JP4707199B2 - Imaging optical system and imaging apparatus using the same - Google Patents

Description

  The present invention relates to an imaging optical system and an imaging apparatus using the imaging optical system, and is particularly mounted in a digital still camera, a digital video camera, a cellular phone, or a personal computer using a solid-state imaging device such as a CCD or a CMOS. The present invention relates to an imaging apparatus such as a small camera or a surveillance camera.

  In recent years, electronic cameras that take a subject using a solid-state imaging device such as a CCD or a CMOS instead of a silver salt film have become widespread. Among such electronic cameras, an imaging device mounted on a portable computer, a cellular phone, or the like is particularly required to be small and light.

  As an imaging optical system used in such an image pickup apparatus, there is a conventional one in which the number of lenses is one or two. However, as is apparent from the aberration theory, it is already known that field curvature cannot be corrected and high performance cannot be expected. Therefore, in order to satisfy high performance, it is necessary to configure with three or more lenses.

  On the other hand, in the case of a CCD, if the off-axis light beam emitted from the imaging lens system is incident at an excessively large angle with respect to the image plane, the condensing performance of the microlens is not fully exhibited, and the brightness of the image is at the center of the image. This causes the problem of extreme changes between the image and the image periphery. Therefore, the light incident angle to the CCD, that is, the exit pupil position is important in design. In the case of an optical system with a small number of sheets, the position of the aperture stop is important.

  Considering these problems, there is a triplet type with a front aperture. Such imaging lenses are disclosed in Patent Literature 1, Patent Literature 2, Patent Literature 3, Patent Literature 4, Patent Literature 5, Patent Literature 6, and the like.

JP-A-1-144007 Japanese Patent Laid-Open No. 2-191907 JP-A-4-153612 Japanese Patent Laid-Open No. 5-188284 Japanese Patent Laid-Open No. 9-288235 JP 2001-750006 A

  However, these prior examples have various problems as shown below.

  In general, when the total length of the optical system is shortened, the exit pupil position must be disposed on the image side as much, so that the light incident angle on the image plane becomes tight. On the contrary, when the exit pupil position is arranged on the object side, the light incident angle on the image plane becomes gentle, but the total length becomes large.

  None of Patent Literature 1, Patent Literature 2, Patent Literature 3, and Patent Literature 5 has a long overall length and cannot be said to have achieved miniaturization. In addition, the half angle of view is about 25, and widening beyond this has a limit in performance. The incident angle of light on the image plane was not small for the angle of view.

  In Patent Literature 4 and Patent Literature 5, although the light incident angle on the image plane is considered, it cannot be said that the total length is short as well.

  As described above, none of the preceding examples has balanced the size of the optical system and the incident angle of light on the image plane. Further, if the angle of view is widened to about 35 °, the incident angle to the optical system is further increased, so that the exit angle, that is, the incident angle to the image plane is also increased, which becomes more severe. There was not.

  The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide an imaging optical system that can simultaneously achieve high performance and miniaturization and can withstand a wide angle, and an imaging apparatus using the same. Is to provide.

  The imaging optical system of the present invention that achieves the above object is arranged in order of an aperture stop, a first positive lens, a second negative lens, and a third positive lens in order from the object side, and satisfies the following conditional expression: It is a feature.

1.5 <d / (f · tan θ) <3.0 (1)
Where d is the distance measured along the optical axis from the aperture stop surface to the image plane of the imaging optical system, θ is the maximum incident angle of the imaging optical system, and f is the focal length of the entire system.

  Another imaging optical system according to the present invention is arranged in the order of an aperture stop from the object side, a first positive meniscus lens having a convex surface directed to the image side, a second negative lens, and a third positive lens. It is characterized by satisfying the formula.

−5.0 <f _2-3 /f<−0.5 (2)
Here, f _2-3 is the combined focal length of the second negative lens and the third positive lens, and f is the focal length of the entire system.

  Hereinafter, the reason and action of the above configuration in the present invention will be described.

  First, the number of lenses will be described. In the present invention, as a result of considering performance and miniaturization, the number of lenses is three. It is clear that the performance will be further improved if the number of lenses is increased to 4 or more. However, as the number of lenses increases, the thickness of the lens, the distance between the lenses, and the space of the frame will increase accordingly. Is inevitable. Further, as described in the section of the prior art above, when the number is two or less, the field curvature is not reduced and the peripheral performance is considerably deteriorated. It is optimal for performance and size to be composed of three pieces.

  Next, in order to reduce the light incident angle to the CCD which is the image pickup device, the brightness stop was disposed on the most object side. The power of the lens may be configured so that the exit pupil position is far from the object side. However, since the number is small, it is most effective to arrange the position of the aperture stop on the object side.

  Here, when the aperture stop is disposed closest to the object side, since there is only one lens with respect to the stop, it is difficult to correct distortion and lateral chromatic aberration, which are peripheral performances, in the optical design. For this reason, by arranging a positive lens, a negative lens, and a positive lens from the object side, powers having different signs are arranged and corrected for the second lens and the third lens having a large light beam height. The central performance is achieved by correcting the spherical aberration and axial chromatic aberration that occur in the first positive lens with the second negative lens, thereby improving the overall performance of the screen.

  In this way, the total length is basically small and the incident angle of light on the image plane can be reduced. However, since the number of lenses is small, the focal length and angle of view must be fully considered. The size cannot be reduced unless the individual surface spacing, thickness, and back focus are set appropriately. Therefore, it is necessary to satisfy the following conditional expression.

1.5 <d / (f · tan θ) <3.0 (1)
Where d is the distance measured along the optical axis from the aperture stop surface to the image plane of the imaging optical system, θ is the maximum incident angle of the imaging optical system, and f is the focal length of the entire system.

  If the upper limit of 3.0 of the conditional expression (1) is exceeded, the total length becomes too large to achieve downsizing, and if the lower limit of 1.5 is exceeded, the power of each lens becomes too strong and the performance deteriorates. In addition, the wall thickness and surface spacing become too narrow, making it difficult to process and assemble.

  Preferably, the following conditional expression is satisfied.

1.8 <d / (f · tan θ) <2.8 (1-1)
Next, a power configuration for more effectively achieving downsizing and higher performance of the imaging optical system will be described. Generally, in order to shorten the overall length with respect to the focal length, it is conceivable to arrange the power in the order of positive and negative telephoto types. However, since negative has a diverging action, the angle as it is incident on the image plane tends to be tight with the configuration as it is. On the other hand, when configuring a wide-angle optical system, it is known that it is advantageous in terms of optical performance to dispose a group having a negative divergence action on the most object side.

  Therefore, in the present invention, first, in order to shorten the overall length, the basic power configuration is made positive and negative, and the negative power is made the configuration of the negative lens and the positive lens in order from the object side. As a result, while forming the telephoto type, the incident angle on the image plane can be relaxed by the convergence effect of the positive lens arranged closest to the image plane side. Further, in order not to deteriorate the performance even if a wide-angle optical system is configured, the entrance surface of the first positive lens is made concave so as to have a diverging action, thereby forming a positive power meniscus shape. As a result, it is possible to sufficiently correct coma and astigmatism of off-axis rays that are likely to occur when the angle is widened.

  At this time, in order to balance the effect of shortening the total length and the angle of incidence on the image plane, the negative power by the second negative lens and the third positive lens must be set appropriately. Therefore, it is necessary to satisfy the following conditional expression.

−5.0 <f _2-3 /f<−0.5 (2)
Here, f _2-3 is the combined focal length of the second negative lens and the third positive lens, and f is the focal length of the entire system.

  If the upper limit of -0.5 of the conditional expression (2) is exceeded, the telephoto effect becomes too strong and the incident angle on the image surface becomes too tight. If the lower limit of -5.0 is exceeded, the telephoto effect becomes weak. Too much will increase the overall length.

  Preferably, the following conditional expression is satisfied.

−3.5 <f _2-3 /f<−0.8 (2-1)
More preferably, the following conditional expression is satisfied.

−2.0 <f _2-3 /f<−0.9 (2-2)
In order to form a telephoto type, it is preferable to give a strong positive power to the first positive lens of the two positive lenses. Therefore, the following conditional expression should be satisfied.

0.1 <f ₁ / f ₃ <0.7 (3)
Here, f ₁ is the focal length of the first positive lens, and f ₃ is the focal length of the third positive lens.

  If the upper limit of 0.7 of the conditional expression (3) is exceeded, the telephoto effect is reduced and the total length is increased, or the power of the second negative lens and the third positive lens becomes too strong, so that coma and astigmatism are reduced. Getting worse. When the lower limit of 0.1 is exceeded, the telephoto effect becomes too strong and the amount of aberration generated in the first positive lens becomes large, or the power of the third positive lens becomes too weak and occurs in the second negative lens. The lateral chromatic aberration and distortion cannot be corrected.

  Preferably, the following conditional expression is satisfied.

0.2 <f ₁ / f ₃ <0.58 (3-1)
Further, the influence of the telephoto effect varies depending on the configuration of the second negative lens and the third positive lens having negative combined power. In addition, since the second negative lens and the third positive lens are arranged far from the aperture stop and the off-axis ray height is high, the occurrence of lateral chromatic aberration and distortion tends to be large. Therefore, the following conditional expression should be satisfied.

−0.6 <f ₂ / f ₃ <−0.1 (4)
Here, f ₂ is the focal length of the second negative lens, and f ₃ is the focal length of the third positive lens.

  If the upper limit of −0.1 of the conditional expression (4) is exceeded, the power of the second negative lens will be weak or the power of the third positive lens will be too strong, and the telephoto effect will be reduced and the total length will be increased. Become. If the lower limit of −0.6 is exceeded, the power of the second negative lens will increase, or the power of the third positive lens will decrease, and the chromatic aberration of magnification and distortion will not be balanced, and the performance will deteriorate.

