JP4608733B2 - Focus detection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a focus detection device that detects a focus adjustment state of a photographing lens such as an autofocus camera or a video.
[0002]
[Prior art]
A focus detection apparatus using a charge storage type image sensor such as a CCD or CMOS is known. With this type of focus detection device, the charge accumulation time of the charge accumulation type image sensor is shortened when the luminance of the subject is high, and conversely, when the luminance is low, the signal level or contrast of the output signal train is always substantially constant. It is controlled to become. Then, the focus detection calculation is performed using this output signal sequence, and the defocus amount (shift amount and shift direction from the in-focus position of the photographing lens) is detected.
[0003]
The subject brightness of the camera usually varies greatly in the range of about Bv-5 to +15 depending on the shooting conditions. In order to cope with such a wide luminance range, it is necessary to control the charge accumulation time in the range of several microseconds to several hundred milliseconds. However, when the charge accumulation time is several hundred milliseconds, the time required for a series of focus detection operations becomes long, and it becomes impossible to follow the moving subject.
[0004]
In order to solve such a problem, a focus detection apparatus including a variable gain amplifier that amplifies an output signal sequence has been proposed (see, for example, Japanese Patent Laid-Open No. 59-140409). This device is equipped with a monitor sensor that monitors the charge accumulation state.After the charge accumulation starts, when the monitor reaches a predetermined level, the accumulation is terminated and the output signal is amplified with a low amplification factor. If the monitor sensor output is low and the brightness is low, the charge accumulation is forcibly terminated, and the gain is set high according to the monitor sensor output at that time to obtain a constant level output signal sequence. ing.
[0005]
There is also known a focus detection device that obtains a constant contrast by increasing the amplification factor when the contrast is low (see, for example, Japanese Patent Laid-Open No. 63-238771).
[0006]
[Problems to be solved by the invention]
However, when the amplification factor of the output signal sequence of the charge storage type image sensor is increased, the noise component included in the output signal is also amplified, so that the S / N ratio of the output signal sequence is lowered. Further, the defocus amount detected based on the output signal sequence having a low S / N ratio includes a lot of errors, resulting in low reliability. This problem is particularly noticeable when the subject has a low contrast. However, if the amplification factor is always set to be low, the focus detection time becomes long for a subject that is not low contrast as described above.
[0007]
An object of the present invention is to obtain a highly reliable defocus amount for a low-contrast subject and to shorten the focus detection time for a high-contrast subject.
[0008]
[Means for Solving the Problems]
The present invention will be described with reference to FIG. 1 showing the configuration of an embodiment.
(1) The invention of claim 1 comprises a plurality of photoelectric conversion elements, a charge storage type photoelectric conversion element array 2 that outputs a signal string corresponding to the light intensity of incident light from each photoelectric conversion element, and a photographing optical system A focus detection optical system 1 that guides a light beam from a subject that has passed through a predetermined region 100 onto the photoelectric conversion element array 2 and forms a subject image on the photoelectric conversion element array 2, and an output signal array of the photoelectric conversion element array 2 A focus detection apparatus including a variable gain amplifying means 3 for amplifying the image and a focus detection calculating means 5 for detecting the focus adjustment state of the imaging optical system 100 by calculating the output signal sequence amplified by the amplifying means 3. Applied. Then, an amplification factor setting unit 7 for setting the amplification factor of the amplification unit 3 to at least a first amplification factor or a second amplification factor lower than the first amplification factor according to the luminance of the subject, and detecting the contrast of the subject Contrast detection means 6 for performing amplification rate setting means 7, A higher threshold is set as the contrast of the subject is higher, and the amplification factor of the amplification means is set to the second amplification factor when the luminance of the subject is equal to or higher than the threshold. The above-mentioned purpose is achieved.
(2) According to a second aspect of the present invention, in the focus detection apparatus according to the first aspect, the charge accumulation time in the photoelectric conversion element is the second gain when the gain is set to the first gain. Shorter than when set to.
[0009]
In the section of the means for solving the above-described problem, a diagram of an embodiment is used for easy understanding of the description. However, the present invention is not limited to the embodiment.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
First, the focus detection operation of the phase difference detection method will be described with reference to FIG.
