JP2012098569A - Position adjustment device for imaging and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize an image obtained by imaging by an image pick-up device through an imaging lens with enlarged depth of field at a higher quality in a position setting device for imaging.SOLUTION: When fixing an imaging position for imaging an optical image formed through the imaging lens 10 by the image pick-up device 20 with enlarged depth of field having the lens Nyquist frequency of the imaging lens 10 being one time or more and four times or less of the sensor Nyquist frequency of the image pick-up device 20: the defocus MTF peak position regarding a subject of infinite distance in the imaging lens 10 is measured by peak position measuring means 210; whether the imaging lens 10 satisfies all of a plurality of conditional expressions regarding the defocus MTF peak position of this imaging lens 10 is determined by determination means 280; and the imaging position is fixed so that the conditional expressions regarding the imaging position are satisfied regarding the imaging lens 10 which is determined to satisfy all of the plurality of conditional expressions above by position setting means 290.

Description

  The present invention relates to an imaging position adjustment device, and more particularly, to an imaging position adjustment device used for determining an imaging position when an optical image formed through an imaging lens is imaged by an imaging device, and an imaging position by the imaging position adjustment device. The present invention relates to an imaging apparatus in which an imaging lens and an imaging element are defined.

  Conventionally, for example, a digital camera having an autofocus function is known as an imaging device for photographing a subject. Such an imaging apparatus captures an optical image of a subject formed on an imaging surface of an image sensor such as a CCD through an imaging lens. When a long-distance subject is focused, an optical image of a short-distance subject is obtained. On the contrary, blurring occurs in an optical image of a long-distance subject when focusing on a short-distance subject.

  Therefore, when shooting a long-distance subject, the imaging surface is positioned at a defocus MTF peak position at a high spatial frequency related to the imaging lens used for the shooting, and when shooting a short-distance subject, the defocus MTF peak position at a low spatial frequency. The imaging position is controlled so that the imaging surface is positioned so that a fine structure is imaged with a higher contrast when shooting a long-distance subject, and a rough structure is imaged with a higher contrast when shooting a short-distance subject. There is known a method for adjusting the value (see cited document 1).

  The defocus MTF peak position is a defocus position where the MTF value is maximum in the defocus MTF curve. The defocus MTF curve is a curve representing a change in the MTF value related to an image obtained when the imaging surface is defocused with respect to the imaging lens.

  There is also known an imaging apparatus in which the focusing function is omitted by mounting an imaging lens with an expanded depth of field. In such an imaging apparatus, the optical image of the subject formed on the imaging surface through the imaging lens has a low contrast as a whole (the value of the defocus MTF is low as a whole), but from a short distance to a long distance. The imaging position can be determined so as to have a certain level of contrast at any of the above positions and at any frequency from a high spatial frequency to a low spatial frequency.

  In such an imaging lens with an increased depth of field, a change in MTF value due to defocusing, that is, a difference in shooting distance (change in MTF value in a defocused MTF curve) has an increased depth of field. Not more gradual than normal lenses.

  An imaging lens with an expanded depth of field has a larger positional shift in the defocus direction (optical axis direction of the imaging lens) of each defocus MTF peak position at different spatial frequencies compared to a normal imaging lens. Furthermore, the shape of the defocus MTF curve is asymmetric.

  Therefore, when an imaging device is manufactured by combining an imaging lens and an imaging element that captures an optical image formed through the imaging lens, the positioning of the imaging surface of the imaging element with respect to the imaging lens is, for example, an actual imaging lens. Through an empirical judgment, an image representing a resolution chart captured by the image sensor is visually observed.

    JP 2003-66317 A

  However, when the position of the imaging surface (imaging position) with respect to the imaging lens is determined by empirical judgment as described above, there is insufficient depth of field or insufficient contrast in the image obtained by actually imaging the subject. There are many cases where this occurs, and there is a problem that large variations in image quality occur.

