JPH08122626A - Focus detector - Google Patents

Abstract

PURPOSE: To eliminate influence by a noise component and to accurately detect focus by comparing a focusing state being focus detection arithmetic result with a focusing allowable range after change and deciding the focusing/out of focusing of a photographing lens. CONSTITUTION: The storage-control of an image sensor 9 is performed according to storage time set in a storage control circuit 12, and a subject image signal is amplified by a signal amplifier circuit 10 at amplification factor set in the control circuit 12. Then, the focusing allowable range is set in accordance with the amplification factor of the subject image signal by a focus detection arithmetic circuit 11, and the subject image signal is read from the amplifier circuit 10 so as to calculate the defocusing amount of the photographing lens 1. When the calculated defocusing amount is out of the set focusing allowable range, a motor 14 is driven and controlled by a motor driving control circuit 13 in accordance with the defocusing amount calculated by the arithmetic circuit 11 so as to drive the photographing lens 1 to a focusing position. Meanwhile, when it is within the focusing allowable range, shutter release is permitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detection device for detecting the focus adjustment state of a taking lens.

[0002]

2. Description of the Related Art A pair of images having a parallax of a subject is guided onto a pair of image sensors, and a relative shift amount between the pair of images is calculated based on the image output of these image sensors, and a focus of a photographing lens is calculated. A phase difference detection type focus detection device that detects an adjustment state is known. An outline of this type of focus detection device will be described with reference to FIG. The light flux from the subject that has entered through the area 21 of the taking lens 1 is focused on the film equivalent surface 6, and then the bandpass filter 7,
Focus detection optical system 8 including a field mask 2, a field lens 3, a diaphragm opening 41, and a re-imaging lens 51.
An image is formed on the sensor array 9A of the image sensor 9 through the. Similarly, the light flux from the subject that has entered through the area 31 of the photographing lens 1 is focused on the film equivalent surface 6, and then the bandpass filter 7, the field mask 2, the field lens 3, the aperture opening 42, and Re-imaging lens 5
An image is formed on the sensor array 9B of the image sensor 9 through the focus detection optical system 8 composed of two. Here, the size of the area 21 of the photographing lens 1 is equal to the back projection image of the field opening 3 of the aperture opening 41, and similarly, the area 3
The size of 1 is equal to the back projection image of the field lens 3 of the diaphragm opening 42.

The secondary image of the pair of subject images formed on the sensor rows 9A and 9B of the image sensor 9 by the focus detection optical system 8 is a sharp image of the subject formed by the taking lens 1 from the planned focal plane. Also approach each other in the so-called front focus state in which the images are formed in front, and conversely move away from each other in the so-called rear focus state in which the images are formed after the planned focal plane. Further, at the time of so-called focusing in which a sharp image of the subject formed by the photographing lens 1 forms an image on the planned focal plane, the subject images on the sensor rows 9A and 9B of the image sensor 9 are relatively matched. Therefore, the secondary images of the pair of subject images formed by the focus detection optical system 8 are photoelectrically converted by the sensor arrays 9A and 9B of the image sensor 9 into electric signals, and the pair of subject image signals are subjected to correlation calculation. By performing the processing to obtain the relative position of the secondary images of the pair of subject images, the photographing lens 1
The focus adjustment state, that is, the amount away from the in-focus state and the direction thereof (hereinafter referred to as the defocus amount) are detected.
The focus detection area is a portion where the sensor arrays 9A and 9B of the image sensor 9 are back-projected by the focus detection optical system 8 and overlap in the vicinity of the planned focal plane.

Next, a calculation processing method for obtaining the defocus amount will be described. Image sensor 9 sensor row 9
Each of A and 9B is composed of a plurality of photoelectric conversion elements, and
As shown in (a) and (b), a plurality of photoelectric conversion outputs a
1. ． ． an, b1. ． ． bn is output. Then, the correlation calculation is performed while relatively shifting each data string by a predetermined amount L of data. Specifically, the correlation amount C (L)
Is calculated by the following formula.

## EQU1 ## C (L) = Σ | ai-bj | where Σ represents the summation operation of i = k to r. Also, L
Is an integer corresponding to the shift amount of the data string, and j−i =
L, L = -lmax, ...,-2, -1,0,1,2, ..., lmax. In Expression 1, the first term k and the last term r may be changed depending on the shift amount L.

