JP4182546B2 - Focus detection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a focus detection device used for a camera or the like, and particularly to a device capable of predicting movement of a subject.
[0002]
[Prior art]
As one of the focus detection methods in a camera, a phase difference for detecting a shift amount (hereinafter referred to as a defocus amount) between a planned focal plane of a photographing lens, that is, a film surface, and a surface on which a subject image is actually formed. The detection method is known.
The pupil division method, which is one of the TTL phase difference detection methods, will be described with reference to FIG. The light beam incident through the region 21 of the photographic lens 1 is focused on the film equivalent surface 6, and then the bandpass filter 7, the field mask 2, the field lens 3, and the aperture opening 41 constituting the focus detection optical system 8. Then, an image is formed on the sensor array 9A of the image sensor 9 through the re-imaging lens 51. Similarly, a light beam incident through the region 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 the re-imaging lens 52. And imaged on the sensor array 9B of the image sensor 9.
[0003]
The size of the area 21 of the photographing lens 1 is equal to the back-projected image of the aperture opening 41 by the field lens 3, and similarly the size of the area 31 is equal to the back-projected image of the aperture opening 42 by the field lens 3. The center-of-gravity interval PF of the photographing lens regions 21 and 31 is an F value corresponding to the size of the detection aperture of the focus detection optical system 8, and is hereinafter referred to as an aperture equivalent F value.
[0004]
A pair of secondary images of the subject image formed on the sensor rows 9A and 9B of the image sensor 9 is a so-called front pin state in which the subject image formed by the photographing lens 1 connects the image before the planned focal plane. In the so-called rear pin state in which the images are separated from each other and the images are connected after the planned focal plane, they approach each other. When the subject image forms an image on the planned focal plane, the relative positions of the pair of secondary images on the sensor rows 9A and 9B of the image sensor 9 match. The image sensor 9 outputs an electrical signal (subject image signal) corresponding to the light intensity distribution of the pair of secondary images formed on the sensor arrays 9A and 9B. These subject image signals are processed and the relative positions of the secondary images of the pair of subject images are obtained to determine the focus adjustment state of the photographing lens 1, that is, the defocus amount and the defocus direction (front pin or rear pin). ) Is obtained.
[0005]
There is known a method of detecting a defocus amount a plurality of times at predetermined time intervals using the above-described focus detection method, and detecting a movement of the subject in the direction of the photographing optical axis based on the defocus amount. One example will be described with reference to FIG.
In FIG. 4, the horizontal axis represents time, and the vertical axis represents the detected defocus amount. The moving speed of the subject image plane is calculated from the defocus amount Dfn at time tn and the defocus amount Dfn + 1 at time tn + 1, and the defocus amount Dfn + 2 at the next time tn + 2 is predicted. Further, the moving speed of the subject is calculated by calculating the shooting magnification of the subject from the focal length of the taking lens and the amount of the lens extended from the infinity end.
[0006]
For example, Japanese Patent Laid-Open No. 60-214325 proposes a method of smoothly following and focusing on a moving subject. This means that the next defocus amount is estimated in consideration of the detected defocus amount for multiple times and the charge accumulation timing and time of the image sensor when calculating the defocus amount, and the subject movement amount It drives the photographic lens that is optimal for the camera.
[0007]
On the other hand, it is conventionally known that the best focus position moves according to the aperture value at the time of shooting. For example, when the aperture equivalent F value PF is F8, if the aperture value at the time of shooting is F8, the best focus position at the aperture value F8 of the shooting lens matches the focus position detected by the focus detection device. Therefore, when shooting at other aperture values, the focus position detected by the focus detection device and the best focus position of the shooting lens will be out of focus, resulting in a poorly focused photo depending on the shooting lens. End up. This will be described with reference to FIG.