  The present invention has been made in view of the above circumstances, and the imaging position is set so as to stabilize the quality of an image obtained by imaging with an imaging element through an imaging lens with an expanded depth of field at a higher quality. It is an object of the present invention to provide an imaging position setting device that can be determined, and an imaging device in which an imaging lens whose imaging position is determined by the imaging position adjustment device and an imaging element are arranged.

The imaging position setting device of the present invention is an imaging position for determining an imaging position when an optical image formed through an imaging lens having an increased depth of field is imaged by an imaging element in which a large number of light receiving pixels are arranged. An adjusting device, the imaging lens is formed so that the lens Nyquist frequency of the imaging lens is 1 to 4 times the sensor Nyquist frequency of the imaging device, and the imaging lens is infinite. Conditional expression (1) when the peak position measuring means for measuring the defocus MTF peak position for a far object and the imaging lens form a light propagation direction when forming an optical image by this imaging lens: F ² ≦ Zp (1/4) −Zp (1/2) ≦ 4 × F ² , (2): F ² ≦ Zp (1/8) −Zp (1/4) ≦ 4 × F ² , (3 ): All ZH <ZL With respect to the determination unit that determines that the image is satisfied and the imaging lens that is determined to satisfy all of the conditional expressions (1), (2), and (3), the imaging position is expressed by conditional expression (4): Zp ( 1/2) <Zt <Zp (1/4) and position setting means for determining so as to be satisfied.

  However, F: F number, Zp (1/2): Defocused MTF peak position for an infinite object related to 1/2 sensor Nyquist frequency, Zp (1/4): About an infinite object related to 1/4 sensor Nyquist frequency Defocus MTF peak position, Zp (1/8): 1/8 sensor defocus MTF peak position for an infinite object related to the Nyquist frequency, ZH: defocus MTF peak position for an infinite object related to a high spatial frequency, ZL : Defocused MTF peak position for an object at infinity with respect to a spatial frequency lower than the high spatial frequency, Zt: imaging position.

  The position setting means may output position information indicating an imaging position that satisfies the conditional expression (4).

  The imaging lens may have a fixed focal length.

  The imaging lens may have a diaphragm aperture fixed.

  The image pickup apparatus of the present invention is characterized in that an image pickup lens whose image pickup position is determined by the image pickup position adjusting device and an image pickup element are arranged.

  The imaging device can be a surveillance camera, a mobile phone, a portable information terminal device, an in-vehicle camera, an interphone camera, or an endoscope.

  The imaging position is a relative position of the imaging surface of the imaging element with respect to the imaging lens.

  The imaging lens with the expanded depth of field is such that the contrast of the optical image of the subject from a long distance to a short distance formed on the imaging surface through the imaging lens is reduced overall (the MTF when defocused). Although the value becomes lower overall, an optical image with a contrast higher than a predetermined value can be obtained for a subject at any position from a short distance to a long distance, and for a subject having any spatial frequency from a high frequency to a low frequency. An imaging lens that can be formed on an imaging surface. Note that an optical image having a predetermined or higher contrast means an optical image having an MTF value of 20% or higher. In addition, the imaging lens with an expanded depth of field is used in a photographing apparatus that photographs a subject without performing focusing.

  A method for obtaining an image with an expanded depth of field by photographing using an imaging lens with an expanded depth of field will be described below.

  Through an imaging lens with an expanded depth of field, an optical image that is blurred on the object to be photographed over the entire distance is imaged, and the resulting original image is subjected to contrast recovery processing, and the original image is blurred. Is known, that is, a method of increasing the contrast of the original image and, as a result, obtaining a blur-free image taken with a lens having a very deep depth of field. An imaging lens with an expanded depth of field used in such a method is called an EDOF (Extended / Extension of Depth of Field / Focus) lens.

  In the contrast recovery process, a restoration filter having an inverse characteristic of the blur characteristic of the imaging lens is applied to the original image obtained through the imaging lens with an expanded depth of field, thereby extending from a short distance to a long distance. The correction is performed so as to increase the contrast of each subject arranged in a wide photographing range (for example, to have a clear outline).

