JP2011075647A - Imaging optical system having autofocus function, and photographing system of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To overcome the problems with a photographing system configured to search the focal position by means of the branching optical system, wherein the autofocus accuracy is deteriorated, when a white balance is taken with a camera having an image sensor, since a color balance difference is made between a branching optical system and an imaging system, and chromatic aberration remains in each of the branching optical system and the imaging system to cause a focal position difference between the respective optical systems. <P>SOLUTION: The camera has the branching optical system to partly branch a luminous flux in an imaging optical system and detect the focusing state of the imaging system by means of the branched luminous flux, and a plurality of channels having sensitivity for a determined wavelength range. The camera is characterized in that focusing processing is changed based on information about a relative intensity ratio between the respective channels of the imaging system. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a zoom lens suitable for an imaging apparatus such as a broadcast television camera or a video camera, and an imaging system thereof.

  In recent years, in the field of broadcast television cameras, HDTV (high-definition) has been advanced, and a photographing system capable of realizing higher-definition video has been demanded.

  In order to satisfy these demands, high-definition imaging elements and high-performance (high resolution) zoom lenses used as photographing optical systems have been performed. When the resolution of the photographing optical system is increased, the high-frequency component of the subject can be resolved. However, since the focal depth of the photographing optical system becomes shallow, fine focus adjustment near the best focus position (best imaging plane) is required.

  In the case of manual focus, the photographer focuses while looking at a relatively small screen such as a viewfinder. For this reason, high-precision focusing has become difficult.

  On the other hand, there is an increasing demand for a zoom lens having an autofocus function (automatic focus detection function).

  There are active and passive autofocus methods as autofocus methods.

  In the active autofocus method, a distance measuring system is provided separately from the imaging system, for example, infrared light is emitted from the distance measuring system to the object side, and infrared light reflected from the object side is received, Ranging on objects.

  This active autofocus method is not suitable for an imaging apparatus such as a television camera because it is necessary to ensure operability and mobility.

  On the other hand, one of the passive autofocus systems is an auto that obtains the best focus position direction determination signal by driving a small amplitude group (wobbling) in the optical axis direction of a part of the lens group or image sensor of the photographing optical system. There is a focus method (so-called hill-climbing autofocus method).

  This method has a problem that since a part of the lens group of the image pickup optical system is driven minutely, the movement for searching for the focus position is captured as an image and is unsightly.

  In addition to this, one of the passive autofocus methods is to split a part of the light beam from the optical path of the imaging optical system that causes the light beam from the subject to enter the image sensor for video, and use the branched light beam for focus detection. There is a method of obtaining an in-focus signal by forming an image on a photoelectric conversion element. Several methods are known in which focusing is determined by a branching optical system (focusing optical system) different from such an imaging optical system (Patent Document 1, Patent Document 2, and Patent Document 3).

Further, in the method of branching a part of the light beam from the image pickup optical system, the amount of light taken into the image pickup device of the camera is reduced and the photographed image is affected. In order to reduce this influence, it has been proposed to branch only the wavelength region near the infrared and detect the in-focus position using the luminous flux. (Patent Document 4)
In addition, as a method for determining an autofocus area in a screen, it has been proposed to detect a predetermined color area from a luminance signal and a color difference signal, and use this area as a photometric area used for autofocus or the like. (Patent Document 5)
By the way, in order to reduce the influence of photographing conditions such as illumination and the spectral transmittance of the replaced zoom lens, white balance is generally taken before photographing. This is to change the relative intensity ratio of each channel when shooting a white subject and to make the output ratio of each color channel the same. It has been proposed that a plurality of images are recorded by automatically changing the spectral sensitivity and the user selects the images to reflect the spectral sensitivity in the subsequent photographing. (Patent Document 6)

JP-A-9-274129 JP 2004-085676 A JP 2003-270517 A JP 2003-322791 A JP-A-6-121332 JP 2005-109621 A

  A method for determining the direction of the best focus position by using a branching optical system that is different from the imaging optical system by providing a branching element for branching a part of the light beam in the optical path of the imaging optical system. Is not reflected in the photographed image.