[0008]
FIG. 5 shows spherical aberration of a photographic lens having an open F value of 1.4. The horizontal axis indicates the amount of aberration, and the vertical axis indicates the F value. The position of “0” on the horizontal axis represents the Gaussian image plane. A2 indicated by a dotted line from the horizontal axis 0 is the best focus surface when the aperture of the photographing lens is F2, similarly, A4 is the best focus surface when the aperture value is F4, and A8 is the best focus surface when the aperture value is F8. For example, when the aperture equivalent F value PF of the focus detection optics is F8, the aperture equivalent F value PF is constant at F8 regardless of the aperture value of the photographing lens, so the best image plane is on the image plane A8. It is detected that the taking lens is in focus when it comes. That is, the position corresponding to the film equivalent plane 6 in FIG. 3 is the plane A8 in FIG. 5, and focus detection is performed at this position.
[0009]
When the shutter release operation is performed after detecting the in-focus state of the photographing lens 1 at such a position, the driving of the photographing lens 1 is prohibited accordingly, and the photographing lens 1 is held at the in-focus position. At the same time, the aperture of the taking lens 1 is reduced to an aperture value at which proper exposure can be obtained. Now, assuming that the aperture value for obtaining a proper exposure is F8, the best image plane position coincides between the film exposure and the focus detection, and the best focus position of the photographing lens 1 comes on the film equivalent plane 6. Shooting that is in focus.
[0010]
On the other hand, if the aperture value for obtaining a proper exposure is, for example, F4, the best focus position at this time is the surface A4. However, since the focus detection device detects the best image plane position of F8, A difference of (A4−A8) occurs on the optical axis of the photographing lens 1 between the best focus position A4 and the best image plane position A8 detected by the focus detection device. Similarly, when the aperture value of the photographing lens is controlled to F2, a difference of (A2−A8) occurs on the optical axis of the photographing lens 1. As described above, when the aperture value at the time of film exposure is different from the aperture equivalent F value PF of the focus detection optical system, the image in which the best focus position of the photographing lens 1 corresponds to the aperture equivalent F value PF of the focus detection optical system. Even if the in-focus state is correctly detected, the film is not correctly focused when the film is exposed. Here, since the aberration of the lens differs for each type of photographing lens, the deviation from the focus detection surface of the focus detection optical system differs for each photographing lens.
[0011]
For example, Japanese Patent Application Laid-Open No. 62-227108 discloses a focus detection device that corrects the movement of the best focus position by the aperture value described above. In this method, information on aberration is stored in advance in a memory in the photographing lens, and the defocus amount is corrected on the camera body side based on this information. With this correction, a photograph that is always in focus can be obtained regardless of the movement of the best focus position due to a change in aperture value. In Japanese Patent Application Laid-Open No. 62-227108, correction is performed at a low image height position near the optical axis of the photographing lens, but it is essentially changed even at a high image height position away from the optical axis of the photographing lens. Rather, JP-A-6-130283 discloses in detail not only the vicinity of the optical axis of the photographic lens but also correction at a high image height position away from the optical axis of the photographic lens.
[0012]
[Problems to be solved by the invention]
As described above, adding the correction for the movement of the best focus position to the defocus amount makes it easy to focus regardless of the aperture value in normal focus adjustment, but this is used for the calculation of the subject movement speed described above. The following problems occur.
That is, when the photographer intentionally or the camera itself changes the aperture value setting of the taking lens in order to obtain an appropriate exposure, the defocus amount is corrected in accordance with the change in the aperture value. The camera that detects the movement speed of the subject misunderstands that the change in the defocus amount is due to the movement of the subject, and even though it is a stationary subject, it predicts the next defocus amount and drives the lens. It will be out of focus.
[0013]
An object of the present invention is to enable accurate calculation of a subject moving speed even with a focus adjustment device that corrects the best focus position.
