JP3550601B2 - Focus detection device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a focus detection device that detects a focus adjustment state of a photographing lens.
[0002]
[Prior art]
A pair of images having a parallax of a subject is guided on a pair of image sensors, a relative shift amount between the pair of images is calculated based on image outputs of these image sensors, and a focus adjustment state of the photographing lens is detected. 2. Description of the Related Art A phase difference detection type focus detection device is known.
An outline of this type of focus detection device will be described with reference to FIG.
The light beam from the subject incident through the area 21 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 41, and the re-imaging. The light passes through a focus detection optical system 8 composed of a lens 51 and forms an image on a sensor array 9A of the image sensor 9. Similarly, the luminous flux from the subject incident 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, The light passes through the focus detection optical system 8 composed of the re-imaging lens 52 and forms an image on the sensor array 9B of the image sensor 9.
Here, the size of the area 21 of the taking lens 1 is equal to the back projection image of the aperture opening 41 by the field lens 3, and similarly, the size of the area 31 is the back projection image of the aperture opening 42 by the field lens 3. equal.
[0003]
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 such that the sharp image of the subject formed by the photographing lens 1 is located before the planned focal plane. In a so-called front focus state where an image is formed, they approach each other, and conversely, in a so-called rear focus state where an image is formed behind a predetermined focal plane, they move away from each other. When a sharp image of a subject formed by the photographing lens 1 forms an image on a predetermined focal plane, that is, when the subject is in focus, the subject images on the sensor arrays 9A and 9B of the image sensor 9 relatively match.
Therefore, the secondary image of the pair of subject images formed by the focus detection optical system 8 is photoelectrically converted by the sensor arrays 9A and 9B of the image sensor 9 and converted into electric signals, and the pair of subject image signals are correlated. By processing and calculating the relative position of the secondary image of the pair of subject images, the focus adjustment state of the photographing lens 1, here, the amount away from the in-focus state and its direction (hereinafter, referred to as defocus amount) To detect.
Note that the focus detection area is a portion where the sensor rows 9A and 9B of the image sensor 9 are back-projected by the focus detection optical system 8 and overlapped near the planned focal plane.
[0004]
Next, an arithmetic processing method for obtaining the defocus amount will be described.
Each of the sensor rows 9A and 9B of the image sensor 9 includes a plurality of photoelectric conversion elements, and as shown in FIGS. 5A and 5B, a plurality of photoelectric conversion outputs a1. . . an, b1. . . bn is output. Then, a 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 the following equation.
(Equation 1)
C (L) = Σ | ai−bj |
Here, Σ represents the summation operation of i = k to r. L is an integer corresponding to the shift amount of the data string, ji = L, L = −lmax,. . . , -2, -1, 0, 1, 2,. . . , Lmax.
In Equation 1, the first term k and the last term r may be changed depending on the shift amount L.
[0005]
Among the correlation amounts C (L) obtained in this manner, the value obtained by multiplying the shift amount giving the minimum correlation value by a constant determined by the pitch width of the photoelectric conversion elements of the optical system and the image sensor shown in FIG. It becomes the focus amount. However, the correlation amount C (L) is a discrete value as shown in FIG. 5C, and the minimum unit of the detectable defocus amount is the pitch of the photoelectric conversion elements of the sensor rows 9A and 9B of the image sensor 9. It is limited by width.
Therefore, a method of calculating a new minimum value Cex by performing an interpolation operation based on the discrete correlation amount C (L) and performing accurate focus detection has been proposed in Japanese Patent Application Laid-Open No. 60-37513. . This is, as shown in FIG. 6, a method of calculating the correlation value C (0), which is the minimum value, and the correlation amounts C (1), C (-1) with the shift amounts on both sides of the correlation value. The given shift amount Fm and defocus amount DF are obtained by the following equations.
(Equation 2)
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)}]
Here, MAX {Ca, Cb} means selecting the larger one of Ca and Cb, and Kf is a constant determined by the pitch width of the photoelectric conversion element of the optical system and the image sensor 9 shown in FIG. .
[0006]
It is necessary to determine whether the defocus amount obtained in this way truly indicates the defocus amount or whether the defocus amount is due to fluctuations in the correlation amount due to noise or the like. There is.
(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 the images, and the closer to 0, the higher the reliability. Will be high. Then, when it is determined that there is reliability, the photographing lens 1 is driven based on the defocus amount DF.
