JP4766908B2 - Electronic imaging device with small photographic optical system - Google Patents

Description

  The present invention relates to an electronic image pickup apparatus including a small photographic optical system that can be applied to an electronic image pickup element such as a CCD (charge coupled device). More specifically, good performance can be obtained even when a CCD having 3M (mega) or more pixels is used, and the ratio of the total lens length to the image height can be 4.5 or less. The present invention relates to an electronic imaging apparatus having a photographing optical system of a single focus lens having an angle of view of 25 degrees or more.

  In recent years, miniaturization and increase in the number of pixels of an electronic imaging apparatus using an electronic imaging system such as a digital camera or a camera-equipped mobile phone have been developed. Therefore, there is a growing demand for further miniaturization and higher performance of lenses used in electronic imaging devices.

  Since the focal length of the single focus lens used in the electronic image pickup device does not change, a half angle of view of 25 degrees or more is taken into consideration that there are various shooting scenes such as person shooting, landscape shooting, and information shooting such as characters. It is easy to use.

  For example, Patent Documents 1 to 5 disclose techniques related to such a versatile single focus imaging optical system having a half angle of view of 25 degrees or more.

JP 2000-321489 A JP 2003-195158 A JP 2001-100092 A Japanese Patent Laid-Open No. 2001-21800 JP 2000-193484 A

  The photographic lens described in Patent Document 1 is composed of two negative lenses and one positive lens in order from the object side.

  In addition, the photographing lens described in Patent Document 2 is configured to have two positive lenses and a diaphragm between them. The ratio of the total lens length to the design image height is as small as about 4.0, and the image pickup unit having the photographing lens and the image pickup element is downsized.

  The optical systems described in Patent Documents 3 to 5 are composed of two or more lenses, and are composed of two lenses like the photographing lenses of Patent Documents 1 and 2 above. Compared with the optical performance, the optical performance is relatively good.

  However, the one described in Patent Document 1 is a retrofocus type lens group arrangement, and the total length of the lens system tends to be long, and there is a problem that the photographing lens cannot be thinned. Further, since there are two lenses constituting the photographing lens, it is difficult to obtain high optical performance. Therefore, when a CCD having 3M or more pixels is used for the light receiving element, there is a problem that sufficient optical performance cannot be obtained.

  Moreover, since the refractive power is concentrated mainly on the exit surface of the image side lens, the aberration described in Patent Document 2 cannot be corrected sufficiently. Therefore, as described above, there is a problem in that sufficient optical performance cannot be obtained when a CCD having 3M or more pixels is used as the light receiving element.

  In addition, those described in Patent Documents 3 to 5 have a problem that the ratio of the total length of the lens system to the design image height is 4.5 or more, and it cannot be said that the photographing optical system is sufficiently thin. Another problem is that unnecessary light reflected by the lens surface of the lens disposed on the image side from the stop is reflected by the lens surface of the lens located on the object side of the stop, and ghost light is easily generated. It was.

  Therefore, the present invention has been made in view of the above-described problems of the conventional configuration. An object of the present invention is to provide an electronic imaging apparatus having a photographic optical system that can be applied to a small electronic imaging system, can secure an appropriate angle of view, is thin in the depth direction, and has high optical performance. It is in. Furthermore, the present invention provides an optical system that can ensure the miniaturization of the optical system unit and the stability against lens decentering.

In order to achieve the above object, an electronic imaging apparatus according to the present invention is an electronic imaging apparatus that includes an imaging optical system and an imaging element that converts an object image formed on an imaging surface by the imaging optical system into an electrical signal. The photographing optical system includes, in order from the object side, a first lens group having a positive refractive power, an aperture stop, a second lens group having a positive refractive power, and a third lens having a positive refractive power. A lens group, and an exit surface of the first lens group and an incident surface of the second lens group both have a convex surface facing the aperture stop, and the first lens group is formed from the object side. turn, a negative meniscus lens, is composed of a positive meniscus lens, the lens surface of said negative meniscus lens and a positive meniscus lens are each at an optical axis and a convex surface facing toward the aperture stop side, the following condition It is characterized by satisfaction.
0.15 ≦ T1 / IH ≦ 0.90
0.5 <R2 / R3 <1.2
0 ≦ D23 / D14 <0.2
However, T1 is the optical on-axis distance to the surface on the most image side from the surface on the most object side of the first lens group, the diagonal of the effective image pickup area of the electronic image pickup device IH is a maximum photographing image height half the length der length Ri, R2 is the paraxial curvature radius of the image side surface of the negative meniscus lens of the first lens group, R3 is near the object side surface of the positive meniscus lens of the first lens group D23 is the air space on the optical axis from the image side surface of the negative meniscus lens of the first lens group to the object side surface of the positive meniscus lens, and D14 is the negative radius of the first lens group. Ru length der on the optical axis from the object side surface of the meniscus lens to the image side surface of the positive meniscus lens.
In addition, the effective imaging area refers to an imaging area used for displaying, printing, and the like of a captured image on the imaging surface of the electronic image sensor.

In the electronic imaging apparatus of the present invention, preferably, the first lens group, the second lens group, a lens having a refractive power of the third lens group, a lens having all 1.7 or more refractive index It is composed of a material.

In the electronic imaging apparatus of the present invention, preferably, the first lens group, characterized in that it is composed of one cemented lens.

In the electronic imaging apparatus of the present invention, preferably, prior Symbol second lens unit, in order from the object side, it is constituted by two positive lens and a negative lens having a convex surface directed toward the object side, the third lens The group is composed of a positive meniscus lens component having a concave surface facing the object side, and the object side surface of the positive meniscus lens component of the third lens group has an aspheric surface whose negative refractive power decreases as it moves away from the optical axis. The image side surface of the positive meniscus lens component of the third lens group has an aspherical surface in which the positive refractive power decreases as the distance from the optical axis increases.
However, the lens component is a lens having only two air contact surfaces on the most object surface side and the most image side surface, and is constituted by a single lens or a cemented lens.

In the electronic imaging apparatus of the present invention, preferably, the first lens group, the second lens group, one lens group of the third lens group, combined to the glass lens and glass lens auxiliary Including a cemented lens having a lens , the following conditional expression is satisfied.
0.05 ≦ DC ≦ 0.3 (mm)
Ndc ≧ 1.65
| Νdm−νdc |> 6
However, DC is the thickness on the optical axis of the auxiliary lens only that are combined in the glass lens, Ndc the refractive index at the d-line of the auxiliary lens are combined to said glass lens (587.56 nm) in it, Nyudm is the Abbe number of the glass lens, Nyudc is the Abbe number of the auxiliary lens are combined in the glass lens.