  However, in the zoom lens in which the relative intensity ratio information of each channel cannot be changed by the photoelectric conversion element for detecting the in-focus position of the branching optical system, when the white balance is taken by the camera, the branching optical system and the imaging system And there is a difference in color balance. Since chromatic aberration remains in each of the branching optical system and the imaging system, the focusing position is different in each optical system. For this reason, in the photographing system that searches for the in-focus position with the branching optical system, the accuracy of the autofocus deteriorates.

  In the present invention, a branching optical system for branching a part of a light beam in the imaging optical system and detecting the in-focus state of the imaging system by the branched light beam, and a channel having sensitivity to a predetermined wavelength range In a camera having a plurality of zoom lenses, a zoom lens and an imaging system are proposed in which focusing processing is changed based on relative intensity ratio information of each channel of the imaging system.

  At this time, it is preferable to obtain the relative intensity ratio information of each channel from the camera having the image sensor and change the focus position information.

  Furthermore, it is preferable to change the in-focus position processing by obtaining information on a filter inserted in the camera from a camera having an image sensor.

  Further, the focus position information may be changed based on the relative intensity ratio information of each channel stored in advance in the zoom lens.

  Preferably, the in-focus position information is calculated according to the following formula based on the acquired relative intensity ratio information of each channel.

BP: In-focus position information after correction n: Number of output signal channels
S _i : Relative intensity of each channel output
d _i : Focus position information of each channel Alternatively, a filter may be inserted into the branch optical system based on the relative intensity ratio information of each channel of the imaging system stored in advance in the zoom lens.

  A filter may be inserted into the branch optical system based on the relative intensity ratio information of each channel acquired from the camera.

  Further, it is preferable to change the spectral sensitivity by a photoelectric conversion element for detecting a focus position in the branch optical system.

  Further, when the acquisition of the relative intensity ratio information of each channel fails, the focusing process should not be changed.

  Alternatively, when the acquisition of the relative intensity ratio information of each channel fails, it is preferable to set the focusing process at the time of factory shipment of the zoom lens.

  Further, it is preferable that the zoom lens can be replaced with the camera.

  According to the present invention, it is possible to realize an autofocus that can accurately search a focus position even if the color temperature of the illumination changes.

2 is a flowchart of the first embodiment. 10 is a flowchart according to the second embodiment. 10 is a flowchart of Example 3. 10 is a flowchart of Example 4. 10 is a flowchart of Example 5. 10 is a flowchart of Example 6. 10 is a flowchart according to the seventh embodiment. 10 is a flowchart of Example 8. 10 is a flowchart of Embodiment 9. 10 is a flowchart of Example 10. FIG. 2 is a schematic diagram of a main part of an imaging system according to Examples 1 to 5. FIG. 11 is a schematic diagram of a main part of an imaging system according to Examples 6 to 10. 2 is a lens cross-sectional view of a zoom lens according to Numerical Example 1. FIG. Explanatory drawing of a branch element. FIG. 7 is a spherical aberration diagram at the wide-angle end and the telephoto end of the zoom lens when the lens unit L22 of Numerical Example 1 is inserted. FIG. 9 is a spherical aberration diagram at the wide-angle end and the telephoto end of the zoom lens when the extender group Ex of Numerical Example 1 is inserted. Signal strength for each channel wavelength.

  Embodiments of an imaging optical system having an autofocus function and a photographing system thereof according to the present invention will be described below.

  FIGS. 11 and 12 are schematic views of the main part of a photographing system (TV camera system) using a zoom lens as a photographing optical system. Reference numeral 101 denotes a zoom lens. Reference numeral 121 denotes a camera as a photographing apparatus. The zoom lens 101 can be attached to and detached from the camera 121. Reference numeral 122 denotes a photographing system configured by attaching the zoom lens 101 to the camera 121.

  The zoom lens 101 includes a focus lens group 102, a variable power lens group 103, a light amount adjusting diaphragm 104, and an imaging lens group 105. 105 has a branch element (not shown). The optical system 109 is a lens unit for detecting the in-focus position using the light beam branched by the branch element.

  Reference numeral 110 denotes a photoelectric conversion element for detecting an in-focus state such as a CCD sensor or a CMOS sensor that receives an image formed by the optical system 109.

  Reference numerals 111 and 112 denote driving mechanisms such as helicoids and cams for driving the focus lens group 102 and the variable power lens group 103, respectively, in the optical axis direction. The drive mechanisms 111 and 112 can be electrically driven by the drive unit 120 and can be manually driven.