[0014]
[Means for Solving the Problems]
The focus detection apparatus according to the present invention performs focus detection on a detection area in a shooting screen, and outputs a focus detection signal, based on data specific to the shooting lens and data specific to the focus detection means, A correction unit that adds a correction according to the focus position shift caused by the aberration of the photographing lens to the focus detection signal; and a prediction unit that predicts the movement of the subject in the optical axis direction of the photographing lens based on the focus detection signal. Applied to the focus detection apparatus. Then, to predict the movement of the object based on the focus detection signal before correction by the correction means applied, the shift of the focus position based on the aperture value of the specific data and the focus detection unit specific data taking lens of the photographic lens , and correcting the prediction result of the predicting means.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a sectional view of a single-lens reflex camera equipped with a focus detection apparatus according to the present invention, and shows a state in which a photographing lens 1 is mounted. Reference numeral 13 is a main mirror, 14 is a sub-mirror, 15 is a film surface, 16 is a finder screen, 17 is a penta roof prism, and 18 is an eyepiece. The light beam from the subject that has passed through the photographing lens 1 is deflected upward by the main mirror 13 and guided to a finder optical system including a finder screen 16, a penta roof prism 17, and an eyepiece lens 18. At the time of shooting, the main mirror 13 and the sub mirror 14 are retracted from the optical path between the shooting lens 1 and the film surface 15, and the luminous flux of the subject that has passed through the shooting lens 1 is exposed to the photosensitive film placed on the film surface 15.
[0016]
A part of the main mirror 13 is semi-transmissive, and a sub mirror 14 is attached behind the semi-transmissive portion. Therefore, a part of the light beam from the subject is transmitted through the main mirror 13, then deflected toward the bottom of the camera body by the sub mirror 14, and guided to the focus detection circuit 20 disposed in the vicinity of the film equivalent surface 6 of the photographing lens 1. It is burned. The focus detection circuit 20 includes a focus detection optical system 8 described with reference to FIG. 3, an image sensor 9, and a focus detection calculation circuit that calculates the focus state of the photographing lens based on an output signal from the image sensor 9.
[0017]
The focus detection optical system 8 and the image sensor 9 are configured such that focus detection can be performed in a focus detection region (for example, the center of the screen) set on the shooting screen. The image sensor 9 photoelectrically converts the secondary image of the subject image formed on the sensor rows 9A and 9B as described above, generates an electrical subject image signal corresponding to the intensity distribution of the subject image, and generates the subject image. The signal is sent to the focus detection arithmetic circuit.
[0018]
The focus detection arithmetic circuit calculates a defocus amount between the imaging surface of the photographing lens 1 and the film equivalent surface 6 from the subject image signal by a known method, and uses the defocus amount as a focus detection signal to the control circuit 23. Send repeatedly. The charge accumulation time of the image sensor 9 may be determined by giving the image sensor 9 itself such a function by devising the device, or processing the subject image signal from the image sensor 9 by a focus detection circuit. Also good. The focus detection circuit 20 sends the determined charge accumulation start and end timings together with the detected defocus amount to the control circuit 23.
[0019]
The control circuit 23 includes a movement detection circuit 21 that detects movement of the subject, a drive control circuit 24 that drives the photographic lens 1, an aperture-equivalent F value of the focus detection optical system 8, a focus detection position in the photographic screen, A body side memory 22 in which unique data relating to the focus detection direction is stored is connected. The photographic lens 1 is connected to a lens-side memory 26 storing lens-specific data relating to the best focus position of the photographic lens 1 and a lens control circuit 25. The lens control circuit 25 determines the focal length and the infinity end of the photographic lens. The photographing magnification calculated from the feed amount when the reference is used is sent to the control circuit 23.
[0020]
FIG. 2 is a flowchart showing a processing procedure of focus adjustment control by the control circuit 23.
When a release switch (not shown) is turned on, the program starts from step S100, and an instruction is given to the focus detection circuit 20 to perform charge accumulation and focus detection calculation in step S101. As described above, the focus detection circuit 20 obtains the charge accumulation start and end timings and the defocus amount of the image sensor 9 and repeatedly sends them to the control circuit 23.