In the electronic imaging apparatus of the present invention, preferably, the first lens group, the Ri cemented lens der, the auxiliary lens combined to the glass lens and the glass lens, the refractive power as the single The signs are opposite , each having a different Abbe number, and each lens shape is a meniscus shape.

In the electronic imaging device of the present invention, it is preferable that an image side lens surface of a lens arranged closest to the image plane of the second lens group is concave with respect to the image side, An air lens having convex surfaces on both sides is provided between the third lens groups, and the following conditional expression is satisfied.
1.4 ≦ | r2R | /IH≦18.0
However, R2R is paraxial curvature radius of the image side lens surface of the lens disposed on the most image side of the second lens group, the IH pairs of the effective imaging area of the imaging device a maximum photographing image height It is half the length of the corner.

In the electronic imaging device of the present invention, it is preferable that the following conditional expression is satisfied.
0.8 ≦ fg2 / fall ≦ 5.5
However, fg2 represents a focal length of the second lens group, fall is the focal length of the photographing optical system as a whole.

In the electronic imaging device of the present invention, preferably, an air lens having convex surfaces on both sides is provided between the second lens group and the third lens group, and the following conditional expression is satisfied: To do.
r2R / r3F ≦ −1
However, R2R is paraxial curvature radius of the image side lens surface of the lens disposed on the most image side of the second lens group at the object side-lens r3F is disposed closest to the object side of the third lens group This is the paraxial radius of curvature of the lens surface.

  In the electronic imaging device of the present invention, it is preferable that the image-side lens surface of the lens disposed closest to the image side of the second lens group is a concave surface and is disposed closest to the object side of the third lens group. The object side lens surface of the lens is a concave surface, and the image side lens surface of the lens disposed closest to the image side is a convex surface.

In the electronic imaging device of the present invention, it is preferable that the following conditional expression is satisfied.
0.3 ≦ | r3F | /IH≦2.5
However, R3F is paraxial radius of curvature of the object side lens surface of the lens disposed closest to the object side of the third lens group, the IH pairs of the effective imaging area of the imaging device a maximum photographing image height corner It is half the length.

In the electronic imaging device of the present invention, it is preferable that the third lens group has an aspherical surface in which the positive power around the lens is loose with respect to the lens center, and the object side surface is an object. It is composed of a single positive meniscus lens having a concave surface on the side.

In the electronic imaging device of the present invention, it is preferable that the following conditional expression is satisfied.
0.6 ≦ | r1F | /IH≦4.0
However, R1F is a paraxial radius of curvature of the object side lens surface of the lens disposed closest to the object side of the first lens group, the IH pairs of the effective imaging area of the imaging device a maximum photographing image height corner It is half the length.

  In the electronic imaging device of the present invention, it is preferable that the second lens group has a concave surface facing the first lens having a positive refractive power and the image side having a negative refractive power in order from the object side. It is characterized by comprising a second lens.

  In the electronic imaging device of the present invention, it is preferable that the second lens group includes a cemented lens of the first lens having the positive refractive power and the second lens having the negative refractive power. It is characterized by that.

In the electronic imaging device of the present invention, it is preferable that the following conditional expression is satisfied.
｜ IH / EP | ≦ 0.455
However, the IH is the length of half a maximum photographing image height the diagonal length of an effective imaging area of the imaging element, EP is the distance to the image plane from the position of the exit pupil of the imaging optical system .

  In the electronic imaging device of the present invention, it is preferable that each of the first lens group, the second lens group, and the third lens group is composed of two or less lenses. .

In the electronic imaging device of the present invention, it is preferable that the following conditional expression is satisfied.
2.5 <TL / IH <4.1
However, TL is the optical on-axis distance to the imaging surface from the incident surface of the first lens group, the IH is a maximum photographing image height half the diagonal length of an effective imaging area of the imaging element with a length is there.

In the electronic imaging device of the present invention, it is preferable that the following conditional expression is satisfied.
0.03 <TS / TL <0.4
However, TS is the total length of the air space on the optical axis between the incident surface of the first lens group to the exit surface of the third lens group, TL from the incident surface of the first lens group This is the distance on the optical axis to the imaging surface.

  According to the present invention, it is possible to provide an electronic imaging apparatus including a photographing optical system that can be applied to a small electronic imaging system, can secure an appropriate angle of view, is thin in the depth direction, and has high optical performance. Is possible. Furthermore, it is possible to provide an optical system that can ensure the miniaturization of the optical system unit and the stability against the decentration of the lens.

  Prior to the description of the embodiment of the present invention, the function and effect of the present invention will be described.

  In the present invention, in order from the object side, a first lens group having a positive refractive power, an aperture stop, a second lens group having a positive refractive power, and a third lens group having a positive refractive power are provided. It is based on the configuration.

  If all the lens groups have positive refractive power as in the present invention, it is possible to share the refractive power of the entire system of the photographing optical system and to make it easy to correct aberrations. Further, by adjusting the positive power distribution among the three lens groups, an advantageous power arrangement for shortening the total length of the optical system can be obtained.

  If the diaphragm is arranged between the first lens group and the second lens group as in the present invention, it is possible to prevent the first lens group and the second lens group located before and after the diaphragm from being enlarged.

  Further, as in the present invention, if a plurality of positive lens groups are arranged from the stop toward the image plane side and the exit pupil position is separated from the image plane, off-axis rays incident on the image sensor can be made to approach vertically. it can. As a result, the incident light is not likely to be reflected by the oblique incident characteristics of the image sensor, so that a reduction in the amount of light can be minimized.

  In addition, since the diaphragm is arranged in an air lens having the main refractive power, it is possible to make it easy to correct aberrations while ensuring the refractive power of the entire optical system.

If all the lens surfaces constituting the first lens group are configured in the same direction as the direction of the convex surface of the exit surface, the thickness of the entire lens constituting the first lens group can be suppressed and the entire length of the optical system can be reduced. Can be reduced, and the lens diameter of the lenses constituting the first lens group can be reduced.

  If all the lenses constituting the first lens group are meniscus lenses, the thickness of the ribs can be easily secured. As a result, the thickness of the lens on the optical axis can be reduced without degrading the workability of the lens.

  Further, since the height of the off-axis incident light can be reduced, the lens diameter after the second lens group can be reduced, and the optical system can be miniaturized.

  If the entrance surface of the first lens group is concave, the outside diameter of the entrance surface side lens can be reduced.

  Further, as in the present invention, when the first lens group is a meniscus lens having a convex surface facing the image side, the light reflected by the lens surface of the lens disposed on the image side from the stop is more object than the stop. Even if it is reflected by the lens surface of the first lens group located on the side, the reflected light is diverged, so that the generation of ghost light or the like can also be suppressed.

