JP2019056780A - Optical system and image capturing device - Google Patents

Abstract

To provide an optical system which improves appearance (color and intensity irregularities) of out-of-focus images while minimizing reduction in light intensity of the out-of-focus images, and to provide an image capturing device having the same.SOLUTION: An optical system 1 comprises an aperture stop and an optical element that provides an apodization effect. The optical element has a transmittance that decreases with a radial distance from an optical axis and is wavelength-dependent. An effective diameter rof the optical system, a radial distance rfrom the optical axis to a point on the optical element where the transmittance is 0.9 times the maximum, a radial distance rfrom the optical axis to a point on the optical element where the transmittance is 0.5 times the maximum, and a radial distance rfrom the optical axis to a point on the optical element where the transmittance is 0.1 times the maximum satisfy predetermined conditional expressions.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an optical system having an optical element, and is particularly suitable for an imaging apparatus such as a silver salt film camera, a digital still camera, a video camera, and a TV camera.

  In general, the optical performance of a photographic lens system is evaluated by the imaging performance of a focused object. However, depending on the use of the photographing lens system, the appearance of an out-of-focus image (front blur, rear blur) may be an important evaluation index for the optical performance of the photographing lens system.

  An optical system including an apodization filter is disclosed in Patent Document 1 as a technique for making an out-of-focus image look preferable. Patent Document 1 uses an apodization filter configured such that the transmittance gradually decreases as it moves away from the optical axis in a direction perpendicular to the optical axis, and the radial transmittance distribution shape is substantially Gaussian. . As a result, an intensity distribution is added to the imaging light flux, and the appearance of an out-of-focus image is preferable.

JP 09-236740 A

  In general, in a wide-angle to medium-telephoto photographing lens system, sagittal halo of off-axis light flux causes uneven intensity of an out-of-focus image in the peripheral portion of the image. For this reason, it is possible to improve the appearance of an out-of-focus image in an off-axis light beam by giving a transmittance distribution to the light beam by an apodization filter and effectively removing sagittal halo. At that time, it is required as the performance of the apodization filter that sagittal halo is effectively removed while suppressing a decrease in the amount of light.

  However, in the conventional technique disclosed in Patent Document 1, since the Gaussian distribution type is adopted for the transmittance distribution of the apodization filter, the transmittance is lowered even for light rays other than the light beam causing sagittal halo near the center of the light beam. It has been.

  Further, in the wide-angle to telephoto shooting lens system, there is a problem that the outline of the rear blur at the center of the image is colored green, which is also a factor that deteriorates the appearance of the out-of-focus image.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a photographing lens system and an imaging apparatus that improve the appearance (color unevenness and intensity unevenness) of an out-of-focus image while suppressing a decrease in the amount of light of the out-of-focus image.

An optical system as one aspect of the present invention is an optical system having an aperture and an optical element that exhibits an apodization effect, and the transmittance of the optical element decreases as the distance from the optical axis increases in the radial direction, the transmittance depends on the wavelength of the incident light, the effective diameter r _a of the optical _system, the distance from the optical axis in the radial direction of the position where the transmittance is 0.9 times the value of the maximum value in the optical element r ₁ , the distance from the optical axis in the radial direction at the position where the transmittance of the optical element is 0.5 times the maximum value is r ₂ , and the transmittance of the optical element is 0.1 times the maximum value. When the distance from the optical axis in the radial direction of the position is r ₃ , a predetermined conditional expression is satisfied.

  An imaging device according to another aspect of the present invention includes the optical system and a light receiving element that receives light from the optical system.

  Other objects and features of the present invention are illustrated in the following examples.

  According to the present invention, it is possible to obtain an excellent defocused image in which a decrease in the amount of light is suppressed with respect to an on-axis light beam and an off-axis light beam, and an optical system and an imaging in which color blurring of rear blur at an on-axis field angle is improved. An apparatus can be provided.

The transmittance distribution of the transmittance distribution element of the present invention and a general apodization element. 2 is a lens cross-sectional view of Embodiment 1. FIG. 2 is an intensity distribution of an out-of-focus image formed by the photographic lens system of Example 1. FIG. 2 is a transmittance distribution of the transmittance distribution element according to the first embodiment. 2 is an intensity distribution of an out-of-focus image controlled by the transmittance distribution element of Example 1. FIG. FIG. 6 is a lens cross-sectional view of Example 2. 4 is a transmittance distribution of the transmittance distribution element according to the second embodiment. 4 is a spectral characteristic of transmittance distribution of the transmittance distribution element of Example 2. 10 is an intensity distribution of an out-of-focus image controlled by the transmittance distribution element according to the second embodiment. FIG. 6 is a lens cross-sectional view of Example 3. 7 is an intensity distribution of an out-of-focus image formed by the photographic lens system of Example 3. FIG. 4 is a transmittance distribution of the transmittance distribution element according to the third embodiment. FIG. 6 is an intensity distribution of an out-of-focus image controlled by the transmittance distribution element of Example 3. FIG. FIG. 6 is a lens cross-sectional view of Example 4. 7 is an intensity distribution of an out-of-focus image formed by the photographic lens system of Example 4. FIG. The transmittance distribution which the transmittance distribution element of Example 4 has. 10 is an intensity distribution of an out-of-focus image controlled by the transmittance distribution element of Example 4. FIG. An image pickup apparatus having the taking lens system of each embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The photographing lens system (optical system) of the present invention is a photographing lens system capable of controlling an out-of-focus image when photographing a three-dimensional object.