In the correlation amount C (L) thus obtained,
The defocus amount is obtained by multiplying the shift amount giving the minimum correlation amount by a constant determined by the pitch width of the photoelectric conversion element of the optical system and the image sensor shown in FIG. However, the correlation amount C (L) is a discrete value as shown in FIG. 5C, and the minimum unit of the defocus amount that can be detected is the sensor rows 9A and 9B of the image sensor 9.
It is limited by the pitch width of the photoelectric conversion element.
Therefore, Japanese Patent Laid-Open No. 60-37513 proposes a method of calculating a new minimum value Cex by performing an interpolation calculation based on the discrete correlation amount C (L) and performing accurate focus detection. . As shown in FIG. 6, this is the correlation amount C (0) which is the minimum value and the correlation amount C between the shift amounts on both sides thereof.
(1), C (-1) is used to calculate the minimum value C
The shift amount Fm and the defocus amount DF that give ex are obtained by the following equations.

DF = Kf * Fm, Fm = L + DL / E, DL = {C (-1) -C (1)} / 2, Cex = C (0)-| DL |, E = MAX [{C (1) -C (0)}, {C (-1)-
C (0)}] where MAX {Ca, Cb} means to select the larger of Ca and Cb, and Kf is the pitch of the photoelectric conversion elements of the optical system and the image sensor 9 shown in FIG. It is a constant determined by the width.

It is necessary to determine whether the defocus amount thus obtained truly indicates the defocus amount or whether it is due to fluctuations in the correlation amount due to noise or the like. When the following conditions are satisfied, the defocus amount is determined. The quantity is reliable.

[Equation 3] E> E1 and Cex / E <G1 Here, E1 and G1 are predetermined values. In Equation 3,
E is a value that depends on the contrast of the subject. The larger the value, the higher the contrast and the higher the reliability.
Cex / E mainly depends on the degree of coincidence of images, and the closer it is to 0, the higher the reliability. Then, when it is determined that there is reliability, the taking lens 1 is driven based on the defocus amount DF.

The sensor rows 9A and 9 of the image sensor 9
The output level of the subject image signal photoelectrically converted by B varies depending on the brightness of the subject. Therefore, it is necessary to amplify the subject image signal so that the subject image signal has a level suitable for focus detection calculation regardless of the luminance of the subject.
Further, by controlling the charge storage time, it is possible to bring the subject image signal to a level suitable for focus detection calculation. By repeatedly performing the focus detection operation by the phase difference detection method described above, the defocus amount of the photographing lens is repeatedly detected. When the detected defocus amount is determined to be reliable, the shooting lens is driven based on the detected defocus amount, and the focus adjustment state of the shooting lens can be regarded as in-focus or in-focus state. Drive is performed until the focus amount is reached. Further, even after it is determined that the focus adjustment state of the taking lens is in focus or the defocus amount which can be regarded as the in-focus state, the focus adjustment state of the taking lens is in focus state by repeatedly performing the focus detection operation. When it is determined that the defocus amount that can be regarded as being exceeded is exceeded, the taking lens can be driven immediately until the defocus amount that can be regarded as the focused state or the focused state is reached.
In this way, by repeatedly performing the focus detection operation, the photographing lens always maintains the in-focus state.

[0008]

However, the object image signals output from the sensor arrays 9A and 9B of the image sensor 9 include noise components from various electric circuits,
Noise components due to dark current of the photoelectric conversion elements are randomly superimposed on each photoelectric conversion element. Further, it is known that the dark current of the photoelectric conversion element increases as the operating temperature increases. Therefore, for example, when the signal amplification circuit amplifies the subject image signal output from the sensor arrays 9A and 9B of the image sensor 9 to a level suitable for focus detection calculation, the signal is superimposed not only on the subject image signal but also on the subject image signal. The noise component that is generated is also amplified.