A light beam incident through the region 101 of the photographing lens 100 passes through the field mask 200, the field lens 300, the aperture opening 401, and the re-imaging lens 501, and passes through a plurality of photoelectric conversion pixels that generate an output corresponding to the light intensity. An image is formed on the A column of the image sensor array 600 arranged in the original shape. Similarly, the light beam incident through the region 102 of the photographing lens 100 passes through the field mask 200, the field lens 300, the aperture opening 402, and the re-imaging lens 502, and forms an image on the B row of the image sensor array 600.
[0011]
A pair of subject images formed on the A and B columns of the image sensor array 600 are close to each other in a so-called front pin state in which the photographing lens 100 forms a sharp image of the subject before the intended focal plane, and on the contrary. In the so-called rear pin state in which the sharp image of the subject is connected behind the focal plane, the subject images are far away from each other. Match. Therefore, the pair of subject images are photoelectrically converted into electric signals by the A and B columns of the image sensor array 600 and converted into electric signals, and these output signal sequences are subjected to a focus calculation process to obtain a relative positional deviation amount between the pair of subject images. Thus, the focus adjustment state of the photographing lens 100, that is, the defocus amount can be obtained.
[0012]
For the image sensor array 600, a charge storage type CCD or CMOS is used. When the luminance of the subject is low and the amount of light incident on the image sensor array 600 is small, the charge accumulation time is lengthened. Conversely, when the luminance of the subject is high and the amount of light incident on the image sensor array 600 is large, the charge accumulation time is shortened. Thus, the signal level of the output signal train of the image sensor array 600 is set to a level suitable for the focus detection calculation process.
[0013]
A variable gain amplifier 700 is provided at the output of the image sensor array 600 to amplify the output signal string at a desired amplification factor. The output signal sequence amplified by the variable gain amplifier 700 is converted into a digital signal and sent to the microcomputer in order to execute a focus detection calculation. At this time, if the signal level of the output signal sequence output from the variable gain amplifier 700 is low, the contrast of the subject cannot be obtained sufficiently. Conversely, if the signal level is too large, the input range of the A / D converter is exceeded. Cannot convert analog / digital correctly. If the accumulation time is too long, output saturation occurs in the image sensor array 600, and an output signal string representing a subject image cannot be obtained. Therefore, it is necessary to appropriately set the charge accumulation time of the image sensor array 600 and the amplification factor of the variable gain amplifier 700.
[0014]
Next, a calculation processing method for obtaining the defocus amount will be described.
Each of the A column and the B column of the image sensor array 600 includes a plurality of photoelectric conversion pixels, and a plurality of output signal columns a [1],..., A [n] and b [1],. b [n] is output (see FIGS. 6a and 6b). Then, the correlation calculation is performed while the data in a predetermined range of the pair of output signal sequences is relatively shifted by L by predetermined data. If the maximum shift number is lmax, the range of L is from −1max to + 1max. Specifically, the correlation amount C [L] is calculated by the following equation.
[Expression 1]
C [L] = Σ | a [i + L] −b [i] |
In Equation 1, Σ represents the sum of i = k (first term) to r (final term), and L = −lmax,..., −2, −1, 0, +1, +2, + lmax.
[0015]
In Equation 1, L is an integer corresponding to the shift amount of the data string as described above. The first term k and the last term r are changed depending on the shift amount L as shown in the following equation, for example.
[Expression 2]
When L ≧ 0,
k = k0 + INT {−L / 2},
r = r0 + INT {−L / 2}
When L <0,
k = k0 + INT {(− L + 1) / 2},
r = r0 + INT {(−L + 1) / 2}
In Equation 2, k0 and r0 are the first term and the last term when the shift amount L is zero.
[0016]
FIG. 7 shows a combination for calculating the absolute value of the difference between the signals in the A column and the B column in Equation 1 when the first term k and the final term r are changed by Equation 2, and the calculation range in which the absolute value of the difference is added. Shown in As shown in FIG. 7, as the shift amount L changes, the ranges used for the correlation calculation between the A column and the B column shift in opposite directions. There is also a method in which the first term k and the last term r are made constant regardless of the shift amount L. In this case, the range used for correlation calculation of one column is always constant, and only the other column is shifted. Since the relative positional deviation amount is the shift amount L when the pair of data match, the shift amount that gives the minimum correlation amount is detected from the correlation amount C [L] thus obtained. 4 is multiplied by a constant determined by the pitch width of the photoelectric conversion pixels of the optical system and the image sensor array 600 shown in FIG. Therefore, the larger the maximum shift number lmax, the greater the defocus amount that can be detected.