  In addition, an imaging lens with an expanded depth of field ideally forms an optical image of a subject to which a constant blur is given regardless of the shooting distance on the imaging surface.

  More specifically, the imaging lens with an expanded depth of field is a point image (a constant image) that represents a point image representing a subject placed at various shooting positions. It is formed on the imaging surface as a deteriorated point image having a light intensity distribution. On the other hand, the contrast recovery processing is performed by using an optical image made up of each degraded point image having the above-mentioned constant light intensity distribution as a target having a light intensity distribution that is a restoration target value of the degraded point image. The image is restored to an image consisting of a point image (for example, a point image having an ideal light intensity distribution).

  According to this technique, an image having a high overall contrast (an image obtained by enlarging the depth of field) for a subject at any shooting distance without reducing the aperture of the imaging lens, that is, without reducing the amount of received light. ) Can be obtained. Regarding the above method, JP-A No. 2000-123168, JP-A No. 2009-124567, JP-A No. 2009-124568, JP-A No. 3275010 and the like can be referred to.

  As the contrast recovery process, for example, an image restoration process using Fourier transform, an edge enhancement process, a gamma correction process, a contrast enhancement process, or the like can be employed.

  According to the imaging position adjusting device of the present invention, the lens Nyquist frequency of the imaging lens is 1 to 4 times the sensor Nyquist frequency of the imaging device in which a large number of light receiving pixels are arranged, and the depth of field is expanded. In determining the imaging position when the optical image formed through the imaging lens is imaged by the imaging element, the defocus MTF peak position of the infinity subject with respect to the imaging lens is measured, and the optical image is obtained by the imaging lens. It is determined that the imaging lens satisfies all of the conditional expressions (1), (2), and (3) for an infinite object when the light propagation direction when forming an image is a positive direction. For the imaging lens determined to satisfy all of the expressions (1), (2), and (3), the imaging position is determined so as to satisfy the conditional expression (4). It can be compared with the case to determine the imaging position in empirical judgment by conventional such visually determined more objectively imaging position. Thereby, the imaging position can be determined so that the quality of the image obtained by imaging the optical image of the subject formed through the imaging lens with the imaging element is stabilized with higher quality.

  Accordingly, an image obtained by imaging an optical image representing a subject formed through the imaging lens with the imaging device using an imaging device in which the imaging lens whose imaging position is determined by the imaging position adjusting device and the imaging device are arranged is obtained. It is possible to suppress the occurrence of insufficient depth of field and insufficient contrast.

The figure which shows schematic structure of the imaging position adjustment apparatus by embodiment of this invention The figure which shows the imaging device of this invention which has arrange | positioned the imaging lens and imaging device by which the imaging position was determined by the imaging position adjustment apparatus of this invention. The figure which shows each defocus MTF curve about the infinite object regarding multiple types of spatial frequencies, and each defocus MTF peak position defined on those curves.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a schematic configuration of an imaging position adjustment device according to an embodiment of the present invention, and FIG. 2 is a diagram illustrating an imaging device including an imaging lens and an imaging element whose positions are determined by the imaging position adjustment device. FIG. 3 is a diagram showing a defocus MTF curve and a defocus MTF peak position on a coordinate plane in which the vertical axis represents the MTF value and the horizontal axis represents the defocus amount.

  An imaging position adjusting apparatus 200 of the present invention shown in FIG. 1 is for determining an imaging position when an imaging element 20 captures an optical image formed through the imaging lens 10.

  The imaging position determined by the imaging position adjusting device 200 is a relative position of the imaging surface 20M of the imaging element 20 with respect to the imaging lens 10 in the optical axis Z1 direction of the imaging lens 10. In addition, the imaging lens 10 and the imaging element 20 whose imaging positions are determined by the imaging position adjusting device 200 can be arranged in the imaging device 100. Note that the imaging element 20 can be a CCD element or a CMOS element. The imaging device 100 can be a surveillance camera, a mobile phone, a portable information terminal device, an in-vehicle camera, an interphone camera, or an endoscope.