  Preferably, the following conditional expression is satisfied.

−0.5 <f ₂ / f ₃ <−0.15 (4-1)
Moreover, although performance will be improved if high refractive index glass is used, cost will become high. Therefore, the following conditional expression should be satisfied.

1.45 <n _avg <1.70 (5)
However, _navg is the average value of the refractive index of the d-line of the first positive lens to the third positive lens.

  If the upper limit of 1.70 in the conditional expression (5) is exceeded, low cost cannot be achieved, and if the lower limit of 1.45 is exceeded, the aberration generation amount of each lens becomes too large and the performance deteriorates.

  Preferably, the following conditional expression is satisfied.

1.5 <n _avg <1.65 (5-1)
In addition, since the first positive lens is closest to the stop, the light flux from the center to the periphery passes through substantially the same region of the lens. In other words, if the aberrations on this surface are not properly corrected, correction may not be possible with the second negative lens and the third positive lens, and the performance of the entire screen, particularly coma and astigmatism, will deteriorate. Resulting in. Therefore, it is preferable that the following conditional expression is satisfied.

1.0 <(r _1f + r _1r ) / (r _1f −r _1r ) <1.7 (6)
Here, r _1f is the object-side paraxial radius of curvature of the first positive lens, and r _1r is the image-side paraxial radius of curvature of the first positive lens.

  If the upper limit of 1.7 of the conditional expression (6) is exceeded, the power of the image side surface of the first positive lens becomes relatively strong, and particularly the spherical aberration and the coma aberration are deteriorated. If it exceeds 1.0, the power of the object-side surface of the first positive lens becomes relatively weak, and off-axis aberrations, particularly astigmatism and coma aberration, deteriorate.

  Preferably, the following conditional expression is satisfied.

1.1 <(r _1f + r _1r ) / (r _1f −r _1r ) <1.6 (6-1)
Further, in order to produce a telephoto effect in order to reduce the overall length, the first positive lens requires a strong positive power. For this reason, if at least one surface of the first positive lens is an aspherical surface, aberration correction can be performed satisfactorily. Therefore, it is desirable to satisfy the following conditional expression.

0.01 <| (r _1s + r _1a ) / (r _1s −r _1a ) −1 | <100
... (7)
Where r _1s is the paraxial radius of curvature of the aspherical surface of the first positive lens, and r _1a is the paraxial curvature within the effective optical range within the radius of curvature r _ASP considering the aspherical surface defined below of the first positive lens. This is the value when the difference from the radius changes the most.

Here, the curvature radius r _ASP considering the aspherical surface is expressed as follows when the aspherical definition formula (a function of the shape when the optical axis traveling direction is positive from the tangential plane in contact with the surface top) is f (y). It is defined by the formula of same as below.

r _ASP = y · (1 + f ′ (y) ² ) ^1/2 / f ′ (y)
Here, y is the height from the optical axis, and f ′ (y) is the first derivative of f (y).

  If the upper limit of 100 of the conditional expression (7) is exceeded, the aspherical effect becomes too weak and the correction becomes insufficient, coma aberration and astigmatism deteriorate, and if the lower limit of 0.01 is exceeded, The aspherical effect becomes too strong, resulting in overcorrection, which degrades performance and makes lens processing difficult.

  Preferably, the following conditional expression is satisfied.

0.05 <| (r _1s + r _1a ) / (r _1s −r _1a ) −1 | <10
... (7-1)
More preferably, the following conditional expression is satisfied.

0.1 <| (r _1s + r _1a ) / (r _1s −r _1a ) −1 | <5
... (7-2)
More preferably, the following conditional expression is satisfied.

0.1 <| (r _1s + r _1a ) / (r _1s −r _1a ) −1 | <3
... (7-3)
Also, in order to produce a telephoto effect in order to reduce the overall length, the second negative lens needs a strong negative power. If at least one surface of the second negative lens is formed of an aspherical surface, it is possible to correct aberrations satisfactorily, and it is desirable that the following conditional expression is satisfied.

0.01 <| (r _2s + r _2a ) / (r _2s −r _2a ) −1 | <100
... (8)
Where r _2s is the paraxial radius of curvature of the aspherical surface of the second negative lens, and r _2a is the paraxial curvature within the effective optical range within the radius of curvature r _ASP considering the aspherical surface defined above of the second negative lens. This is the value when the difference from the radius changes the most.

  If the upper limit of 100 of the conditional expression (8) is exceeded, the aspherical effect becomes too weak and the correction becomes insufficient, coma aberration and astigmatism deteriorate, and if the lower limit of 0.01 is exceeded, The aspherical effect becomes too strong and overcorrected, resulting in degraded performance and difficult lens processing.

  Preferably, the following conditional expression is satisfied.

0.1 <| (r _2s + r _2a ) / (r _2s −r _2a ) −1 | <5
... (8-1)
In addition, when a CCD is used as the image sensor, if the off-axis light beam emitted from the imaging optical system is incident at an excessively large angle with respect to the image plane, the brightness of the image changes at the image center and the image periphery. End up. On the other hand, if the light is incident on the image plane at a small angle, this problem is reduced, but this time the total length of the optical system becomes large. Therefore, the following conditional expression should be satisfied.

10 ° <α <40 ° (9)
Where α is the incident angle of the chief ray on the image plane at the maximum image height.

  If the upper limit of 40 ° in this conditional expression is exceeded, the angle of incidence on the CCD becomes too large, and the brightness at the periphery of the image decreases, and if the lower limit of 10 is exceeded, the total length becomes too large.

  Preferably, the following conditional expression is satisfied.

15 ° <α <35 ° (9-1)
More preferably, the following conditional expression is satisfied.

17.5 ° <α <25 ° (9-2)
The present invention includes an imaging apparatus having the above-described imaging optical system of the present invention and an imaging element arranged on the image side.

  The first image pickup apparatus of the present invention includes an aperture stop from the object side, a first positive lens having a convex surface facing the image side, a second negative lens having a concave surface facing the image side, and a third positive lens in this order. An image forming optical system disposed, and an image pickup device disposed on the image side, the aperture stop having a fixed aperture shape through which the optical axis passes, and an outer peripheral surface of the aperture It is characterized in that it is inclined at an inclination angle equal to or greater than the incident angle of the most off-axis light beam so as to approach the optical axis toward the image plane side.

  Explaining the operation of this configuration, when reflected light from the periphery of the aperture stop enters the imaging optical system, phenomena such as ghost and flare tend to occur. In particular, in the small imaging optical system in which the aperture stop, the first positive lens, the second negative lens, and the third positive lens are arranged in this order from the object side as in the present invention, the imaging surface of the imaging element is also small. Therefore, the influence of the reflected light on the outer peripheral surface of the aperture stop becomes relatively large.

  Therefore, in the present invention, by utilizing the fact that the aperture stop is arranged closest to the object side, the most off-axis light beam is incident so that the outer peripheral surface of the aperture of the aperture stop approaches the optical axis toward the image plane side. It has a fixed shape that is inclined at an inclination angle greater than the angle.

With such a configuration, the light beam reflected by the outer peripheral surface of the opening becomes difficult to enter the image sensor,
It becomes possible to reduce the influence of flare and ghost.

  Further, the second imaging device of the present invention includes an aperture stop from the object side, a first positive lens having a convex surface facing the image side, a second negative lens having a concave surface facing the image side, and a third positive lens in this order. A lens frame having an imaging optical system arranged and an imaging device arranged on the image side, holding the imaging optical system and the imaging device, and integrally forming the aperture stop with the same resin material It is characterized by comprising.

  The operation of this configuration will be described. In the optical system of the present invention, the aperture stop is positioned closest to the object side. Therefore, each lens after the stop has a larger effective surface as the lens disposed on the image side. Become. Therefore, by integrally molding the lens frame for holding these lenses with the same resin that can be easily formed, the lens can be positioned by inserting the lens from the image surface side of the frame, so that the manufacturing is facilitated.

  At that time, by integrating the configuration of the aperture stop into the lens frame, the manufacturing process is greatly reduced, and by providing the lens frame itself with a holding function for the image sensor, dust is contained in the frame. It becomes possible to make the configuration difficult to enter.

  Further, the third imaging device of the present invention includes an aperture stop from the object side, a first positive lens having a convex surface facing the image side, a second negative lens having a concave surface facing the image side, and a third positive lens in this order. An imaging optical system disposed; and an imaging device disposed on the image side thereof; and a lens frame that holds the imaging optical system, wherein at least each of the first positive lens and the third positive lens An inclined portion is provided on the outer periphery so as to be closer to the optical axis toward the object side, and the inclined portion is in contact with the lens frame.

  The operation of this configuration will be described. In the optical system of the present invention, the aperture stop is positioned closest to the object side. Therefore, each lens after the stop has a larger effective surface as the lens disposed on the image side. Become. This is particularly noticeable with the first positive lens and the third positive lens. Therefore, the lens outer shape along the off-axis light beam is obtained by the above-described configuration, the size is reduced while suppressing the vignetting, and the lens can be positioned by inserting the lens from the image surface side of the frame, which facilitates manufacturing. .

  Furthermore, an inclined portion that is inclined so as to approach the optical axis toward the object side may be provided on the outer periphery of all the lenses, and the inclined portion may contact the lens frame.

  Further, the fourth imaging device of the present invention includes an aperture stop from the object side, a first positive lens having a convex surface facing the image side, a second negative lens having a concave surface facing the image side, and a third positive lens in this order. When the image forming optical system is arranged and an image pickup device arranged on the image side thereof, the lens frame holding the image forming optical system is provided, and the shape of the first positive lens is viewed from the incident side The third positive lens has a shape in which the length in the direction corresponding to the short side direction of the effective imaging region of the image sensor corresponds to the long side direction of the effective imaging region when viewed from the incident side. It is characterized by being shorter than that.