  Here, the three-dimensional subject is a subject composed of a plurality of parts with different distances in the optical axis direction, and particularly a subject having a point more than the depth of field from the focal plane of the photographing lens system at the time of photographing. . At this time, an out-of-focus image is formed on the imaging surface, and when the diameter of the out-of-focus image is larger than about 1 to 2% with respect to the image circle radius of the photographing lens system, it can be recognized as an out-of-focus image.

  Here, the image circle is a circle on which a light beam passing through the effective diameter of the lens forms an image. When the optical system of the embodiment is used as a photographing lens system for a digital still camera or a video camera, the imaging surface corresponds to an imaging surface of a semiconductor imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor. In addition, when the optical system of the embodiment is used as a photographing lens system for a silver salt camera, the imaging surface corresponds to a film surface. The image circle radius described above may be the maximum image height of the imaging surface and the film surface in the imaging device.

  “Controlling” an out-of-focus image means that the optical element (transmittance distribution element) that exhibits an apodization effect gives a transmittance distribution to the light flux at each angle of view, compared to the case where there is no transmittance distribution element. This is to change the light amount distribution of the out-of-focus image. Since an out-of-focus image with a large amount of light at the outer peripheral portion has a strong contour and is not preferable, the transmittance of the peripheral portion of the out-of-focus image should be lower than that in the central portion. In the following description, it is assumed that the transmittance distribution of the transmittance distribution element is centrally symmetric and the transmittance is smaller in the peripheral portion than in the central portion.

  The photographic lens system of the present invention has a diaphragm and has at least one transmittance distribution element.

  Here, the transmittance distribution element means an optical element having a transmittance distribution with respect to the radial direction of the lens, and an absorbing material or a reflective material is vapor-deposited so as to have a predetermined transmittance distribution on a transparent glass plate or lens surface. Or by applying a photosensitive material and exposing to a predetermined density. Moreover, you may use the concave lens produced with the substance (ND glass) which has light absorption. Further, the transmittance distribution may be variable using an electrochromic material or the like.

  As a conventional method for improving an out-of-focus image, a photographic lens system in which a transmittance distribution element having a Gaussian distribution of radial transmittance distribution as shown in FIG. ing. By disposing the transmittance distribution element in the vicinity of the stop, it is possible to remove the sagittal halo causing the intensity unevenness of the out-of-focus image, and it is possible to make the out-of-focus image look preferable.

  However, in the Gaussian distribution type transmittance distribution, the effect of reducing the transmittance is given even to a light beam that passes through the vicinity of the center, which is not related to the intensity unevenness of the defocused image. As a result, a reduction in the size of the out-of-focus image is inevitable.

  Therefore, the present invention uses an optical element having a transmittance distribution as shown in FIG. 1A to improve the appearance of an out-of-focus image while suppressing a decrease in the amount of light near the center of the light beam. Yes.

  Further, in a general photographing lens system, vignetting is seen in the off-axis light beam. Here, vignetting means that part of the luminous flux is vignetted and is also called vignetting. In a photographic lens system with vignetting, since the axial light beam and the off-axis light beam pass through the stop do not coincide, the effect obtained by the transmittance distribution element differs depending on the angle of view.

  In general, the off-axis light beam passes through a narrower range than the on-axis light beam. Therefore, when the transmittance distribution is matched to the on-axis light beam, the off-axis light beam cannot be affected by the transmittance distribution. In addition, when the transmittance distribution element is arranged at a position away from the stop, the center of the off-axis light beam is separated from the optical axis, and therefore the transmittance of the off-axis light beam is asymmetric in the center-symmetric transmittance distribution. .

  Therefore, in the present invention, attention is paid to the fact that the shape of the off-axis light beam is inverted upside down at a position away from the stop toward the object side and a position away from the stop toward the image side. By disposing at least one transmittance distribution element before and after the stop, the pupil transmittance distribution of the off-axis light beam can be equivalently brought close to the central symmetry. As a result, when importance is attached to the effect of improving the out-of-focus image at the off-axis field angle, an apodization effect is effectively obtained even for off-axis light beams by arranging optical elements having a transmittance distribution before and after the stop. .