  The imaging lens 10 is configured to increase the depth of field, and the lens Nyquist frequency of the imaging lens 10 is the sensor Nyquist frequency of the imaging device 20 in which a large number of light receiving pixels are arranged. 1 to 4 times or less.

  That is, the image sensor 20 is configured such that the sensor Nyquist frequency of the image sensor 20 is not more than 1 time and not less than 1/4 times the lens Nyquist frequency of the image pickup lens 10.

  Note that the imaging position adjusting device 200 is configured so that when the lens Nyquist frequency of the imaging lens 10 with an increased depth of field and the sensor Nyquist frequency of the imaging device 20 satisfy the above relationship, the imaging lens 10 and the imaging device. 20 is an adjustment target.

  Here, the imaging lens 10 is a lens that does not have a focusing mechanism and a diaphragm mechanism (a diaphragm aperture is fixed) and has a focal length fixed at 3.5 mm. Although the lens 10 has no focusing mechanism, it can be a lens having a diaphragm mechanism or a zoom lens having a variable focal length.

  The imaging position adjusting apparatus 200 measures the peak position of the defocus MTF peak position for the subject at infinity of the imaging lens 10 for each of the 1/2, 1/4, and 1/8 sensor Nyquist frequencies of the imaging device 20. When the propagation direction of light when forming an optical image through the peak position measurement unit 210 and the imaging lens 10 is a positive direction (+ Z direction), the imaging lens 10 satisfies the following conditions for an infinite object. A determination unit 280 that is a determination unit that determines that all of the expressions (1), (2), and (3) are satisfied, and imaging that is determined to satisfy the conditional expressions (1), (2), and (3) For the lens 10, data indicating the defocus MTF peak position measured by the peak position measuring unit 210 is input, and the imaging position satisfies the following conditional expression (4). And a position setting unit 290 is a position setting means for determining.

  The peak position measurement unit 210 includes an MTF measurement chart 220, a collimator lens 225, a lens mount 230, a linear slide 235 with a length measuring device, and a base table 215 on which the above-described components are arranged.

  Further, the peak position measurement unit 210 includes an imaging unit 240 for MTF measurement and a defocus MTF peak position calculation unit 245. The imaging unit 240 can be a CCD element or a CMOS element.

  The linear slide 235 with a length measuring device has a slide part 235S that can move in the optical axis Z2 direction (arrow Z direction in the figure) of the collimator lens 225, and the imaging part for MTF measurement is provided on the slide part 235S. 240 is arranged.

  Here, the position setting unit 290 outputs position information indicating an imaging position that satisfies the conditional expression (4).

  The conditional expressions (1) to (4) are shown below.

  Conditional expression (1): F2 ≦ [Zp (1/4) −Zp (1/2)] ≦ 4 × F2, conditional expression (2): F2 ≦ [Zp (1/8) −Zp (1/4) ] ≦ 4 × F2, conditional expression (3): ZH <ZL, conditional expression (4): Zp (1/2) <Zt <Zp (1/4).

  The symbol F is a value of the F number. Here, the value of the F number is 3.0.

  The symbol Zp (1/2) is the defocus MTF peak position for the ½ sensor Nyquist frequency for an object at infinity.

  A symbol Zp (1/4) is a defocus MTF peak position with respect to a 1/4 sensor Nyquist frequency for a subject at infinity.

  A symbol Zp (1/8) is a defocus MTF peak position with respect to a 1/8 sensor Nyquist frequency for an object at infinity.

  Further, symbol ZH is a defocus MTF peak position for a high spatial frequency related to a specific subject distance, and symbol ZL is a defocus MTF peak for a spatial frequency lower than the high spatial frequency related to the subject distance similar to the above. Position. Here, the specific subject distance is infinity.