  The operation of this configuration will be described. In the optical system of the present invention, the aperture stop is positioned closest to the object side. Therefore, each lens after the stop has a larger effective surface as the lens disposed on the image side. Become. Further, the effective luminous flux approaches the shape of the effective imaging area of the imaging device toward the image plane side. Therefore, with the above-described configuration, a lens outer shape along the effective light beam is obtained, and the size can be reduced while suppressing vignetting.

  In addition, in common with each of the above conditional expressions, only the upper limit value of the lower conditional expression that limits each conditional expression range or only the lower limit value is limited as the upper limit value or lower limit value of the higher conditional expression. It may be.

  Moreover, the effect of this invention can be heightened more by combining the above conditional expressions arbitrarily.

  According to the present invention, it is possible to obtain an imaging optical system that has a short overall length and can withstand high-performance wide-angle and a small and high-performance imaging device using the imaging optical system.

It is a lens sectional view at the time of infinity object point focusing of Example 1 of the imaging optical system of the present invention. FIG. 6 is a lens cross-sectional view similar to FIG. 1 of the imaging optical system of Example 2. FIG. 6 is a lens cross-sectional view similar to FIG. 1 of the imaging optical system of Example 3. FIG. 5 is a lens cross-sectional view similar to FIG. 1 of the imaging optical system of Example 4. FIG. 6 is a lens cross-sectional view similar to FIG. 1 of the imaging optical system of Example 5. FIG. 6 is an aberration diagram for Example 1 upon focusing on an object point at infinity. FIG. 6 is an aberration diagram for Example 2 upon focusing on an object point at infinity. FIG. 10 is an aberration diagram for Example 3 upon focusing on an object point at infinity. FIG. 10 is an aberration diagram for Example 4 upon focusing on an object point at infinity. FIG. 10 is an aberration diagram for Example 5 upon focusing on an object point at infinity. FIG. 3 is a cross-sectional view of a configuration example in which the imaging optical system of Example 1 and a CCD disposed on the image plane are fixed to a lens frame integrally formed of a resin material. It is a typical disassembled perspective view in the case of making the 3rd positive lens of an imaging optical system into an oval shape. It is a figure which shows the transmittance | permeability characteristic of an example of a near-infrared sharp cut coat. It is a figure which shows the transmittance | permeability characteristic of an example of the color filter provided in the emission surface side of a low-pass filter. It is a figure which shows the color filter arrangement | positioning of a complementary color mosaic filter. It is a figure which shows an example of the wavelength characteristic of a complementary color mosaic filter. It is a figure which shows having opened the aperture shape of the aperture_diaphragm | restriction. It is a figure which shows the state which made the aperture shape of an aperture_diaphragm | restriction 2 steps aperture. It is a perspective view which shows the structure of the imaging optical system of this invention which has arrange | positioned the turret which provided the several aperture stop of the shape fixation from which a shape differs in the transmittance | permeability. It is a front view which shows another turret instead of the turret shown in FIG. It is a figure which shows another turret-shaped light quantity adjustment filter which can be utilized in this invention. It is a figure which shows the example of the filter which suppresses light quantity nonuniformity. It is the back view and front view which show the example of a rotary focal plane shutter. It is a figure which shows a mode that the rotary shutter curtain of the shutter of FIG. 23 rotates. It is operation | movement explanatory drawing of interlace type CCD imaging. It is operation | movement explanatory drawing of progressive CCD imaging. It is a front perspective view which shows the external appearance of the digital camera incorporating the imaging optical system by this invention. FIG. 28 is a rear perspective view of the digital camera of FIG. 27. It is sectional drawing of the digital camera of FIG. It is the front perspective view which opened the cover of the personal computer in which the imaging optical system by this invention was integrated as an objective optical system. It is sectional drawing of the imaging optical system of a personal computer. It is a side view of the state of FIG. 1 is a front view, a side view, and a sectional view of a photographing optical system of a mobile phone in which an imaging optical system according to the present invention is incorporated as an objective optical system.

  Examples 1 to 5 of the imaging optical system according to the present invention will be described below. FIGS. 1 to 5 show lens cross-sectional views of Examples 1 to 5 when focusing on an object point at infinity, respectively. In the drawing, the aperture stop is indicated by S, the first positive lens is indicated by L1, the second negative lens is indicated by L2, the third positive lens is indicated by L3, the cover glass of the electronic image sensor is indicated by CG, and the image plane is indicated by I. In addition, you may give the multilayer film for wavelength range limitation to the surface of the cover glass CG. Further, the cover glass CG may have a low-pass filter function.

  As shown in FIG. 1, the imaging optical system of Example 1 includes, in order from the object side, an aperture stop S, a double-sided aspherical first positive meniscus lens L1 having a convex surface facing the image side, and a double-concave double-sided surface. It includes a spherical second negative lens L2, a biconvex double-sided aspherical third positive lens L3, and a cover glass CG. In this embodiment, the first lens L1 to the third lens L3 are all made of plastic, the first lens L1 and the third lens L3 are made of amorphous polyolefin ZEONEX (trade name), and the second lens L2 is made of polycarbonate. Yes.

The specification of this example is a wide-angle optical system having a focal length f = 3.3 mm, an image height of 2.4 mm, and a half angle of view ω = 36 °. The optical effective diameter (one side) of each lens is 0.647 mm, 0.969 mm, 1.146 mm, 1.241 mm, 1.661 mm, 1 in order of the second surface r ₂ to the seventh surface r _7. 920 mm.

  As shown in FIG. 2, the imaging optical system according to the second embodiment includes, in order from the object side, an aperture stop S, a first aspherical first positive meniscus lens L1 having a convex surface facing the image side, and a convex surface facing the object side. A double-sided aspheric second negative meniscus lens L2, a biconvex double-sided aspheric third positive lens L3, and a cover glass CG. In this embodiment, the first lens L1 and the second lens L2 are made of glass, the third lens L3 is made of plastic, and the third lens L3 is made of amorphous polyolefin ZEONEX.

The specification of this embodiment is a wide-angle optical system having a focal length f = 3.3 mm, an image height of 2.4 mm, and a half angle of view ω = 36 °. The effective optical diameter (one side) of each lens is 0.656 mm, 1.142 mm, 1.277 mm, 1.344 mm, 1.527 mm, 1 in order of the second surface r ₂ to the seventh surface r _7. .776 mm.

  As shown in FIG. 3, the imaging optical system of Example 3 includes, in order from the object side, the aperture stop S, the first aspherical positive meniscus lens L1 with the convex surface facing the image side, and the double-sided double-sided non-side surface. It is composed of a spherical second negative lens L2, a biconvex double-sided aspherical third positive lens l3, and a cover glass CG. In this embodiment, the first lens L1 is made of plastic, the second lens L2 and the third lens L3 are made of glass, and the first lens L1 is made of amorphous polyolefin ZEONEX.

The specification of this example is a wide-angle optical system having a focal length f = 3.3 mm, an image height of 2.4 mm, and a half angle of view ω = 36 °. The optical effective diameter (one side) of each lens is 0.674 mm, 1.201 mm, 1.384 mm, 1.672 mm, 1.652 mm, 1 in order of the second surface r ₂ to the seventh surface r _7. 801 mm.

As shown in FIG. 4, the imaging optical system of Example 4 includes, in order from the object side, the aperture stop S, the first aspherical first positive meniscus lens L1 with the convex surface facing the image side, and the convex surface on the object side. A double-sided aspherical second negative meniscus lens L2, a double-sided aspherical third positive lens L3 with a convex surface facing the image side,
It is comprised from the cover glass CG. In this embodiment, the first lens L1 to the third lens L3 are all made of plastic, the first lens L1 and the third lens L3 are made of amorphous polyolefin ZEONEX, and the second lens L2 is made of polycarbonate.

The specification of this example is a wide-angle optical system having a focal length f = 3.3 mm, an image height of 2.4 mm, and a half angle of view ω = 36 °. The effective optical diameter (one side) of each lens is 0.651 mm, 1.109 mm, 1.330 mm, 1.439 mm, 1.445 mm, 1 in order of the second surface r ₂ to the seventh surface r _7. 717 mm.

  As shown in FIG. 5, the imaging optical system of Example 5 includes, in order from the object side, an aperture stop S, a double-sided aspherical first positive meniscus lens L1 having a convex surface facing the image side, and a convex surface facing the object side. A double-sided aspheric second negative meniscus lens L2, a double-sided aspherical third positive meniscus lens L3 convex toward the object side, and a cover glass CG. In this embodiment, the first lens L1 and the second lens L2 are made of glass, the third lens L3 is made of plastic, and the third lens L3 is made of amorphous polyolefin ZEONEX.

The specification of this example is a wide-angle optical system having a focal length f = 3.3 mm, an image height of 2.4 mm, and a half angle of view ω = 36 °. The effective optical diameter (one side) of each lens is 0.630 mm, 0.942 mm, 1.245 mm, 1.202 mm, 1.350 mm, 1 in the order of the second surface r ₂ to the seventh surface r _7. .599 mm.

Hereinafter, the numerical data of each embodiment described above, symbols described above, r _1, r ₂ ... curvature radius of each lens surface, d _1, d ₂ ... the spacing between the lens surfaces, n _d1 , N _d2 ... Is the refractive index of the d-line of each lens, and ν _d1 , ν _d2 ... Are the Abbe numbers of each lens. The aspherical shape is represented by the following formula, where x is an optical axis with the light traveling direction being positive, and y is a direction orthogonal to the optical axis.

x = (y ² / r) / [1+ {1- (K + 1) (y / r) ² } ^1/2 ]
+ A ₄ y ⁴ + A ₆ y ⁶ + A ₈ y ⁸ + A ₁₀ y ¹⁰
Here, r is a radius of curvature on the optical axis, K is a conical coefficient, and A ₄ , A ₆ , A ₈ , and A ₁₀ are fourth-order, sixth-order, eighth-order, and tenth-order aspherical coefficients, respectively.