[0021]
In step S102, the image plane moving speed of the subject is calculated from the defocus amount repeatedly sent from the focus detection circuit 20 and the charge accumulation start and end timings, and the subject is in the optical axis direction of the photographing lens. A determination is made as to whether the object is moving or stationary, and an instruction is issued to the movement detection circuit 21 to calculate the subject movement speed. The movement detection circuit 21 calculates the object movement speed based on the defocus amount detected repeatedly, the timing of the charge accumulation time, and the photographing magnification data received from the lens control circuit 25 via the control circuit 23. Then, the detected defocus amount is corrected in accordance with the subject moving speed so as to perform smoother follow-up focusing, and is sent to the control circuit 23.
Here, the defocus amount is used to calculate the subject moving speed, but this defocus amount does not include the correction related to the best focus position performed in step S103.
[0022]
In step S103, from data recorded in the lens-side memory 26 (such as data relating to the best focus position of the photographing lens 1) and data stored in the body-side memory 22 (such as an aperture equivalent F value of the focus detection optical system 8). A correction amount for the best focus surface according to the aperture value at the time of shooting is calculated, and this correction amount is added to the defocus amount (the defocus amount corrected in step S102) for correction. The aperture value at the time of shooting is an aperture value determined by the photographer or an aperture value determined by the camera itself as appropriate exposure. By this correction, proper focus adjustment can be performed even when the aperture equivalent F value of the focus detection optical system 8 and the aperture value of the photographing lens 1 are different.
[0023]
In step S <b> 104, the lens driving amount and the driving direction for guiding the photographing lens to the in-focus position are obtained based on the corrected defocus amount, and these are output to the drive control circuit 24. The drive control circuit 24 drives the photographing lens 1 based on the input information and focuses on a predetermined subject. Thereafter, the focus adjustment operation is terminated in step S105.
[0024]
As described above, in the present embodiment, the defocus amount is used to calculate the subject moving speed. However, since the defocus amount does not include the correction related to the best focus position performed in step S103, the above correction is performed. Therefore, it is possible to accurately predict the movement without misunderstanding that the change in the defocus amount due to the movement of the subject.
[0025]
【The invention's effect】
According to the present invention, since the movement of the subject is predicted based on the focus detection signal before the correction according to the shift of the focus position caused by the aberration of the photographing lens, the change in the focus detection signal due to the correction described above. Therefore, the movement can be accurately predicted without being mistaken for the movement of the subject.
[Brief description of the drawings]
FIG. 1 is a schematic side view of a camera according to an embodiment of the present invention.
FIG. 2 is a flowchart showing the operation of the embodiment.
FIG. 3 is a diagram showing an optical system and an image sensor of a focus detection device.
FIG. 4 is a schematic diagram illustrating movement of a subject.
FIG. 5 is a schematic diagram for explaining an aberration of a photographing lens.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Shooting lens 2 Field mask 3 Field lens 6 Film equivalent surface 7 Band pass filter 8 Focus detection optical system 9 Image sensor 14 Main mirror 15 Sub mirror 16 Film surface 17 Viewfinder screen 18 Pentadah prism 19 Eyepieces 21 and 31 Reverse of aperture Projected images 41, 42 Aperture apertures 51, 52 Re-imaging lens

Claims (2)

Focus detection means for performing focus detection on a detection area in the photographing screen and outputting a focus detection signal;
Correction means for adding correction to the focus detection signal according to the shift of the focus position caused by the aberration of the photographic lens based on the data specific to the photographic lens and the data specific to the focus detection means,
In a focus detection apparatus comprising prediction means for predicting movement of a subject in the optical axis direction of the photographing lens based on the focus detection signal,
The prediction means predicts the movement of the object based on the focus detection signal before correction is applied by the correction means,
The correction unit corrects the shift of the focus position based on the unique data of the photographing lens, the unique data of the focus detection unit, and the aperture value of the photographing lens with respect to the prediction result by the prediction unit. Focus detection device. A focus detection apparatus according to claim 1;
  A camera comprising: drive means for moving the photographing lens in the optical axis direction based on a prediction result of the prediction means.

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