In the present invention, the following conditional expression (1) is satisfied.
0.15 ≦ T1 / IH ≦ 0.90 (1)
Where T1 is the distance on the optical axis from the most object-side surface to the most image-side surface of the first lens group, and IH is the maximum photographed image height, which is the diagonal length of the effective imaging region of the electronic image sensor. Half length.

  Conditional expression (1) is the distance T1 on the optical axis from the most object-side surface to the most image-side surface of the first lens group, and the diagonal length of the effective image-capturing area of the electronic image sensor, which is the maximum captured image height. The ratio to the half length IH is defined.

If the value of T1 / IH exceeds the upper limit of conditional expression (1), the height of the incident light beam in the first lens group becomes too high, so that the incident angle of the light beam on the incident surface that is concave on the object side is It tends to vary from an on-axis light beam to an off-axis light beam, making it difficult to correct aberrations at all angles of view. For this reason, an aspherical surface with a unique shape is used, which is not preferable because the manufacturing cost increases.

  Further, the diameter and thickness of the lens of the first lens group located closest to the object side are increased, which makes it difficult to reduce the size of the optical system.

On the other hand, if the value of T1 / IH falls below the lower limit of conditional expression (1), the on-axis light beam and the off-axis light beam are too close at the incident surface of the first lens group, and the incident surface of the first lens group. This is not preferable because it is difficult to balance the aberrations of both the on-axis light beam and the off-axis light beam.
In addition, since the thickness of the first lens group becomes too thin, the processability of the lens deteriorates when the lens is manufactured and processed, which is not preferable.

In addition, it is more preferable that the conditional expression (1) satisfies the following conditional expression (1-1).
0.20 ≦ T1 / IH ≦ 0.80 (1-1)
Furthermore, it is more preferable that conditional expression (1) satisfies the following conditional expression (1-2).
0.25 ≦ T1 / IH ≦ 0.70 (1-2)
Furthermore, it is more preferable that conditional expression (1) satisfies the following conditional expression (1-3).
0.30 ≦ T1 / IH ≦ 0.65 (1-3)

  In addition, if a high refractive index lens material having a refractive index of 1.7 or more is used as in the present invention, the curvature of the lens surface of each lens can be reduced, and aberration correction can be easily performed favorably. it can. Further, the optical system can be further downsized by suppressing the thickness on the optical axis while securing the thickness required for processing.

  Further, as in the present invention, if the first lens unit is composed of two lenses, a negative meniscus lens and a positive meniscus lens, in order from the object side, chromatic aberration and other off-axis aberrations can be effectively corrected with a small number of lenses. can do.

Moreover, it is preferable that the following conditional expressions (2) and (3) are satisfied as in the present invention.
0.5 <R2 / R3 <1.2 (2)
0 ≦ D23 / D14 <0.2 (3)
Where R2 is the paraxial radius of curvature of the image side surface of the negative meniscus lens of the first lens group, R3 is the paraxial radius of curvature of the object side surface of the positive meniscus lens of the first lens group, and D23 is the first lens group. Is the air space on the optical axis from the image side surface of the negative meniscus lens to the object side surface of the positive meniscus lens, and D14 is the length on the optical axis from the object side surface of the negative meniscus lens to the image side surface of the positive meniscus lens. .

  Conditional expression (2) defines the ratio between the paraxial curvature radius R2 of the image side surface of the negative meniscus lens of the first lens group and the paraxial curvature radius R3 of the object side surface of the positive meniscus lens of the first lens group. It is.

  Conditional expression (3) indicates that the air distance D23 on the optical axis from the image side surface of the negative meniscus lens of the first lens group to the object side surface of the positive meniscus lens, and from the object side surface of the negative meniscus lens to the image side surface of the positive meniscus lens. The ratio with the length D14 on the optical axis is defined.

  If the conditional expressions (2) and (3) are satisfied, the optical system can be reduced in size while ensuring aberration performance.

  If the value of R2 / R3 exceeds the upper limit of conditional expression (2), the object side surface of the positive meniscus lens becomes deep, and aberrations at the positive meniscus lens are likely to occur. In addition, it is difficult to reduce the thickness of the first lens group on the optical axis.

  On the other hand, if the value of R2 / R3 is below the lower limit of conditional expression (2), the radius of curvature of the object side surface of the negative meniscus lens becomes small, and correction of off-axis aberrations becomes difficult.

  If the value of D23 / D14 exceeds the upper limit of the conditional expression (3), the height of the incident light beam of the off-axis light beam at the negative meniscus lens becomes too high, and correction of distortion aberration etc. is made in the negative meniscus shape having a concave surface on the object side. Becomes difficult.

  On the other hand, when the value of D23 / D14 is below the lower limit of the conditional expression (3), the on-axis light beam and the off-axis light beam on the incident surface of the first lens group become too close to each other, It is difficult to balance the aberrations of both the luminous fluxes.

In the present invention, it is preferable to set the lower limit of conditional expression (2) to 0.7. Furthermore, it is more preferable that the lower limit value is 0.8. Furthermore, it is more preferable that the lower limit value is 0.9.
In the present invention, it is preferable to set the upper limit of conditional expression (2) to 1.1. Furthermore, the upper limit is more preferably set to 1.05.

In addition, it is more preferable that conditional expression (3) satisfies the following conditional expression (3-1).
0 ≦ D23 / D14 <0.1 (3-1)
Furthermore, it is more preferable that the conditional expression (3) satisfies the following conditional expression (3-2).
0 ≦ D23 / D14 <0.05 (3-2)

  Further, if the first lens group is configured by one cemented lens as in the present invention, the eccentricity of the lenses can be reduced as compared with the eccentricity of the lenses by assembling to the lens frame. As a result, it is possible to suppress the influence of aberration due to decentration, and it is advantageous to reduce the size of the first lens group.

  Further, as in the present invention, the refractive power in the first lens group including two lenses, a negative meniscus lens having a concave surface facing the object side and a positive meniscus lens having a concave surface facing the object side, and the object If the refractive power of the second lens group composed of two lenses, a positive lens having a convex surface on the side and a negative lens, is symmetric with respect to the stop, various aberrations caused by the first lens group and the second lens group are reduced. Good correction can be made with a small number of lenses.

  Further, as in the present invention, if the lens component constituting the third lens group disposed at a position far from the stop is a single positive meniscus lens component with the concave surface facing the object side, off-axis aberrations are mainly reduced. It is possible to correct well and to make the emitted light beam close to vertical.

  More preferably, if the lens component constituting the third lens group is constituted by a single lens, the total length of the optical system can be shortened, and the lens component constituting the third lens group can be reduced in size. .