Example 1
r ₁ = ∞ (aperture) d ₁ = 0.1500
r ₂ = -7.5279 (aspherical surface) d ₂ = 1.0750 n _d1 = 1.52542 ν _d1 = 55.78
r ₃ = -0.7163 (aspherical surface) d ₃ = 0.1010
r ₄ = -12.1467 (aspherical surface) d ₄ = 0.6000 n _d2 = 1.58423 ν _d2 = 30.49
r ₅ = 0.8291 (aspherical surface) d ₅ = 0.6439
r ₆ = 3.4262 (aspherical surface) d ₆ = 1.2447 n _d3 = 1.52542 ν _d3 = 55.78
r ₇ = -3.5308 (aspherical surface) d ₇ = 0.5000
r ₈ = ∞ d ₈ = 1.0000 n _d4 = 1.51633 ν _d4 = 64.10
r ₉ = ∞ d ₉ = 0.3259
r ₁₀ = ∞ (image plane)
Aspheric coefficient 2nd surface K = 7.7613
A ₄ = -2.0650 × 10 ^-1
A ₆ = 2.3824 × 10 ^-1
A ₈ = -1.1397
A ₁₀ = 8.3716 × 10 ^-1
Third side K = -2.9922
A ₄ = -1.9180 × 10 ^-1
A ₆ = -2.0698 × 10 ^-2
A ₈ = 4.7778 × 10 ^-2
A ₁₀ = -7.0770 × 10 ^-2
4th surface K = 0
A ₄ = 8.5549 × 10 ^-3
A ₆ = -3.3173 × 10 ^-3
A ₈ = 2.0235 × 10 ^-2
A ₁₀ = -4.9724 × 10 ^-3
Fifth side K = -5.4085
A ₄ = -9.8822 × 10 ^-3
A ₆ = 3.8108 × 10 ^-2
A ₈ = -2.3110 × 10 ^-2
A ₁₀ = 6.2728 × 10 ^-3
6th surface K = 0
A ₄ = -6.0997 × 10 ^-2
A ₆ = 3.5388 × 10 ^-2
A ₈ = -9.3482 × 10 ^-3
A ₁₀ = 5.1984 × 10 ^-4
Surface 7 K = -21.9717
A ₄ = -3.8938 × 10 ^-2
A ₆ = 1.7109 × 10 ^-2
A ₈ = -1.2600 × 10 ^-3
A ₁₀ = -4.5069 × 10 ^-4 .

Example 2
r ₁ = ∞ (aperture) d ₁ = 0.1500
r ₂ = -5.7501 (aspherical surface) d ₂ = 1.5214 n _d1 = 1.64000 ν _d1 = 60.10
r ₃ = -0.8591 (aspherical surface) d ₃ = 0.1000
r ₄ = 9.5700 (aspherical surface) d ₄ = 0.6000 n _d2 = 1.71736 ν _d2 = 29.50
r ₅ = 0.8679 (aspherical surface) d ₅ = 0.6846
r ₆ = 66.8603 (aspherical surface) d ₆ = 1.2746 n _d3 = 1.52542 ν _d3 = 55.78
r ₇ = -1.9604 (aspherical surface) d ₇ = 0.2000
r ₈ = ∞ d ₈ = 2.0000 n _d4 = 1.51633 ν _d4 = 64.14
r ₉ = ∞ d ₉ = 0.1502
r ₁₀ = ∞ (image plane)
Aspheric coefficient 2nd surface K = -81.2346
A ₄ = -1.6822 × 10 ^-1
A ₆ = 2.5291 × 10 ^-1
A ₈ = -7.9239 × 10 ^-1
A ₁₀ = 7.2511 × 10 ^-1
Third side K = -3.4464
A ₄ = -1.1481 × 10 ^-1
A ₆ = 1.4273 × 10 ^-2
A ₈ = -1.9287 × 10 ^-3
A ₁₀ = -2.7564 × 10 ^-3
4th surface K = 0
A ₄ = -3.2122 × 10 ^-2
A ₆ = -1.4090 × 10 ^-3
A ₈ = 1.2145 × 10 ^-3
A ₁₀ = 2.2021 × 10 ^-3
Fifth side K = -5.3622
A ₄ = 1.2231 × 10 ^-2
A ₆ = 5.9299 × 10 ^-3
A ₈ = -1.3334 × 10 ^-2
A ₁₀ = 4.7568 × 10 ^-3
6th surface K = 0
A ₄ = -6.4796 × 10 ^-2
A ₆ = 7.8540 × 10 ^-2
A ₈ = -2.7986 × 10 ^-2
A ₁₀ = 2.8273 × 10 ^-3
Surface 7 K = -2.5423
A ₄ = -2.7889 × 10 ^-2
A ₆ = -1.9066 × 10 ^-3
A ₈ = 8.8761 × 10 ^-3
A ₁₀ = -2.0576 × 10 ^-3 .

Example 3
r ₁ = ∞ (aperture) d ₁ = 0.1500
r ₂ = -11.1500 (aspherical surface) d ₂ = 1.7182 n _d1 = 1.52542 ν _d1 = 55.78
r ₃ = -0.7398 (aspherical surface) d ₃ = 0.1176
r ₄ = -5.1048 (aspherical surface) d ₄ = 0.6000 n _d2 = 1.70514 ν _d2 = 41.20
r ₅ = 0.9630 (aspherical surface) d ₅ = 0.4287
r ₆ = 52.7268 (aspherical surface) d ₆ = 1.1705 n _d3 = 1.65156 ν _d3 = 56.20
r ₇ = -1.7038 (aspherical surface) d ₇ = 1.0000
r ₈ = ∞ d ₈ = 1.5000 n _d4 = 1.51633 ν _d4 = 64.10
r ₉ = ∞ d ₉ = 0.5257
r ₁₀ = ∞ (image plane)
Aspherical coefficient second surface K = 0
A ₄ = -8.5390 × 10 ^-2
A ₆ = 2.1454 × 10 ^-1
A ₈ = -6.7874 × 10 ^-1
A ₁₀ = 7.1918 × 10 ^-1
Third side K = -3.2699
A ₄ = -9.4083 × 10 ^-2
A ₆ = 2.1539 × 10 ^-2
A ₈ = -4.7321 × 10 ^-3
A ₁₀ = 6.1547 × 10 ^-3
4th surface K = 11.3618
A ₄ = -2.5013 × 10 ^-2
A ₆ = -1.7135 × 10 ^-2
A ₈ = 2.4028 × 10 ^-2
A ₁₀ = -2.5184 × 10 ^-3
Fifth side K = -8.0182
A ₄ = -6.4582 × 10 ^-2
A ₆ = 4.4917 × 10 ^-2
A ₈ = -1.8056 × 10 ^-2
A ₁₀ = 1.5135 × 10 ^-3
6th surface K = 0
A ₄ = -7.2737 × 10 ^-2
A ₆ = 6.7906 × 10 ^-2
A ₈ = -1.8897 × 10 ^-2
A ₁₀ = 2.5877 × 10 ^-4
7th surface K = -2.9885
A ₄ = -4.5662 × 10 ^-2
A ₆ = 4.2454 × 10 ^-4
A ₈ = 6.9167 × 10 ^-3
A ₁₀ = -1.1382 × 10 ^-3 .

Example 4
r ₁ = ∞ (aperture) d ₁ = 0.1500
r ₂ = -4.6301 (aspherical surface) d ₂ = 1.4219 n _d1 = 1.52542 ν _d1 = 55.78
r ₃ = -0.7717 (aspherical surface) d ₃ = 0.1000
r ₄ = 14.7558 (aspherical surface) d ₄ = 0.6000 n _d2 = 1.58423 ν _d2 = 30.49
r ₅ = 0.8247 (aspherical surface) d ₅ = 0.5796
r ₆ = -70.4957 (aspherical surface) d ₆ = 1.2848 n _d3 = 1.52542 ν _d3 = 55.78
r ₇ = -1.7517 (aspherical surface) d ₇ = 0.5000
r ₈ = ∞ d ₈ = 1.0000 n _d4 = 1.51633 ν _d4 = 64.10
r ₉ = ∞ d ₉ = 0.8550
r ₁₀ = ∞ (image plane)
Aspheric coefficient 2nd surface K = -25.5256
A ₄ = -1.5903 × 10 ^-1
A ₆ = 2.8109 × 10 ^-1
A ₈ = -9.4603 × 10 ^-1
A ₁₀ = 9.6575 × 10 ^-1
Third side K = -3.1402
A ₄ = -1.2192 × 10 ^-1
A ₆ = 5.8307 × 10 ^-3
A ₈ = 1.2448 × 10 ^-2
A ₁₀ = -7.1920 × 10 ^-3
4th surface K = 0
A ₄ = -1.6052 × 10 ^-2
A ₆ = -2.7695 × 10 ^-2
A ₈ = 2.4775 × 10 ^-2
A ₁₀ = -3.9737 × 10 ^-3
Fifth side K = -5.2890
A ₄ = -6.1415 × 10 ^-3
A ₆ = 1.9045 × 10 ^-2
A ₈ = -1.8452 × 10 ^-2
A ₁₀ = 4.8187 × 10 ^-3
6th surface K = 0
A ₄ = -6.2427 × 10 ^-2
A ₆ = 7.8799 × 10 ^-2
A ₈ = -2.5631 × 10 ^-2
A ₁₀ = 6.4222 × 10 ^-5
Surface 7 K = -1.5765
A ₄ = -1.3739 × 10 ^-2
A ₆ = -8.3395 × 10 ^-3
A ₈ = 1.1410 × 10 ^-2
A ₁₀ = -2.7793 × 10 ^-3 .