[0017]
By the way, the correlation amount C [L] is a discrete value as shown in FIG. 6C, and the minimum unit of the defocus amount that can be detected is the photoelectric conversion pixel of the A column and the B column of the image sensor array 600. It is limited by the pitch width. Therefore, a method has been proposed in which a true minimum value Cex is newly calculated by performing an interpolation operation using a discrete correlation amount C [L], and fine focus detection is performed (for example, Japanese Patent Laid-Open No. Sho 60). No. 037513). This method uses the correlation value C [Le], which is the minimum value shown in FIG. 5, and the correlation values C [Le + 1] and C [Le-1] at the shift amounts on both sides thereof, and the true minimum value Cex. The shift amount Ls that gives is calculated by Equation 3 and Equation 4.
[Equation 3]
DL = (C [Le-1] -C [Le + 1]) / 2
Cex = C [Le]-| DL |,
E = MAX {C [Le + 1] -C [Le], C [Le-1] -C [Le]}
[Expression 4]
Ls = Le + DL / E
In Equation 3, MAX {Ca, Cb} indicates that the larger one of Ca and Cb is selected.
[0018]
The defocus amount DF is calculated by the mathematical formula 5 from the shift amount Ls.
[Equation 5]
DF = Kf · Ls
In Equation 5, Kf is a constant determined by the pitch width of the photoelectric conversion pixels of the optical system and the image sensor array 600 shown in FIG. It is necessary to determine whether the defocus amount DF thus obtained truly indicates the defocus amount or due to fluctuation of the correlation amount due to noise or the like. When the condition shown in Equation 6 is satisfied, the defocus amount The quantity DF is assumed to be reliable.
[Formula 6]
E> E1 & Cex / E <G1
E1 and G1 in Equation 6 are predetermined threshold values. The numerical value E indicates how the correlation amount changes, and 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 is a difference when a pair of data most closely matches, and is originally 0. However, due to the influence of noise and further, parallax is generated between the area 101 and the area 102, a subtle difference occurs between the pair of subject images and does not become zero. Since the influence of noise and subject image differences is smaller as the subject contrast is higher, Cex / E is used as a numerical value representing the degree of coincidence between a pair of data. Of course, the closer Cex / E is to 0, the higher the degree of coincidence of the pair of data and the higher the reliability.
[0019]
When it is determined that there is reliability, the photographing lens 100 is driven or displayed based on the defocus amount DF. When the reliability is low, the calculated defocus amount DF includes many error components, so that the reproducibility is low, and lens driving and display become unstable. Therefore, the determination is performed using a predetermined threshold value as described above. There is also a method in which the contrast of the subject is calculated by calculating the sum of adjacent differences in the output signal sequence instead of the numerical value E, and the reliability is determined using this.
[0020]
FIG. 1 is a diagram showing the configuration of an embodiment of the invention.
The focus detection optical system 1 includes the field mask 200, the field lens 300, the aperture openings 401 and 402, and the re-imaging lenses 501 and 502 shown in FIG. 4, and the light from the subject that has passed through the photographing lens 100 is image sensor. Lead to 2. The image sensor 2 is composed of a pair of photoelectric conversion element rows A and B as in the image sensor array 600 shown in FIG. 4, and output signal rows a [i] and b [i] (i = 1 to n). ) Is output.
[0021]
The variable gain amplifier 3 amplifies the output signal sequences a [i] and b [i] of the image sensor 2 with the amplification factor set by the accumulation condition setting unit 7. In this embodiment, three types of amplification factors of 1, 4, and 8 can be set.
[0022]
The A / D converter 4 converts the output signal sequences a [i] and b [i] amplified by the variable gain amplifier 3 into digital signals. The focus detection calculation unit 5 performs focus detection calculation according to the above Equations 1 to 6 using the output signal sequences a [i] and b [i] converted into digital signals by the A / D converter 4, and the defocus amount DF is calculated.
[0023]
The contrast determination unit 6 evaluates the contrast of the subject using the numerical value E calculated by the focus detection calculation unit 5. The accumulation condition setting unit 7 is based on the output signal sequence a [i], b [i], the numerical value E calculated by the focus detection calculation unit 5, the accumulation time at this time, and the amplification factor of the variable gain amplifier 3. The charge accumulation time at the next accumulation and the gain of the variable gain amplifier 3 are set.
