obtained by multiplying a constant determined by the pitch width of the photoelectric conversion elements of the image sensor arrays 3a and 3b. However, the correlation amount C (L) is a discrete value as shown by a white circle in FIG. 3C, and the minimum unit of the detectable defocus amount is the image sensor array 3a,
It is limited by the pitch width of the photoelectric conversion element 3b.

Therefore, a method has been proposed in which a minimum value C _ex is newly calculated by performing an interpolation operation from the discrete correlation amount C (L) to perform a precise focus detection. (JP-A-60-
No. 37513). This is a method of calculating the correlation amount C ₀ which is the minimum value and the correlation amounts C ₁ and C _-1 at the shift amounts on both sides thereof as shown in FIG. 4 which is a partially enlarged view of FIG. The shift amount Fm giving the value C _ex and the defocus amount DF are obtained by the following equations.

Fm = L + DL / E Equation (2) DF = Kf * Fm Equation (3) E = MAX {(C ₁ −C ₀ ), (C ₋₁ −C ₀ )} Equation (4) DL = (C ₋₁ −C ₁ ) / 2 Equation (5) C _ex = C ₀ − | DL | Equation (6) where MAX {Ca, Cb} is the larger of Ca and Cb. This means that selection is made, and Kf is a constant determined by the optical systems 300, 501, and 502 shown in FIG. 2 and the pitch width of the photoelectric conversion elements of the image sensor arrays 3a and 3b.

It is necessary to determine whether the defocus amount DF obtained in this way truly indicates the defocus amount or whether the defocus amount DF is due to fluctuations in the correlation amount due to noise or the like. The focus amount is reliable.

E> E1 Equation (7) and Cex / E <G1 Equation (8) Here, E1 and G1 are predetermined values.

E is a value that depends on the contrast of the object. The larger the value, the higher the contrast and the higher the reliability. Cex / E mainly depends on the degree of coincidence of the images, and 0
The closer to, the higher the reliability. Then, when it is determined that there is reliability, the objective lens 1 is driven based on the defocus amount DF.

-Adjustment of Signal Output from Image Sensor 3-Whether or not the above-described focus adjustment state can be detected, or the reliability of the obtained detection result, depends on the contrast of the light luminance distribution of the subject. Depends heavily on height. Therefore, it is necessary to optimally reflect the contrast of the subject on the output from the image sensor 3.

For example, when a pattern as shown in FIG.
It is desirable that a signal as shown in FIG. In FIG. 5, V _sat indicates the saturation voltage of the photoelectric conversion element.

If the accumulation time is shorter than the ideal state shown in FIG. 5C, the contrast becomes lower as shown in FIG. 5B. Conversely, if the accumulation time is long, the contrast which should be originally present may be lost as shown in FIG. Therefore, it is necessary to control the signal output from the image sensor 3 to have an appropriate magnitude, that is, a magnitude suitable for a focus detection calculation described later. The control of the accumulation time is performed for this purpose. The control of the accumulation time calculates the accumulation time such that the peak value of the output in the next accumulation operation becomes an appropriate value based on the accumulation time in the previous accumulation operation and the level of the signal output from the image sensor. Control. This allows
The contrast is obtained from the signal output from the image sensor 3.

For example, it is assumed that an output as shown in FIG. 5B is obtained from the image sensor 3 and the accumulation time at that time is Tb and the peak output (the peak value of the signal output from the image sensor 3) is Vb. I do. In this case, in order to obtain an output as shown in FIG. 5C from the image sensor 3 by the next accumulation operation, the accumulation time Tc may be obtained by the following equation.

Tc = (Vc / Vb) × Tb Equation (9)

In the equation (9), Vc is a target peak output value in the next accumulation operation. This target peak output value Vc creates a saturated state in the image sensor 3 in the camera assembling / adjustment process, and the output from the image sensor 3 at that time is defined as V _sat , and Vc is calculated from the following equation and stored in the camera. I do.

Vc = A × V _sat Equation (10) Here, A is a positive real number less than 1, and the level of A determines the level of the signal output from the image sensor 3. That is, if this A is small, the contrast of the signal output from the image sensor 3 will always be low,
Conversely, if it is large, the signal output from the image sensor 3 is immediately saturated even if the brightness of the subject changes slightly.