  The photographic lens system (optical system) of the present invention includes an aperture and an optical element that exhibits an apodization effect. The transmittance of the optical element decreases with increasing distance from the optical axis in the radial direction, and the transmittance varies depending on the wavelength of incident light.

The effective diameter of the optical system is r _a , the distance from the optical axis in the radial direction at the position where the transmittance of the optical element is 0.9 times the maximum value is r ₁ , and the transmittance of the optical element is 0 at the maximum value. When the distance from the optical axis in the radial direction at the position of 5 times is r ₂ , and the distance from the optical axis in the radial direction at the position where the transmittance is 0.1 times the maximum value in the optical element is r ₃ ,
0.6 ≦ r ₂ / r _a ≦ 0.9 (1)
0.1 ≦ (r ₃ −r ₁ ) / r _a (2)
The following conditional expression is satisfied.

  In order to improve an off-focus image with a large amount of light at the peripheral portion, it is necessary to lower the transmittance at the peripheral portion of the light beam than at the central portion of the light beam. If this condition is not satisfied, the amount of light at the peripheral part of the light beam becomes stronger than the central part of the light beam, resulting in a dirty defocused image with a more effective edge. For this reason, it is preferable that the transmittance of the transmittance distribution element decreases as the distance from the center in the peripheral portion increases in the radial direction.

  In order to improve an out-of-focus image in which the peripheral portion is colored, it is necessary to change the shape of the transmittance distribution in the radial direction according to the wavelength. If this condition is not satisfied, for example, the size of the out-of-focus image differs depending on the wavelengths of red, green, and blue, and the outline of the out-of-focus image is colored, so that the appearance of the out-of-focus image is deteriorated. By using a material that absorbs only light in each of the red, green, and blue wavelength ranges as the absorbing material of the transmittance distribution element at a desired ratio, the transmittance can be given spectral characteristics. Furthermore, by changing the ratio of the absorbing material according to the radial distance from the optical axis, it is possible to manufacture a transmittance distribution element in which the shape of the radial transmittance distribution differs depending on the wavelength. Also, in the case of a multilayer film using a dielectric or metal thin film, the shape of the transmittance distribution in the radial direction can be similarly varied depending on the wavelength by making the configuration of the multilayer film different in the radial distance from the optical axis. Different transmittance distribution elements can be manufactured.

  Conditional expressions (1) and (2) are expressions relating to the shape of the transmittance distribution of the transmittance distribution element. The amount of light captured by the lens system can be increased by not reducing the transmittance in a certain range from the center. Note that the transmittance may be constant in a certain range at the center of the light beam. In addition, when a transmittance distribution element using an electrochromic material is used, it is difficult to create a distribution in which the transmittance changes smoothly, and the transmittance may be changed step by step.

  If the lower limit of conditional expression (1) is not reached, the region where the transmittance is less than 50% of the maximum transmittance becomes too wide. As a result, light rays other than the sagittal halo component causing uneven intensity of the out-of-focus image are removed, and the amount of light of the out-of-focus image becomes too low, which is not preferable. If the upper limit of conditional expression (1) is exceeded, the region where the transmittance is less than 50% of the maximum transmittance becomes too narrow. As a result, the effect of improving the out-of-focus image by the transmittance distribution element is reduced, resulting in an out-of-focus image with an edge, which is not preferable.

  If the lower limit of conditional expression (2) is not reached, the width of the region where the transmittance changes from 90% to 10% of the maximum transmittance becomes too narrow. This causes the transmittance distribution in the radial direction to change sharply, making it difficult to gently change the intensity of the outline of the defocused image and reducing the effect of improving the appearance of the defocused image. This is not preferable.

The photographing lens system of the present invention is characterized in that the distribution shape satisfies the following conditional expression (3) with respect to wavelengths of three colors of red, green, and blue.
r _2G / r _a <r _2R / r _a or r _2G / r _a <r _2B / r _a (3)
However, r _2R is the distance where the transmittance for the red wavelength is 50% of the maximum transmittance, r _2G is the distance where the transmittance for the green wavelength is 50% of the maximum transmittance, and r _2B is the transmission for the blue wavelength. Let the rate be a distance that is 50% of the maximum transmittance. That is, r _2R is the distance from the optical axis in the radial direction at a position where the transmittance for the red wavelength in the optical element is 0.5 times the maximum value, and r _2G is the transmittance for the green wavelength in the optical element. The distance from the optical axis in the radial direction at the position where the value is 0.5 times the maximum value, r _2B is the radial direction at the position where the transmittance for the blue wavelength in the optical element is 0.5 times the maximum value. Is the distance from the optical axis.

  In general, in a wide-angle to medium telephoto photographic lens system, the outline of an out-of-focus image near the center of the image is colored green. This is because the size of the out-of-focus image formed by the light having the green wavelength is larger than that of red or blue. To solve this problem, the radial transmittance distribution shape for the green wavelength is used. It is necessary to make the width narrower than the wavelength of other colors.