Example 5
r ₁ = ∞ (aperture) d ₁ = 0.1500
r ₂ = -3.5483 (aspherical surface) d ₂ = 0.9441 n _d1 = 1.52542 ν _d1 = 55.78
r ₃ = -0.7869 (aspherical surface) d ₃ = 0.1000
r ₄ = 5.1411 (aspherical surface) d ₄ = 0.6000 n _d2 = 1.58423 ν _d2 = 30.49
r ₅ = 0.8668 (aspherical surface) d ₅ = 0.5579
r ₆ = 2.7069 (aspherical surface) d ₆ = 0.7310 n _d3 = 1.52542 ν _d3 = 55.78
r ₇ = 40.9062 (aspherical surface) d ₇ = 0.5000
r ₈ = ∞ d ₈ = 1.0000 n _d4 = 1.51633 ν _d4 = 64.10
r ₉ = ∞ d ₉ = 0.5575
r ₁₀ = ∞ (image plane)
Aspheric coefficient 2nd surface K = 4.8164
A ₄ = -2.0149 × 10 ^-1
A ₆ = 1.6121 × 10 ^-1
A ₈ = -7.0842 × 10 ^-1
A ₁₀ = 4.7295 × 10 ^-1
3rd side K = -3.2085
A ₄ = -1.9378 × 10 ^-1
A ₆ = -1.2206 × 10 ^-2
A ₈ = 8.1481 × 10 ^-2
A ₁₀ = -1.0139 × 10 ^-1
4th surface K = 0
A ₄ = 5.3097 × 10 ^-2
A ₆ = 2.9052 × 10 ^-2
A ₈ = -1.8627 × 10 ^-2
A ₁₀ = 1.7525 × 10 ^-3
Fifth side K = -5.2416
A ₄ = 3.9126 × 10 ^-2
A ₆ = 3.2573 × 10 ^-2
A ₈ = 2.9813 × 10 ^-3
A ₁₀ = -7.9290 × 10 ^-3
6th surface K = 0
A ₄ = -8.4473 × 10 ^-2
A ₆ = 3.2379 × 10 ^-2
A ₈ = -1.0481 × 10 ^-2
A ₁₀ = 2.9594 × 10 ^-4
Surface 7 K = 0
A ₄ = 1.3909 × 10 ^-2
A ₆ = -9.6102 × 10 ^-3
A ₈ = 1.8961 × 10 ^-3
A ₁₀ = -9.8080 × 10 ^-4 .

Aberration diagrams when focusing on infinity in Examples 1 to 5 are shown in FIGS. In these aberration diagrams, “SA” indicates spherical aberration, “AS” indicates astigmatism, “DT” indicates distortion, and “CC” indicates lateral chromatic aberration. In each aberration diagram, “ω” indicates a half angle of view.

  Next, the values of the conditions (1) to (13) in the above embodiments will be shown.

Conditional Example Example 1 Example 2 Example 3 Example 4 Example 5
(1) 2.35 2.78 2.92 2.71 2.14
(2) -1.24 -1.86 -3.09 -3.38 -0.99
(3) 0.41 0.39 0.56 0.46 0.31
(4) -0.37 -0.36 -0.43 -0.45 -0.34
(5) 1.545 1.628 1.627 1.545 1.545
(6) 1.21 1.35 1.14 1.40 1.57
(7) 0.58 1.73 1.97 2.42 1.52
5.45 4.79 3.19 4.30 6.38
(8) 0.72 1.98 3.90 1.84 1.65
3.13 2.91 1.40 2.65 3.85
(9) 19.2 ° 20.0 ° 16.2 ° 18.7 ° 29.8 °
(Note) The numerical values of conditional expressions (7) and (8) are the numerical values of the object-side surface and the lower values of the image-side surface.

  Although each of the above embodiments is small, good images are obtained as shown in the aberration diagrams of FIGS.

  In the above embodiment of the present invention, a cover glass may be disposed immediately before the aperture stop S.

  In the above embodiments of the present invention, the lens made of plastic may be made of glass. For example, it is needless to say that higher performance can be achieved by using a glass having a higher refractive index than the plastic of any of the embodiments. Needless to say, the use of special low dispersion glass is effective in correcting chromatic aberration. In particular, when it is made of plastic, it is preferable to use a low moisture-absorbing material because performance deterioration due to environmental changes is reduced (for example, ZEONEX (trade name) manufactured by ZEON Corporation).

  Further, a flare stop other than the brightness stop S may be arranged in order to cut unnecessary light such as ghost and flare. In the above embodiment, any one between the aperture stop S and the first lens L1, between the first lens L1 and the second lens L2, between the second lens L2 and the third lens L3, and between the third lens L3 and the image plane I. A flare stop may be arranged at the location. Further, the flare beam may be cut by the frame, or the flare stop may be formed by using another member. Further, it may be printed directly on the optical system, painted, or bonded with a seal or the like. Further, the shape may be any shape such as a circle, an ellipse, a rectangle, a polygon, or a range surrounded by a function curve. Further, not only the harmful light flux but also the light flux such as coma flare around the screen may be cut.

  Each lens may be provided with an antireflection coating to reduce ghost and flare. A multi-coat is desirable because it can effectively reduce ghosts and flares. Moreover, you may perform an infrared cut coat on a lens surface, a cover glass, etc.

  Further, focusing may be performed to adjust the focus. Focusing may be performed by extending the entire lens system, or a part of the lenses may be extended, or focusing may be performed by retraction.

  Further, the brightness decrease in the peripheral portion of the image may be reduced by shifting the micro lens of the CCD. For example, the design of the CCD microlens may be changed in accordance with the incident angle of the light beam at each image height. Further, the amount of decrease in the peripheral portion of the image may be corrected by image processing.

  FIG. 11 shows the light of the imaging optical system 5 in a configuration example in which the imaging optical system 5 of the first embodiment and the CCD 6 arranged on the image plane I are fixed to a lens frame 7 integrally molded with a resin material. FIG. 2 is a cross-sectional view taken in a diagonal direction of the image plane I of the CCD 6 including an axis, and the aperture stop S is integrally formed with a resin lens frame 7. In this way, it is easy to manufacture the lens frame 7 that holds the imaging optical system 5. Also, by integrating the configuration of the aperture stop S with the lens frame 7, the manufacturing process is greatly reduced, and the lens frame 7 itself is provided with a holding function for the CCD 6 of the image pickup device, so that the lens frame It becomes difficult for garbage etc. to enter 7.

Further, as apparent from FIG. 11, the outer periphery 8 of each of the first positive lens L1, the second negative lens L2, and the third positive lens L3 of the imaging optical system 5 is inclined so as to approach the optical axis toward the object side. By providing the inclined surface and allowing the lens frame 7 to contact and fix the inclined surface, the lenses L1 to L3 can be dropped into the lens frame 7 from the image surface side to be positioned and fixed.

  Further, as shown in a schematic exploded perspective view in FIG. 12, the shape of the first positive lens L1 of the imaging optical system held in the lens frame 7 formed of plastic is the first positive lens L1, the second negative lens, and the like. The lens L2 has a circular shape when viewed from the incident side, and the third positive lens L3 has an oval shape in which an upper portion and a lower portion are cut based on a circular lens. And the outer periphery 8 of each lens L1-L3 inclines to the aperture_diaphragm | restriction S side. The inner surface of the lens frame 7 is also formed to be inclined corresponding to the inclination.

  In this way, the shape of the first positive lens L1 is circular when viewed from the incident side, and the shape of the third positive lens L3 is the direction corresponding to the short side direction of the effective imaging region of the CCD 6 of the image sensor when viewed from the incident side. The first positive lens L1, the second negative lens L2, and the third positive lens L3 of the imaging optical system are made effective by making the length of the lens shorter than the length corresponding to the long side direction of the effective imaging region. The lens outer shape along the light beam can be obtained, and the size can be reduced while suppressing vignetting. In this example as well, the inclined surfaces of the outer periphery 8 of each of the first positive lens L1, the second negative lens L2, and the third positive lens L3 of the imaging optical system 5 are contacted and fixed in the lens frame 7. By doing so, the lenses L1 to L3 can be dropped into the lens frame 7 from the image plane side and positioned and fixed.

  Further, it is desirable that the peripheral surface of the aperture of the aperture stop S is tilted toward the lens L1 as shown in the cross-sectional view of FIG. In addition, since the inclination angle is large and the corner portion on the most lens side substantially serves as a diaphragm, the light beam reflected by the outer peripheral surface of the aperture portion of the aperture stop S hardly enters the CCD 6 of the image sensor. Thus, the influence of flare and ghost can be reduced.

  By the way, in each above-mentioned Example, you may give a near-infrared sharp cut coat to the entrance plane side of cover glass CG as mentioned above. This near-infrared sharp cut coat is configured such that the transmittance at a wavelength of 600 nm is 80% or more and the transmittance at a wavelength of 700 nm is 10% or less. Specifically, it is a multilayer film composed of the following 27 layers, for example. However, the design wavelength is 780 nm.