Hereinafter, in this specification, determining the accumulation time in the next accumulation operation based on equation (9) is hereinafter referred to as "performing AGC processing" (Automatic Gain Control). Further, the target peak output value Vc is referred to as “AGC target value”.
Called.

Here, the operation of determining whether AGC is possible or not by the arithmetic unit 5 will be described. The calculation unit 5 obtains a peak value from signals input from the image sensor 3 via the A / D conversion unit 4. Then, based on this peak value, it is determined whether or not the output of the image sensor 3 is in a state where AGC is applied. Here, "AGC is applied" means that the peak value satisfies the following expression.

| V _peak −Vc | <B Equation (11) where V _peak is the above-mentioned peak value, Vc is the AGC target value of the image sensor 3, and B is the allowable value.

In the AGC availability determination operation, the arithmetic unit 5 may make the determination based on an average value instead of the peak value of the signal output from the image sensor 3.

FIG. 6 shows a flowchart of a focus detection program, and FIG. 6 shows a flowchart of the focus detection program.
Referring to FIG. 7 showing the timing of the accumulation operation in FIG. The execution of the focus detection program shown in the flowchart of FIG. 6 is started by the calculation unit 5 when the photographer half-presses a release button (not shown).

In step S701, the arithmetic section 5 initializes the photometric circuit 12 and the IC of the image sensor 3 (corresponding to the "initialization" timing in FIG. 7). In step S702, the arithmetic unit 5 inputs the subject luminance measurement result measured by the photometry circuit 12, that is, the photometry result (corresponding to the timing of “photometry 1” in FIG. 7). The photometry circuit 12 repeats the photometry operation at a predetermined timing as shown in FIG. 7 as “photometry 1”, “photometry 2”, and “photometry 3”. In step S703, the arithmetic unit 5 executes step S703.
In 702, the accumulation time T of the first accumulation operation is calculated based on the photometry result input from the photometry circuit 12 as described below. This is because the AGC process cannot be performed based on the result of the previous storage operation during the first storage operation. The calculation method of the accumulation time T is as follows.

A memory (not shown) connected to the arithmetic unit 5 has an optimum storage time for a certain field luminance, for example, 50 ms for the BV0 subject luminance.
It is stored as follows. Based on the relationship between the subject luminance and the storage time stored in this way and the photometry result input from the photometry circuit 12, the calculation unit 5 calculates the storage time T by the following equation (12).

T = 50 × 20 ^-BV (msec.) Expression (12) Here, BV indicates a photometric result (BV value) output from the photometric circuit 12. For example, if the photometric result BV output from the photometric circuit 12 is -1,

T = 50 × 2 ^{0 + 1} = 100 (msec.) Expression (13)

In step S704, the arithmetic unit 5 determines that the accumulation time T calculated in step S703 is equal to the time limit TL.
It is determined whether or not it is longer than 1;
The process branches to 705 to set T = TL1 and proceeds to step S706. If the result is negative, the process proceeds to step S706 without doing anything. The time limit TL1 provided for the first accumulation time T is set shorter than the time limit TL2 provided for the second or later accumulation time T described later.

In step S706, the arithmetic unit 5 determines whether the release button is half-pressed. If the determination is negative, the operation returns. On the other hand, if it is determined that the release button is half-pressed, the operation proceeds to step S707. In step S707, the arithmetic unit 5 calculates the accumulation time T obtained as described above.
Sends a control signal to the sensor controller 11 so that the image sensor 3 performs an accumulation operation. In response, the image sensor 3 starts the accumulation operation (corresponding to the timing of “accumulation 1” in FIG. 7).

In step S708, the calculation unit 5 performs the focus detection calculation described above to calculate the defocus amount. In step S709, the calculation unit 5 determines that the defocus amount calculated in step S708 is reliable.
Whether or not focus detection is possible is determined based on Expressions (7) and (8). If the determination in step S709 is affirmed, the calculation unit 5 branches to step S710, while if it is denied, it branches to step S713. The processing in steps S710 to S712 will be described later.

In step S713, the arithmetic unit 5 calculates an accumulation time T for the next accumulation based on the above equation (9). That is, this processing corresponds to the above-mentioned AGC processing. In step S714, the arithmetic unit 5 performs step S714.
The calculation result of the accumulation time T in 713 is the time limit TL2
It is determined whether the length is longer than the above.
The process branches to 15 and sets T = TL2, and proceeds to step S716. If the result is negative, the process proceeds to step S716 without doing anything.