  In addition, as in the present invention, a glass lens is used as a lens constituting the optical system to ensure the strength of the entire lens, and a thin and high refractive index material is used for the auxiliary lens combined with the glass lens. The lens can be effectively thinned.

Moreover, it is preferable that the following conditional expressions (4), (5), and (6) are satisfied as in the present invention.
0.05 ≦ DC ≦ 0.3 (mm) (4)
Ndc ≧ 1.65 (5)
| Νdm−νdc |> 6 (6)
However, DC is the thickness on the optical axis of the single auxiliary lens combined with the glass lens, Ndc is the refractive index with respect to the d-line (587.56 nm) of the auxiliary lens combined with the glass lens, νdm is the Abbe number of the glass lens, and νdc is the Abbe number of the auxiliary lens combined with the glass lens.

  If the conditional expressions (4), (5), and (6) are satisfied, the thickness of the cemented lens having the glass lens and the auxiliary lens combined with the glass lens can be shortened, and the optical system can be shortened. .

  Further, according to the present invention, it is possible to make the surface shape effective in correcting aberrations, and to make the principal point arrangement effective for downsizing, so that the optical system can be downsized.

  If the value of DC exceeds the upper limit of conditional expression (4), the cemented lens becomes thick, which is not preferable.

  On the other hand, if the value of DC falls below the lower limit of conditional expression (4), it is difficult to bond the glass lens and the auxiliary lens.

  If the value of Ndc is less than the lower limit of conditional expression (5), the lens action on the air contact surface is reduced, or the difference between the inner thickness and the edge thickness is increased, which is not preferable.

  If the value of | νdm−νdc | is less than the lower limit of conditional expression (6), it is not preferable because correction of chromatic aberration cannot be performed effectively and the function of the cemented lens cannot be fully exhibited.

In the present invention, it is more preferable that the following conditional expression (4-1) is satisfied.
0.10 ≦ DC ≦ 0.27 (mm) (4-1)
Furthermore, it is more preferable that the following conditional expression (4-2) is satisfied.
0.15 ≦ DC ≦ 0.23 (mm) (4-2)

In the present invention, it is more preferable that the following conditional expression (5-1) is satisfied.
Ndc ≧ 1.69 (5-1)
Furthermore, it is more preferable that the following conditional expression (5-2) is satisfied.
Ndc ≧ 1.72 (5-2)

In the present invention, it is more preferable that the following conditional expression (6-1) is satisfied.
| Νdm−νdc |> 10.0 (6-1)
Furthermore, it is more preferable that the following conditional expression (6-2) is satisfied.
| Νdm−νdc |> 13.0 (6-2)

  Further, as in the present invention, if the refractive power of the glass lens and the auxiliary lens combined with the glass lens is reversed, the various aberrations such as chromatic aberration in the cemented lens can be adjusted satisfactorily. be able to.

  Further, if the lens shape of both the glass lens and the auxiliary lens combined with the glass lens is changed to a meniscus shape as in the present invention, the junction lens can be made thinner.

  Further, as in the present invention, even if the first lens group is composed of a cemented lens of meniscus lenses of the glass lens and the auxiliary lens combined with the glass lens, the glass lens and the auxiliary lens If they have opposite refractive powers, it is possible to advantageously reduce the size of the entire optical system and correct chromatic aberration while maintaining the thinness of the cemented lens.

  In addition, according to the present invention, it is possible to dispose a lens group having a shape close to symmetry with respect to the stop for the first lens group and the second lens group. As a result, the peripheral performance of the lens can be improved.

Moreover, it is preferable that the following conditional expression (7) is satisfied as in the present invention.
1.4 ≦ | r2R | /IH≦18.0 (7)
Where r2R is the paraxial radius of curvature of the image side lens surface of the lens disposed closest to the image plane of the second lens group, and IH is the maximum captured image height and the diagonal length of the effective imaging area of the image sensor. Half the length.

  If the conditional expression (7) is satisfied, the spherical aberration can be corrected satisfactorily.

  If the value of | r2R | / IH exceeds the upper limit of the conditional expression (7), it is difficult to correct the aberration in the second lens group.

  On the other hand, if the value of | r2R | / IH falls below the lower limit of conditional expression (7), off-axis aberrations such as field curvature and distortion in the second lens group increase, and good performance is ensured. It becomes difficult.

In the present invention, it is more preferable that the following conditional expression (7-1) is satisfied.
1.6 ≦ | r2R | /IH≦15.0 (7-1)
Furthermore, it is more preferable that the following conditional expression (7-2) is satisfied.
1.75 ≦ | r2R | /IH≦10.0 (7-2)

Moreover, it is preferable that the following conditional expression (8) is satisfied as in the present invention.
0.8 ≦ fg2 / fall ≦ 5.5 (8)
Here, fg2 is the focal length of the second lens group, and fall is the focal length of the entire photographing optical system.

  Conditional expression (8) defines the ratio between the focal length fg2 of the second lens group and the focal length fall of the entire photographing optical system. If the conditional expression (8) is satisfied, good aberration can be obtained and the overall length of the optical system can be shortened.

  If the value of fg2 / fall exceeds the upper limit of the conditional expression (8), the positive action by the second lens group is reduced, so that it is difficult to shorten the total length of the optical system. As a result, the total length of the optical system with respect to the photographic image height to be used becomes long.

  On the other hand, if the value of fg2 / fall falls below the lower limit of conditional expression (8), aberrations in the second lens group are likely to occur. Therefore, it is necessary to increase the number of lenses in order to suppress the occurrence of aberrations, and it becomes difficult to shorten the total length of the optical system.

In the present invention, it is more preferable that the following conditional expression (8-1) is satisfied.
1.0 ≦ fg2 / fall ≦ 4.5 (8-1)
Furthermore, it is more preferable that the following conditional expression (8-2) is satisfied.
1.2 ≦ fg2 / fall ≦ 4.0 (8-2)

Moreover, it is preferable that the following conditional expression (9) is satisfied as in the present invention.
r2R / r3F ≦ −1 (9)
Where r2R is the paraxial radius of curvature of the image side lens surface of the lens arranged closest to the image side of the second lens group, and r3F is the object side lens surface of the lens arranged closest to the object side of the third lens group. Is the paraxial radius of curvature.

  Conditional expression (9) indicates that the paraxial radius of curvature r2R of the image side lens surface of the lens arranged closest to the image side of the second lens group and the object side lens of the lens arranged closest to the object side of the third lens group. The ratio to the paraxial radius of curvature r3F of the surface is defined.

  If the value of r2R / r3F exceeds the upper limit of the conditional expression (9), the light beam jumps up on the exit surface of the second lens group, and off-axis aberration is likely to occur. In addition, it becomes difficult to correct spherical aberration with an air lens having convex surfaces on both sides between the second lens group and the third lens group.