[0007]
The output level of the subject image signal photoelectrically converted by the sensor arrays 9A and 9B of the image sensor 9 differs depending on the brightness of the subject. Therefore, it is necessary to amplify the subject image signal so that the subject image signal is at a level suitable for the focus detection calculation regardless of the brightness of the subject. Further, by controlling the charge accumulation time, the subject image signal can be set to a level suitable for the focus detection calculation.
By repeatedly performing the focus detection operation using the above-described phase difference detection method, the defocus amount of the photographing lens is repeatedly detected. When it is determined that the detected defocus amount is reliable, the photographing lens is driven based on the detected defocus amount, and the focus adjustment state of the photographing lens is defocused or defocused. Drive is performed until the focus amount is reached.
Further, even after it is determined that the focus adjustment state of the photographing lens is in focus or a defocus amount that can be regarded as the in-focus state, the focus adjustment state of the photographing lens is in the focused state by repeatedly performing the focus detection operation. When it is determined that the defocus amount has exceeded the defocus amount that can be considered, the imaging lens can be driven immediately until the focus or the defocus amount that can be considered as the focused state is reached.
As described above, by repeatedly performing the focus detection operation, the photographing lens always maintains the in-focus state.
[0008]
[Problems to be solved by the invention]
However, noise components from various electric circuits and noise components due to dark current of photoelectric conversion elements are randomly superimposed on the subject image signals output from the sensor arrays 9A and 9B of the image sensor 9 for each photoelectric conversion element. are doing. It is known that the dark current of a photoelectric conversion element increases as the operating temperature increases.
Therefore, for example, when the subject image signals output from the sensor arrays 9A and 9B of the image sensor 9 are amplified to a level suitable for focus detection calculation by a signal amplification circuit, the subject image signals are superimposed on the subject image signals as well as the subject image signals. Noise component is also amplified.
[0009]
This problem will be described in detail with reference to FIG.
The graph shown in FIG. 3 is a diagram illustrating a state in which a noise component is superimposed on the subject image signal. In the figure, the vertical axis indicates the magnitude of the signal output, and the dashed line with v indicates the output level suitable for the focus detection calculation. The horizontal axis represents the photoelectric conversion elements a1. . . Indicates the arrangement of an. Hereinafter, it is assumed that the subject image signal includes a signal component of the subject image and a noise component, and these are referred to as a subject image component and a noise component, respectively.
3 (a), (b) -1 and (c) -1 show the signal outputs before the amplification of the subject image signal, and FIGS. 3 (b) -2 and (c) -2 show the signal outputs after the amplification of the subject image signal. 3 shows the signal output. In the graph shown in FIG. 3, An1, Bn1, Bn2, Cn1, and Cn2 represent the magnitude of the noise component, and As1, Bs1, Bs2, Cs1, and Cs2 represent the magnitude of the subject image component.
Since the output signal from the image sensor 9 shown in FIG. 3A is at an appropriate level for the focus detection calculation, there is no need to amplify this subject image signal (amplification factor is 1). On the other hand, the output of the subject image signal shown in FIG. 3B-1 is about half of the output of the subject image signal of FIG. 3A. It is necessary to amplify by a factor of two. FIG. 3B-2 shows the result of amplification at a double amplification rate. Since the size Bs1 of the subject image component shown in FIG. 3B-1 is doubled, Bs2 is about twice as large as Bs1. However, since the noise component is also amplified in the same manner as 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.
[0010]
Similarly, the output of the subject increase signal shown in FIG. 3 (c) -1 is about 1/4 of the output of the subject increase signal shown in FIG. 3 (a). Need to be amplified with an amplification factor of about 4 times. FIG. 3 (c) -2 shows the result of amplification at a 4-fold amplification rate. 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 also amplified in the same manner as the subject image component, Cn1 is about four times as large as Cn2.
That is, the ratio of the noise component Cn2 to the subject image signal Cs2 in FIG. 3C-2 is larger than the ratio of the noise component Bn2 to the subject image signal Bs2 in FIG.
From the above, it can be seen that as the amplification factor for the subject image signal increases, the ratio of the noise component to the subject image component increases.
Since the above-mentioned noise appears at random in the plurality of photoelectric conversion elements of the pair of sensor rows 9A and 9B of the image sensor 9, the above-described correlation operation has a great effect on the degree of coincidence of the pair of secondary images. In addition, the focus detection calculation results greatly vary.