When focusing at infinity, it is preferable to satisfy the following conditional expression (4), where f is the focal length of the photographic lens system and Fno is the open F value.
8mm ≦ f / Fno ≦ 70mm (4)
Conditional expression (4) is an expression relating to the entrance pupil diameter of the photographing lens. If the lower limit value of conditional expression (4) is not reached, the area occupied by each out-of-focus image on the imaging surface becomes too small. At this time, the transmittance distribution given to the out-of-focus image is too small on the imaging surface, so that the effect of improving the out-of-focus image by the transmittance distribution element is reduced. In the first place, since the out-of-focus image is small, a dirty out-of-focus image is unlikely to be a problem during photographing. When the upper limit value of conditional expression (4) is exceeded, the defocused image becomes large, and the area occupied by each defocused image on the imaging surface becomes too large. An out-of-focus image with an edge is formed corresponding to the aberration of the photographic lens system. However, in a large out-of-focus image exceeding the upper limit value of the conditional expression (4), the influence of the aberration on the light amount distribution of the out-of-focus image. Therefore, a dirty out-of-focus image is less likely to be a problem during shooting. Conditional expression (4) is more preferably set as the following (4a).
10 mm ≦ f / Fno ≦ 65 mm (4a)
The half angle of view ω of the photographic lens preferably satisfies the following conditional expression (5).
9 ° ≦ ω ≦ 45 ° (5)
Conditional expression (5) is an expression relating to the half angle of view of the photographing lens. An out-of-focus image with an edge is formed corresponding to the aberration of the photographic lens system, but in the photographic lens system that falls below the lower limit of conditional expression (5), an aberration that deteriorates the light amount distribution of the defocused image is designed. Easy to suppress. Therefore, a dirty out-of-focus image is hardly generated in the first place, and the effect of the transmittance distribution element is reduced. When the lower limit value of the conditional expression (5) is satisfied, a small dot-like or thin linear light source or subject tends to be generated in the background due to the background compression effect caused by the perspective of the photographing lens. In such a subject, the outline of the out-of-focus image is easily noticeable, and the effect of the transmittance distribution element is more effective. If the upper limit value of conditional expression (5) is exceeded, vignetting in the off-axis light beam becomes severe. At this time, it is difficult to simultaneously give an improvement effect of an out-of-focus image to the on-axis light beam and the off-axis light beam, which is not preferable.

  The photographic lens system 1 of each embodiment is shown in FIGS. 2, 6, 10, and 14. FIG. In the figure, 11 corresponds to the axial light beam, and 12 corresponds to the most off-axis light beam. An off-axis light beam is a light beam that forms an image off the optical axis, and a light beam that forms an image at the extreme end of the imaging surface is called an off-axis light beam. In the figure, the light beam incident on the photographing lens system from below the optical axis is representatively shown. Li (i is a natural number) is a lens group, SP is a stop, IP is an image plane, and F1 or F2 is a transmittance distribution element.

The intensity distribution of the out-of-focus image of red, green, and blue wavelengths formed on the imaging surface in the configuration in which the transmittance distribution element is not provided with the transmittance distribution element in the imaging lens system of each embodiment is shown in FIGS. 11 and FIG. In the figure, 21 is an intensity distribution of an out-of-focus image at an on-axis field angle of a light beam having a green wavelength (550 nm), 22 is an intensity distribution of an off-focus image at an on-axis field angle of a light beam having a red wavelength (650 nm), Reference numeral 23 denotes an intensity distribution of an out-of-focus image at an axial angle of view of a light beam having a blue wavelength (450 nm). I (r) represents the intensity at the position r, and I ₀ represents the intensity at the position where the principal ray is incident on the imaging surface. The intensity distribution of the out-of-focus image was evaluated on a cross section perpendicular to the meridional plane and passing through the incident position of the principal ray.

  The intensity distribution of the out-of-focus image of red, green, and blue wavelengths formed on the imaging surface in the configuration in which the transmittance distribution element is provided with the transmittance distribution element in the imaging lens system of each embodiment is shown in FIGS. FIG. 13 and FIG.

The transmittance distribution of the transmittance distribution element of each embodiment is shown in FIGS. 4, 7, 12, and 16. FIG. In the figure, 31 is the transmittance distribution for the green wavelength (550 nm), 32 is the transmittance distribution for the red wavelength (650 nm), and 33 is the transmittance distribution for the blue wavelength (450 nm). T (r) represents the transmittance at the position r, and T ₀ represents the maximum transmittance.

  Next, each embodiment of the present invention will be described in detail.

  FIG. 2 is a sectional view of the photographic lens system of Example 1. A transmittance distribution element F1 is disposed at the stop position. With this transmittance distribution element F1, pupil intensity distribution is given to light beams of all angles of view from the on-axis light beam 11 to the off-axis light beam 12, thereby improving the appearance of an out-of-focus image.