In order to give a correction effect to the aberration on the exit side surface of the second lens group, it is preferable to set a lower limit value in the conditional expression (9), so that the following conditional expression (9-1) is satisfied. Good.
-25.0 ≦ r2R / r3F ≦ −1.0 (9-1)

In the present invention, it is more preferable that the following conditional expression (9-2) is satisfied.
-15.0 ≦ r2R / r3F ≦ −1.01 (9-2)
Furthermore, it is more preferable that the following conditional expression (9-3) is satisfied.
−8.0 ≦ r2R / r3F ≦ −2.0 (9-3)

  Further, as in the present invention, if the surface disposed on the most object side of the third lens group is a concave surface and the surface disposed on the most image side is a convex surface, the axis on the incident surface of the third lens group is The occurrence of external aberration can be suppressed and the power of the third lens group can be increased. Therefore, even if the third lens group is configured with a small number of lenses, it is possible to easily ensure good performance.

Moreover, it is preferable that the following conditional expression (10) is satisfied as in the present invention.
0.3 ≦ | r3F | /IH≦2.5 (10)
However, r3F is the paraxial radius of curvature of the object side lens surface of the lens disposed closest to the object side in the third lens group, and IH is the maximum imaged image height, which is the diagonal length of the effective imaging region of the image sensor. Half length.

  Conditional expression (10) indicates that the paraxial radius of curvature r3F of the object side lens surface of the lens arranged closest to the object side in the third lens group and the diagonal length of the effective imaging region of the imaging element with the maximum captured image height. The ratio with the half length IH is defined. If the conditional expression (10) is satisfied, even better performance can be ensured.

  When the value of | r3F | / IH exceeds the upper limit of the conditional expression (10), the curvature radius of the surface disposed closest to the object side of the third lens group is large, so that the correction of spherical aberration is reduced. It becomes difficult to shorten the overall length of the optical system.

  On the other hand, if the value of | r3F | / IH falls below the lower limit of the conditional expression (10), the radius of curvature of the surface disposed closest to the object side of the third lens group is small, and therefore the object side of the third lens group It is necessary to increase the positive power of the surface on the image side relative to the surface on which it is arranged. Therefore, in order to obtain good performance, the number of lenses constituting the third lens group needs to be increased.

In the present invention, it is more preferable that the following conditional expression (10-1) is satisfied.
0.5 ≦ | r3F | /IH≦2.0 (10-1)
Furthermore, it is more preferable that the following conditional expression (10-2) is satisfied.
0.7 ≦ | r3F | /IH≦1.2 (10-2)

  In addition, as in the present invention, if the third lens group is an aspherical surface having a shape in which the positive power around the lens center is reduced, distortion can be effectively corrected.

  Further, if the third lens group is composed of a single positive meniscus lens whose object side surface is concave on the object side, the overall length of the optical system can be further shortened.

Moreover, it is preferable that the following conditional expression (11) is satisfied as in the present invention.
0.6 ≦ | r1F | /IH≦4.0 (11)
However, r1F is the paraxial radius of curvature of the object side lens surface of the lens disposed closest to the object side in the first lens group, and IH is the maximum photographed image height and the diagonal length of the effective imaging region of the image sensor. Half length.

  Conditional expression (11) indicates that the absolute value | r1F | of the paraxial radius of curvature of the object-side lens surface of the lens disposed closest to the object side in the first lens group and the maximum imaged image height and effective imaging of the image sensor. A ratio with the length IH which is half the diagonal length of the region is defined.

If the conditional expression (11) is satisfied, the lens outer diameter can be reduced, the total length of the optical system can be shortened, and aberrations can be easily corrected.
Further, if the first lens group is composed of two or less lenses, the optical system can be further miniaturized.

  If the value of | r1F | / IH exceeds the upper limit of the conditional expression (11), the position of the entrance pupil easily enters the image side, and it is difficult to reduce the lens outer diameter on the entrance side.

  On the other hand, if the value of | r1F | / IH falls below the lower limit of conditional expression (11), the back focus becomes too long, and it is difficult to reduce the total length of the optical system.

In the present invention, it is more preferable that the following conditional expression (11-1) is satisfied.
0.8 ≦ | r1F | /IH≦3.0 (11-1)
Furthermore, it is more preferable that the following conditional expression (11-2) is satisfied.
0.9 ≦ | r1F | /IH≦1.5 (11-2)

  If the second lens group is composed of two lenses as in the present invention, the optical system can be miniaturized.

  If the lens surface located closest to the object side of the second lens group is a convex surface and the lens surface closest to the image side is a concave surface, especially coma, astigmatism and distortion are effective. Thus, the chromatic aberration can be corrected satisfactorily.

  Further, as in the present invention, the second lens group is a cemented lens composed of two lenses of a first lens having a positive refractive power and a second lens having a negative refractive power in order from the object side. If configured, the entire lens can be shortened.

  In addition, the performance degradation caused by the decentration between the first lens having a positive refractive power and the second lens having a negative refractive power can be suppressed.

Moreover, it is preferable that the following conditional expression (12) is satisfied as in the present invention.
| IH / EP | ≦ 0.455 (12)
However, IH is the maximum captured image height, which is half the diagonal length of the effective imaging area of the image sensor, and EP is the distance from the position of the exit pupil of the imaging optical system to the imaging plane.

  Conditional expression (12) indicates that the maximum captured image height and the length IH which is half the diagonal length of the effective imaging region of the image sensor and the distance EP from the position of the exit pupil of the imaging optical system to the imaging plane It is specified by the ratio.

  If the conditional expression (12) is satisfied, the peripheral light amount can be secured.

  If the value of | IH / EP | exceeds the upper limit of conditional expression (12) or falls below the lower limit of conditional expression (12), the influence of shading tends to occur around the screen.

Furthermore, it is more preferable that conditional expression (12) satisfies the following conditional expression (12-1).
−0.1 <| IH / EP | ≦ 0.455 (12-1)

  If the conditional expression (12-1) is satisfied, it is possible to prevent the diameter of the third lens group from increasing.

  Further, as in the present invention, since the number of lenses in each lens group is configured to be two or less, it is possible to configure an imaging apparatus having an optical system having a small number of lenses.

Moreover, it is preferable that the following conditional expression (13) is satisfied as in the present invention.
2.5 <TL / IH <4.1 (13)
However, TL is the distance on the optical axis from the incident surface of the first lens group to the imaging surface, and IH is the maximum captured image height, which is half the diagonal length of the effective imaging region of the image sensor.

  Conditional expression (13) indicates that the distance TL on the optical axis from the entrance surface of the first lens group to the imaging surface, the maximum captured image height, and the length IH that is half the diagonal length of the effective imaging region of the image sensor. The ratio is defined.