This problem will be described in detail with reference to FIG. The graph shown in FIG. 3 is a diagram showing how a noise component is superimposed on a subject image signal. In the figure, the vertical axis indicates the magnitude of the signal output, and the broken line with v indicates the output level suitable for focus detection calculation. Further, the horizontal axis represents the photoelectric conversion elements a1. ． ． The sequence of an is shown. In the following, the subject image signal includes a subject image signal component and a noise component, which are referred to as a subject image component and a noise component, respectively. 3 (a), (b) -1, and (c) -1 show signal outputs before amplification of the subject image signal, and FIGS. 3 (b) -2 and (c) -2 show after signal amplification of the subject image signal. The signal output of is shown. An1, Bn1, Bn2, Cn1, and Cn2 in the graph shown in FIG. 3 represent the magnitudes of noise components, and As1, Bs1, Bs2, and C
s1 and Cs2 represent the size of the subject image component. FIG.
Since the output signal from the image sensor 9 shown in (a) is at a level suitable for focus detection calculation, it is not necessary to amplify this subject image signal (amplification factor is 1). On the other hand, FIG.
Since the output of the subject image signal shown in (b) -1 is about half of the output of the subject image signal of FIG. 3 (a), in order to obtain an output level suitable for focus detection calculation, amplification of about twice is required. Need to be amplified at a rate. The result of amplification with a double amplification factor is shown in FIG. Since the size Bs1 of the subject image component shown in FIG. 3B-1 is doubled, Bs2 is B
It is about twice the size of s1. However, since the noise component is also amplified as in the subject image signal, Bn1 is about twice as large as Bn2. That is, the ratio of the noise component Bn2 to the subject image component Bs2 in FIG. 3B-2 is larger than the ratio of the noise component An1 to the subject image component As1 in FIG. 3A.

Similarly, the output of the subject increase signal shown in FIG. 3 (c) -1 is about 1 of the output of the subject increase signal shown in FIG. 3 (a).
Therefore, in order to obtain an output level suitable for focus detection calculation, it is necessary to perform amplification with a gain of about 4 times. Four
The result of amplification with a double amplification factor is shown in FIG. Since the size Cs1 of the subject image component shown in FIG. 3C-1 is amplified four times, Cs2 is about four times as large as CS1. However, since the noise component is amplified in the same manner as the subject image component, Cn1 becomes about four times as large as Cn2.
That is, rather than the ratio of the noise component Bn2 to the subject image signal Bs2 in FIG. 3B-2, FIG.
Noise component Cn2 for the subject image signal Cs2 at
The ratio becomes larger. From the above, it can be seen that the higher the amplification factor for the subject image signal, the greater the ratio of the noise component to the subject image component. The above-mentioned noise is caused by the pair of sensor rows 9 of the image sensor 9.
Since they appear randomly in the plurality of photoelectric conversion elements A and 9B, the correlation calculation described above has a great influence on the degree of coincidence between the secondary images of the pair, and the focus detection calculation result greatly varies.

Also, the noise component increases when the accumulation time is lengthened. This will be described in detail with reference to FIG. 3 (a), 3 (b) -1 and 3 (c) -1 assume that the charges are accumulated in the same accumulation time.
(C) -2 indicates that the charge is accumulated by setting the accumulation time at which the subject image signal shown in FIGS. 3 (b) -1 and 3 (c) -1 becomes an output level suitable for the focus detection calculation. To do. Moreover, An1, Bn1, Bn2, Cn1, and Cn2 represent the magnitude of dark current, and other symbols are as described above. In FIG. 3A, it is assumed that the charge is stored for a storage time in which the output of the image sensor 9 is at a level suitable for focus detection calculation. The output of the subject image signal shown in FIG. 3B-1 is about the same as the output of the subject image signal of FIG. 3A even though the accumulation is performed in the same accumulation time as in the case of FIG. It is half. Therefore, in the case of FIG. 3B-1, in order to obtain an output level suitable for the focus detection calculation, FIG.
It is necessary to perform the storage in about twice as long as the storage time of FIG. 3B-2 shows the result of accumulation at twice the accumulation time. The magnitude Bs2 of the subject image component shown in FIG.
Has a value of Bs2, which is about twice as large as Bs1 because the data is stored for twice the storage time. However, since the dark current is also accumulated in twice the accumulation time, Bn1 is about twice as large as Bn2. That is, the ratio of the dark current An1 to the subject image component As1 in FIG.
Dark current Bn2 for the subject image component Bs2 at −2
It turns out that the ratio of is larger.

Similarly, the output of the subject image signal shown in FIG. 3 (c) -1 is about 1/4 of the output of the subject image signal shown in FIG. 3 (a), so that an output level suitable for focus detection calculation is obtained. In order to achieve this, it is necessary to carry out the storage in a storage time of about 4 times. Fig. 3 shows the result of charge accumulation with a quadruple charge time.
(C) -2. The size Cs2 of the subject image component shown in FIG. 3C-2 is about four times as large as Cs1 because the image is stored for four times as long as the storage time. However, since the dark current is also accumulated in the accumulation time of 4 times, Cn1 is also about 4 times.
It is twice as large as Cn2. That is, the ratio of the dark current Cn2 to the subject image signal Cs2 shown in FIG. 3C-2 is larger than the ratio of the dark current Bn2 to the subject image signal Bs2 shown in FIG. 3B-2. From the above, it can be seen that the ratio of dark current to the subject image component increases as the accumulation time increases. That is, even if the accumulation time is lengthened, the noise component of the dark current in the subject image signal increases. Therefore, if the above-described correlation calculation is performed, the degree of coincidence between the pair of secondary images is greatly affected, and the focus detection calculation result is It will vary greatly.