In step S716, the arithmetic unit 5 determines whether or not the auxiliary light source 10 is set to the light-off state, and if not, returns to step S706. here,
“It is set to the light-off state” refers to step S707
Means that the auxiliary light source 10 is set not to emit light in conjunction with the accumulation operation of the image sensor 3 performed in the step (1).

If the determination in step S716 is affirmative, the arithmetic unit 5 proceeds to step S717, and determines whether the accumulation time T is longer than the determination time TL3. The calculation unit 5
If the determination in step S717 is negative, step S7
On the other hand, when the determination is affirmative, the process proceeds to step S718. Here, the determination time TL3 is a determination criterion for determining whether or not the subject brightness is such that it is determined that a preferable result is obtained when the auxiliary light source 10 emits light in conjunction with the accumulation operation of the image sensor. is there. Step S71
In step 8, the arithmetic unit 5 sets the auxiliary light source 10 to a lighting state, that is, sets the auxiliary light source 10 to light in conjunction with the accumulation operation of the image sensor 3 performed in step S707, and returns to step S706.

The operation of the arithmetic unit 5 after step S710, which is the branch destination when the determination in step S709 is affirmed, will be described. In step S710, the calculation unit 5 drives the objective lens 1 based on the focus detection calculation result in step S708. In step S711, the calculation unit 5 determines whether or not the release button is fully pressed. If the result is affirmative, the process proceeds to step S712. If the result is negative, the process branches to step S713. The arithmetic unit 5 controls operations related to a series of photographing operations such as opening and closing the shutter in step S712, and returns.

When the release button is half-pressed by the photographer, the arithmetic unit 5 repeats the focus detection and the driving of the objective lens 1 as described above, and the half-pressed state of the release button is released, or Until the button is fully pressed, “accumulation 1”, “accumulation 2”,... In FIG. 7 are repeated.

The above focus detection program will be further described. The calculation unit 5 calculates the first accumulation time T based on the photometry result input from the photometry circuit 12 (Step S).
701-703). And because the subject brightness is low,
If it is determined that the calculated first accumulation time T is longer than the predetermined time limit TL1, the first accumulation time T is set to TL1.
(Steps S704 to S705). The accumulation operation and the focus detection calculation are performed based on the accumulation time T obtained as described above, and if it is determined that the focus can be detected, the objective lens 1 is driven (steps S706 to S7).
10). If the focus cannot be detected, or if the release button has not been fully pressed after the objective lens 1 is driven, the accumulation time at the next accumulation operation is calculated (step S713). This accumulation time is the time limit TL2
If it is longer, the storage time is set to TL2 (step S2).
714 to S715), and determines whether or not the auxiliary light source 10 is set to the “light-off state” (step S71).
6). If it is set to "light-off state", it is determined whether to set to "light-on state" (step S71).
7 to S718), returning to step S706 and repeating the focus detection operation. In the flowchart of FIG. 6, the auxiliary light extinguishing control is not particularly described, but it is necessary to return when the determination in step S706 is denied or to return after completing the release processing in step S712. The light-off control may be appropriately performed according to the request.

The time limit TL1 is 2 as described above.
Time limit TL2 provided for the accumulation operation after the first time
It is set shorter than This is because, when the subject luminance is considerably low, the possibility that the defocus amount calculated by performing the accumulation operation during the time TL2 when the time limit is full is low is determined to be reliable. That is, when the subject luminance is low, it is unlikely that a reliable defocus amount can be obtained in the first accumulation operation and the focus detection calculation.
The time limit TL1 set for the first accumulation operation is shortened. This will be described with reference to FIG. As indicated by a broken line in the timing chart relating to the accumulation operation of the image sensor in FIG. 7, since the first accumulation operation is performed in the time limit TL2 in the focus detection device according to the related art, the second accumulation operation start timing (auxiliary The light emission timing of the light source 10) is t2. On the other hand, according to the focus detection device applied to the embodiment of the present invention, the second accumulation operation timing can be advanced to t1, and the focus adjustment can be completed earlier.