  Reference sign Zt is an imaging position, that is, a relative position of the imaging surface 20M of the imaging element 20 with respect to the imaging lens 10 in the optical axis Z1 direction of the imaging lens 10.

  The lens Nyquist frequency of the imaging lens 10 is a value obtained as follows.

  That is, here, the F-number of the imaging lens 10 is 3.0, and the representative value (design reference wavelength) of the wavelength used for imaging with the imaging device 20 through the imaging lens 10 is 588 nm, so the lens Nyquist frequency is 1 / 3.0 / 0.000588≈567 / mm.

  Further, the 1/2, 1/4, and 1/8 sensor Nyquist frequencies of the image sensor 20 are values obtained as follows.

  Here, since the pitch of the pixels arranged in the image sensor 20 is 0.0014 mm, the sensor Nyquist frequency is a spatial frequency of 1/2 / 0.0014≈357 lines / mm.

  Therefore, the 1/2 sensor Nyquist frequency is 357 / 2≈179 lines / mm, the 1/4 sensor Nyquist frequency is 357 / 4≈89 lines / mm, and the 1/8 sensor Nyquist frequency is The spatial frequency is 357 / 8≈45 lines / mm.

  Next, the operation of the imaging position adjustment device 200 configured as described above will be described.

  First, the peak position measurement unit 210 measures the defocus MTF peak position of the imaging lens 10 with respect to the infinity subject. Here, the spatial frequency when the defocus MTF peak position is measured is 179 lines / mm which is a 1/2 sensor Nyquist frequency, 89 lines / mm which is a 1/4 sensor Nyquist frequency, and 1/8 sensor Nyquist frequency. There are 45 / mm, 20 / mm, and 10 / mm.

  First, the imaging lens 10 is arranged on the lens mount 230 so that the optical axis Z2 of the collimator lens 225 and the optical axis Z1 of the imaging lens 10 coincide.

  Accordingly, an image representing the MTF chart 220 is formed on the imaging surface 240M of the imaging unit 240 arranged on the slide unit 235S through the collimator 225 and the imaging lens 10.

  The imaging unit 240 includes a chart portion indicating 179 lines / mm, which is the 1/2 sensor Nyquist frequency, a chart portion indicating 89 lines / mm, which is the 1/4 sensor Nyquist frequency, and 1/1 in the MTF chart 220. The optical axes Z1 and Z2 as the slide portion 235S moves while imaging a chart portion indicating 45 / mm, a chart portion indicating 20 / mm, and a chart portion indicating 10 / mm, which are 8 sensor Nyquist frequencies. It is transferred in the direction of arrow Z in the figure, which is a parallel direction.

  The imaging unit 240 outputs, to the defocus MTF peak position calculation unit 245, image data D1 indicating each chart portion obtained by imaging the MTF chart 220 while being transferred in the Z direction.

  Further, the linear slide 235 with the length measuring device indicates the position data D2 indicating the position of the imaging unit 240 when the image indicated by the image data is captured, that is, the position in the Z direction of the imaging surface 240M of the imaging unit 240. The position data D2 shown is output.

  The image data D1 output from the imaging unit 240 and the position data D2 output from the linear slide 235 with a length measuring device are input to the defocus MTF peak position calculation unit 245.

  The defocus MTF peak position calculation unit 245 calculates the 1/2, 1/4, 1/8 sensor Nyquist frequency, 20 lines / mm, and the like by the calculation using the input image data D1 and the position data D2. Defocus MTF curves Mf (1/2), Mf (1/4), Mf (1/8), Mf (20), and Mf (10) are obtained for each spatial frequency of 10 lines / mm (see FIG. 3). ).

  Further, as shown in FIG. 3, the defocus MTF peak position calculation unit 245 has Pm (1/2) and Pm (1/4) that are the peak positions at which the MTF value is maximum on each defocus MTF curve. , Pm (1/8), Pm (20), Pm (10), the positions in the defocus direction (arrow Z direction in FIG. 1), that is, defocus MTF peak positions Zp (1/2), Zp ( 1/4), Zp (1/8), Zp (20), Zp (10) are obtained.