As described above, the focus detection calculation result varies due to the noise component superimposed on the subject image signal, and even after the photographic lens is once in focus, it is finely driven in the vicinity of the in-focus state and the focus adjustment state of the photographic lens is adjusted. The display in the viewfinder shown is also unstable, which makes the photographer annoyed. In addition, shutter release is allowed only when the shooting lens is in focus, so-called focus priority shooting, the focus detection calculation result varies due to superposition of noise components,
Even if the taking lens is near the in-focus state, shutter release is prohibited, which may miss a shutter chance.

It is an object of the present invention to provide a focus detection device which eliminates the influence of noise components superimposed on a subject image signal to perform accurate focus detection.

[0015]

In order to achieve the above object, the invention of claim 1 passes through a photoelectric conversion element array for outputting a subject image signal according to the light intensity distribution of the subject image and a photographing lens. A focus detection optical system that guides the light flux from the subject to the photoelectric conversion element array to form the subject image, a signal amplification unit that amplifies the subject image signal output from the photoelectric conversion element array, and the signal amplification unit. The focus detection calculation means for calculating the focus adjustment state of the photographing lens based on the subject image signal amplified by the above, and the focus adjustment state calculated by the focus detection calculation means is compared with a predetermined focus allowable range, A focus detection device comprising a focus determination means for determining focus / non-focus of a photographing lens, wherein a focus allowable range of the focus determination means is changed according to an amplification factor of the signal amplification means. Focus tolerance Provided with a circumference change means. According to a second aspect of the present invention, a photoelectric conversion element array that outputs a subject image signal according to the light intensity distribution of the subject image, and a light flux from the subject that has passed through the photographic lens is guided to the photoelectric conversion element array to generate the subject image. A focus detection optical system for forming an image, a storage control means for controlling a charge storage time of the photoelectric conversion element array, and a focus adjustment state of the photographing lens based on a subject image signal output from the photoelectric conversion element array. And a focus determination unit that compares the focus adjustment state calculated by the focus detection calculation unit with a predetermined focus allowable range to determine whether the photographing lens is in focus or out of focus. The focus detection apparatus further includes focusing allowable range changing means for changing the focusing allowable range of the focusing determination means according to the charge accumulation time of the accumulation control means. According to a third aspect of the present invention, a photoelectric conversion element array that outputs a subject image signal corresponding to the light intensity distribution of the subject image and a light flux from the subject that has passed through the photographing lens are guided to the photoelectric conversion element array to generate the subject image. A focus detection optical system for forming an image, a signal amplification means for amplifying a subject image signal output from the photoelectric conversion element array, an accumulation control means for controlling a charge accumulation time of the photoelectric conversion element array, and the signal amplification means. The focus detection calculation means for calculating the focus adjustment state of the photographing lens based on the subject image signal amplified by the above, and the focus adjustment state calculated by the focus detection calculation means is compared with a predetermined focus allowable range, A focus detection device comprising focus determination means for determining focus / non-focus of a taking lens, wherein the focus is determined according to an amplification factor of the signal amplification means and a charge storage time of the storage control means. Size Comprising a focusing allowable range changing means for changing the focus tolerance means. According to a fourth aspect of the present invention, a photoelectric conversion element array that outputs a subject image signal according to the light intensity distribution of the subject image, and a light flux from the subject that has passed through the photographing lens is guided to the photoelectric conversion element array to generate the subject image. A focus detection optical system for forming an image, a focus detection calculation means for calculating a focus adjustment state of the photographing lens based on a subject image signal output from the photoelectric conversion element array, and a focus calculated by the focus detection calculation means. A focus detection device comprising: a focus determination unit that compares an adjustment state with a predetermined focus allowable range to determine whether the photographing lens is in focus or out of focus, and detects a surrounding temperature of the photoelectric conversion element array. The temperature detecting means for detecting the temperature and the focus allowable range changing means for changing the focus allowable range of the focus determining means according to the ambient temperature detected by the temperature detecting means. 6. The focus detection device according to claim 5, further comprising a temperature detection unit that detects an ambient temperature of the photoelectric conversion element array, and the focus permission range changed by the focus permission range change unit according to the charge accumulation time of the accumulation control unit. The range is corrected based on the ambient temperature detected by the temperature detecting means. 7. The focus detection device according to claim 6, further comprising temperature detection means for detecting an ambient temperature of the photoelectric conversion element array, wherein the focusing permissible range changing means allows the amplification factor of the signal amplification means and the charge accumulation of the accumulation control means. The permissible focusing range changed according to time is corrected based on the ambient temperature detected by the temperature detecting means.