[0024]
The accumulation control unit 8 accumulates charges in the image sensor 2 for the accumulation time set by the accumulation condition setting unit 7. The lens driving unit 9 drives the photographing lens 100 based on the defocus amount DF calculated by the focus detection calculation unit 5. The focus detection calculation unit 5, the contrast determination unit 6, the accumulation condition setting unit 7, and the accumulation control unit 8 are formed by a microcomputer or the like.
[0025]
FIG. 2 is a flowchart showing the focus detection operation. The focus detection operation of the embodiment will be described with reference to this flowchart.
When the focus detection operation is started by operating a switch (not shown) or the like, first, in step 1, the storage condition setting unit 7 sets an appropriate initial value for the initial charge storage time IT. Note that the initial value of the accumulation time IT may be set based on the photometric result of the photometric device. In the subsequent step 2, the accumulation condition setting unit 7 sets the amplification factor for amplifying the first output signal sequence to 4 times, which is a medium amplification factor.
[0026]
In step 3, charge accumulation of the image sensor 2 is started by the accumulation control unit 8. In step 4, the process waits for the time IT to elapse from the start of storage, and proceeds to step 5 after the IT time elapses. In step 5, the accumulation control unit 8 ends the charge accumulation of the image sensor 2. In step 6, the output signal sequence output in time series from the image sensor 2 by the variable gain amplifier 3 is amplified by the set gain Gn, and the amplified output signal sequence is converted to a digital signal by the A / D converter 4. To do.
[0027]
In step 7, the focus detection calculation unit 5 calculates the correlation amount by the above formulas 1 and 2, and in step 8 the focus detection calculation unit 5 calculates the defocus amount DF and the numerical value E corresponding to the contrast by the above formulas 3-5. To do. In the subsequent step 9, the focus detection calculation unit 5 determines the reliability of the defocus amount DF according to the above equation 6. In Step 10, if the obtained defocus amount DF is reliable, the process proceeds to Step 11, and if not reliable, the process proceeds to Step 13.
[0028]
If the defocus amount DF is reliable, it is determined in step 11 whether or not the taking lens 100 is in focus. If it is in focus, the process is terminated. In this in-focus determination, for example, in-focus is determined when the amount of defocus obtained in step 8 is within a predetermined value. In step 12, the photographing lens 100 is driven based on the defocus amount DF calculated by the focus detection calculation unit 5 by the lens driving unit 9.
[0029]
In step 13, the accumulation condition setting unit 7 detects a value (a value indicating the highest luminance) Pk indicating the maximum value from the output signal sequences a [i] and b [i] (i = 1 to n).
[0030]
In subsequent step 14, the contrast of the subject is evaluated as follows based on the numerical value E calculated by the focus detection calculation unit 5 by the contrast evaluation unit 6.
[Expression 7]
When E ≧ Ca: High contrast,
When Ca> E ≧ Cb: Medium contrast,
When Cb> E: Low contrast,
However, it is assumed that Ca> Cb.
[0031]
In step 15, the accumulation condition setting unit 7 sets a scheduled gain Gf at the next accumulation of the variable gain amplifier 3 based on the contrast of the subject evaluated by the contrast evaluation unit 6.
[Equation 8]
For high contrast: Gf = 8 times
Medium contrast: Gf = 4 times
For low contrast: Gf = 1x
[0032]
Next, at step 16, the storage condition setting unit 7 updates the storage time IT according to the following equation based on the storage time IT, the gain Gn, the peak value Pk (step 13), and the planned gain Gf (step 15).
[Equation 9]
IT = IT · (Gn / Gf) · (Vp / Pk)
Here, Vp is a target value of the peak value. The peak value of the output signal sequence obtained by performing charge accumulation with the accumulation time IT obtained by Equation 9 and amplifying with the expected gain Gf should be Vp. When the planned gain Gf is high, the accumulation time is short, and when the planned gain Gf is low, the accumulation time IT is long.
[0033]
In step 17, the scheduled gain Gf updated in step 15 is set in the gain Gn, and the process returns to step 3. Then, charge accumulation is performed for the accumulation time set in step 16, and a series of focus detection operations for amplifying the output signal sequence with the amplification factor set in step 17 is repeated.
[0034]
In this way, when the contrast of the subject is low, a low amplification factor is preferentially set, so that focus detection calculation can be performed with an output signal sequence having a good S / N ratio, and stable and highly reliable data can be obtained. A focus amount can be obtained. In addition, when the contrast of the subject is high and is not easily affected by noise, a high amplification factor is set with priority, so that the charge accumulation time is shortened and the focus detection time can be shortened.