  In this way, the defocus MTF peak position calculation unit 245 determines the defocus MTF peak position Zp (1/2) for the infinity subject relating to the 1/2 sensor Nyquist frequency and the infinity subject relating to the 1/4 sensor Nyquist frequency. Defocus MTF peak position Zp (1/4), and defocus MTF peak position Zp (1/8) for an object at infinity with respect to 1/8 sensor Nyquist frequency, defocus for an object at infinity with 20 lines / mm The MTF peak position Zp (20) and the defocused MTF peak position Zp (10) for an infinitely far subject for 10 lines / mm are obtained.

  As can be seen from FIG. 3, Zp (1/2) = 0 μm, Zp (1/4) = 15 μm, Zp (1/8) = 27 μm, Zp (20) = 38 μm, Zp (10) = 51 μm. . The value of each defocus MTF peak position is a value when the defocus MTF peak position for an object at infinity at the 1/2 sensor Nyquist frequency is set to the reference position 0.

  Further, at each peak position Pm (1/2), Pm (1/4), Pm (1/8), Pm (20), and Pm (10) at which the MTF value is maximum on each defocused MTF curve. Are M (1/2), M (1/4), M (1/8), M (20), and M (10), the MTF values are M (1/2) = 30%, M (1/4) = 46%, M (1/8) = 65%, M (20) = 80%, M (10) = 95%.

  The defocus MTF peak position calculation unit 245 outputs the measurement data D3 regarding the defocus MTF peak position obtained as described above to the determination unit 280.

  In addition, the measurement of the said defocus MTF peak position by the peak position measurement part 210 can use the method known conventionally, for example, can refer to the above-mentioned Unexamined-Japanese-Patent No. 2003-66317 etc., for example.

  Next, the determination unit 280 that has input the measurement data D3 related to the defocus MTF peak position uses the measurement data D3 and the imaging lens 10 satisfies all of the conditional expressions (1), (2), and (3). It is determined whether or not to do.

Conditional expression (1): For F ² ≦ [Zp (1/4) −Zp (1/2)] ≦ 4 × F ² , F ² = 3 × 3 = 9, and [Zp (1/4) − Since Zp (1/2)] = 15−0 = 15 and 4 × F ² = 36, it can be seen that the imaging lens 10 satisfies the conditional expression (1).

Next, for conditional expression (2): F ² ≦ [Zp (1/8) −Zp (1/4)] ≦ 4 × F ² , F ² = 3 × 3 = 9, and [Zp (1 / 8) −Zp (1/4)] = 27−15 = 12, and 4 × F ² = 36, it can be seen that the imaging lens 10 satisfies the conditional expression (2).

  Subsequently, for conditional expression (3): ZH <ZL, defocus MTF peak position Zp (1/2) = 0 at a spatial frequency of 179 lines / mm = 0, defocus MTF peak position Zp (1 at a spatial frequency of 89 lines / mm) / 4) = 15 μm, defocus MTF peak position Zp (1/8) = 27 μm at a spatial frequency of 45 lines / mm, defocus MTF peak position Zp (20) = 38 μm, spatial frequency of 10 lines at a spatial frequency of 20 lines / mm Defocus MTF peak position Zp (10) at / mm: 51 μm, and the lower the spatial frequency, the larger the value of the defocus MTF peak position for an infinite subject. That is, it can be seen that the defocus MTF peak position is further away from the imaging lens as the spatial frequency is lower. More specifically, as shown in FIG. 3, Zp (1/2) <Zp (1/4) <Zp ( It can be seen that 1/8) <Zp (20) <Zp (10). Therefore, the determination unit 280 determines that the imaging lens 10 satisfies the conditional expression (3): ZH <ZL.