  FIG. 3 shows an intensity distribution of an out-of-focus image with an on-axis field angle formed on the imaging surface in a configuration in which no transmittance distribution is given to the transmittance distribution element. The out-of-focus image in the first embodiment is an out-of-focus image of an object that is 235f away from the imaging surface in a state where the focal length of the photographing lens system is f, and the focal point is 50f away from the imaging surface. As is apparent from FIG. 3, the size of the defocused image of the green wavelength is larger than that of red and blue. Further, the intensity distribution of each wavelength increases at the end of the distribution.

  In order to improve the color unevenness and intensity unevenness of the out-of-focus image, the transmittance distribution shown in FIG. 4 was given to the transmittance distribution element F1 of Example 1.

  FIG. 5 shows the intensity distribution of an out-of-focus image with an on-axis field angle formed on the imaging surface in the configuration in which the transmittance distribution of FIG. 4 is given to the transmittance distribution element F1. As can be seen from FIG. 5, the magnitude of the intensity distribution is equal at each wavelength, and the intensity at the end of the distribution also decreases gradually. At that time, there is no decrease in strength near the center.

  Therefore, the transmittance distribution element F1 of the first embodiment suppresses a decrease in the amount of light, and the defocused image with an edge that is colored in the peripheral portion is not decolored in the peripheral portion and the intensity is gradually reduced. The image has improved.

  6 is a cross-sectional view of the taking lens system of Example 2. FIG. A transmittance distribution element F1 is disposed closer to the object side than the stop, and a transmittance distribution element F2 is disposed closer to the image side than the stop. At that time, in order to make the pupil transmittance distribution of the off-axis light beam equivalently close to the central symmetry, the transmittance distribution elements F1 and F2 are arranged on two surfaces where the shape of the off-axis light beam is close to the central symmetry. The transmittance distribution element has a transmittance distribution on a lens surface having a curvature. With the transmittance distribution elements F1 and F2, pupil intensity distribution is given to light beams of all angles of view from the on-axis light beam 11 to the off-axis light beam 12, thereby improving the appearance of the out-of-focus image.

  In order to improve color unevenness and intensity unevenness of an out-of-focus image, the transmittance distribution shown in FIG. 7 was given to the transmittance distribution element F1 and the transmittance distribution element F2 of Example 2.

Figure 8 shows the spectral characteristics of the transmittance distribution in the 50% and a position of the radial distance is the effective diameter r _a of the optical axis. The transmittance distribution element, by a multilayer film of 5-layer structure, the transmittance of each wavelength (lambda) satisfies the relationship of FIG. 7 at the position where the distance in the radial direction is 5% of the effective diameter r _a Spectral characteristics can be realized.

  FIG. 9 shows the intensity distribution of an out-of-focus image with an on-axis field angle formed on the imaging surface when the transmittance distribution element F1 and the transmittance distribution element F2 are provided with the transmittance distribution of FIG. . As can be seen from FIG. 9, the magnitude of the intensity distribution is the same for each wavelength, and the intensity at the end of the distribution also gradually decreases. At that time, there is no decrease in strength near the center.

  Therefore, the transmittance distribution element F1 and the transmittance distribution element F2 of Example 2 suppress the decrease in the amount of light, and the edge-colored defocused image in which the peripheral portion is colored is not colored in the peripheral portion and the intensity is moderated. It has improved to a good out-of-focus image that decreases.

  FIG. 10 is a sectional view of the taking lens system of Example 3. A transmittance distribution element F1 is disposed on the image side of the stop. With this transmittance distribution element F1, pupil intensity distribution is given to light beams of all angles of view from the on-axis light beam 11 to the off-axis light beam 12, thereby improving the appearance of an out-of-focus image.

  FIG. 11 shows the intensity distribution of an out-of-focus image with an on-axis field angle formed on the imaging surface in a configuration in which no transmittance distribution is given to the transmittance distribution element. The out-of-focus image in the third embodiment is an out-of-focus image of an object 90 f away from the imaging surface in a state where the focal length of the photographing lens system is f, and the focal point is 50 f away from the imaging surface. As is apparent from FIG. 11, the size of the defocused image of the green and red wavelengths is larger than that of blue. Further, the intensity distribution of each wavelength increases at the end of the distribution.

  In order to improve the color unevenness and intensity unevenness of the out-of-focus image, the transmittance distribution shown in FIG. 12 was given to the transmittance distribution element F1 of Example 3.

  FIG. 13 shows an intensity distribution of an out-of-focus image with an on-axis field angle formed on the imaging surface in a configuration in which the transmittance distribution of FIG. 12 is given to the transmittance distribution element F1. As can be seen from FIG. 13, the magnitude of the intensity distribution is the same for each wavelength, and the intensity at the end of the distribution also gradually decreases. At that time, there is no decrease in strength near the center.