[0016]

According to another aspect of the present invention, the focus detection apparatus according to claim 1 changes the focus allowable range of the photographing lens according to the amplification factor of the object image signal, and compares the focus adjustment state of the focus detection calculation result with the changed focus allowable range. Then, the focus / non-focus of the photographing lens is determined. As a result, even if the amplification factor of the subject image signal is increased and the noise component of the subject image signal is increased, and the focus detection calculation result largely varies, the focusing allowable range is changed so as to cancel the variation, Accurate in-focus / out-of-focus determination is performed, and the movement of the taking lens near the in-focus state and the in-focus display on the display are stabilized. In the focus detection device according to claim 2,
The focus allowable range of the photographing lens is changed according to the charge accumulation time of the photoelectric conversion element array, and the focus adjustment state of the focus detection calculation result is compared with the changed focus allowable range to determine the focus of the photographing lens.
Determine out of focus. As a result, even if the charge accumulation time becomes long, the noise component of the subject image signal increases, and the focus detection calculation result greatly varies, the focus allowable range is changed so as to cancel the variation. Focus / non-focus is determined, and the movement of the taking lens near the focus and the focus display on the display are stabilized. In the focus detecting device according to claim 3, the focusing allowable range of the photographing lens is changed according to the amplification factor of the subject image signal and the charge accumulation time of the photoelectric conversion element array, and after changing the focus adjustment state of the focus detection calculation result. The in-focus / non-in-focus state of the taking lens is compared with the in-focus allowable range of. As a result, the amplification factor becomes high, the charge accumulation time becomes long, the noise component of the subject image signal output from the photoelectric conversion element array increases, and even if the focus detection calculation result largely varies, the variation is canceled. Since the permissible focus range is changed as described above, accurate in-focus / out-of-focus determination is performed, and the movement of the photographing lens near the in-focus state and the in-focus display on the display are stable. In the focus detection device according to claim 4, the focus allowable range of the photographing lens is changed according to the ambient temperature of the photoelectric conversion element array, and the focus adjustment state of the focus detection calculation result is compared with the changed focus allowable range. Focus of shooting lens /
Determine out of focus. As a result, even if the ambient temperature rises and the noise component of the dark current of the subject image signal output from the photoelectric conversion element array increases, and the focus detection calculation result largely fluctuates, the focus is allowed to cancel the fluctuation. Since the range is changed, accurate in-focus / out-of-focus determination is performed, and the movement of the photographing lens near the in-focus state and the in-focus display on the display are stable. In the focus detection device of the fifth aspect, the permissible focusing range changed according to the charge accumulation time is corrected based on the ambient temperature of the photoelectric conversion element array. As a result, accurate in-focus / out-of-focus determination is made, and the movement of the photographing lens near the in-focus state and the in-focus display on the display are stabilized. Claim 6
In the focus detection device, the allowable focus range changed according to the amplification factor of the subject image signal and the charge accumulation time of the photoelectric conversion element array is corrected based on the ambient temperature of the photoelectric conversion element array. As a result, accurate in-focus / out-of-focus determination is made, and the movement of the photographing lens near the in-focus state and the in-focus display on the display are stabilized.

[0017]

EXAMPLE An example in which the focus detection device of the present invention is applied to a single-lens reflex camera will be described. FIG. 1 is a sectional view of a single-lens reflex camera equipped with a focus detection device. It should be noted that the same reference numerals are given to the same devices as those shown in FIG. 4, and the description thereof will be omitted. In the figure, 10 is a signal amplification circuit, 11 is a focus detection calculation circuit, 12 is an accumulation control circuit,
13 is a motor drive control circuit, 14 is a motor, 15 is a main mirror, 16 is a sub-mirror, 17 is a film surface, 18
Is a finder screen, 19 is a penta roof prism, 20 is an eyepiece lens, and 22 is a temperature detecting device. The light flux from the subject that has passed through the taking lens 1 is deflected upward by the main mirror 15, and the finder screen 1
8, a penta roof prism 19, and an eyepiece lens 20 lead to a finder optical system. A photosensitive film is arranged on the film surface 17 arranged behind the main mirror 15. Main mirror 15 and sub mirror 1 at the time of shooting
6 is retracted from the optical paths of the taking lens 1 and the film surface 17, and the light beam from the subject passing through the taking lens 1 exposes the photosensitive film arranged on the film surface 17.