[0011]
Also, when the accumulation time is increased, the noise component increases. This will be described in detail with reference to FIG. Here, FIGS. 3 (a), (b) -1, and (c) -1 assume that electric charges are accumulated in the same accumulation time, and FIGS. 3 (b) -2 and (c) -2 show the figures. It is assumed that charge accumulation is performed by setting an accumulation time during which the subject image signals shown in 3 (b) -1 and (c) -1 have output levels suitable for focus detection calculation. Also, An1, Bn1, Bn2, Cn1, and Cn2 represent the magnitude of the dark current, and the other symbols are as described above.
In FIG. 3A, it is assumed that charge accumulation is performed during an accumulation time when the output of the image sensor 9 is at a level suitable for the focus detection calculation. The output of the subject image signal shown in FIG. 3B-1 is approximately equal to the output of the subject image signal of FIG. Half. Therefore, in the case of FIG. 3 (b) -1, it is necessary to perform the accumulation in about twice as long as in FIG. 3 (a) in order to make the output level suitable for the focus detection calculation. FIG. 3B-2 shows the result of performing the accumulation for twice the accumulation time. The size Bs2 of the subject image component shown in FIG. 3B-2 is about twice as large as Bs1 because the accumulation is performed in twice the accumulation time. However, since the dark current is also accumulated in twice the accumulation time, Bn1 is about twice as large as Bn2.
That is, it can be seen that the ratio of the dark current Bn2 to the subject image component Bs2 in FIG. 3B-2 is larger than the ratio of the dark current An1 to the subject image component As1 in FIG.
[0012]
Similarly, the output of the subject image signal shown in FIG. 3 (c) -1 is about １ ／ of the output of the subject image signal shown in FIG. 3 (a), so that the output level is suitable for focus detection calculation. Needs to be accumulated in about four times the accumulation time. FIG. 3C-2 shows the result of accumulating the electric charges in four times the accumulation time. The size Cs2 of the subject image component shown in FIG. 3C-2 is about four times Cs2 since Cs1 is accumulated for four times the accumulation time. However, since the dark current is also accumulated in four times as long as the accumulation time, Cn1 is about four times 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.
From the above, it can be seen that the ratio of the dark current to the subject image component increases as the accumulation time increases.
That is, even when the accumulation time is lengthened, the noise component of the dark current occupying the subject image signal increases. Therefore, when the above-described correlation operation is performed, the degree of coincidence between the paired secondary images is greatly affected. It will vary greatly.
[0013]
As described above, the focus detection calculation result fluctuates due to the noise component superimposed on the subject image signal, and even after the photographing lens is once focused, it is finely driven in the vicinity of the in-focus state. Is also unstable, giving the photographer annoyance. In addition, in the case of so-called focusing priority, the focus detection calculation result fluctuates due to the superposition of noise components, and the shutter release is performed even when the shooting lens is in the vicinity of focus. You will be banned and you may miss a photo opportunity.
[0014]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a focus detection device that performs accurate focus detection while eliminating the influence of a noise component superimposed on a subject image signal.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes a photoelectric conversion element array that outputs a subject image signal according to a light intensity distribution of a subject image, and a photoelectric conversion element that outputs a light flux from a subject that has passed through a photographic lens. A focus detection optical system that guides the subject image to the column, forms an image of the subject, a signal amplifying unit that amplifies a subject image signal output from the photoelectric conversion element row, and a subject image signal amplified by the signal amplifying unit. Focus detection calculating means for calculating the focus adjustment state of the photographic lens, and comparing the focus adjustment state calculated by the focus detection calculation means with a predetermined allowable focus range to focus or defocus the photographic lens. A focus detection device comprising: The higher the Focusable range of the focus determination means So that It is provided with a focusing allowable range changing means for changing.
According to a second aspect of the present invention, a photoelectric conversion element array for outputting a subject image signal according to a light intensity distribution of a subject image, and a light beam from a subject that has passed through a photographic lens are guided to the photoelectric conversion element row to convert the subject image. A focus detection optical system that forms an image; an accumulation control unit that controls a charge accumulation 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 for comparing the focus adjustment state calculated by the focus detection calculation unit with a predetermined allowable focus range to determine whether the photographing lens is in focus or out of focus. A focus detection device, wherein the charge storage time of the storage control means is The longer Focusable range of the focus determination means So that It is provided with a focusing allowable range changing means for changing.