  Therefore, the transmittance distribution element F1 of Example 3 suppresses a decrease in the amount of light, and a defocused image with an edge that is colored in the peripheral portion is not decolored in the peripheral portion. The image has improved.

  FIG. 14 is a sectional view of the taking lens system of Example 4. A transmittance distribution element F1 is disposed closer to the object side than the stop, and a transmittance distribution element F2 is disposed closer to the image side than the stop. At that time, in order to make the pupil transmittance distribution of the off-axis light beam equivalently close to the central symmetry, the shape of the off-axis light beam is arranged on two surfaces close to the central symmetry. The transmittance distribution element has a transmittance distribution on a lens surface having a curvature. With the transmittance distribution elements F1 and F2, pupil intensity distribution is given to light beams of all angles of view from the on-axis light beam 11 to the off-axis light beam 12, thereby improving the appearance of the out-of-focus image.

  FIG. 15 shows the intensity distribution of an out-of-focus image with an on-axis field angle formed on the imaging surface in a configuration in which no transmittance distribution is given to the transmittance distribution element. The out-of-focus image in the fourth embodiment is an out-of-focus image of an object at an infinite distance from the imaging surface in a state where the imaging lens system is focused at a position 16 f away from the imaging surface, where f is the focal length of the imaging lens system. As is apparent from FIG. 15, the size of the defocused image of the green wavelength is larger than that of red and blue. Further, the intensity distribution of each wavelength increases at the end of the distribution.

  In order to improve the color unevenness and intensity unevenness of the out-of-focus image, the transmittance distribution shown in FIG. 16 was given to the transmittance distribution element F1 and the transmittance distribution element F2 of Example 4.

  FIG. 17 shows the intensity distribution of an out-of-focus image with an on-axis field angle formed on the imaging surface when the transmittance distribution element F1 and the transmittance distribution element F2 are provided with the transmittance distribution of FIG. . As can be seen from FIG. 17, the magnitude of the intensity distribution is the same for each wavelength, and the intensity at the end of the distribution is gradually decreasing. At that time, there is no decrease in strength near the center.

  Therefore, the transmittance distribution element F1 and the transmittance distribution element F2 of Example 4 suppress the decrease in the amount of light, and the edge-colored defocused image in which the peripheral portion is colored is not colored in the peripheral portion and the intensity is moderated. It has improved to a good out-of-focus image that decreases.

  In each of the above-described embodiments, the wavelengths of 650, 550, and 450 nm are described as the wavelengths of red, green, and blue. However, the same idea can be applied to other wavelength combinations (for example, 656.3, 587.6, 486.1, a combination of 435.8, etc.).

  Numerical examples 1 to 4 corresponding to the first to fourth embodiments of the present invention will be described below. In each numerical example, r is the radius of curvature (mm) of the i-th surface from the object side, d is the surface interval (mm) on the i-th and i + 1-th axes from the object side, and nd and vd are the first The refractive index and the Abbe number of the i-th optical member. The focal length f (mm), the F number Fno, and the angle of view ω (degrees) are values when focusing on an object at infinity. BF is the back focus, and the total lens length represents the distance from the first surface to the image plane. An aspheric surface is represented by adding a symbol * after the surface number. In the aspherical shape, X is the amount of variation from the surface vertex in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, r is the paraxial radius of curvature, K is the conic constant, A4, A6, When each of A8 and A10 is an aspheric coefficient,

It is expressed by the following formula. The display of “e ± Z” means “10 ^{± Z} ”.
[Numerical Example 1]
Unit mm

Surface data surface number rd nd vd Effective diameter
1 ∞ 2.00 42.78
2 57.520 5.50 1.77250 49.6 38.04
3 395.282 2.80 36.09
4 ∞ -1.60 33.81
5 25.921 5.00 1.83481 42.7 31.97
6 43.002 1.20 29.70
7 59.016 2.00 1.64769 33.8 29.56
8 17.697 9.00 25.24
9 (Aperture) ∞ 0.00 24.55
10 ∞ 0.50 1.51633 64.1 24.55
11 ∞ 6.00 24.55
12 -19.448 2.00 1.80518 25.4 24.15
13 280.464 6.50 1.75700 47.8 28.14
14 -37.481 0.20 29.83
15 -74.530 4.50 1.88300 40.8 30.67
16 -30.712 -0.80 31.22
17 ∞ 1.00 30.14
18 124.396 3.00 1.80400 46.6 29.66
19 -111.454 0.00 30.02
20 ∞ 0.00 30.32
21 ∞ (variable) 30.32
Image plane ∞