[0035]
<< Modification of Embodiment of Invention >>
Next, another setting example of the planned gain Gf will be described.
In the above-described embodiment, an example in which the expected gain Gf at the next accumulation is set according to the contrast in step 15 of FIG. In this modification, the subject luminance is compared with the amplification factor switching parameters EL and EM (EL> EM), and when the subject luminance is equal to or higher than EL, a low amplification factor of 1 is selected, the subject luminance is less than EL, and EM In the above case, a medium amplification factor of 4 is selected, and when the subject brightness is less than EM, a high amplification factor of 8 is selected. Further, the amplification factor switching parameters EL and EM are changed based on the contrast, and the low amplification factor is preferentially selected when the contrast is low, and the high amplification factor is preferentially selected when the contrast is high.
[0036]
FIG. 3 is a flowchart showing the setting operation of the planned gain Gf according to the modification. This setting operation is executed in step 15 of FIG.
In step 31, the current charge accumulation time IT (step 1 in FIG. 2), the current gain Gn (step 2 in FIG. 2), the contrast evaluation result (step 14 in FIG. 2), and the maximum value Pk (step in FIG. 2). Based on 13), the subject brightness OB is calculated by the following equation.
[Expression 10]
OB = Pk / (IT · Gn)
[0037]
In steps 32 and 34, the result of the contrast evaluation performed in step 14 of FIG. 2 is confirmed. If the contrast is low, the process proceeds to step 33. If the contrast is medium, the process proceeds to step 36. If the contrast is high, the process proceeds to step 35. move on. In the case of low contrast, the amplification factor switching parameters EL and EM are set as follows in step 33, and the process proceeds to step 37.
## EQU11 ##
EL = Ea1,
EM = Eb1
[0038]
In the case of medium contrast, the amplification factor switching parameters EL and EM are set as follows in step 36, and the process proceeds to step 37.
[Expression 12]
EL = Ea2,
EM = Eb2
[0039]
In the case of high contrast, the amplification factor switching parameters EL and EM are set as follows in step 35, and the process proceeds to step 37.
[Formula 13]
EL = Ea3
EM = Eb3
[0040]
Here, Ea1, Ea2, Ea3, Eb1, Eb2, and Eb3 have the following relationship.
[Expression 14]
Ea1 <Ea2 <Ea3
Eb1 <Eb2 <Eb3
In this way, a parameter representing lower luminance is set as the contrast becomes lower.
[0041]
In steps 37 and 39, the subject brightness OB is compared with the amplification factor switching parameters EL and EM. If the brightness is higher than EL, the process proceeds to step 38. If less than EL and greater than EM, the process proceeds to step 41. If so, go to Step 40. If the subject brightness OB is equal to or higher than EL, the scheduled gain Gf is set to 1 which is a low gain in step 38, and the process proceeds to step 16 in FIG. If it is less than EL but greater than or equal to EM, in step 41, the planned amplification factor Gf is set to 4 times, which is a medium amplification factor, and the process proceeds to step 16 in FIG. Further, when the subject brightness OB is less than EM, the process proceeds to step 40, the scheduled gain Gf is set to 8 times that is a high gain, and the process proceeds to step 16 in FIG.
[0042]
Normally, a low gain is set when the subject brightness is high, and a high gain is set when the subject brightness is low so that an output signal sequence of the image sensor 2 at a substantially constant level can be obtained even if the subject brightness changes. Set. However, according to this modification, a high amplification factor is set when the subject contrast is high even when the subject luminance is high, and a low amplification factor is set when the subject contrast is low even when the subject luminance is low. Therefore, a low amplification factor is preferentially set when the contrast of the subject is low, regardless of the subject brightness, so that focus detection calculation can be performed with an output signal sequence having a good S / N ratio, and stable and reliable. A high defocus amount can be obtained. In addition, when the contrast of the subject is high and it is difficult to be affected by noise, a high amplification factor is preferentially set, so that the charge accumulation time is shortened and the focus detection time can be shortened.
[0043]
In the above-described modification of the embodiment, an example in which a high amplification factor is set when the subject contrast is high even when the subject luminance is high is shown. However, in such a case, the low amplification factor is kept. May be. In that case, the focus detection time cannot be shortened.
[0044]
In the above-described embodiment and its modification, the example in which the contrast of the subject is detected based on the numerical value E of the focus detection calculation result is shown. However, the method for detecting the contrast of the subject is not limited to the above-described method. The difference between the maximum value and the minimum value of the output signal level may be detected as the contrast of the subject by using one of the output signal trains A and B of the image sensor 2, or the CdS cell nonlinearity The contrast of the subject may be detected using the property, that is, the contrast dependency.