A part of the main mirror 15 is semi-transmissive, and the sub-mirror 16 is behind the semi-transmissive part.
Is attached. The light flux from the subject that has passed through the semi-transmissive portion of the main mirror 15 is deflected by the sub-mirror 16 toward the bottom of the camera body and is guided to the focus detection optical system 8 arranged near the film equivalent surface 6 of the taking lens 1. . Further, the light flux from the subject that has passed through the focus detection optical system 8 is guided to the charge storage type image sensor 9. The focus detection optical system 8 and the image sensor 9 are configured so that focus detection can be performed in the focus detection area set on the photographing screen. The image sensor 9 photoelectrically converts the secondary image of the subject image formed on the sensor rows 9A and 9B, generates an electrical subject image signal corresponding to the light intensity distribution of the subject image, and sends it to the signal amplification circuit 10. send.

The signal amplifier circuit 10 includes an image sensor 9
The subject image signal output from the amplifier is amplified and sent to the focus detection calculation circuit 11. The storage control circuit 12 controls the amplification factor of the signal amplification circuit 10. The focus detection calculation circuit 11 processes the subject image signal by the focus detection calculation described above, and calculates the defocus amount between the image forming surface of the photographing lens 1 and the film equivalent surface 6. Further, the focus detection calculation circuit 11 sends the information of the amplified subject image signal to the storage control circuit 12.
The storage control circuit 12 determines the next charge storage time and the amplification factor, and controls the charge storage operation of the sensor arrays A and B of the image sensor 9. The motor drive control circuit 13 controls the drive direction and drive amount of the motor 14 based on the defocus amount calculated by the focus detection calculation circuit 11. The motor 14 is mechanically coupled to the taking lens 1, and the motor drive control circuit 13 controls the drive amount and drive speed.
The taking lens 1 is brought into the in-focus state.

In the configuration of the above embodiment, the image sensor 9 is the photoelectric conversion element array, the focus detection calculation circuit 11 is the focus detection calculation means, the focus determination means and the focus allowable range change means, and the storage control circuit 12 is the storage control circuit 12. The temperature detecting device 22 constitutes the temperature detecting means and the accumulation controlling means. In addition,
Each of these means is not limited to the above embodiment.

FIG. 2 is a flow chart showing the focus detection operation. The focus detection operation of the embodiment will be described with reference to FIG. Step (hereinafter, simply referred to as S in the drawings) 10
At 0, when the main switch of the camera (not shown) is turned on or the release button (not shown) is half-pressed, the focus detection operation is started. In step 101, the accumulation control of the image sensor 9 is performed for the accumulation time set in the accumulation control circuit 12, and the object image signal is amplified by the signal amplification circuit 10 at the amplification factor set in the accumulation control circuit 12. Since there is no information for performing the storage control immediately after starting the focus detection operation, the storage control is performed according to the initial setting. In step 102, the focus detection calculation circuit 11 sets the permissible focusing range according to the amplification factor of the subject image signal. For example, if the reference allowable focus range is Do, the magnification of the amplification factor is Gn, and the predetermined value is α, the allowable focus range D is calculated by the following equation.

## EQU4 ## D = ± {Do + α * (Gn-1)}

In step 103, the focus detection calculation circuit 11
Thus, the subject image signal is read from the signal amplification circuit 10 and the defocus amount of the taking lens 1 is calculated. In the following step 104, it is determined whether or not the defocus amount calculated by the focus detection calculation circuit 11 is within the focus allowable range set in step 102. If the focus is within the permissible range, the process proceeds to step 106, and if it is out of the permissible range, the process proceeds to step 105. If the focus is out of the allowable range, step 105
Then, according to the defocus amount calculated by the focus detection calculation circuit 11, the motor drive control circuit 13 drives and controls the motor 14 to drive the taking lens 1 to the in-focus position. On the other hand, when the focus is within the allowable range, the shutter release is permitted in step 106. In this way, when the amplification factor of the subject image signal is high, even if the focus detection calculation result varies due to the noise component of the subject image signal, a stable shooting operation becomes possible.

In the above-described embodiment, the so-called focus priority is given and the release permission is given in step 106. However, when the so-called release priority is given, the focus display may be performed on the display device in step 106.