Various data Zoom ratio 1.00

Focal length 52.43
F number 1.49
Angle of View 22.42
Statue height 21.64
Total lens length 88.51
BF 39.71

d21 39.71

Entrance pupil position 30.97
Exit pupil position -33.10
Front principal point position 45.65
Rear principal point position -12.71

Zoom lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 52.43 48.80 45.65 -12.71

Single lens Data lens Start surface Focal length
1 1 86.53
2 5 68.99
3 7 -39.78
4 10 0.00
5 12 -22.52
6 13 44.06
7 15 56.44
8 18 73.53
[Numerical Example 2]
Unit mm

Surface data surface number rd nd vd Effective diameter
1 ∞ 2.00 42.78
2 57.520 5.50 1.77250 49.6 38.04
3 395.282 2.80 36.09
4 ∞ -1.60 33.81
5 25.921 5.00 1.83481 42.7 31.97
6 43.002 1.20 29.70
7 59.016 2.00 1.64769 33.8 29.56
8 17.697 9.00 25.24
9 (Aperture) ∞ 6.50 24.55
10 -19.448 2.00 1.80518 25.4 24.15
11 280.464 6.50 1.75700 47.8 28.14
12 -37.481 0.20 29.83
13 -74.530 4.50 1.88300 40.8 30.67
14 -30.712 -0.80 31.22
15 ∞ 1.00 30.14
16 124.396 3.00 1.80400 46.6 29.66
17 -111.454 0.00 30.02
18 ∞ 0.00 30.32
19 ∞ (variable) 30.32
Image plane ∞

Various data Zoom ratio 1.00

Focal length 52.50
F number 1.49
Angle of View 22.40
Statue height 21.64
Total lens length 88.49
BF 39.69

d19 39.69

Entrance pupil position 30.97
Exit pupil position -33.78
Front principal point position 45.96
Rear principal point position -12.81

Zoom lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 52.50 48.80 45.96 -12.81

Single lens Data lens Start surface Focal length
1 1 86.53
2 5 68.99
3 7 -39.78
4 10 -22.52
5 11 44.06
6 13 56.44
7 16 73.53

[Numerical Example 3]
Unit mm

Surface data surface number rd nd vd Effective diameter
1 106.149 9.00 1.48749 70.2 67.53
2 -290.997 0.50 66.86
3 51.244 9.50 1.49700 81.5 59.18
4 231.499 3.00 57.79
5 -630.036 3.50 1.83400 37.2 57.25
6 93.250 2.50 53.57
7 60.005 8.00 1.49700 81.5 52.05
8 -624.746 0.50 51.23
9 29.265 3.20 1.71736 29.5 42.22
10 24.308 12.50 37.88
11 (Aperture) ∞ (Variable) 35.40
12 -2278.322 4.50 1.84666 23.9 33.80
13 -55.787 2.00 1.72000 50.2 33.04
14 41.821 4.00 29.79
15 ∞ 0.50 1.51633 64.1 29.50
16 ∞ 0.00 29.42
17 ∞ (variable) 29.42
18 -30.566 2.50 1.74077 27.8 25.98
19 196.247 8.50 1.77250 49.6 28.59
20 -39.608 0.50 31.93
21 106.631 6.00 1.83400 37.2 35.15
22 -195.173 (variable) 35.74
Image plane ∞

Various data Zoom ratio 1.00

Focal length 133.12
F number 2.06
Angle of View 9.23
Statue height 21.64
Total lens length 154.90
BF 54.23

d11 2.28
d17 17.69
d22 54.23

Entrance pupil position 74.83
Exit pupil position -89.01
Front principal point 84.24
Rear principal point position -78.89

Zoom lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 93.89 52.20 -8.11 -44.04
2 12 -65.39 11.00 3.68 -4.24
3 18 82.08 17.50 17.56 10.42

Single lens Data lens Start surface Focal length
1 1 160.74
2 3 130.14
3 5 -97.18
4 7 110.58
5 9 -273.90
6 12 67.48
7 13 -32.92
8 15 0.00
9 18 -35.53
10 19 43.34
11 21 83.44

[Numerical Example 4]
Unit mm

Surface data surface number rd nd vd Effective diameter
1 ∞ 1.50 54.03
2 79.773 2.00 1.60311 60.6 46.37
3 28.865 8.00 39.23
4 117.212 4.00 1.77250 49.6 37.77
5 -212.879 (variable) 36.80
6 84.814 1.50 1.48749 70.2 24.71
7 19.679 10.00 21.16
8 22.595 3.50 1.91082 35.3 14.46
9 -45.147 1.00 1.73800 32.3 13.37
10 26.917 3.50 12.87
11 (Aperture) ∞ (Variable) 12.80
12 111.141 1.50 1.72916 54.7 12.69
13 -73.101 (variable) 12.63
14 -13.184 1.50 1.74000 28.3 12.65
15 -132.829 4.50 1.69680 55.5 15.15
16 -17.844 0.80 17.62
17 * -53.671 3.20 1.58313 59.4 19.54
18 -18.948 0.00 20.58
19 ∞ (variable) 22.26
Image plane ∞