According to a third 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 beam from the subject that has passed through a photographic lens is guided to the photoelectric conversion element row to convert the subject image. A focus detection optical system that forms an image; a signal amplifying unit that amplifies a subject image signal output from the photoelectric conversion element array; an accumulation control unit that controls a charge accumulation time of the photoelectric conversion element array; Focus detection calculating means for calculating the focus adjustment state of the photographing lens based on the subject image signal amplified by the above, and comparing the focus adjustment state calculated by the focus detection calculation means with a predetermined in-focus allowable range, A focus detection device comprising: focus determination means for determining whether the photographing lens is in focus or out of focus, wherein the focus is determined in accordance with an amplification factor of the signal amplification means and a charge accumulation time of the accumulation control means. Size Change the focus allowable range of means However, the higher the amplification rate and the longer the charge accumulation time, the wider the focusing allowable range. And a focus permissible range changing unit.
According to a fourth aspect of the present invention, a photoelectric conversion element array that outputs a subject image signal according to a light intensity distribution of a subject image, and a light beam from a subject that has passed through a photographic lens are guided to the photoelectric conversion element row to convert the subject image. A focus detection optical system for forming an image; 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 determining unit for comparing the adjustment state with a predetermined allowable focus range to determine whether the photographing lens is in focus or out of focus. Temperature detecting means to be detected and the ambient temperature detected by the temperature detecting means The higher the Focusable range of the focus determination means So that Focusing range changing means for changing.
6. The focus detection device according to claim 5, further comprising a temperature detection unit for detecting an ambient temperature of the photoelectric conversion element array, wherein the focus allowable range changed by the focus allowable range changing unit in accordance with 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 a temperature detection unit for detecting an ambient temperature of the photoelectric conversion element array, wherein the focus allowable range changing unit changes an amplification factor of the signal amplification unit and a charge accumulation of the accumulation control unit. The focus permissible range changed according to time is corrected based on the ambient temperature detected by the temperature detecting means.
[0016]
[Action]
In the focus detection device according to the first aspect, the amplification factor of the subject image signal The higher the Focusing range of shooting lens So that Then, the focus adjustment state of the focus detection calculation result is compared with the changed allowable focus range to determine whether the photographing lens is in focus or out of focus. As a result, even if the amplification factor of the subject image signal increases, the noise component of the subject image signal increases, and even if the focus detection calculation results vary widely, the allowable focus range is set so as to cancel the variation. Wide Since the focus is changed, an 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 by the display unit are stabilized.
In the focus detection device according to the second aspect, the charge accumulation time of the photoelectric conversion element array The longer Focusing range of shooting lens So that Then, the focus adjustment state of the focus detection calculation result is compared with the changed focus allowable range to determine whether the photographing lens is in focus or out of focus. As a result, even if the charge accumulation time is prolonged and the noise component of the subject image signal increases, and the focus detection calculation result greatly varies, the allowable focus range is set so as to cancel the variation. Wide Since the focus is changed, an 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 by the display unit are stabilized.
In the focus detection device according to the third aspect, the amplification factor of the subject image signal Is higher, Charge accumulation time of photoelectric conversion element row Is longer, Focusing range of shooting lens So that Then, the focus adjustment state of the focus detection calculation result is compared with the changed allowable focus range to determine whether the photographing lens is in focus or out of focus. As a result, the amplification factor increases, the charge accumulation time increases, the noise component of the subject image signal output from the photoelectric conversion element array increases, and even if the focus detection calculation results vary widely, the variations are canceled. Focus tolerance Wide Since the focus is changed, an 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 by the display unit are stabilized.
In the focus detection device according to the fourth aspect, the ambient temperature of the photoelectric conversion element row The higher the Focusing range of shooting lens So that Then, the focus adjustment state of the focus detection calculation result is compared with the changed allowable focus range to determine whether the photographing lens is in focus or out of focus. As a result, the noise component of the dark current of the subject image signal output from the photoelectric conversion element array increases due to an increase in the ambient temperature, and even when the focus detection calculation result greatly varies, the focus tolerance is set so as to cancel the variation. Range Wide Since the focus is changed, an 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 by the display unit are stabilized.
According to a fifth aspect of the present invention, the allowable focus 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 taking lens near the in-focus state and the in-focus display by the display unit are stabilized.
According to another aspect of the present invention, 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 taking lens near the in-focus state and the in-focus display on the display are stabilized.