  Reference numerals 113 to 115 denote motors (drive means) that electrically drive the drive mechanisms 111 and 112 and the light amount adjusting diaphragm 104.

  Reference numerals 116 to 118 denote detectors such as an encoder, a potentiometer, or a photosensor for detecting the positions of the focus lens group 102 and the variable power lens group 103 on the optical axis and the aperture diameter of the light amount adjusting diaphragm 104. .

  123 is stored in advance at the time of shipment from the factory, or can be arbitrarily stored by the user, focusing position information and spectral sensitivity information for autofocusing, or the imaging lens group 105 and the photoelectric conversion element 110. This is a memory for storing filter information to be inserted between.

  A CPU 119 calculates the in-focus position information from the obtained spectral sensitivity information, and selects a filter to be inserted between the imaging unit 105 and the light receiving element 110.

  A member 124 is used by the user to instruct or select spectral sensitivity information necessary for changing the focusing process or changing the focusing process based on the spectral sensitivity information of the imaging system.

  In the camera 121, reference numeral 125 denotes a member that instructs the user to take a white balance when the color temperature of the illumination changes.

  White balance is to make the output ratio of each channel set for the wavelength range the same.

  Reference numeral 106 denotes a camera optical system including a color temperature conversion filter, an ND filter, and a color separation prism. Reference numeral 107 denotes an image sensor (photoelectric conversion element) such as a CCD sensor or a CMOS sensor that receives a subject image formed by the zoom lens 101. Reference numeral 108 denotes a CPU that performs white balance adjustment by processing the signal intensity obtained from the image sensor 107. Reference numeral 126 denotes a memory for storing white balance information obtained by the calculation process.

  Reference numeral 127 denotes an information transmission member such as a cable or a contact connector that can transmit white balance information and the like between the camera 121 and the CPU 119 that controls the zoom lens 101.

  An autofocus process in the photographing system 122 will be described. In the zoom lens 101, the light beam branched by the branching optical system in the imaging unit 105 is guided to the photoelectric conversion element 110 by the optical system 109. The focus position information stored in the memory 123 is read from the zoom, focus, and aperture position information obtained at 116 to 118 and the signal obtained by the photoelectric conversion element 110, and the focus position calculated by the CPU 119 is read. The focus lens group 102 is driven using a motor 113.

  Next, an embodiment in which in-focus position information is changed when the color temperature of illumination changes in the photographing system 122 will be described. The following Example 1 to Example 5 (FIGS. 1 to 5) correspond to the configuration of the schematic diagram of FIG. Further, the following Example 6 to Example 10 (FIGS. 6 to 10) correspond to the configuration of the schematic diagram of FIG.

  FIG. 1 shows a flowchart of the first embodiment. When the instruction member 125 of the camera 121 instructs the white balance to be completed, and the zoom lens 101 is completed (S11), the zoom lens 101 is inserted into the camera optical system 106 through the information transmission member 127. And the relative intensity ratio information of each channel from the camera memory 126 (S12). Calculation processing is performed by the CPU 119 of the zoom lens 101 from the obtained filter information and relative intensity ratio information of each channel (S13), and in-focus position information as a calculation result is stored in the memory 123 (S14).

  FIG. 2 shows a flowchart of the second embodiment. When the member 124 is instructed to calculate the in-focus position information based on the relative intensity ratio information of each channel stored in the camera memory 126 (S21), the zoom lens 101 passes the information transmission member 127 to the camera. Information on the color temperature conversion filter inserted in the optical system 106 and information on the relative intensity ratio of each channel are acquired from the camera memory 126 (S22). Calculation processing is performed by the CPU 119 of the zoom lens 101 from the obtained white balance information (S23), and in-focus position information as a calculation result is stored in the memory 123 (S24).

  FIG. 3 shows a flowchart of the third embodiment. When it is instructed by the member 124 to change the in-focus position information (S31), the user arbitrarily selects the member 124 from the relative intensity ratio information of several channels stored in the memory 123 in advance. Then, the CPU 119 of the zoom lens 101 performs calculation processing from the selected information (S33), and the focus position information as the calculation result is stored in the memory 123 (S34).