To further explain that the time limit TL1 is made shorter than the time limit TL2, when the subject luminance is considerably low, it is advantageous to make the time limit TL1 as short as possible for shortening the time until the completion of the focus adjustment. .
That is, if it is expected that the probability of being able to perform focus detection based on the result of the first accumulation operation is low because the luminance of the subject is considerably low, the first accumulation operation is immediately terminated and the second and subsequent accumulation operations are terminated. It is more efficient to use the auxiliary light source 10 in the storing operation. However, the luminance of the subject varies, and if the time limit TL1 is too short, the first accumulation operation is terminated despite the fact that focus detection can be accurately performed without using the auxiliary light source 10. Then, the probability that focus detection becomes possible based on the result of the first accumulation operation is reduced, which is not efficient.

By the way, in step S717, the arithmetic unit 5 determines whether the accumulation time T at the next accumulation calculated in step S713 is longer than the judgment time TL3. That is, it is determined whether or not the luminance of the focus detection range of the subject is somewhat dark. The determination time TL3 is determined in consideration of the focus detection accuracy and the time required for the completion of the focus adjustment, and is determined in accordance with the subject luminance such that the use of the auxiliary light source 10 provides more preferable results. Therefore, it is desirable that the time limit TL1 be substantially equal to the above-described determination time TL3. That is, 1 calculated in step S703
If the third accumulation time T is not longer than the determination time TL3, the luminance of the focus detection range of the subject is expected to be "high enough to enable focus detection with high accuracy without using the auxiliary light source 10." Is done. Therefore, the time limit TL1 is changed to the determination time T
By making it equal to L3, the probability that the focus can be detected in the first accumulation operation is increased, and the expected value of the time required for completing the focus adjustment can be shortened.

Second Embodiment In a second embodiment of the present invention, as shown in FIG. 8, the auxiliary light source unit 40A is not built in the camera 100A, and is, for example, an electronic flash unit (hereinafter, referred to as an electronic flash unit). Is referred to as a “flash unit”) and is removably attached to the camera 100A.
In FIG. 8, components other than the above are the camera 1 in which the focus detection device 30 according to the first embodiment is incorporated.
00, which is the same as that shown in FIG.

The focus detection program executed by the arithmetic section 5 will be described with reference to FIG. As described above, in the present embodiment, the auxiliary light source unit 40A is
It is attached to and removable from 00A. Therefore, the focus detection program (FIG. 9) executed by the arithmetic unit 5 in the present embodiment has a step of determining whether or not the auxiliary light source unit 40A is mounted in the arithmetic unit 5 of the first embodiment. This is different from the focus detection program (FIG. 6) to be executed. Other steps are the same as those of the focus detection program shown in FIG.

In step S901, the arithmetic unit 5 initializes the photometric circuit 12 and the IC of the image sensor 3. In step S902, the arithmetic unit 5 sets the photometric circuit 1
Input the photometry result from Step 2. In step S903, the calculation unit 5 determines the accumulation time T of the first accumulation operation based on the photometry result input from the photometry circuit 12 in step S902.
Is calculated. Note that the method of calculating the accumulation time T is the first method.
The description is omitted because it is the same as that described in the embodiment.

In step S904, the arithmetic unit 5 determines whether or not the auxiliary light source unit 40A is mounted on the camera 100A. If the result is affirmative, the process proceeds to step S905, while if the result is negative, the process branches to step S915.

In step S905, the arithmetic unit 5 determines that the accumulation time T calculated in step S903 is equal to the time limit TL.
It is determined whether or not it is longer than 1;
The process branches to 906 to set T = TL1 and proceeds to step S907. If the result is negative, the process proceeds to step S907 without doing anything. The time limit TL1 provided for the first accumulation time T is set shorter than the time limit TL2 provided for the second or later accumulation time T described later.

In step S907, the arithmetic unit 5 determines whether or not the release button is half-pressed. If the result is negative, the operation returns. On the other hand, if it is determined that the release button is half-pressed, the flow proceeds to step S908. Step S9
At 08, the arithmetic unit 5 issues a control signal to the sensor control unit 11 so that the image sensor 3 performs an accumulation operation at the accumulation time T obtained as described above. In response, the image sensor 3 starts the accumulation operation.