[0017]
【Example】
An embodiment 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 cross-sectional view of a single-lens reflex camera provided with a focus detection device. The same reference numerals are given to the same devices as those shown in FIG. 4, and the description is omitted.
In the figure, 10 is a signal amplifier circuit, 11 is a focus detection arithmetic circuit, 12 is a storage 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, and 18 is a finder. A screen, 19 is a penta roof prism, 20 is an eyepiece, and 22 is a temperature detecting device.
The light beam from the subject that has passed through the taking lens 1 is deflected upward by the main mirror 15 and guided to a finder optical system including a finder screen 18, a penta roof prism 19, and an eyepiece 20.
A photosensitive film is arranged on a film surface 17 arranged behind the main mirror 15. At the time of photographing, the main mirror 15 and the sub-mirror 16 are retracted from the optical path between the photographing lens 1 and the film surface 17, and the light beam from the subject passing through the photographing lens 1 exposes the photosensitive film disposed on the film surface 17.
[0018]
A part of the main mirror 15 is semi-transmissive, and a sub-mirror 16 is mounted behind the semi-transmissive part. The light beam from the subject transmitted through the semi-transmissive part 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 photographing lens 1. . Further, the light beam from the subject that has passed through the focus detection optical system 8 is guided to the charge accumulation type image sensor 9.
Note that the focus detection optical system 8 and the image sensor 9 are configured so that focus can be detected in a focus detection area set on a shooting screen.
The image sensor 9 photoelectrically converts a 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 the signal to the signal amplifier circuit 10. send.
[0019]
The signal amplification circuit 10 amplifies the subject image signal output from the image sensor 9 and sends the amplified signal to the focus detection calculation circuit 11. The accumulation 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 above-described focus detection calculation, and calculates a defocus amount between the imaging surface of the photographing lens 1 and the film equivalent surface 6. Further, the focus detection calculation circuit 11 sends the amplified information of the subject image signal to the accumulation control circuit 12. The accumulation control circuit 12 determines the next charge accumulation time and amplification factor, and controls the charge accumulation operation of the sensor arrays A and B of the image sensor 9.
The motor drive control circuit 13 controls the drive direction and the drive amount of the motor 14 based on the defocus amount calculated by the focus detection calculation circuit 11. The motor 14 is mechanically connected to the taking lens 1, and the driving amount and the driving speed are controlled by the motor drive control circuit 13 to bring the taking lens 1 into a focused state.
[0020]
In the configuration of the above embodiment, the image sensor 9 is a photoelectric conversion element array, the focus detection calculation circuit 11 is a focus detection calculation unit, a focus determination unit and a focus allowable range changing unit, and the accumulation control circuit 12 is a storage control unit. And the temperature detecting device 22 constitutes a temperature detecting means. Incidentally, these means are not limited to the above embodiment.
[0021]
FIG. 2 is a flowchart showing the focus detection operation. The focus detection operation of the embodiment will be described with reference to FIG.
In step (hereinafter simply referred to as S in the drawings) 100, when a main switch of a camera (not shown) is turned on or a release button (not shown) is half-pressed, a 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 subject image signal is amplified by the signal amplification circuit 10 at the amplification factor set in the accumulation control circuit 12. Immediately after the start of the focus detection operation, there is no information for performing the accumulation control, so the accumulation control is performed according to the initial setting.
In step 102, the focus detection calculation circuit 11 sets an allowable focusing range according to the amplification factor of the subject image signal. For example, assuming that the reference focus allowable range is Do, the amplification factor magnification is Gn, and the predetermined value is α, the focus allowable range D is obtained by the following equation.
(Equation 4)
D = ± {Do + α * (Gn−1)}
[0022]
In step 103, the focus detection calculation circuit 11 reads the subject image signal from the signal amplification circuit 10 and calculates the defocus amount of the photographic lens 1. 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 allowable focus range set in step 102. If it is within the allowable focus range, the process proceeds to step 106, and if it is outside the allowable range, the process proceeds to step 105. If it is out of the permissible focusing range, in step 105, the motor drive control circuit 13 drives and controls the motor 14 in accordance with the defocus amount calculated by the focus detection calculation circuit 11, and drives the photographing lens 1 to the in-focus position. . On the other hand, if it is within the allowable focus range, the shutter release is permitted in step 106.
As described above, 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 can be performed.