Aspheric data 17th surface
K = 0.00000e + 000 A 4 = -2.50000e-005 A 6 = 4.20000e-008 A 8 = -6.00000e-010 A10 = 2.00000e-012

Various data Zoom ratio 1.00

Focal length 28.50
F number 2.85
Angle of view 37.20
Statue height 21.64
Total lens length 99.00
BF 38.00

d 5 7.00
d11 4.00
d13 3.50
d19 38.00

Entrance pupil position 28.63
Exit pupil position -29.20
Front principal point position 45.04
Rear principal point position 9.50

Zoom lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 -528.68 15.50 -39.98 -57.63
2 6 374.88 19.50 48.86 38.18
3 12 60.69 1.50 0.53 -0.35
4 14 61.47 10.00 17.07 15.27

Single lens Data lens Start surface Focal length
1 1 -76.12
2 4 98.37
3 6 -52.96
4 8 16.95
5 9 -22.72
6 12 60.69
7 14 -19.88
8 15 29.12
9 17 48.58
Tables 1 and 2 below show the numerical values of the conditional expressions for the transmittance distribution shapes given to the transmittance distribution elements of Numerical Examples 1 to 4. The unit of the numerical value of conditional expression (5) in Table 2 is degree (°).

  Finally, an embodiment of the imaging apparatus of the present invention will be described. FIG. 18 is a schematic diagram of an imaging apparatus (digital still camera) 100 of the present embodiment. The imaging apparatus 100 includes a camera body 90, the photographing lens (optical system) 1 of the above-described embodiment, and a light receiving element (imaging element) 92 that photoelectrically converts an image formed by the photographing lens 1.

  The imaging apparatus 100 according to the present embodiment can obtain a high-quality image formed by the photographing lens 1 having high optical performance.

  Note that an image sensor such as a CCD sensor or a CMOS sensor can be used as the light receiving element 92. At this time, the image quality of the output image can be improved by electrically correcting various aberrations such as distortion and chromatic aberration of the image acquired by the light receiving element 92.

  Note that the photographic lenses of the above-described embodiments can be applied not only to the digital still camera shown in FIG. 18 but also to various optical devices such as a silver salt film camera, a video camera, and a telescope.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

SP aperture,
F1, F2 transmittance distribution element,

Claims (10)

An optical system having an aperture and an optical element that exhibits an apodization effect,
The transmittance of the optical element decreases with increasing radial distance from the optical axis,
The transmittance depends on the wavelength of incident light,
The effective diameter of the optical system is r _a , the distance from the optical axis in the radial direction at the position where the transmittance of the optical element is 0.9 times the maximum value is r ₁ , and the transmittance of the optical element is The distance from the optical axis in the radial direction at a position that is 0.5 times the maximum value is r ₂ , and the optical element has a distance from the optical axis in the radial direction at a position where the transmittance is 0.1 times the maximum value. when the distance between _{r 3,}
0.6 ≦ r ₂ / r _a ≦ 0.9
0.1 ≦ (r ₃ −r ₁ ) / r _a
An optical system characterized by satisfying the following conditional expression:   The optical system according to claim 1, wherein the transmittance is constant within a predetermined range from the center of the optical element.   The optical system according to claim 1, wherein the transmittance decreases stepwise as the distance from the optical axis increases in the radial direction. In the optical element, the distance from the optical axis in the radial direction at the position where the transmittance for the red wavelength is 0.5 times the maximum value is r _2R , and the transmittance for the green wavelength is the maximum value in the optical element. The distance from the optical axis in the radial direction of the position where the value is 0.5 times the value of r _2G , and the radial direction of the position where the transmittance for the blue wavelength in the optical element is 0.5 times the maximum value _Where r _2B is the distance from the optical axis at
For red, green and blue wavelengths
r _2G / r _a <r _2R / r _a or r _2G / r _a <r _2B / r _a
The optical system according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the optical system is f and the open F value is Fno when focusing at infinity,
8mm ≦ f / Fno ≦ 70mm
The optical system according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the optical system is f and the open F value is Fno when focusing at infinity,
10mm ≦ f / Fno ≦ 65mm
The optical system according to claim 1, wherein the following conditional expression is satisfied. When the half angle of view of the optical system is ω,
9 ° ≦ ω ≦ 45 °
The optical system according to claim 1, wherein the following conditional expression is satisfied.   The optical system according to claim 1, wherein the optical element is disposed at a position where the diaphragm is disposed.   The optical system according to any one of claims 1 to 7, wherein the optical element is disposed at a position closer to the object side than the stop or an image side relative to the stop.   An imaging apparatus comprising: the optical system according to claim 1; and a light receiving element that receives light from the optical system.