  Then, the determination unit 280 outputs determination result data D4 representing the determination result and the measurement data D3 to the position setting unit 290.

  The position setting unit 290 that has input the determination result data D4 and the measurement data D3 output from the determination unit 280 performs imaging for the imaging lens 10 determined to satisfy the conditional expressions (1), (2), and (3). The position is determined so as to satisfy the conditional expression (4): Zp (1/2) <Zt <Zp (1/4).

  That is, the position setting unit 290 captures the defocused MTF peak position Zp (1/2) of the imaging lens 10 for the infinity subject at the 1/2 sensor Nyquist frequency and the imaging for the infinity subject at the 1/4 sensor Nyquist frequency. The position of the imaging surface 20M of the imaging device 20 is determined between the lens 10 and the defocus MTF peak position Zp (1/4).

  More specifically, the position setting unit 290 determines the reference position 0 on the optical axis Z1 of the imaging lens 10 that is the defocus MTF peak position Zp (1/2) in the imaging lens 10 and the defocus MTF peak position Zp. Position data D5, which is position information for determining the position of the imaging surface 20M, is output between the reference position 0, which is (1/4), and a position 15 μm away in the + Z direction.

  For example, a position that is 7.5 μm away from the reference position 0 on the optical axis Z1 of the imaging lens 10 in the + Z direction, that is, the defocus MTF peak position Zp (1/2) and the defocus MTF peak position Zp (1/4). ) Position data D5 is output as position information for determining the position of the imaging surface 20M at an intermediate position between the positions.

  Note that the position of the imaging surface 20M with respect to the imaging lens 10 is not limited to the case where the reference position 0 is used as a reference, and the mounting of the imaging lens 10 that serves as an attachment surface when the imaging lens 10 is attached to the imaging device 100. The position setting unit 290 may generate the position data D5 so that the position of the imaging surface 20M with respect to the imaging lens 10 is determined with respect to the surface.

  Note that the imaging position is not necessarily determined at the intermediate position, and as long as it is between the defocus MTF peak position Zp (1/2) and the defocus MTF peak position Zp (1/4) as described above. The position of the imaging surface 20M may be determined at any position.

  Note that the action of determining the imaging position so as to satisfy the conditional expression (4) is not limited to the case where the position information is output by the position setting unit 290, but actually the position of the imaging surface 20M of the imaging element 20 with respect to the imaging lens 10 May be determined.

  In such a case, instead of attaching the imaging lens 10 to the lens mount 230, the imaging device 100 to which the imaging lens 10 is attached is attached to the lens mount 230. Further, instead of arranging the imaging unit 240 with respect to the slide part 235S of the linear slide 235 with a length measuring device, the imaging element 20 is arranged on the slide part 235S.

  Then, the position setting unit 290 outputs position data D5 indicating an imaging position that satisfies the conditional expression (4) obtained in the same manner as described above to the linear slide 235 with a length measuring device. Then, the linear slide 235 with a length measuring device to which the position data D5 is input moves the slide portion 235S on which the image sensor 20 is arranged, and the image pickup surface 20M of the image sensor 20 is positioned at the image pickup position indicated by the position data D5. Let At this time, the imaging apparatus 100 is in a state where the cover 102 is removed from the main body 101.

  Thereafter, the imaging element 20 positioned at the imaging position is fixed to the imaging device 100. Thereby, the position of the imaging element 20 with respect to the imaging lens 10 is fixed, and the imaging surface 20M of the imaging element 20 can be arranged at a predetermined imaging position (imaging position indicated by the position data D5) with respect to the imaging lens 10. .

  Finally, the cover 102 is attached to the main body 101, and the imaging apparatus 100 is ready for photographing.

  In such a case, the linear slide 235 with a length measuring device serving as a peak position measuring means also serves as a position setting means.