Substrate material Physical film thickness (nm) λ / 4
───────────────────────────────
First layer Al ₂ O ₃ 58.96 0.50
Second layer TiO ₂ 84.19 1.00
Third layer SiO ₂ 134.14 1.00
Fourth layer TiO ₂ 84.19 1.00
5th layer SiO ₂ 134.14 1.00
Sixth layer TiO ₂ 84.19 1.00
Seventh layer SiO ₂ 134.14 1.00
Eighth layer TiO ₂ 84.19 1.00
Ninth layer SiO ₂ 134.14 1.00
10th layer TiO ₂ 84.19 1.00
11th layer SiO ₂ 134.14 1.00
12th layer TiO ₂ 84.19 1.00
13th layer SiO ₂ 134.14 1.00
14th layer TiO ₂ 84.19 1.00
15th layer SiO ₂ 178.41 1.33
16th layer TiO ₂ 101.03 1.21
17th layer SiO ₂ 167.67 1.25
18th layer TiO ₂ 96.82 1.15
19th layer SiO ₂ 147.55 1.05
20th layer TiO ₂ 84.19 1.00
21st layer SiO ₂ 160.97 1.20
22nd layer TiO ₂ 84.19 1.00
23rd layer SiO ₂ 154.26 1.15
24th layer TiO ₂ 95.13 1.13
25th layer SiO ₂ 160.97 1.20
26th layer TiO ₂ 99.34 1.18
27th layer SiO ₂ 87.19 0.65
───────────────────────────────
Air.

  The transmittance characteristics of the near infrared sharp cut coat are as shown in FIG.

  Further, by providing a color filter that reduces the transmission of colors in the short wavelength region as shown in FIG. 14 or coating on the exit surface side of the low-pass filter, the color reproducibility of the electronic image is further improved. Yes.

  Specifically, with this filter or coating, the ratio of the transmittance of the wavelength of 420 nm to the transmittance of the wavelength having the highest transmittance at a wavelength of 400 nm to 700 nm is 15% or more, and 400 nm to the transmittance of the highest wavelength. It is preferable that the ratio of the transmittances of the wavelengths is 6% or less.

  Thereby, it is possible to reduce the difference between the recognition of the color of the human eye and the color of the image to be captured and reproduced. In other words, it is possible to prevent deterioration of the image due to the human eye easily recognizing a short wavelength color that is difficult to be recognized by human vision.

  If the ratio of the transmittance at the wavelength of 400 nm exceeds 6%, the short wavelength castle which is difficult to be recognized by the human eye is regenerated to a wavelength that can be recognized. Conversely, the ratio of the transmittance at the wavelength of 420 nm is reversed. If the value is smaller than 15%, the reproduction of the wavelength castle that can be recognized by humans becomes low, and the color balance becomes poor.

  Such means for limiting the wavelength is more effective in an imaging system using a complementary color mosaic filter.

  In each of the above embodiments, as shown in FIG. 14, the coating has a transmittance of 0% at a wavelength of 400 nm, a transmittance of 90% at 420 nm, and a transmittance peak of 100% at 440 nm.

  By multiplying the action with the above-mentioned near infrared sharp cut coat, the transmittance at 400 nm is peaked at 99%, the transmittance at 400 nm is 0%, the transmittance at 420 nm is 80%, and the transmittance at 600 nm is 82%. The transmittance at 700 nm is 2%. As a result, more faithful color reproduction is performed.

  The low-pass filter can be used by superimposing three types of filters with crystal axes in the horizontal (= 0 °) and ± 45 ° directions when projected on the image plane in the optical axis direction. Can be suppressed by shifting by SQRT (1/2) × a horizontally in the direction of a μm and ± 45 °. Here, SQRT is a square route and means a square root.

Further, on the image pickup surface I of the CCD, as shown in FIG. 15, a complementary color mosaic filter in which four color filters of cyan, magenta, yellow, and green are provided in a mosaic pattern corresponding to the image pickup pixels is provided. ing. These four types of color filters are arranged in a mosaic so that each of them has approximately the same number and adjacent pixels do not correspond to the same type of color filter. Thereby, more faithful color reproduction becomes possible.

  Specifically, the complementary color mosaic filter is composed of at least four types of color filters as shown in FIG. 15, and the characteristics of the four types of color filters are preferably as follows.

The green color filter G has a spectral intensity peak at the wavelength _GP ,
Yellow filter element Y _e has a spectral strength peak at a wavelength Y _P,
Each cyan filter element C has a spectral strength peak at a wavelength C _P,
The magenta color filter M has peaks at wavelengths M _P1 and M _P2 and satisfies the following conditions.

510 nm <G _P <540 nm
5 nm <Y _P −G _P <35 nm
−100 nm <C _P −G _P <−5 nm
430 nm <M _P1 <480 nm
580 nm <M _P2 <640 nm
Further, the green, yellow, and cyan color filters have an intensity of 80% or more at a wavelength of 530 nm with respect to each spectral intensity peak, and the magenta color filter has an intensity of 10% at a wavelength of 530 nm. From the viewpoint of improving the color reproducibility, it is more preferable that the strength is 50% to 50%.

FIG. 16 shows an example of each wavelength characteristic in each of the above embodiments. The green color filter G has a spectral intensity beak at 525 nm. The yellow color filter Y _e has a spectral intensity peak at 555 nm. The cyan color filter C has a spectral intensity peak at 510 nm. The magenta color filter M has peaks at 445 nm and 620 nm. In each color filter at 530 nm, G is 99%, _Ye is 95%, C is 97%, and M is 38% with respect to the respective spectral intensity peaks.

In the case of such a complementary color filter, the following signal processing is performed electrically with a controller (not shown) (or a controller used in a digital camera),
Luminance signal Y = | G + M + Y _e + C | × 1/4
Color signal R−Y = | (M + Y _e ) − (G + C) |
B−Y = | (M + C) − (G + Y _e ) |
The signal is converted into R (red), G (green), and B (blue) signals.

  By the way, the arrangement position of the above-mentioned near infrared sharp cut coat may be any position on the optical path. The number of low-pass filters may be two or one.

  In the image pickup apparatus of the present invention, for adjusting the light amount, a variable aperture may be used in which the brightness stop S is configured with a plurality of aperture blades and the aperture shape is variable. FIG. 17 is an explanatory diagram showing an example of the aperture shape at the time of opening, and FIG. 18 is an explanatory diagram showing an example of the aperture shape at the time of two-stage aperture. 17 and 18, OP represents the optical axis, Da represents six diaphragm plates, and Xa and Xb represent openings. In the present invention, the aperture shape of the aperture can be set to only two types: an open state (FIG. 17) and an aperture value (a two-stage aperture, FIG. 18) that provides an F value that satisfies a predetermined condition.

  Or, using a turret provided with a plurality of fixed-shaped brightness stops with different shapes or transmittances, depending on the required brightness, place any brightness stop on the object-side optical axis of the imaging optical system. With the arrangement, the diaphragm mechanism can be thinned. In addition, a configuration in which a light amount reduction filter having a transmittance lower than the transmittance of other aperture stops is arranged in the aperture that reduces the amount of light most among the apertures of the aperture stops arranged on the turret. Good. Accordingly, the aperture diameter of the diaphragm is not excessively narrowed, and deterioration of the imaging performance due to diffraction that occurs due to the small aperture diameter of the diaphragm can be suppressed.

  FIG. 19 is a perspective view showing a configuration of an example in this case. Brightness can be adjusted in 0, −1, −2, −3, and −4 stages at the position of the stop S on the optical axis on the object side of the first positive lens L1 of the imaging optical system. A turret 10 is arranged.

  The turret 10 has an opening 1A (a transmittance of 100% for a wavelength of 550 nm) having a circular aperture with a maximum aperture diameter and a fixed aperture of 0 stage, and an opening of the opening 1A for -1 stage correction. An opening 1B made of a transparent parallel plate having a fixed opening shape having an opening area that is about half the area (the transmittance for the wavelength of 550 nm is 99%), a circular opening having the same area as the opening 1B, and −2 steps In order to correct to -3 and -4 stages, apertures 1C, 1D, and 1E provided with ND filters having transmittances of 50%, 25%, and 13% for a wavelength of 550 nm, respectively, are provided.

  The light quantity is adjusted by arranging one of the apertures at the aperture position by turning around the rotation shaft 11 provided in the turret 10.

  Moreover, it can replace with the turret 10 shown in FIG. 19, and the turret 10 'shown in the front view of FIG. 20 can be used. Brightness can be adjusted in 0, −1, −2, −3, and −4 stages at the position of the stop S on the optical axis on the object side of the first positive lens L1 of the imaging optical system. A turret 10 'is arranged.

  The turret 10 ′ has an opening shape for adjusting the zero stage having a circular and fixed opening 1 A ′ having a maximum aperture diameter, and an opening area that is about half of the opening area of the opening 1 A ′ for −1 stage correction. The opening 1B ′ having a fixed opening shape and the opening areas 1C ′, 1D ′, and 1E ′ having fixed shapes for the correction to the −2 step, the −3 step, and the −4 step are further reduced in order. Have.

  The light quantity is adjusted by arranging any opening at the stop position by turning around the rotation shaft 11 provided in the turret 10 '.

  In order to reduce the thickness, the aperture of the aperture stop S may be an aperture having a fixed shape and position, and the light amount adjustment may be performed by electrically adjusting an output signal from the image sensor. Alternatively, the light amount may be adjusted by inserting and removing an ND filter between other spaces in the lens system, for example, the third positive lens L3 and the CCD cover glass CG. FIG. 21 is a diagram showing an example of this. The opening 1A ″ of the turret 10 ″ is a through surface or a hollow opening, the opening 1B ″ is an ND filter having a transmittance of 1/2, and the opening 1C ″ has a transmittance of 1/4. The ND filter, aperture 1D ″ is a turret-shaped filter provided with an ND filter having a transmittance of 1/8, and any aperture is arranged at any position in the optical path by rotation around the central rotation axis. To adjust the light intensity.