  At this time, the relative intensity ratio information of each of the channels stored in advance in the memory 123 assumes various illumination conditions at the time of photographing at the time of factory shipment. Also, the relative intensity ratio information of each channel acquired from the camera 121 in the first and second embodiments and stored in the memory 123 may be selected.

  Further, the information stored in advance in the memory 123 is not the relative intensity ratio information of each channel shown in the flowchart (S32) of the third embodiment, but the focus position information of the calculation result stored in (S34). But you can. Further, the focus position information calculated in the flowcharts (S14) and (S24) of the first embodiment and the second embodiment and stored in the memory 123 may be used. As a result, since the in-focus position information that has already been calculated is used, the calculation process of the flowchart (S33) of the third embodiment may not be performed.

  FIG. 4 shows a flowchart of the fourth embodiment. In Example 4, the white balance can be achieved by the photoelectric conversion element 110 of the branching optical system. As a result, the color balance of the branching optical system is equivalent to the color balance in the imaging system, and a highly accurate in-focus position search is possible. When the instruction member 125 of the camera 121 instructs the white balance to be completed, and the zoom lens 101 completes the process (S41), the zoom lens 101 performs white balance by the photoelectric conversion element 110 of the branch optical system, and relative to each channel. The intensity ratio information is acquired (S42). The relative intensity ratio information of each channel is stored in the memory 123 (S43), and thereafter, the output signal from the photoelectric conversion element 110 is processed based on the relative intensity ratio information of each channel.

  FIG. 5 shows a flowchart of the fifth embodiment. In Example 5, it is possible to achieve white balance with the photoelectric conversion element 110 of the branch optical system. As a result, the color balance of the branching optical system is equivalent to the color balance in the imaging system, and a highly accurate in-focus position search is possible. When it is instructed to obtain the relative intensity ratio information of each channel of the branch optical system from the member 124 (S51), the white balance is taken by the photoelectric conversion element 110 of the branch optical system, and the relative intensity ratio information of each channel is obtained. Acquired (S52), the relative intensity ratio information of each channel is stored in the memory 123 (S53), and thereafter, the output signal from the photoelectric conversion element 110 is processed based on the relative intensity ratio information of each channel.

  Next, FIG. 12, which is a configuration diagram of the sixth to tenth embodiments (FIGS. 6 to 10), will be described. The light beam branched by the branching optical system in the imaging unit 105 is guided to the light receiving element 110 through the optical system 109 and the filter 128. The member 129 holds a plurality of filters 128, and an arbitrary filter selected by the CPU 119 can be inserted on the optical axis of the optical system 109 by a motor (driving means) 130 that is electrically driven.

  FIG. 6 shows a flowchart of the sixth embodiment. When the instruction member 125 of the camera 121 is instructed to achieve white balance and that is completed (S61), the zoom lens 101 is inserted into the camera optical system 106 through the information transmission member 127. And the relative intensity ratio information of each channel are acquired from the camera memory 126 (S62). The CPU 119 selects a preset filter 128 for the relative intensity ratio information of each channel (S63), drives the member 129 with the motor 130, and selects the filter selected in (S63) with the optical system. It is inserted on the optical axis 109 (S64). Thereby, since the color balance between the branching optical system and the imaging system approaches, the focusing accuracy is improved.

  FIG. 7 shows a flowchart of the seventh embodiment. When the member 124 is instructed to insert a filter into the branching optical system (S71), the zoom lens 101 transmits information about the color temperature conversion filter inserted into the camera optical system 106 through the information transmission member 127, and the camera. The relative intensity ratio information of each channel is acquired from the memory 126 (S72). The CPU 119 selects a preset filter 128 for the relative intensity ratio information of each channel (S73), drives the member 129 with the motor 130, and selects the filter selected in (S73) with the optical system. It is inserted on the optical axis 109 (S74).

  FIG. 8 shows a flowchart of the eighth embodiment. When it is instructed to insert a filter into the branching optical system from the member 124 (S81), the user arbitrarily selects the member 124 from the relative intensity ratio information of several channels stored in the memory 123 in advance. Select (S82), the CPU 119 selects a preset filter 128 for the relative intensity ratio information of each channel (S83), drives the member 129 with the motor 130, and is selected in (S83) The filter is inserted on the optical axis of the optical system 109 (S84).