  Note that the peak position measurement unit 210 may measure only the defocus MTF peak positions for an infinitely distant subject related to, for example, 1/2, 1/4, and 1/8 sensor Nyquist frequencies. In such a case, if the inequality Zp (1/2) <Zp (1/4) <Zp (1/8) is satisfied for each defocus MTF peak position, the determination unit 280 determines that the imaging lens 10 is Conditional expression (3): It is determined that ZH <ZL is satisfied.

  In this way, by determining the imaging position by the imaging position adjusting device 200, it is possible to determine the imaging position more objectively as compared to the case where the imaging position is determined by visual empirical judgment as in the prior art. The imaging position can be determined so that the quality of the image captured by the imaging element is stabilized at a higher quality. Thereby, it is possible to suppress the occurrence of insufficient depth of field and insufficient contrast of an image obtained by imaging an optical image of a subject formed through the imaging lens with the imaging device.

  In addition to the monitoring camera and the mobile phone, the imaging device 100 may be, for example, a portable information terminal device, an in-vehicle camera, an interphone camera, an endoscope, or the like.

  The preferred embodiments of the imaging position adjusting apparatus according to the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without changing the gist of the invention. is there.

DESCRIPTION OF SYMBOLS 10 Imaging lens 20 Imaging element 200 Imaging position adjustment apparatus 210 Peak position measurement means 280 Determination means 290 Position setting means

Claims (11)

An imaging position adjustment device for determining an imaging position when an optical image formed through an imaging lens having an extended depth of field is imaged by an imaging element in which a large number of light receiving pixels are arranged,
The imaging lens is formed such that the lens Nyquist frequency of the imaging lens is 1 to 4 times the sensor Nyquist frequency of the imaging element,
Peak position measuring means for measuring a defocus MTF peak position for an infinitely distant subject relating to the imaging lens;
It is determined that the imaging lens satisfies all the following conditional expressions (1), (2), and (3) when the propagation direction of light when forming the optical image is a positive direction. A determination means;
Position setting means for determining the imaging position of the imaging lens determined to satisfy all of the conditional expressions (1), (2), and (3) so as to satisfy the following conditional expression (4): An imaging position adjusting device comprising:
F ² ≦ Zp (1/4) −Zp (1/2) ≦ 4 × F ² Conditional expression (1)
F ² ≦ Zp (1/8) −Zp (1/4) ≦ 4 × F ² Conditional expression (2)
ZH <ZL ... conditional expression (3)
Zp (1/2) <Zt <Zp (1/4) ... Conditional expression (4)
However,
F: F number Zp (1/2): Defocus MTF peak position for an infinite object with respect to 1/2 sensor Nyquist frequency Zp (1/4): Defocus MTF with respect to an infinite object for 1/4 sensor Nyquist frequency Peak position Zp (1/8): Defocused MTF peak position ZH for an infinite object related to 1/8 sensor Nyquist frequency: Defocused MTF peak position ZL for an infinite object related to a high spatial frequency: More than the high spatial frequency Defocus MTF peak position Zt for an object at infinity with a low spatial frequency: imaging position   2. The imaging position adjusting apparatus according to claim 1, wherein the position setting means outputs position information indicating an imaging position that satisfies the conditional expression (4).   The imaging position adjusting device according to claim 1, wherein the imaging lens has a fixed focal length.   The imaging position adjusting apparatus according to claim 1, wherein the imaging lens has a fixed aperture stop.   An imaging apparatus comprising: an imaging lens having an imaging position determined by the imaging position adjustment apparatus according to claim 1; and an imaging element.   The imaging apparatus according to claim 5, wherein the imaging apparatus is a surveillance camera.   The imaging apparatus according to claim 5, wherein the imaging apparatus is a mobile phone.   6. The imaging apparatus according to claim 5, wherein the imaging apparatus is a portable information terminal device.   The imaging apparatus according to claim 5, wherein the imaging apparatus is an in-vehicle camera.   The imaging apparatus according to claim 5, wherein the imaging apparatus is an interphone camera.   The imaging apparatus according to claim 5, wherein the imaging apparatus is an endoscope apparatus.

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