Further, in the above-mentioned embodiment, the permissible focusing range is set based on the amplification factor of the subject image signal, but the permissible focusing range may be set based on the charge accumulation time. In this case, the reference focus allowable range is Do, the reference accumulation time is To,
If the accumulation time is Tn and the predetermined value is β, the focus allowable range D
Is calculated by the following equation.

[Equation 5] D = ± {Do + β * (Tn-To)}, where Tn = To when Tn <To

Further, the focusing allowable range may be set based on the amplification factor of the subject image signal and the accumulation time. In this case, assuming that the standard focus allowable range is Do, the amplification factor magnification is Gn, the predetermined value is α, the reference accumulation time is To, the accumulation time is Tn, and the predetermined value is β, the focus allowable range D is Required by.

## EQU6 ## D = ± {Do + α * (Gn-1) + β * (Tn
-To)}, where Tn <To when Tn <To

Furthermore, the dark current is detected by the image sensor 9
The higher the operating temperature, the higher the temperature.
The permissible focusing range D may be set based on the temperature detected by 2. In this case, the predetermined permissible range D of Equation 5 or Equation 6 is determined by Equation 7 or Equation 8 as a variable β (k) depending on the temperature k, which becomes larger as the temperature increases, respectively.

(7) D = ± {Do + β (k) * (Tn-To)}, where Tn <To when Tn <To

## EQU8 ## D = ± {Do + α * (Gn-1) + β (k) *
(Tn-To)}, where Tn <To when Tn <To

[0027]

As described above, according to the invention of claim 1, the permissible focusing range of the photographing lens is changed according to the amplification factor of the subject image signal, and the focus adjustment state of the focus detection calculation result is changed. Since the in-focus / out-of-focus of the taking lens is determined by comparing with the in-focus permissible range, the amplification factor of the subject image signal increases and the noise component of the subject image signal increases, which enables focus detection. Even if there is a large variation in the calculation result, the focus allowable range is changed to cancel the variation and accurate focus / non-focus determination is made, and the movement of the shooting lens near the focus and the display Focus display is stable. According to the invention of claim 2, the focusing allowable range of the photographing lens is changed according to the charge accumulation time of the photoelectric conversion element array, and the focus adjustment state of the focus detection calculation result is compared with the changed focusing allowable range. Since the in-focus / out-of-focus state of the taking lens is determined by using the charge accumulation time, the noise component of the subject image signal increases, and even if the focus detection calculation result varies greatly, the variation can be reduced. The permissible focus range is changed so as to cancel, and accurate in-focus / out-of-focus determination is made, and the movement of the photographing lens near the in-focus state and the in-focus display on the display are stabilized. According to the invention of claim 3, the permissible focusing range of the photographing lens is changed according to the amplification factor of the subject image signal and the charge accumulation time of the photoelectric conversion element array, and the focus adjustment state of the focus detection calculation result is changed. Since the in-focus / out-of-focus of the taking lens is determined by comparing with the in-focus permissible range, the amplification factor is high and the charge accumulation time is long, so that the subject image output from the photoelectric conversion element array is increased. Even if the noise component of the signal increases and the result of the focus detection calculation fluctuates greatly, the focus allowable range is changed to cancel the fluctuation, and accurate in-focus / out-of-focus determination is made. The movement of the taking lens in the vicinity and the focus display on the display are stable. According to the invention of claim 4, the focus allowable range of the photographing lens is changed according to the ambient temperature of the photoelectric conversion element array, and the focus adjustment state of the focus detection calculation result is compared with the focus allowable range after the change. Since the focus / non-focus of the photographing lens is determined, the ambient temperature rises and the noise component of the dark current of the subject image signal output from the photoelectric conversion element array increases,
As a result, even if the focus detection calculation result largely varies, the focus allowable range is changed so as to cancel the variation, and accurate focus / non-focus determination is performed. The focus display on the display is stable. According to the fifth aspect of the invention, the focus allowable range changed according to the charge accumulation time is corrected based on the ambient temperature of the photoelectric conversion element array, so accurate focus / non-focus determination can be made. The movement of the taking lens near the in-focus state and the in-focus display on the display are stabilized. According to the invention of claim 6,
The permissible focusing range changed according to the amplification factor of the subject image signal and the charge accumulation time of the photoelectric conversion element array is corrected based on the ambient temperature of the photoelectric conversion element array. The focus is determined, and the movement of the taking lens near the focus and the focus display on the display are stabilized.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing a focus detection operation of one embodiment.

FIG. 3 is an explanatory diagram of a subject image signal.