  FIG. 9 shows a flowchart of the ninth embodiment. In Example 9, the photoelectric conversion element 110 of the branching optical system can acquire the relative intensity ratio information of each channel, but the relative intensity ratio information of each channel can be stored in the memory 123, It is assumed that the output signal from the photoelectric conversion element 110 cannot be processed based on the relative intensity ratio information of the channel. When the instruction member 125 of the camera 121 instructs the white balance to be completed, and the zoom lens 101 is completed (S91), the zoom lens 101 performs white balance with the photoelectric conversion element 110 of the branching optical system, and relative to each channel. The intensity ratio information is acquired (S92). The CPU 119 selects a preset filter 128 for the relative intensity ratio information of each channel (S93), drives the member 129 with the motor 130, and selects the filter selected in (S93) with the optical system. It is inserted on the optical axis 109 (S94). Thereby, since the color balance between the branching optical system and the imaging system approaches, the focusing accuracy is improved.

  FIG. 10 shows a flowchart of the tenth embodiment. In Example 10, the photoelectric conversion element 110 of the branch optical system can acquire the relative intensity ratio information of each channel, but stores the relative intensity ratio information of each channel in the memory 123, It is assumed that the output signal from the photoelectric conversion element 110 cannot be processed based on the relative intensity ratio information of the channel. When it is instructed to obtain the relative intensity ratio information of each channel of the branch optical system from the member 124 (S101), the zoom lens 101 takes white balance by the photoelectric conversion element 110 of the branch optical system, and Relative intensity ratio information is acquired (S102). The CPU 119 selects a preset filter 128 for the relative intensity ratio information of each channel (S103), drives the member 129 with the motor 130, and selects the filter selected in (S103) with the optical system. It is inserted on the optical axis 109 (S104). Thereby, since the color balance between the branching optical system and the imaging system approaches, the focusing accuracy is improved.

  In FIG. 12, the filter 128 is inserted between the optical system 109 and the photoelectric conversion element 110, but between the imaging lens group 105 and the photoelectric conversion element 110 and on the optical axis of the optical system 109. If present, the insertion location is arbitrary.

  Next, numerical examples of the present invention will be shown. As Numerical Example 1, a zoom lens is shown.

  (Numerical example 1)

  The zoom lens according to Numerical Example 1 is a photographing lens system used in an imaging apparatus for television broadcasting.

  i indicates the order of the surfaces from the object side, ri is the radius of curvature of each surface, di is the lens thickness and spacing between the i-th surface and the i + 1-th surface, and ni and νi are based on the d-line, respectively. Refractive index and Abbe number are shown. F indicates a focal length and Fno indicates an F number. R58 and r59 are glass materials corresponding to color separation prisms. Further, r40 and r41 indicate the surfaces of the branch elements. Further, the focal length range can be changed by switching the extender portion from r42 to r46.

  FIG. 13 is a lens cross-sectional view at the wide-angle end of the zoom lens according to Numerical Example 1. In the lens cross-sectional view, the left side is the subject side (front), and the right side is the image side (rear). In order from the object side to the image side, a focusing unit LF including a focusing lens unit L11, and a zooming unit including two lens units (variator lens unit L12 and compensator lens unit L13) that move on the optical axis for zooming. LZ, an aperture stop SP that limits the amount of light passing therethrough, and an imaging unit LR that includes a plurality of lens groups for imaging. The imaging unit LR includes lens groups L21, L22, and L23.

  The lens group L21 is a lens group including a branch element LD that branches an incident light beam into a plurality of optical paths.

  The lens unit L21 includes an anti-vibration lens IS that moves a part of the lens units so as to have a component perpendicular to the optical axis (parallel decentering or rotational decentering) to change the image position.

  The anti-vibration lens group IS is arranged on the object side with respect to the branch element LD for branching a part of the light flux for imaging. In this way, the focus detection means for searching for the best focus position arranged after the branching obtains a stable signal that is anti-vibrated and detects the more accurate best focus position.

