JP2006135513A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of a fault that the position of a focus detected by a focus detecting apparatus differs from a focus position necessary for an imaging apparatus, when there is chromatic aberration in its lens. <P>SOLUTION: To raise the precision of focusing, this imaging apparatus has a spectral intensity distribution determination apparatus for determining the spectral intensity distribution of the light of an object; a focus detecting apparatus which receives the light of the object having passed through a taking lens; and a means which computes a correction value for correcting the difference of the amount of focusing from information concerning the focuses by wavelengths of the taking lens, the focus detecting device, and information on the spectral distribution sensitivity of the color imaging apparatus on the basis of the determination result of the spectral intensity distribution determination apparatus, and which changes an AF correction value by the correction value according to the color of an object image to be corrected. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a focus detection apparatus, and more particularly to an imaging apparatus related to a focus detection apparatus that can satisfactorily correct a focus detection error due to chromatic aberration of a lens or the like.

  In a focus detection apparatus that detects a focal position by receiving a part of a light beam from a subject that has passed through the photographic lens, there may be a focus shift detection result that differs from the photographic focus shift amount due to residual aberration of the photographic lens. Even in such a case, if the spectral sensitivity of the wavelength received by the image sensor matches the spectral sensitivity of the wavelength received by the focus detection device, the influence of the wavelength-dependent aberration is reduced, and the image obtained by the image sensor Depending on the wavelength of the subject at that time, the image will be almost in focus, but by correcting with a correction value that takes into account the difference between the shooting focus and the detection focus in the same wavelength range, more accurate focus can be obtained. I can do it.

However, in general, the spectral sensitivity distribution of the image sensor and the spectral sensitivity distribution of the focus detection device are not the same. In general, an image pickup device receives light from a subject by installing three color filters on a fine silicon photodiode for the purpose of capturing a color image. On the other hand, since the focus detection apparatus does not need to capture an image as a color image, the focus detection apparatus includes a visible region and a light receiving element having sensitivity to wavelengths other than the visible region without applying a color filter.
Japanese Patent Application Laid-Open No. 2000-266988

  In such an apparatus, when the lens has chromatic aberration, there arises a problem that the focal position detected by the focal point detection apparatus is different from the focal position necessary for the imaging apparatus. For example, consider photographing with photographing lenses having different focal positions in red and blue.

  If the focus detection device mainly receives red light and the imaging device has red and blue equal sensitivity, the photographing lens is adjusted to the red focus position by performing focus adjustment according to the detection result of the focus detection device. However, since the imaging device is also sensitive to blue, the center of gravity of the focus moves there, resulting in a blurred photo.

  Originally, the focal point should be adjusted to a focal position corresponding to the ratio of red, green, and blue sensitivities (spectral sensitivity distribution). In many cases, the photographic lens only corrects aberrations in the wavelength range used for taking pictures. For example, the wavelength range used only for the focus detection system, such as the infrared range, is caused by various remaining aberrations. The difference in detection focus from the reference wavelength tends to be very large, and the difference between the spectral sensitivity and the focus detection spectral sensitivity of the image pickup device is a big problem for the automatic focus adjustment device.

  The relationship between this chromatic aberration and the occurrence of a focus detection error will be described in detail.

  FIG. 1 shows the relationship between the relative spectral distribution and wavelength of various light sources that illuminate a subject. The vertical axis represents the relative spectral distribution, and the horizontal axis represents the wavelength. Graph A shows the light of the fluorescent lamp, graph B shows the tungsten lamp, and graph C shows the sunlight of the daytime.

  FIG. 2 shows the spectral sensitivity of the light receiving element of the focus detection device. The sensitivity of the AF sensor A shown by the solid line in FIG. 4 is that of the AF sensor alone, and has sensitivity up to infrared with a peak at around the wavelength of 700 nm. A graph of the AF sensor B indicated by a dotted line in the figure indicates the total spectral sensitivity obtained by combining the infrared sensor with the one indicated by the AF sensor A.