  If the conditional expression (13) is satisfied, the imaging optical system can be reduced in size, and good aberration correction can be performed.

  When the value of TL / IH exceeds the upper limit of the conditional expression (13), the entire length of the optical system becomes long, and it is difficult to reduce the size of the imaging device.

  On the other hand, if the value of TL / IH falls below the lower limit of conditional expression (13), the total length of the optical system can be shortened, but aberration correction becomes difficult.

Moreover, it is preferable that the following conditional expression (14) is satisfied as in the present invention.
0.03 <TS / TL <0.4 (14)
Where TS is the total length of the air gap on the optical axis from the entrance surface of the first lens group to the exit surface of the third lens group, and TL is from the entrance surface of the first lens group to the imaging surface. On the optical axis.

  Conditional expression (14) indicates that the total length TS of the air interval on the optical axis from the entrance surface of the first lens group to the exit surface of the third lens group, and the imaging surface from the entrance surface of the first lens group. The ratio to the distance TL on the optical axis is defined.

  If the conditional expression (14) is satisfied, the imaging optical system can be reduced in size, and good aberration correction can be performed.

  If the value of TS / TL exceeds the upper limit of conditional expression (14), the length of the air gap on the optical axis from the entrance surface of the first lens group to the exit surface of the third lens group increases. Therefore, it is difficult to reduce the size of the photographing optical system.

  On the other hand, if the value of TS / TL falls below the lower limit of conditional expression (14), the air lens between the first lens group and the second lens group, and the second lens group and the third lens group It becomes difficult to correct aberrations with a certain air lens.

In the present invention, it is more preferable that the following conditional expression (14-1) is satisfied.
0.05 <TS / TL <0.3 (14-1)
Furthermore, it is more preferable that the following conditional expression (14-2) is satisfied.
0.07 <TS / TL <0.25 (14-2)

  In each conditional expression, only the upper limit value or only the lower limit value may be limited to a more preferable value.

  Embodiments 1 to 6 of the present invention will be described below with reference to the drawings.

First Embodiment FIG. 1 is a first embodiment of an image pickup apparatus according to the present invention, and is a sectional view along an optical axis showing an optical configuration. FIG. 2 is a diagram illustrating spherical aberration, astigmatism, distortion, and chromatic aberration of magnification when the imaging apparatus according to the first embodiment is in focus at infinity.

  As shown in FIG. 1, the image pickup apparatus of the first embodiment has a photographing optical system and a CCD as an electronic image pickup element in order from the object side. In FIG. 1, I is the imaging surface of the CCD. Between the imaging optical system and the imaging surface I, a parallel plate-shaped optical low-pass filter LF and a CCD cover glass CG are provided.

  In each embodiment, for the near infrared sharp cut coat, for example, the optical low-pass filter LF may be directly coated, or an infrared cut absorption filter may be provided separately, or a transparent flat plate Alternatively, a near-infrared sharp cut coat may be used on the incident surface.

  The photographing optical system includes a first lens group G1, an aperture stop S, a second lens group G2, and a third lens group G3 in order from the object side toward the imaging surface I.

  In each embodiment, each lens in the first lens group G1, the second lens group G2, and the third lens group G3 is formed of a glass lens.

  The first lens group G1 includes, in order from the object side, a cemented lens in which a negative meniscus lens L11 having a concave surface facing the object side and a positive meniscus lens L12 having a concave surface facing the object side are cemented. And has a positive refractive power as a whole.

  The second lens group G2 includes a cemented lens in which a biconvex positive lens L21 and a biconcave negative lens L22 are cemented in order from the object side, and has a positive refractive power as a whole.

  The third lens group G3 includes a positive meniscus lens L31 having a concave surface directed toward the object side in the vicinity of the optical axis (lens center portion), and has a positive refractive power as a whole. Note that the object side surface of the positive lens L31 has a configuration in which the negative refractive power gradually decreases from the center to the periphery of the lens. Further, the image-side surface of the positive meniscus lens L31 has a configuration in which the positive refractive power decreases from the center to the periphery of the lens.

  The aspheric surfaces are provided on both surfaces of the positive meniscus lens L31 having a concave surface facing the object side in the vicinity of the optical axis (lens center portion) of the third lens group G3.

  Next, numerical data of optical members constituting the image pickup apparatus according to the first embodiment of the present invention are shown below.

In the numerical data, r ₁ , r ₂ ... Are curvature radii (mm) of the surfaces of the optical members, d ₁ , d _2. ), N _d1 , n _d2 ... Is the refractive index of each optical member at the wavelength of d-line (587.6 nm), and ν _d1 , ν _d2 ... Are Abbe's at the wavelength of d-line of each optical member (587.6 nm). Represents a number. f represents the focal length of the entire system.
Further, the aspherical shape to be rotated with respect to the optical axis is such that the optical axis direction is z, the direction orthogonal to the optical axis is y, the direction orthogonal to z and y is x, the cone coefficient is k, the optical axis When the aspheric coefficients to be rotated are A ₄ , A ₆ , A ₈ , and A ₁₀ , they are defined by the following equations.
z = (y ² / r) / [1+ [1- (1 + k) (y / r) ² ] ^1/2 ] + A ₄ y ⁴
+ A ₆ y ⁶ + A ₈ y ⁸ + A ₁₀ y ¹⁰
These symbols are also common in numerical data of Examples 2 to 6 described later.

Numerical data 1
Focal length f: 6.45mm
Fno. (F number): 2.85
Image height (half the diagonal length of the effective imaging area): 3.60 mm
Half angle of view (ω): 29.67 °
r ₁ = -3.771 d ₁ = 0.700 n _d1 = 1.71300 ν _d1 = 53.87
r ₂ = -11.144 d ₂ = 1.372 n _d2 = 1.88300 ν _d2 = 40.76
r ₃ = -4.680 d ₃ = 0.500
r ₄ = ∞ (aperture) d ₄ = 0.600
r ₅ = 5.522 d ₅ = 2.710 n _d5 = 1.80400 ν _d5 = 46.57
r ₆ = -3.844 d ₆ = 0.700 n _d6 = 1.84666 ν _d6 = 23.78
r ₇ = 28.663 d ₇ = 1.035
r ₈ = -3.235 (aspherical surface) d ₈ = 2.322 n _d8 = 1.80610 ν _d8 = 40.73
r ₉ = -3.450 (aspherical surface) d ₉ = 2.202
r ₁₀ = ∞ d ₁₀ = 0.760 n _d10 = 1.54771 ν _d10 = 62.84
r ₁₁ = ∞ d ₁₁ = 0.600
r ₁₂ = ∞ d ₁₂ = 0.500 n _d12 = 1.51633 ν _d12 = 64.14
r ₁₃ = ∞ d ₁₃ = 0.560
r ₁₄ = ∞ (imaging surface)

Aspherical coefficients <br/> Face Number _{k A 4 A 6 A 8 A} 10
8 -0.8665 -3.2517 × 10 ^-4 4.9730 × 10 ^-4 1.5563 × 10 ^-7 1.9310 × 10 ^-9
9 -0.6303 2.1339 × 10 ^-3 1.4734 × 10 ^-4 7.5163 × 10 ^-6 1.6279 × 10 ^-7

Second Embodiment FIG. 3 shows a second embodiment of the image pickup apparatus according to the present invention, and is a cross-sectional view along the optical axis showing the optical configuration. FIG. 4 is a diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration when the imaging apparatus according to the second embodiment is focused on infinity.