  LA is a branching optical system. The branching optical system LA is used to obtain a focus detection signal of the photographing optical system (zoom lens) by a known method using a part of the photographing light beam branched by the branching element LD. For example, in the phase difference method, a secondary imaging lens that forms a subject image for each of the plurality of regions by light beams emitted from a plurality of regions of the exit pupil of the zoom lens, and a position where a plurality of subject images are formed, respectively. It has the light-receiving part provided. The light amount distribution of the subject image is converted into an electrical signal by the light receiving unit, and the focal point information of the zoom lens is obtained by the calculation means from the relative positional relationship of the plurality of subject images using the signal at this time.

  FIG. 14 shows a schematic diagram of the branch element LD and the branch optical system LA in this numerical example. In FIG. 10, x is the optical axis of the imaging system (zoom lens), y is the optical axis of the branching optical system LA, and S is the reflecting surface for branching the light beam.

  The reflecting surface S branches incident light into transmitted light and reflected light at a predetermined ratio. In consideration of the direction in which the optical path is to be branched (optical axis y), the optical path is arranged at an appropriate angle with respect to the optical axis x. Further, the ratio of reflection and transmission of the reflecting surface S is appropriately distributed in consideration of the amount of light required for the imaging system and the branch optical system LA.

  The lens unit L22 is inserted into and removed from the optical path so as to be convertible with the extender lens unit Ex in order to shift the focal length range of the entire system.

  The lens group L23 is a fixed group for image formation. The lens unit L23 is movable in the optical axis direction during flange back adjustment and macro photography.

  G denotes an optical block corresponding to a color separation prism, an optical filter, a face plate, a quartz low-pass filter, an infrared cut filter, or the like.

  IP is an image plane, and corresponds to an imaging plane of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor when used as an imaging optical system of a television camera, a video camera, or a digital still camera.

  FIGS. 15A and 15B are spherical aberration diagrams at the wide-angle end and (B) telephoto end when the object distance is infinity in the zoom lens of Numerical Example 1 in which the lens unit L22 is inserted. It is. FIGS. 16A and 16B show the zoom lens of Numerical Example 1 in which the extender lens group Ex is inserted, at (A) the wide angle end and (B) the telephoto end when the object distance is infinity. It is a spherical aberration diagram. In the figure, the solid line represents the e line, the one-point oblique line represents the C line, and the two-point oblique line represents the f line. 15 and 16, it can be seen that the focus positions at the respective wavelengths are different. It can also be seen that the focus position of each wavelength is larger at the telephoto end than at the wide-angle end. This is because the difference in vertical magnification at each wavelength becomes significant on the telephoto side. Further, at the telephoto end, the entrance pupil diameter increases to secure the F number, and the amount of spherical aberration increases. When white balance is achieved with a camera having an image sensor, a difference in color balance occurs between the branching optical system and the imaging system, and the focus position is different in each optical system. For this reason, in an imaging system that searches for the in-focus position using the branching optical system, a difference occurs between the in-focus position searched for by the branching optical system and the in-focus position of the captured image by the camera, and the focusing accuracy of autofocus deteriorates. End up.

  In order to prevent the deterioration of focusing accuracy, first, in the same photographing system as in FIG. 11 in which the zoom lens of the numerical value example 1 is attached to the camera, based on the white balance information, the above equation (1) is used. An embodiment for calculating in-focus position information will be described.

  The photographing system of the present embodiment has three RGB channels. FIG. 17 shows a schematic diagram thereof.

  The horizontal axis represents wavelength, and the vertical axis represents signal intensity. R, G, and B in the figure indicate an R channel, a G channel, and a B channel, respectively. FIG. 17A shows an output signal of each channel from the camera when photographing under certain illumination. If white balance is achieved with the camera in this state, an output signal shown in FIG. At this time, the ratio of the integrated value of the signal intensity to the wavelength of each channel, that is, the output ratio is the same.

  Table 5 shows the constituent wavelengths and sensitivity ratios of the respective channels in this embodiment. The sensitivity in Table 5 assumes the spectral transmittance of the zoom lens and the spectral sensitivity of the image sensor and color separation optical system in the camera, and does not consider the color temperature of the photographic illumination. In other words, the sensitivity at each wavelength of each channel with respect to the color temperature of the photographic illumination is assumed to be a value of 1 state.