[0023]
In the above-described embodiment, the so-called focus priority is set, and the release permission is given in step 106. However, when the so-called release priority is set, focus display may be performed on the display in step 106.
[0024]
In the above-described embodiment, the allowable focusing range is set based on the amplification factor of the subject image signal. However, the allowable focusing range may be set based on the charge accumulation time. In this case, assuming that the reference focus allowable range is Do, the reference accumulation time is To, the accumulation time is Tn, and the predetermined value is β, the focus allowable range D is obtained by the following equation.
(Equation 5)
D = ± {Do + β * (Tn−To)},
However, when Tn <To, Tn = To
[0025]
Further, the allowable focusing range may be set based on the amplification factor and the accumulation time of the subject image signal. In this case, if the reference focus allowable range is Do, the amplification factor magnification is Gn, the predetermined value is α, the reference storage time is To, the storage time is Tn, and the predetermined value is β, the focus allowable range D is given by the following equation. Required by
(Equation 6)
D = ± {Do + α * (Gn−1) + β * (Tn−To)},
However, when Tn <To, Tn = To
[0026]
Furthermore, since the dark current increases as the operating temperature of the image sensor 9 increases, the focusing allowable range D may be set based on the temperature detected by the temperature detecting device 22. In this case, the focus allowable range D is obtained by using the predetermined value β of Expression 5 or Expression 6 as a variable β (k) depending on the temperature k, which becomes larger as the temperature becomes higher.
(Equation 7)
D = ± {Do + β (k) * (Tn−To)},
However, when Tn <To, Tn = To
(Equation 8)
D = ± {Do + α * (Gn−1) + β (k) * (Tn−To)},
However, when Tn <To, Tn = To
[0027]
【The invention's effect】
As described above, according to the first aspect of the invention, the amplification factor of the subject image signal The higher the Focusing range of shooting lens So that The focus adjustment state of the focus detection calculation result is compared with the changed focus allowable range to determine whether the photographing lens is in focus or out of focus, so that the amplification factor of the subject image signal increases. Even if the noise component of the subject image signal increases and the focus detection calculation result greatly fluctuates, the allowable focus range is canceled so as to cancel the variation. Wide The in-focus / out-of-focus determination is made by the change, 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 2, the charge storage time of the photoelectric conversion element array The longer Focusing range of shooting lens So that The focus adjustment state of the focus detection calculation result is compared with the changed permissible focusing range to determine whether the photographing lens is in focus or out of focus. Noise component increases and the focus detection calculation results vary widely, so that the allowable focus range is set to cancel the variation. Wide The in-focus / out-of-focus determination is made by the change, 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 amplification factor of the subject image signal Is higher, Charge accumulation time of photoelectric conversion element row Is longer, Focusing range of shooting lens So that The focus adjustment state of the focus detection calculation result is compared with the focus allowable range after the change to determine whether the photographing lens is in focus or out of focus, so that the amplification factor is increased and the charge accumulation time is increased. Is longer, the noise component of the subject image signal output from the photoelectric conversion element array increases, and as a result, even if the focus detection calculation result greatly varies, the allowable focus range is set so as to cancel the variation. Wide The focus and the out-of-focus are accurately determined by the change, and the movement of the photographing lens in the vicinity of the in-focus state and the in-focus display by the display are stabilized.
According to the invention of claim 4, the ambient temperature of the photoelectric conversion element row The higher the Focusing range of shooting lens So that The focus adjustment state of the focus detection calculation result is compared with the changed focus allowable range to determine whether the photographing lens is in focus or out of focus. Even if the noise component of the dark current of the subject image signal output from the device increases, and the focus detection calculation result varies greatly, the focus allowable range is set so as to cancel the variation. Wide The in-focus / out-of-focus determination is made by the change, 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 fifth aspect of the present invention, the in-focus allowable range changed in accordance with the charge accumulation time is corrected based on the ambient temperature of the photoelectric conversion element array, so that accurate in-focus / out-of-focus determination is made. Is performed, and the movement of the taking lens in the vicinity of the in-focus state and the in-focus display on the display unit are stabilized.
According to the invention of claim 6, the allowable focus range changed in accordance with 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 taking lens near the in-focus state and the in-focus display on the display are stabilized.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment.
FIG. 2 is a flowchart illustrating a focus detection operation according to 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 focus detection device using a phase difference detection method.
FIG. 5 is an explanatory diagram of a correlation operation.