  As shown in FIG. 3, the image pickup apparatus of the second embodiment has a photographing optical system and a CCD as an electronic image pickup element in order from the object side. In FIG. 3, I is the imaging surface of the CCD. Between the imaging optical system and the imaging surface I, a parallel plate-like optical low-pass filter LF and a CCD cover glass CG are provided.

  The photographing optical system includes a first lens group G1, an aperture stop S, a second lens group G2, and a third lens group G3 in order from the object side toward the imaging surface I.

  The first lens group G1 is composed of a cemented lens in which, from the object side X, a negative meniscus lens L11 having a concave surface facing the object side and a positive meniscus lens L12 having a concave surface facing the object side are cemented. And has a positive refractive power as a whole.

  The second lens group G2 includes a cemented lens in which a biconvex positive lens L21 and a biconcave negative lens L22 are cemented in order from the object side, and has a positive refractive power as a whole.

  The third lens group G3 includes a positive meniscus lens L31 having a concave surface directed toward the object side in the vicinity of the optical axis (lens center portion), and has a positive refractive power as a whole. Incidentally, the object side surface of the positive meniscus lens L31 having a concave surface facing the object side in the vicinity of the optical axis (lens center portion) has a configuration in which the negative refractive power gradually decreases from the lens center portion to the peripheral portion. ing. Further, the image side surface of the positive meniscus lens L31 has a configuration in which the positive refractive power becomes weaker from the center to the periphery of the lens.

  The aspheric surfaces are provided on both surfaces of the positive meniscus lens L31 having a convex surface facing the object side in the vicinity of the optical axis (lens center portion) of the third lens group G3.

  Next, numerical data of optical members constituting the image pickup apparatus according to the second embodiment of the present invention are shown below.

Numerical data 2
Focal length f: 6.45mm
Fno. (F number): 2.86
Image height (half the diagonal length of the effective imaging area): 3.60 mm
Half angle of view (ω): 29.66 °
r ₁ = -3.816 d ₁ = 0.700 n _d1 = 1.71300 ν _d1 = 53.87
r ₂ = -13.959 d ₂ = 1.465 n _d2 = 1.88300 ν _d2 = 40.76
r ₃ = -4.757 d ₃ = 0.500
r ₄ = ∞ (aperture) d ₄ = 0.367
r ₅ = 5.592 d ₅ = 2.718 n _d5 = 1.80400 ν _d5 = 46.57
r ₆ = -3.698 d ₆ = 0.700 n _d6 = 1.84666 ν _d6 = 23.78
r ₇ = 23.008 d ₇ = 1.097
r ₈ = -3.336 (aspherical surface) d ₈ = 2.388 n _d8 = 1.80610 ν _d8 = 40.73
r ₉ = -3.450 (aspherical surface) d ₉ = 2.200
r ₁₀ = ∞ d ₁₀ = 0.760 n _d10 = 1.54771 ν _d10 = 62.84
r ₁₁ = ∞ d ₁₁ = 0.600
r ₁₂ = ∞ d ₁₂ = 0.500 n _d12 = 1.51633 ν _d12 = 64.14
r ₁₃ = ∞ d ₁₃ = 0.560
r ₁₄ = ∞ (imaging surface)

Aspherical coefficients <br/> Face Number _{k A 4 A 6 A 8 A} 10
8 -1.3797 -3.0058 × 10 ^-3 4.1817 × 10 ^-4 1.5506 × 10 ^-6 -1.1743 × 10 ^-9
9 -0.5361 2.0251 × 10 ^-3 9.6106 × 10 ^-5 1.0907 × 10 ^-5 -1.0905 × 10 ^-7

Third Embodiment FIG. 5 shows a third embodiment of the image pickup apparatus according to the present invention, and is a cross-sectional view along the optical axis showing the optical configuration. FIG. 6 is a diagram illustrating spherical aberration, astigmatism, distortion, and chromatic aberration of magnification when the imaging apparatus according to the third example is focused at infinity.

  As shown in FIG. 5, the image pickup apparatus of the third embodiment has a photographing optical system and a CCD as an electronic image pickup element in order from the object side. In FIG. 5, I is the imaging surface of the CCD. Between the imaging optical system and the imaging surface I, a parallel plate-like optical low-pass filter LF and a CCD cover glass CG are provided.

  The photographing optical system includes a first lens group G1, an aperture stop S, a second lens group G2, and a third lens group G3 in order from the object side toward the imaging surface I.

  The first lens group G1 includes, in order from the object side, a cemented lens in which a negative meniscus lens L11 having a concave surface facing the object side and a positive meniscus lens L12 having a concave surface facing the object side are cemented. And has a positive refractive power as a whole.

  The second lens group G2 includes, in order from the object side, a cemented lens in which a biconvex positive lens L21 and a negative meniscus lens L22 ′ having a concave surface facing the object side are cemented, and has a positive refractive power as a whole. is doing.

  The third lens group G3 includes a positive meniscus lens L31 having a concave surface directed toward the object side in the vicinity of the optical axis (lens center portion), and has a positive refractive power as a whole. Incidentally, the object side surface of the positive meniscus lens L31 having a concave surface facing the object side in the vicinity of the optical axis (lens center portion) has a configuration in which the negative refractive power gradually decreases from the lens center portion to the peripheral portion. ing. Further, the image-side surface of the positive meniscus lens L31 has a configuration in which the positive refractive power decreases from the center to the periphery of the lens.

  The aspheric surfaces are provided on both surfaces of the positive meniscus lens L31 having a concave surface facing the object side in the vicinity of the optical axis (lens center portion) of the third lens group G3.

  Next, numerical data of optical members constituting the image pickup apparatus according to the third embodiment of the present invention are shown below.