  FIG. 3 shows the spectral sensitivity distribution of the image sensor. In order to obtain color information, the imaging device divides the visible region into B, G, and R regions.

  FIG. 4 shows the relationship between chromatic aberration and wavelength of the taking lens. The vertical axis in the figure indicates the amount of focus shift with respect to the reference wavelength focusing position, and the horizontal axis indicates the wavelength. The solid line in the figure is the focus position with respect to the reference wavelength detected by the focus detection system (AF), and the dotted line is the focus position with respect to the reference wavelength of the captured image. In general, the light beam captured by the focus detection system is a part of the photographic light beam, so that there may be a slight difference from the focal position determined by the entire photographic light beam due to various aberrations remaining in the photographic lens.

  As can be seen from FIGS. 2 and 3, since the spectral sensitivity of the image sensor and the spectral sensitivity of the focus detection device are different, the detection result of the focus detection device and the photographing focus position differ depending on the spectral distribution of the subject. If the lens has small chromatic aberration and other residual aberrations, the two data in the graph of FIG. 4 match, and the detection result of the focus detection device and the photographing focus position difference are small regardless of the spectral distribution, but the telephoto In a lens having a relatively large chromatic aberration such as a lens, the difference may be large.

  An object of the present invention is to provide an imaging apparatus that removes a focus detection error due to residual aberration of a photographing lens without limiting the detectable wavelength region or the spectral sensitivity distribution of the imaging element.

  The present invention is a camera that can include a photographing lens, a color imaging device, and a spectral intensity distribution determining device that determines a spectral intensity distribution of subject light, and a focus detection device that receives subject light that has passed through the photographing lens. And, based on the determination result of the spectral intensity distribution determination device, calculates a correction value for correcting the shift of the focus adjustment amount from the information on the focus for each wavelength of the photographing lens and the spectral distribution sensitivity information of the focus detection device and the color imaging device, A correction unit that corrects based on the correction value, and drives the photographic lens based on a value obtained by correcting the focus adjustment state of the photographic lens based on an output of the focus detection device and a value corrected by the correction unit. And a lens driving means.

  According to the present invention, it is possible to perform accurate focus adjustment by calculating for each wavelength by storing data that requires a minimum defocus correction value due to lens-specific aberration.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 5 shows an outline of the main part of the imaging apparatus according to the embodiment of the present invention. Reference numeral 1 denotes a photographic lens, which can be attached and detached from the camera body 2. Reference numeral 3 denotes a photographing optical system, and the focal position can be adjusted by the focus adjustment device 4. Four focusing devices are controlled by five microcomputers. Reference numeral 6 denotes a storage device that stores information unique to the photographing lens 1. The unique information stored in 6 is information on the imaging focus difference of each wavelength with respect to the reference wavelength, information on the difference in focus detection position at each wavelength with respect to the reference wavelength, information on drive sensitivity of the focus adjustment device, lens F value, focal length and so on. A part of the information stored in 6 is transferred to the microcomputer 14 of the camera body via 7 contacts.

  Reference numeral 2 denotes a camera body that has a mechanism that transmits and receives information through the contact 7 and that can be attached and detached by physical contact with the lens 1. The light flux from the subject forms an image on the image sensor 16 by the photographing lens 3. A part of the light beam from the photographic lens 3 to the image pickup device 16 is guided to the focal plate 9 by the half mirror 8 which is disposed in the middle of the light beam. One transmitted light beam is guided to the focus detection device 13 by the reflection mirror 12.

  The microcomputer 14 in the camera calculates the amount of focus shift from the output of the focus detection device 13. At that time, the spectral sensitivity distribution of the imaging device 16 and the focus detection device stored in the storage device 15, information on the lens chromatic aberration sent from the lens 1, and the spectral distribution of the light beam passing through the lens 3 from the subject are determined. The focus displacement amount is instructed to the microcomputer of the lens 1 by calculating the correction amount for the focus shift amount detected based on the output of the spectral intensity distribution determination device 17 and correcting the correction amount.