FIG. 6 is an explanatory diagram of a correlation operation.
[Explanation of symbols]
1 Shooting lens
2 Field mask
3 Field lens
6 Film equivalent surface
7 Bandpass filter
8 Focus detection optical system
9 Image sensor
15 Main mirror
16 sub mirror
17 Film side
18 Finder screen
19 penta roof prism
20 eyepieces
21, 31 Back projection image of aperture opening
22 Temperature detector
41, 42 aperture opening
51,52 Re-imaging lens

Claims (6)

A photoelectric conversion element array that outputs a subject image signal according to the light intensity distribution of the subject image,
A focus detection optical system that guides a light beam from the subject that has passed through the taking lens to the photoelectric conversion element array, and forms the subject image;
Signal amplifying means for amplifying a subject image signal output from the photoelectric conversion element array, focus detection calculating means for calculating a focus adjustment state of the photographing lens based on the subject image signal amplified by the signal amplifying means,
A focus detection device comprising: a focus determination unit configured to compare the focus adjustment state calculated by the focus detection calculation unit with a predetermined allowable focus range to determine whether the photographing lens is in focus or out of focus. ,
A focus detection device comprising: a focus permissible range changing unit that changes the focus permissible range of the focus determining unit so that the focus permissible range increases as the amplification factor of the signal amplifying unit increases . A photoelectric conversion element array that outputs a subject image signal according to the light intensity distribution of the subject image,
A focus detection optical system that guides a light beam from the subject that has passed through the taking lens to the photoelectric conversion element array, and forms the subject image;
Accumulation control means for controlling the charge accumulation time of the photoelectric conversion element row,
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 row;
A focus detection device comprising: a focus determination unit configured to compare the focus adjustment state calculated by the focus detection calculation unit with a predetermined allowable focus range to determine whether the photographing lens is in focus or out of focus. ,
Focus detecting apparatus comprising: a focus tolerance range changing means for changing to focus allowable range of the focus determination unit as the charge accumulation time becomes longer wider of said storage control means. A photoelectric conversion element array that outputs a subject image signal according to the light intensity distribution of the subject image,
A focus detection optical system that guides a light beam from the subject that has passed through the taking lens to the photoelectric conversion element array, and forms the subject image;
Signal amplification means for amplifying a subject image signal output from the photoelectric conversion element array,
Accumulation control means for controlling the charge accumulation time of the photoelectric conversion element row,
Focus detection calculating means for calculating the focus adjustment state of the photographing lens based on the subject image signal amplified by the signal amplifying means;
A focus detection device comprising: a focus determination unit configured to compare the focus adjustment state calculated by the focus detection calculation unit with a predetermined allowable focus range to determine whether the photographing lens is in focus or out of focus. ,
The focus permissible range of the focus determination unit is changed according to the amplification factor of the signal amplifying unit and the charge accumulation time of the accumulation control unit. As the amplification factor increases, the focus permissible range increases as the charge accumulation time increases. A focus allowable range changing means for widening the focus detection range. A photoelectric conversion element array that outputs a subject image signal according to the light intensity distribution of the subject image,
A focus detection optical system that guides a light beam from the subject that has passed through the taking lens to the photoelectric conversion element array, and forms the subject image;
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 row;
A focus detection device comprising: a focus determination unit configured to compare the focus adjustment state calculated by the focus detection calculation unit with a predetermined allowable focus range to determine whether the photographing lens is in focus or out of focus. ,
Temperature detection means for detecting the ambient temperature of the photoelectric conversion element row,
A focus detection device comprising: a focus permissible range changing unit that changes the focus permissible range of the focus determination unit so that the focus permissible range becomes wider as the ambient temperature detected by the temperature detector becomes higher . The focus detection device according to claim 2,
A temperature detecting unit for detecting an ambient temperature of the photoelectric conversion element row,
The focus detection device according to claim 1, wherein the focus allowable range changing unit corrects the focus allowable range changed according to the charge storage time of the storage control unit based on an ambient temperature detected by the temperature detection unit. apparatus. The focus detection device according to claim 3,
A temperature detecting unit for detecting an ambient temperature of the photoelectric conversion element row,
The focus permissible range changing unit is configured to set a focus permissible range changed according to an amplification factor of the signal amplifying unit and a charge accumulation time of the accumulation control unit based on an ambient temperature detected by the temperature detecting unit. A focus detection device for performing correction.

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