  Further, as a filter for adjusting the light amount, a filter surface capable of adjusting the light amount so as to suppress unevenness in the light amount may be provided. For example, as shown in FIG. 22, the light intensity is centered concentrically so that the transmittance is made uniform with priority given to securing the light quantity at the center for dark subjects and the uneven brightness is compensated only for bright subjects. It is good also as a structure which arrange | positions the filter which falls so much.

  Further, as the diaphragm S, the peripheral portion on the incident surface side of the first positive lens L1 may be painted black.

  When the imaging apparatus according to the present invention stores an image as a still image like a camera or the like, a shutter for adjusting the amount of light may be disposed in the optical path.

  As such a shutter, a focal plane shutter, a rotary shutter, or a liquid crystal shutter disposed immediately before the CCD may be used, or the aperture stop itself may be configured as a shutter.

  FIG. 23 shows an example of the shutter. FIG. 23 shows an example of a rotary focal plane shutter which is one of the focal plane shutters. FIG. 23A is a view seen from the back side, and FIG. 23B is a view seen from the front side. is there. A shutter substrate 15 is arranged immediately before the image plane or at an arbitrary optical path position. The substrate 15 is provided with an opening 16 that transmits an effective light beam of the optical system. Reference numeral 17 denotes a rotary shutter curtain. Reference numeral 18 denotes a rotary shaft of the rotary shutter curtain 17. The rotary shaft 18 rotates with respect to the substrate 15 and is integrated with the rotary shutter curtain 17. The rotating shaft 18 is connected to gears 19 and 20 on the surface of the substrate 15. The gears 19 and 20 are connected to a motor (not shown).

  In such a configuration, the rotary shutter curtain 17 is configured to rotate about the rotation shaft 18 via the gears 19 and 20 and the rotation shaft 18 by driving a motor (not shown).

  The rotary shutter curtain 17 is formed in a substantially semicircular shape and shields and retreats the opening 16 of the substrate 15 by rotation, thereby serving as a shutter. The shutter speed is adjusted by changing the rotating speed of the rotary shutter curtain 17.

  24A to 24D are views of the rotary shutter curtain 17 rotating from the image plane side. It moves in the order of (a), (b), (c), (d), and (a) in the figure with time.

  As described above, the aperture stop S with a fixed shape and a filter or shutter that adjusts the amount of light are placed at different positions in the lens system. In addition, an imaging apparatus capable of reducing the overall length of the lens system can be obtained.

  Further, a configuration may be adopted in which electrical control is performed so as to obtain a still image by extracting a part of the electrical signal of the CCD without using a mechanical shutter. An example of such a configuration will be described with reference to FIG. 25 and FIG. FIG. 25 is an explanatory diagram of an operation of CCD imaging in which signals are sequentially read out by an interlace method (interlaced scanning method). In FIG. 25, Pa to Pc are photosensitive sections using photodiodes, Va to Vc are vertical transfer sections using CCD, and Ha is a horizontal transfer section using CCD. The A field indicates an odd field, and the B field indicates an even field.

In the configuration of FIG. 25, the basic operation is performed as follows. That is, (1) signal charge accumulation (photoelectric conversion) by light in the photosensitive part, (2) signal charge shift (field shift) from the photosensitive part to the vertical transfer part, and (3) signal charge in the vertical transfer part. Transfer (vertical transfer), (4) Transfer of signal charge from vertical transfer unit to horizontal transfer unit (line shift), (5) Transfer of signal charge in horizontal transfer unit (horizontal transfer), (6) Horizontal transfer unit The signal charge is detected (detected) at the output terminal. Such sequential reading can be performed using either the A field (odd field) or the B field (even field).

  In the interlaced (interlaced scanning) CCD imaging shown in FIG. 25, the accumulation timing of the A field and the B field is shifted by 1/60 in the TV broadcast system and the analog video system. If this is used as it is as a DSC (Digital Spectral Compatible) image to form a frame image, blurring like a double image occurs in the case of a moving subject. Therefore, in this type of CCD imaging, the A and B fields are simultaneously exposed to mix the signals of adjacent fields. Then, after the fluorescent light is illuminated at the end of exposure with a mechanical shutter, the A field and the B field are read out separately to synthesize signals.

  In the present invention, the mechanical shutter functions only for smear prevention and only the A field is sequentially read out, or the A and B fields are simultaneously mixed readout. The high-speed shutter can be released regardless of the shutter speed (because it can be controlled only with an electronic shutter). In the example of FIG. 25, the number of CCDs in the vertical transfer unit is half of the number of photodiodes constituting the photosensitive unit, and thus there is an advantage that the size can be easily reduced.

  FIG. 26 is a diagram for explaining the operation of CCD imaging in which sequential readout of signals is performed in a progressive manner. In FIG. 26, Pd to Pf are photosensitive portions using photodiodes, Vd to Vf are vertical transfer portions by CCD, and Hb is a horizontal transfer portion by CCD.

  In FIG. 26, since reading can be performed in the pixel arrangement order, all charge accumulation and reading operations can be electronically controlled. Therefore, the exposure time can be shortened to about (1/10000 seconds). In the example of FIG. 26, the number of vertical CCDs is larger than in the case of FIG. 25, and there is a disadvantage that downsizing is difficult. However, because of the advantages as described above, in the present invention, FIG. Any of these methods can be employed.

  The imaging apparatus according to the present invention as described above is an imaging apparatus that forms an object image with an imaging optical system and receives the image on an imaging element such as a CCD, and more particularly a digital camera, video camera, information processing It can be used for personal computers, telephones, and especially mobile phones that are convenient to carry. The embodiment is illustrated below.

  27 to 29 are conceptual diagrams of a configuration in which the imaging optical system according to the present invention is incorporated in a photographing optical system 41 of a digital camera. 27 is a front perspective view showing the appearance of the digital camera 40, FIG. 28 is a rear perspective view thereof, and FIG. 29 is a cross-sectional view showing the configuration of the digital camera 40. In this example, the digital camera 40 includes a photographing optical system 41 having a photographing optical path 42, a finder optical system 43 having a finder optical path 44, a shutter 45, a flash 46, a liquid crystal display monitor 47, and the like. When the shutter 45 disposed in the position is pressed, photographing is performed through the photographing optical system 41, for example, the imaging optical system of the first embodiment in conjunction therewith. An object image formed by the photographing optical system 41 is formed on the imaging surface of the CCD 49 through a cover glass CG provided with a near-infrared cut coat and having a low-pass filter function. The object image received by the CCD 49 is displayed as an electronic image on the liquid crystal display monitor 47 provided on the back of the camera via the processing means 51. Further, the processing means 51 is connected to a recording means 52 so that a photographed electronic image can be recorded. The recording means 52 may be provided separately from the processing means 51, or may be configured to perform recording / writing electronically using a floppy disk, memory card, MO, or the like. Further, it may be configured as a silver salt camera in which a silver salt film is arranged in place of the CCD 49.

  Further, a finder objective optical system 53 is disposed on the finder optical path 44. The object image formed by the finder objective optical system 53 is formed on the field frame 57 of the Porro prism 55 which is an image erecting member. Behind this polyprism 55 is an eyepiece optical system 59 that guides the erect image to the observer eyeball E. Note that cover members 50 are disposed on the incident side of the photographing optical system 41 and the finder objective optical system 53 and on the exit side of the eyepiece optical system 59, respectively.

  The digital camera 40 configured as described above can achieve high performance and downsizing since the photographing optical system 41 is high performance and small.

  In the example of FIG. 29, a parallel plane plate is disposed as the cover member 50, but a lens having power may be used.

  Next, a personal computer which is an example of an information processing apparatus in which the imaging optical system of the present invention is incorporated as an objective optical system is shown in FIGS. 30 is a front perspective view with the cover of the personal computer 300 opened, FIG. 31 is a sectional view of the photographing optical system 303 of the personal computer 300, and FIG. 32 is a side view of the state of FIG. As shown in FIGS. 30 to 32, a personal computer 300 includes a keyboard 301 for a writer to input information from the outside, information processing means and recording means not shown, and a monitor for displaying information to the operator. 302 and a photographing optical system 303 for photographing the operator himself and surrounding images. Here, the monitor 302 may be a transmissive liquid crystal display element that is illuminated from the back by a backlight (not shown), a reflective liquid crystal display element that reflects and displays light from the front, a CRT display, or the like. Further, in the drawing, the photographing optical system 303 is built in the upper right of the monitor 302. However, the imaging optical system 303 is not limited to the place, and may be anywhere around the monitor 302 or the keyboard 301.

  The photographing optical system 303 has an objective lens 112 including an imaging optical system (abbreviated in the drawing) according to the present invention and an image pickup element chip 162 that receives an image on a photographing optical path 304. These are built in the personal computer 300.

  Here, a cover glass CG having a low-pass filter function is additionally attached on the image pickup element chip 162 to be integrally formed as an image pickup unit 160, and can be touched at the rear end of the lens frame 113 of the objective lens 112 with one touch. Since it can be fitted and attached, it is not necessary to align the center of the objective lens 112 and the image pickup element chip 162 and to adjust the surface interval, and the assembly is simplified. A cover glass 114 for protecting the objective lens 112 is disposed at the tip of the lens frame 113.

  The object image received by the image sensor chip 162 is input to the processing means of the personal computer 300 via the terminal 166 and is displayed on the monitor 302 as an electronic image. FIG. A captured image 305 is shown. The image 305 can also be displayed on the personal computer of the communication partner from a remote location via the processing means, the Internet, or the telephone.