  The light beam guided to the focusing screen 9 by the half mirror 8 is subjected to a diffusing action, and the finder image can be observed by the photographer by the eyepiece 11 through the penta roof prism 10 having an image inverting action, and the spectral intensity distribution. A part of the light beam also enters the determination means 17.

  An example of the spectral intensity distribution determining means will be described with reference to FIGS. Reference numeral 17-1 in FIG. 6 denotes an imaging lens, which has an effect of forming an image by the photographing lens 3 formed on the focusing plate on the sensor 17-2. The sensor 17-2 is composed of a number of light receiving elements divided as shown in FIG. 7, and a color filter is attached to each of the light receiving elements. This color filter may be of three colors such as RGB used for an image sensor or the like, or may be a finer wavelength-divided one. In any case, the spectral intensity of the incident light beam can be found from the output intensity ratio of each color filter having different characteristics.

  The wavelength resolving power of this spectral intensity distribution depends on the number of characteristics of the color filter, that is, depends on the type of wavelength to be transmitted. By finely dividing the wavelength, it becomes possible to perform finer focus correction calculation for each wavelength. However, even if the calculation is performed with three points of RGB, the accuracy of the focus adjustment is increased as compared with the conventional case. It is also desirable that the sensitivity distribution between the image sensor and the focus detection system can measure the intensity distribution in an extremely different wavelength region (for example, near infrared region).

  This is because, in such a region, only one focus having sensitivity is affected, so that the correction value may be increased depending on the spectral intensity distribution of the subject. In order to obtain a finer spectral intensity ratio from a small spectral intensity ratio, a method of estimating the spectral intensity ratio from previously stored light source data is also conceivable.

  As shown in FIG. 1, the spectral distribution intensity ratio is characteristic depending on the type of light source. When the obtained small intensity ratio data varies greatly in the visible range, it is assumed that the fluorescent lamp has a discrete spectral distribution, and when the intensity ratio increases on the long wavelength side, it is assumed that it is a flood lamp. It is easy to specify the light source from the intensity ratio. If the light source can be specified, data relating to the spectral intensity ratio of the light source can be used for calculation of the correction value by preparing in the storage device 15.

  Next, a series of operations will be described along the flow of FIG. The numbers correspond to those shown in FIG. When the lens 1 is mounted on the camera 2, information necessary for correction value calculation and focusing operation is transmitted from the lens 2 to the camera 1 via the contact 7. The lens data necessary for calculating the correction value includes information on chromatic aberration shown in FIG. 4, that is, the shift amount of the photographing focus position for each wavelength with respect to the reference wavelength and the shift amount of the detection focus position for each wavelength with respect to the reference wavelength. At this time, if the difference between the deviation amount of the photographing focal position and the deviation amount of the detection focal position is small, either one may be transmitted to the camera.

Here, the shift amount of the photographing focus position for each wavelength is defined as _P (λ), and the shift amount AF _P (λ) of the detection focus position for each wavelength is defined.

  In step 101, a release operation is performed by a photographer's operation. In step 102, the spectral intensity ratio of the subject is measured. Next, in step 103, calculation of in-focus position correction information is performed. The focus position correction calculation in step 103 will be described.

Set the amount of focus deviation for the final focus adjustment operation to P
AF amount of focus detected by the focus detection system AF
The in-focus position correction amount obtained by calculation is BP,
It is assumed that the following expression is satisfied: P = AF + BP (1)

  This means that a correct focus shift amount is obtained by adding a correction value to the detected focus shift amount, and focusing is obtained by performing focus driving by that amount.

  In step 103, the BP is calculated by the microcomputer 14.

  The correction value BP can be obtained by the following equation.