In step S909, the calculation unit 5 performs the focus detection calculation described in the first embodiment to calculate a defocus amount. In step S910, the calculation unit 5 determines whether the defocus amount calculated in step S909 is reliable and whether or not focus detection is possible based on equations (7) and (8). When the determination in step S910 is affirmed, the calculation unit 5 branches to step S911, and when denied, the calculation unit 5 branches to step S914. The processing in steps S911 to S913 will be described later.

In step S914, the calculation unit 5 calculates an accumulation time T for the next accumulation based on the equation (9).
That is, AGC processing is performed. In step S915, the calculation unit 5 determines whether or not the calculation result of the accumulation time T in step S914 is longer than the time limit TL2. If the result is affirmative, the process branches to step S916, sets T = TL2, and proceeds to step S917. If not, the process proceeds to step S917 without doing anything.

In step S917, the arithmetic unit 5 determines whether or not the auxiliary light source unit 40A is mounted on the camera 100A. If the result is affirmative, the process proceeds to step S918. If the result is negative, the process returns to step S907.

In step S918, the arithmetic unit 5 determines whether or not the auxiliary light source 10 is set to the light-off state. If the result is negative, the process returns to step S907. Step S
If the determination at 918 is affirmative, the arithmetic unit 5 proceeds to step S9
Proceeding to 19, it is determined whether the accumulation time T is longer than the determination time TL3. Arithmetic unit 5 returns to step S907 if the determination in step S919 is denied, or proceeds to step S920 if affirmative. Here, the judgment time TL3
Is the subject brightness level at which it is determined that a preferable result is obtained when the auxiliary light source 10 emits light in conjunction with the accumulation operation of the image sensor in the same manner as described in the first embodiment. Is a criterion for judging. In step S920, the arithmetic unit 5 sets the auxiliary light source 10 to the lighting state, that is, the auxiliary light source 1 in conjunction with the accumulation operation of the image sensor 3 performed in step S908.
0 is set to be turned on, and the process returns to step S907.

The operation of the arithmetic unit 5 after step S911, which is the branch destination when the determination in step S910 is affirmed, will be described. In step S911, the calculation unit 5 drives the objective lens 1 based on the focus detection calculation result in step S909. In step S912, the calculation unit 5 determines whether or not the release button is fully pressed. If the result is affirmative, the process proceeds to step S913. If the result is negative, the process branches to step S914. The calculation unit 5
In step S913, control relating to a series of photographing operations such as opening and closing of a shutter is performed, and the process returns.

The focus detection program shown in FIG. 9 will be further described. The calculation unit 5 calculates the first accumulation time T based on the photometric result input from the photometric circuit circuit 12 (steps S901 to S903). Next, the arithmetic unit 5 determines whether or not the auxiliary light source unit 40A is mounted (step S904), and when the determination is affirmative, performs the same processing as in the first embodiment. That is, the arithmetic unit 5 sets the accumulation time T to T when the initial accumulation time T is longer than the time limit TL1.
The storage operation is performed as L1 (step S908). On the other hand, when it is determined that the auxiliary light source unit 40A is not mounted, the calculation unit 5 branches to step S915 to determine whether the accumulation time T is longer than the time limit TL2,
If the result is affirmative, the accumulation time T is set to the time limit TL2 (steps S915 to S916). The calculation unit 5 further determines whether or not the auxiliary light source unit 40A is attached to the camera 100A in step S917. If the determination is negative, the processing in steps S917 to S920 is not performed, and the processing in step S917 is not performed.
Return to 907.

That is, when the auxiliary light source unit 40A is not mounted, in other words, when the auxiliary light source 10 cannot emit light, the time limit set for the first accumulation time is set to two.
There is no point in making the time shorter than the time limit set for the accumulation time after the first time. Not only does it have no meaning, but when the brightness of the subject is low, the time required for completing the focus adjustment may be extended. Therefore, in the present embodiment, the calculation unit 5 determines whether or not the auxiliary light source unit 40A is mounted, and if it is determined that the auxiliary light source unit 40A is mounted, the focus adjustment is performed in the same procedure as that described in the first embodiment. On the other hand, if it is determined that the camera is not mounted, the same time limit is set for the first and second and subsequent accumulation times. For this reason, when the auxiliary light source unit 40A is mounted in a situation where the subject luminance is somewhat dark, the initial accumulation time can be reduced, and the time required for completing the focus adjustment can be reduced. When the unit 40A is not mounted, the time required for completing the focus adjustment does not undesirably increase.