Table 6 at the time of lens groups L22 insert, showing the position information d _i focus each channel case of the wide-angle end and the telephoto end. The focus position information d _i (i is the channel name) in this numerical example is the focus position on the optical axis of the zoom lens. Here, the values are shown when the zoom position is at the wide-angle end and the telephoto end and the object distance is infinite. The in-focus position was defined as the peak value of MTF at the center of the photographic field for the 25 lp / mm chart on the imaging plane. At this time, the focusing position of the G channel was set to zero at both the wide angle end and the telephoto end.

  For example, suppose that shooting is performed under a light source with a color temperature of 3200K. Table 7 shows the intensity ratio at each wavelength and the intensity ratio at each channel of the 3200K light source.

  The intensity ratio in each channel in Table 7 was calculated from the integrated value (sum) of the intensity ratios at each wavelength constituting the channel.

In the NTSC television camera system, the luminance signal forming the image is composed of the intensity ratio G: R: B = 6: 3: 1 of each channel. In this embodiment, the relative intensity S _i (i is the channel name) of the output in each channel incident on the image sensor of the imaging system is the intensity ratio value of each channel shown in Table 7 above, and the intensity of the luminance signal. Multiply the ratio. The spectral sensitivity information described above in the present embodiment indicates this relative intensity ratio S _i . It indicates the relative intensity ratio S _i of each channel in Table 8. The relative intensity ratio S _i of each channel was set so that the intensity of the G channel was 1.

  When shooting under a light source with a color temperature of 3200K, if the white balance is taken with the camera, the intensity ratio of each RGB channel is corrected to 1: 1: 1. At this time, the in-focus position information BP serving as a target value at the time of autofocus is obtained by the above equation (1). Table 4 shows the calculation result of the above equation (1). Table 6 shows the in-focus position information d for each channel necessary for the calculation of the equation (1).

Although not shown in this numerical example, the color inserted into the camera optical system 106 obtained from the camera 121 through the information transmission member 127 in calculating the relative intensity S _i of the output in each channel of Table 8 is shown. It is good to consider the information of the temperature conversion filter. In this case, the color temperature relative transmission of each channel of the conversion filter it is sufficient multiplying the S _i.

  In Table 6, for the sake of simplicity, only the values at the zoom position at the wide angle end and the telephoto end and the object distance at infinity are shown, but the focus position information d at a plurality of zoom positions and object distances is shown. The in-focus position information BP is preferably calculated using the value of the in-focus position information d that is close to the shooting conditions and is stored in advance in the memory 123. Thereby, high-precision autofocus can be realized.

  By the way, in this numerical example, the branch element LD is arranged on the object side from the lens group L22 or the extender Ex. Thereby, even if the field angle of view changes due to the insertion / extraction of the lens unit L22 and the extender Ex, the light flux taken into the branch optical system LA does not change. That is, it is not necessary to change the autofocus process by inserting and removing the lens group, and an autofocus imaging system can be realized with a relatively simple configuration.

  On the other hand, the branch element LD may be disposed closer to the image plane than the lens unit L22 or the extender Ex. However, at this time, since the photographing light beam and the light beam taken into the branching optical system LA change in the same manner due to the insertion and removal of the lens group, the focusing position information d in each channel when the lens group L22 is inserted in Table 6 In addition, it is necessary to previously store d in the memory 123 when the extender Ex is inserted.

Table 9 shows at the time of the extender Ex group insertion, the position information d _i focus each channel case of the wide-angle end and the telephoto end. Here, the values are shown when the zoom position is at the wide-angle end and the telephoto end and the object distance is infinite. The in-focus position was defined as the peak value of MTF at the center of the photographic field for the 25 lp / mm chart on the imaging plane. At this time, the focusing position of the G channel was set to zero at both the wide angle end and the telephoto end. The values shown in Table 5 were used for the constituent wavelengths and sensitivity ratios of each channel.

Also, shown in Table 10, similarly to the above Table 8, the relative intensity ratio S _i of each channel, the focus position information BP calculated in equation (1).

  As described above, when the branch element LD is disposed closer to the image plane than the lens group L22 or the extender lens group Ex, it is determined whether the lens group L22 or the extender lens group Ex is inserted in the zoom lens (not shown). It is necessary to calculate using the values in Table 6 when the lens unit L22 is inserted and using the values in Table 9 when the extender lens unit Ex is inserted.