Where E _S (λ): spectral sensitivity distribution of the image sensor (stored in the storage device 15 of the camera 2)
E _AF (λ): spectral sensitivity distribution of the focus detection system (stored in the storage device 15 of the camera 2)
P (λ): Focal position shift amount for each wavelength with respect to the reference wavelength of the photographing lens (stored in the storage device 6 of the lens 1)
AF P _(lambda): focus detecting position deviation amount for each wavelength with respect to the reference wavelength of the taking lens (stored in the storage device 6 of the lens 1)
S (λ): spectral intensity distribution of the subject (determined in step 102)

  Here, the range in which the sum of several sequences is taken is 350 nm to 800 nm that covers the wavelength in the visible range, but of course this range may be changed according to the wavelength range used for imaging. The sensitivity distribution and the amount of defocus amount may be calculated by expressing each function using the wavelength λ as a variable and calculating a value at a necessary wavelength, or a finite number of data may be stored for each wavelength.

  In any case, the calculation is performed based on the wavelength points of the spectral intensity distribution detectable in step 102. If the spectral intensity distribution of the wavelength detected in step 102 is not used as S (λ) as it is, but the light source is identified from the spectral intensity ratio and the correction value is calculated, the calculation at more points is possible. become.

  The expression (2) expresses the contribution of each focus correction value corresponding to the sensor spectral sensitivity ratio between the image sensor and the focus detection system to each wavelength, and represents it in the form of a function of the wavelength λ. Since this can be calculated when the lens 1 is attached to the camera 2, it can be performed before the release operation 101. If the lens information used for the calculation changes due to the zooming or focusing of the lens, the calculation may be performed sequentially when the lens information changes.

  In equation (3), a correction value corresponding to the spectral intensity distribution of the subject luminous flux is calculated from the value obtained in equation (2).

  Next, in step 104, a focus detection operation is performed to measure the amount of focus shift detected by the focus detection system 13. In step 105, in order to correct the result of step 104 with the correction value calculated in step 103, the amount of photographing focus shift is calculated by the microcomputer 14 based on the equation (1) and transmitted to the lens microcomputer 5. In step 106, focus adjustment is performed based on the amount of focus shift calculated in step 105, and the image is focused. In step 107, the image sensor is exposed. At that time, the mirrors 8 and 12 exit.

Graph showing relative spectral intensity distribution of various light sources Graph showing the spectral sensitivity distribution of the focus detection system Graph showing spectral sensitivity distribution including color filter of image sensor A graph showing the amount of defocus relative to the reference wavelength generated by the remaining collection in the imaging system and focus detection system Schematic diagram of the main part of the camera according to the present invention Schematic diagram of spectral intensity distribution measuring device Conceptual diagram of sensor used in spectral intensity distribution measuring device Implementation flowchart of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lens 2 Camera 5, 14 Microcomputer 6, 15 Memory | storage means 17 Spectral intensity distribution measuring means

Claims (3)

  A camera that can include a photographing lens, a color imaging device, and a spectral intensity distribution determination device that determines a spectral intensity distribution of subject light, a focus detection device that receives subject light that has passed through the photographing lens, and a spectral intensity Based on the determination result of the distribution determination device, calculates a correction value for correcting the shift of the focus adjustment amount from the information on the focus for each wavelength of the photographing lens and the spectral distribution sensitivity information of the color imaging device, and the correction value And a lens driving unit that drives the photographic lens based on a value obtained by correcting the result of detecting the focus adjustment state of the photographic lens based on the output of the focus detection device. An image pickup apparatus comprising:   The imaging apparatus according to claim 1, wherein the spectral intensity distribution determination apparatus is a spectral intensity distribution measuring apparatus and calculates a correction value based on the measured spectral intensity distribution.   2. The imaging apparatus according to claim 1, wherein the spectral intensity distribution determination device is a light source type determination device, and selects a spectral distribution intensity stored in advance according to the determined type of light source and uses it for calculation of a correction value.