Next, FIG. 33 shows a telephone which is an example of an information processing apparatus in which the imaging optical system of the present invention is incorporated as a photographing optical system, particularly a portable telephone which is convenient to carry. 33A is a front view of the mobile phone 400, FIG. 33B is a side view, and FIG. 33C is a cross-sectional view of the photographing optical system 405. As shown in FIGS. 33A to 33C, the mobile phone 400 includes a microphone unit 401 that inputs an operator's voice as information, a speaker unit 402 that outputs a voice of a call partner, and an operator who receives information. An input dial 403 for inputting information, a monitor 404 for displaying information such as a photographed image and a telephone number of the operator and the other party, a photographing optical system 405, an antenna 406 for transmitting and receiving communication radio waves, and an image And processing means (not shown) for processing information, communication information, input signals, and the like. Here, the monitor 404 is a liquid crystal display element. In the drawing, the arrangement positions of the respective components are not particularly limited to these. The photographing optical system 405 includes an objective lens 112 including an imaging optical system (abbreviated in the drawing) according to the present invention disposed on a photographing optical path 407, and an image sensor chip 162 that receives an object image. These are built in the mobile phone 400.

  Here, a cover glass CG having a low-pass filter function is additionally attached on the image pickup element chip 162 to be integrally formed as an image pickup unit 160, and can be touched at the rear end of the lens frame 113 of the objective lens 112 with one touch. Since it can be fitted and attached, it is not necessary to align the center of the objective lens 112 and the image pickup element chip 162 and to adjust the surface interval, and the assembly is simplified. A cover glass 114 for protecting the objective lens 112 is disposed at the tip of the lens frame 113.

  The object image received by the imaging element chip 162 is input to the processing means (not shown) via the terminal 166 and displayed as an electronic image on the monitor 404, the monitor of the communication partner, or both. . Further, when transmitting an image to a communication partner, the processing means includes a signal processing function for converting information of an object image received by the image sensor chip 162 into a signal that can be transmitted.

  Each of the embodiments described above can be variously modified in accordance with the configuration of the claims.

  In the present invention, the imaging optical system can also be configured as follows.

    [1] In order from the object side, the aperture stop, the first positive lens, the second negative lens, and the third positive lens are arranged in this order, and at least the first positive lens has an aspherical surface and satisfies the following conditional expression: An imaging optical system characterized by the above.

−5.0 <f _2-3 /f<−0.5 (2)
Here, f _2-3 is the combined focal length of the second negative lens and the third positive lens, and f is the focal length of the entire system.

    [2] In order from the object side, the aperture stop, the first positive lens, the second negative lens, and the third positive lens are arranged in this order, and at least the second negative lens has an aspherical surface and satisfies the following conditional expression: An imaging optical system characterized by the above.

−5.0 <f _2-3 /f<−0.5 (2)
Here, f _2-3 is the combined focal length of the second negative lens and the third positive lens, and f is the focal length of the entire system.

    [3] In order from the object side, an aperture stop, a first positive meniscus lens having a convex surface facing the image side, a second negative lens, and a third positive lens are arranged in this order, and satisfy the following conditional expression: Imaging optical system.

0.2 <f ₁ / f ₃ <0.58 (3-1)
Here, f ₁ is the focal length of the first positive lens, and f ₃ is the focal length of the third positive lens.

  According to the present invention, it is possible to obtain an imaging optical system that has a short overall length and can withstand high-performance wide-angle and a small and high-performance imaging device using the imaging optical system.

S ... Brightness stop L1 ... 1st positive lens L2 ... 2nd negative lens L3 ... 3rd positive lens CG ... Cover glass I ... Image plane OP ... Optical axis Da ... Diaphragm plate Xa, Xb ... Opening part Pa-Pf ... Photosensitivity Portions Va to Vf ... Vertical transfer portion Ha, Hb ... Horizontal transfer portion E ... Observer eyeballs 1A, 1B, 1C, 1D, 1E ... Opening 1A ', 1B', 1C ', 1D', 1E '... Opening 1A ", 1B ", 1C", 1D "... Aperture 5 ... Imaging optical system 6 ... CCD
7 ... Lens frame 8 ... Lens outer periphery 10 ... Turret 10 '... Turret 10 "... Turret 11 ... Rotating shaft 15 ... Shutter substrate 16 ... Opening 17 ... Rotary shutter curtain 18 ... Rotating shaft 19, 20 ... Gear 40 ... Digital camera 41 ... Optical optical system 42 ... Optical optical path 43 ... finder optical system 44 ... optical path for finder 45 ... shutter 46 ... flash 47 ... liquid crystal display monitor 49 ... CCD
DESCRIPTION OF SYMBOLS 50 ... Cover member 51 ... Processing means 52 ... Recording means 53 ... Finder objective optical system 55 ... Porro prism 57 ... Field frame 59 ... Eyepiece optical system 112 ... Objective lens 113 ... Lens frame 114 ... Cover glass 160 ... Imaging unit 162 ... Image sensor chip 166 ... Terminal 300 ... Personal computer 301 ... Keyboard 302 ... Monitor 303 ... Shooting optical system 304 ... Shooting optical path 305 ... Image 400 ... Mobile phone 401 ... Microphone unit 402 ... Speaker unit 403 ... Input dial 404 ... Monitor 405 ... Shooting optics System 406 ... Antenna 407 ... Imaging optical path

Claims (20)

Imaging optics characterized in that, in order from the object side, an aperture stop, a first positive meniscus lens having a convex surface facing the image side, a second negative lens, and a third positive lens are arranged in this order and satisfy the following conditional expression: system.
−5.0 <f _2-3 /f<−0.5 (2)
Here, f _2-3 is the combined focal length of the second negative lens and the third positive lens, and f is the focal length of the entire system. The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
−3.5 <f _2-3 /f<−0.8 (2-1) The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
0.1 <f ₁ / f ₃ <0.7 (3)
Here, f ₁ is the focal length of the first positive lens, and f ₃ is the focal length of the third positive lens. The imaging optical system according to claim 3, wherein the following conditional expression is satisfied.
0.2 <f ₁ / f ₃ <0.58 (3-1) The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
−0.6 <f ₂ / f ₃ <−0.1 (4)
Here, f ₂ is the focal length of the second negative lens, and f ₃ is the focal length of the third positive lens. The imaging optical system according to claim 5, wherein the following conditional expression is satisfied.
−0.5 <f ₂ / f ₃ <−0.15 (4-1) The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
1.45 <n _avg <1.70 (5)
However, _navg is the average value of the refractive index of the d-line of the first positive lens to the third positive lens. The imaging optical system according to claim 7, wherein the following conditional expression is satisfied.
1.5 <n _avg <1.65 (5-1) The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
1.0 <(r _1f + r _1r ) / (r _1f −r _1r ) <1.7 (6)
Here, r _1f is the object-side paraxial radius of curvature of the first positive lens, and r _1r is the image-side paraxial radius of curvature of the first positive lens. The imaging optical system according to claim 9, wherein the following conditional expression is satisfied.
1.1 <(r _1f + r _1r ) / (r _1f −r _1r ) <1.6 (6-1) 11. The imaging optical system according to claim 1, wherein the first positive lens has at least one aspherical surface that satisfies the following conditional expression.
0.01 <| (r _1s + r _1a ) / (r _1s −r _1a ) −1 | <100
... (7)
However, r _1s is the paraxial radius of curvature of the aspherical surface of the first positive lens, and r _1a is the most different from the paraxial radius of curvature within the effective optical range of the radius of curvature considering the aspherical surface of the first positive lens. This is the value when changed. The imaging optical system according to claim 11, wherein the following conditional expression is satisfied.
0.05 <| (r _1s + r _1a ) / (r _1s −r _1a ) −1 | <10
... (7-1) The imaging optical system according to any one of claims 1 to 12, wherein the second negative lens has at least one aspherical surface that satisfies the following conditional expression.
0.01 <| (r _2s + r _2a ) / (r _2s −r _2a ) −1 | <100
... (8)
However, r _2s is the paraxial radius of curvature of the aspherical surface of the second negative lens, and r _2a is the most different from the paraxial radius of curvature within the effective optical range of the radius of curvature considering the aspherical surface of the second negative lens. This is the value when changed. The imaging optical system according to claim 13, wherein the following conditional expression is satisfied.
0.1 <| (r _2s + r _2a ) / (r _2s −r _2a ) −1 | <5
... (8-1) The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
10 ° <α <40 ° (9)
Where α is the incident angle of the chief ray on the image plane at the maximum image height. The imaging optical system according to claim 15, wherein the following conditional expression is satisfied.
15 ° <α <35 ° (9-1) The imaging optical system according to any one of claims 1 to 16, and an imaging device arranged on an image side thereof, wherein the aperture stop has a fixed aperture shape through which an optical axis passes. In addition, the imaging apparatus is characterized in that the outer peripheral surface of the opening is inclined at an inclination angle equal to or greater than the incident angle of the most off-axis light beam so as to approach the optical axis toward the image plane side. The imaging optical system according to claim 1, and an imaging device disposed on an image side thereof, holding the imaging optical system and the imaging device, and reducing the brightness stop An image pickup apparatus comprising a lens frame integrally formed of the same resin material. An imaging optical system according to any one of claims 1 to 16, and an imaging device arranged on the image side thereof, comprising a lens frame that holds the imaging optical system, and at least the first positive optical system. An imaging apparatus, wherein an inclined portion that is inclined so as to approach the optical axis toward the object side is provided on an outer periphery of each of the lens and the third positive lens, and the inclined portion is in contact with the lens frame. 17. The first positive lens, comprising: the imaging optical system according to claim 1; and an image pickup element disposed on an image side thereof; and a lens frame that holds the imaging optical system. The shape of the third positive lens is circular when viewed from the incident side, and the length of the third positive lens has a length in a direction corresponding to the short side direction of the effective imaging region of the image sensor when viewed from the incident side. An imaging apparatus characterized by being shorter than a length corresponding to a long side direction of a region.

Images