FIG. 4 is a diagram showing an optical system and an image sensor of a phase difference detection type focus detection device.

FIG. 5 is an explanatory diagram of correlation calculation.

FIG. 6 is an explanatory diagram of correlation calculation.

[Explanation of symbols]

 1 Photographic lens 2 Field mask 3 Field lens 6 Equivalent surface of film 7 Bandpass filter 8 Focus detection optical system 9 Image sensor 15 Main mirror 16 Sub-mirror 17 Film surface 18 Finder screen 19 Penta roof prism 20 Eyepiece lens 21, 31 Inverse of aperture opening Projected image 22 Temperature detection device 41, 42 Aperture opening 51, 52 Re-imaging lens

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Claims (6)

[Claims] 1. A photoelectric conversion element array that outputs an object image signal according to a light intensity distribution of an object image, and a luminous flux from an object that has passed through a photographing lens is guided to the photoelectric conversion element array to form the object image. Focus detection optical system, signal amplification means for amplifying a subject image signal output from the photoelectric conversion element array, and a focus adjustment state of the photographing lens is calculated based on the subject image signal amplified by the signal amplification means. And a focus detection calculation unit that compares the focus adjustment state calculated by the focus detection calculation unit with a predetermined focus allowable range.
A focus detection apparatus comprising a focus determination means for determining non-focus, wherein a focus allowable range changing means for changing a focus allowable range of the focus determination means according to an amplification factor of the signal amplification means. A focus detection device comprising: 2. A photoelectric conversion element array that outputs an object image signal according to the light intensity distribution of the object image, and a luminous flux from the object that has passed through a photographing lens is guided to the photoelectric conversion element array to form the object image. A focus detection optical system, a storage control unit that controls the charge storage time of the photoelectric conversion element array, and a focus that calculates the focus adjustment state of the photographing lens based on a subject image signal output from the photoelectric conversion element array. The detection / calculation means and the focus adjustment state calculated by the focus detection / calculation means are compared with a predetermined focusing permissible range to focus / focus the photographing lens.
A focus detection device comprising a focus determination means for determining out-of-focus, wherein a focus allowable range is changed to change a focus allowable range of the focus determination means according to a charge accumulation time of the accumulation control means. A focus detection device comprising means. 3. A photoelectric conversion element array that outputs an object image signal according to the light intensity distribution of the object image, and a luminous flux from the object that has passed through a photographing lens is guided to the photoelectric conversion element array to form the object image. Focus detection optical system, signal amplification means for amplifying a subject image signal output from the photoelectric conversion element array, storage control means for controlling charge storage time of the photoelectric conversion element array, and amplification by the signal amplification means. Focus detection calculation means for calculating the focus adjustment state of the photographing lens based on the subject image signal thus obtained, and the focus adjustment state calculated by the focus detection calculation means compared with a predetermined permissible focusing range. Focus of /
A focus detection device comprising focus determination means for determining out-of-focus, wherein focus determination of the focus determination means is determined according to an amplification factor of the signal amplification means and a charge storage time of the storage control means. A focus detection apparatus comprising a focus allowable range changing means for changing a range. 4. A photoelectric conversion element array that outputs an object image signal according to the light intensity distribution of the object image, and a luminous flux from the object that has passed through a photographing lens is guided to the photoelectric conversion element array to form the object image. Focus detection optical system, focus detection calculation means for calculating the focus adjustment state of the photographing lens based on the subject image signal output from the photoelectric conversion element array, and focus adjustment state calculated by the focus detection calculation means Is compared with a predetermined permissible focusing range,
A focus detection device comprising a focus determination means for determining out-of-focus, wherein a temperature detection means for detecting an ambient temperature of the photoelectric conversion element array, and an ambient temperature detected by the temperature detection means. A focus detection apparatus comprising: a focus allowable range changing unit that changes a focus allowable range of the focus determination unit. 5. The focus detection device according to claim 2, further comprising a temperature detection unit that detects an ambient temperature of the photoelectric conversion element array, and the permissible focusing range change unit is a charge storage time of the storage control unit. The focus detection device is characterized in that the permissible focusing range changed according to the above is corrected based on the ambient temperature detected by the temperature detection means. 6. The focus detection device according to claim 3, further comprising: a temperature detection unit that detects an ambient temperature of the photoelectric conversion element array, wherein the focusing allowable range changing unit includes an amplification factor of the signal amplification unit. A focus detection device, characterized in that the focus allowable range changed according to the charge storage time of the storage control means is corrected based on the ambient temperature detected by the temperature detection means.