  Next, in the same photographing system as in FIG. 12 in which the zoom lens of the numerical example 1 is attached to the camera, based on the relative intensity ratio information of each channel obtained from the photoelectric conversion element of the camera or the branch optical system, An embodiment in which a filter is inserted for the branched light beam will be described.

For example, suppose that shooting is performed under a light source with a color temperature of 3200K. The relative intensity ratio information of each channel obtained from the camera 121 or the photoelectric conversion element of the branch optical system is the relative intensity ratio S _i of each channel shown in Table 8. At this time, in order, with the same color balance in the imaging system and the branching optical system, a filter having a transmittance of the inverse of the relative intensity ratio S _i of each channel may be inserted into the branch optical system. Table 11 shows the relative intensity of each channel of the transmitted light amount of the filter to be inserted. The intensity of the G channel was set to 1.

  Here, the filter inserted under the light source having a color temperature of 3200K has been described. However, a plurality of filters corresponding to various color temperature conditions are provided in advance in the member 128, and the CPU 119 determines from the spectral sensitivity information obtained. It is preferable to select a filter closest to the color balance of the imaging system and insert it on the optical axis of the optical system 109 by the motor 130.

  As described above, more accurate autofocus can be realized by inserting an appropriate filter into the branching optical system for the obtained relative intensity ratio information of each channel.

  In Embodiments 1 to 10 or Numerical Embodiment 1, when the CPU 119 fails to obtain the relative intensity ratio information of each channel from the camera 121 or the memory 123, the calculation of the in-focus position information is not performed or the branch is performed. Do not insert a filter into the optical system. Alternatively, the color temperature setting at the time of shipment of the zoom lens 101 (in-focus position information BP or a branch optical system filter) may be restored. Although the color temperature setting at the time of factory shipment in the numerical example 1 is described above, the sensitivity at each wavelength of each channel is assumed to be one color temperature.

  As described above, according to each embodiment, it is possible to realize autofocus that can accurately search for the in-focus position even when the color temperature of illumination changes.

LF focusing section LZ zooming section LR imaging section LA branching optical system LD branching element L11 focusing lens group L12 variator lens group L13 compensator lens group L21 lens group L21
L22 Lens unit L22
L23 Lens unit L23
Ex Extender lens group SP Aperture stop G Glass block IS Anti-vibration lens group

Claims (12)

  A branching optical system for branching a part of a light beam in an imaging optical system and detecting the in-focus state of the imaging system by the branched light beam, and a camera having a plurality of channels having sensitivity to a predetermined wavelength range The zoom lens for changing the focusing process based on the relative intensity ratio information of each channel of the imaging system.   2. The zoom lens according to claim 1, wherein information on a filter inserted in the camera is obtained from a camera having an image sensor and the focus position process is changed.   3. The zoom lens according to claim 1, wherein the relative position ratio information of each channel is obtained from a camera having an image sensor and the focus position information is changed.   2. The zoom lens according to claim 1, wherein focus position information is changed based on relative intensity ratio information of each channel stored in advance in the zoom lens. 5. The photographing system having a zoom lens according to claim 1, wherein the focus position information is calculated according to the following expression based on the acquired relative intensity ratio information of each channel.

BP: In-focus position information after correction n: Number of output signal channels
S _i : Relative intensity of each channel output
d _i : Focus position information for each channel   2. The zoom lens according to claim 1, wherein a filter is inserted into the branch optical system based on relative intensity ratio information of each channel of the imaging system stored in advance in the zoom lens.   3. The zoom lens according to claim 1, wherein a filter is inserted into the branch optical system based on the relative intensity ratio information of each channel acquired from the camera.   2. The zoom lens according to claim 1, wherein a relative intensity ratio of each channel is changed by a photoelectric conversion element for detecting a focus position in the branch optical system.   2. The zoom lens according to claim 1, wherein when the acquisition of the relative intensity ratio information of each channel fails, the focusing process is not changed.   2. The zoom lens according to claim 1, wherein when the acquisition of the relative intensity ratio information of each channel fails, a focusing process at the time of factory shipment of the zoom lens is set.   An imaging system comprising the zoom lens according to claim 1.   12. The photographing system according to claim 11, wherein a zoom lens is replaceable with respect to the camera.

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