[0045]
Further, in the modification of the embodiment described above, based on the charge accumulation time IT of the image sensor 2, the gain Gn of the variable gain amplifier 3, and the maximum value Pk of the output signal sequence of the image sensor 2, 10 shows an example in which the subject brightness OB is calculated. According to the subject luminance detection method of this modification, there is no need to install a photometric device that measures the subject luminance, but of course, the subject luminance measured by the photometric device may be used in a camera equipped with the photometric device.
[0046]
Since the charge accumulation time IT calculated in step 16 in FIG. 2 may be too long, the charge accumulation time IT may be limited to a predetermined time.
[0047]
In the above-described embodiment and its modification, an example in which the gain of the variable gain amplifier 3 is set to three stages has been described, but it may be two stages or four or more stages.
[0048]
In the above-described embodiment, an example is shown in which the contrast evaluation is performed using the numerical value E. However, the contrast evaluation may be performed using the sum of adjacent differences in the output signal sequence instead of the numerical value E. Alternatively, contrast evaluation may be performed using Cex / E calculated by Expression 6, and in that case, the lower the gain, the higher the numerical value.
[0049]
Furthermore, although the monitor sensor is not included in the configuration of the above-described embodiment, the present invention is also applied to a focus detection apparatus (see, for example, Japanese Patent Laid-Open No. 59-140409) provided with a monitor sensor. Can do. In this case, based on the contrast evaluation results, the longest accumulation time is shortened when the contrast is high, and the longest accumulation time is changed when the contrast is low. As a result, a high gain is preferentially set when the contrast is high. At the time of contrast, a low amplification factor is preferentially set, and the same operation and effect are obtained as in the operation of the embodiment described above.
[0050]
【The invention's effect】
Less than As explained above Book According to the invention , Covered When the contrast of the subject is low, a low amplification factor is preferentially set, so that focus detection calculation can be performed with an output signal sequence having a good S / N ratio, and a stable and reliable defocus amount can be obtained. Obtainable. In addition, when the contrast of the subject is high and it is difficult to be affected by noise, a high amplification factor is preferentially set, so that the charge accumulation time is shortened and the focus detection time can be shortened.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an embodiment.
FIG. 2 is a flowchart illustrating a focus detection operation according to an embodiment.
FIG. 3 is a flowchart showing a method for setting a planned amplification factor according to a modification.
FIG. 4 is a flowchart showing a configuration of a focus detection optical system.
FIG. 5 is a diagram for explaining a focus detection calculation;
FIG. 6 is a diagram for explaining a focus detection calculation;
FIG. 7 is a diagram for explaining a correlation calculation.
[Explanation of symbols]
1 Focus detection optical system
2 Image sensor
3 Variable gain amplifier
4 A / D converter
5 Focus detection calculator
6 Contrast evaluation section
7 Accumulation condition setting section
8 Accumulation control unit
9 Lens drive unit
100 Photography lens

Claims (2)

A charge storage type photoelectric conversion element array that includes a plurality of photoelectric conversion elements and outputs a signal string corresponding to the light intensity of incident light from each photoelectric conversion element;
A focus detection optical system that guides a light beam from a subject that has passed through a predetermined region of the photographing optical system onto the photoelectric conversion element array, and forms a subject image on the photoelectric conversion element array;
Amplifying means having a variable amplification factor for amplifying an output signal string of the photoelectric conversion element string;
In a focus detection apparatus comprising a focus detection calculation means for calculating a focus adjustment state of the photographing optical system by performing a calculation process on the output signal sequence amplified by the amplification means,
Amplification factor setting means for setting the amplification factor of the amplification means to at least a first amplification factor or a second amplification factor lower than the first amplification factor according to the luminance of the subject;
Contrast detection means for detecting the contrast of the subject,
The amplification factor setting means sets a larger threshold value as the contrast of the subject is higher, and sets the amplification factor of the amplification means to the second amplification factor when the luminance of the subject is equal to or higher than the threshold value. A focus detection device. The focus detection apparatus according to claim 1,
The focus detection apparatus characterized in that the charge accumulation time in the photoelectric conversion element is shorter when the amplification factor is set to the first amplification factor than when the amplification factor is set to the second amplification factor.

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