In the above embodiment, an example has been described in which the auxiliary light source unit 40A is built in the flash unit. However, the auxiliary light source unit 40A may be built in another attachment that can be inserted into and removed from the camera 100A. .
Alternatively, the auxiliary light source unit 40A alone
It may be one that is detachably attached to A. Also,
Using the discharge tube of the flash unit as an auxiliary light source,
The light may be emitted from the discharge tube.

In the correspondence between the above-described embodiment and the claims, the field lens 300 and the re-imaging lenses 501 and 502 serve as a focus detection optical system, and the image sensor 3
Is the photoelectric conversion unit, the auxiliary light source 10 is the light emitting unit, the time limit TL1 is the first time limit, the time limit TL2 is the second time limit, and the calculation unit 5 performs steps S717 to S717 in FIG.
Step S718 in FIG.
The processing of 919 to S920 constitutes the determination means.

[0067]

As described above, (1) According to the first aspect of the present invention, when it is possible to emit illumination light toward a subject, the storage time in the first storage operation is reduced. The first time limit provided is shorter than the second storage time provided for the second and subsequent storage operations, thereby shortening the time required from the start of focus detection to the irradiation of illumination light. It is possible to do. As a result, the time required for focus detection can be reduced. (2) According to the second aspect of the present invention, an output suitable for focus detection can be obtained from the photoelectric conversion unit under a brightness serving as a determination boundary of whether or not the light emitting unit emits light. Since the first time limit is set so as to be substantially equal to the accumulation time, the following effects are obtained. That is, the probability that focus detection can be performed based on the first accumulation operation under such a condition that an output suitable for focus detection is obtained from the photoelectric conversion unit without causing the light emitting unit to emit light is increased. It becomes possible to shorten the expected value of the time required.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a camera in which a focus adjustment device according to a first embodiment of the present invention is incorporated.

FIG. 2 is a diagram illustrating an optical system and an image sensor of a focus detection unit.

FIG. 3 is a diagram for explaining how a correlation operation is performed on signals output from a pair of image sensor arrays;
(A) and (b) show an example of an output signal from the image sensor, and (c) shows a change in the correlation amount.

FIG. 4 is a diagram illustrating a state in which a defocus amount is obtained by a correlation operation.

5A and 5B are diagrams illustrating signals output from an image sensor, wherein FIG. 5A shows a contrast pattern of a focus detection area of a subject, and FIGS. 7 shows how a signal output from an image sensor changes.

FIG. 6 is a flowchart illustrating a focus detection program executed by a calculation unit of the focus detection device according to the first embodiment of the present invention.

7 is a timing chart showing a state in which the accumulation operation of the image sensor and the lighting control of the auxiliary light source are performed with execution of the focus detection program shown in FIG. 6;

FIG. 8 is a diagram illustrating a configuration of a camera in which a focus adjustment device according to a second embodiment of the present invention is incorporated.

FIG. 9 is a flowchart illustrating a focus detection program executed by a calculation unit of the focus detection device according to the second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Objective lens 2 Focus detection optical system 3 Image sensor 3a, 3b Image sensor array 4 A / D conversion part 5 Operation part 9 Auxiliary light control part 10 Auxiliary light source 11 Sensor control part 12 Photometric circuit 13 Drive control part 14 Motor 20 Focus detection Unit 30 Focus detection device 40, 40A Auxiliary light source unit 100, 100A Camera

Claims (2)

[Claims] A focus detection optical system that forms a light beam from a subject; a photoelectric conversion unit that outputs a signal corresponding to the light intensity of the subject image formed by the focus detection optical system; When the light emitting unit that emits the illumination light is capable of emitting the illumination light, it is provided for the accumulation time of the first accumulation operation in the accumulation operation of the photoelectric conversion unit that is repeatedly performed after the focus detection operation is started. A focus detection device, wherein the first time limit is shorter than a second time limit provided for the accumulation time in the second and subsequent accumulation operations. 2. The focus detection device according to claim 1, further comprising: a determination unit configured to determine whether or not the light emitting unit emits light, wherein the first time limit is determined by the determination unit. Focus detection characterized by being substantially equal to an accumulation time such that an output suitable for focus detection is obtained from the photoelectric conversion means under a brightness serving as a determination boundary when determining whether or not to emit light. apparatus.