Numerical data 3
Focal length f: 6.45mm
Fno. (F number): 2.85
Image height (half the diagonal length of the effective imaging area): 3.60 mm
Half angle of view (ω): 29.45 °,
r ₁ = −4.078 d ₁ = 0.200 n _d1 = 1.72916 ν _d1 = 54.68
r ₂ = -17.443 d ₂ = 1.400 n _d2 = 1.88300 ν _d2 = 40.76
r ₃ = -4.924 d ₃ = 0.500
r ₄ = ∞ (aperture) d ₄ = 0.600
r ₅ = 6.719 d ₅ = 2.834 n _d5 = 1.81600 ν _d5 = 46.62
r ₆ = -3.568 d ₆ = 0.700 n _d6 = 1.80810 ν _d6 = 22.76
r ₇ = -122.924 d ₇ = 0.961
r ₈ = -2.457 (aspherical surface) d ₈ = 1.700 n _d8 = 1.88300 ν _d8 = 40.76
r ₉ = -2.832 (aspherical surface) d ₉ = 2.769
r ₁₀ = ∞ d ₁₀ = 0.760 n _d10 = 1.54771 ν _d10 = 62.84
r ₁₁ = ∞ d ₁₁ = 0.600
r ₁₂ = ∞ d ₁₂ = 0.500 n _d12 = 1.51633 ν _d12 = 64.14
r ₁₃ = ∞ d ₁₃ = 0.560
r ₁₄ = ∞ (imaging surface)

Aspherical coefficients <br/> Face Number _{k A 4 A 6 A 8 A} 10
8 -1.0202 -2.3598 × 10 ^-3 1.3305 × 10 ^-3 -4.9553 × 10 ^-6 -1.5105 × 10 ^-8
9 -1.6704 -3.7687 × 10 ^-3 3.3568 × 10 ^-4 2.4 150 × 10 ^-5 3.6030 × 10 ^-7

Fourth Embodiment FIG. 7 shows a fourth embodiment of the image pickup apparatus according to the present invention, and is a cross-sectional view along the optical axis showing the optical configuration. FIG. 8 is a diagram illustrating spherical aberration, astigmatism, distortion, and chromatic aberration of magnification when the imaging apparatus according to the fourth example is in focus at infinity.

  As shown in FIG. 7, the image pickup apparatus according to the fourth embodiment includes a photographing optical system and a CCD as an electronic image pickup element in order from the object side. In FIG. 7, I is the imaging surface of the CCD. Between the imaging optical system and the imaging surface I, a parallel plate-like optical low-pass filter LF and a CCD cover glass CG are provided.

  The photographing optical system includes a first lens group G1, an aperture stop S, a second lens group G2, and a third lens group G3 in order from the object side toward the imaging surface I.

  The first lens group G1 includes, in order from the object side, a cemented lens in which a negative meniscus lens L11 having a concave surface facing the object side and a positive meniscus lens L12 having a concave surface facing the object side are cemented. And has a positive refractive power as a whole.

  The second lens group G2 includes a cemented lens that is cemented with a biconvex positive lens L21 and a biconcave negative lens L22 in order from the object side, and has a positive refractive power as a whole.

  The third lens group G3 includes a positive meniscus lens L31 having a concave surface directed toward the object side in the vicinity of the optical axis (lens center portion), and has a positive refractive power as a whole. Incidentally, the object side surface of the positive meniscus lens L31 having a concave surface facing the object side in the vicinity of the optical axis (lens center portion) has a configuration in which the negative refractive power gradually decreases from the lens center portion to the peripheral portion. ing. Further, the image-side surface of the positive meniscus lens L31 has a configuration in which the positive refractive power decreases from the center to the periphery of the lens.

  The aspheric surfaces are provided on both surfaces of the positive meniscus lens L31 having a convex surface facing the object side in the vicinity of the optical axis (lens center portion) of the third lens group G3.

  Next, numerical data of optical members constituting the image pickup apparatus according to the fourth embodiment of the present invention are shown below.

Numerical data 4
Focal length f: 6.45mm
Fno. (F number): 2.85
Image height (half the diagonal length of the effective imaging area): 3.60 mm
Half angle of view (ω): 29.44 °
r ₁ = -3.981 d ₁ = 0.700 n _d1 = 1.71300 ν _d1 = 53.87
r ₂ = -6.568 d ₂ = 1.097 n _d2 = 1.88300 ν _d2 = 40.76
r ₃ = -4.714 d ₃ = 0.600
r ₄ = ∞ (aperture) d ₄ = 0.500
r ₅ = 5.987 d ₅ = 3.127 n _d5 = 1.83481 ν _d5 = 42.71
r ₆ = -3.183 d ₆ = 0.200 n _d6 = 1.84666 ν _d6 = 23.78
r ₇ = 63.032 d ₇ = 1.050
r ₈ = -2.628 (aspherical surface) d ₈ = 2.000 n _d8 = 1.80610 ν _d8 = 40.73
r ₉ = -2.960 (aspherical surface) d ₉ = 2.657
r ₁₀ = ∞ d ₁₀ = 0.760 n _d10 = 1.54771 ν _d10 = 62.84
r ₁₁ = ∞ d ₁₁ = 0.600
r ₁₂ = ∞ d ₁₂ = 0.500 n _d12 = 1.51633 ν _d12 = 64.14
r ₁₃ = ∞ d ₁₃ = 0.560
r ₁₄ = ∞ (imaging surface)

Aspherical coefficients <br/> Face Number _{k A 4 A 6 A 8 A} 10
8 -1.0152 -2.7000 × 10 ^-3 1.1412 × 10 ^-3 2.2729 × 10 ^-6 1.2910 × 10 ^-9
9 -0.9135 5.0276 × 10 ^-4 1.5139 × 10 ^-4 2.8159 × 10 ^-5 -2.0422 × 10 ^-7

Fifth Embodiment FIG. 9 shows a fifth embodiment of the imaging apparatus according to the present invention, and is a cross-sectional view along the optical axis showing the optical configuration. FIG. 10 is a diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration when the imaging apparatus according to the fifth example is focused at infinity.

  As shown in FIG. 9, the image pickup apparatus of the fifth embodiment has a photographing optical system and a CCD as an electronic image pickup element in order from the object side. In FIG. 9, I is the imaging surface of the CCD. Between the imaging optical system and the imaging surface I, a parallel plate-like optical low-pass filter LF and a CCD cover glass CG are provided.

  The photographing optical system includes a first lens group G1, an aperture stop S, a second lens group G2, and a third lens group G3 in order from the object side toward the imaging surface I.

  The first lens group G1 includes, in order from the object side, a cemented lens in which a negative meniscus lens L11 having a concave surface facing the object side and a positive meniscus lens L12 having a concave surface facing the object side are cemented. And has a positive refractive power as a whole.

  The second lens group G2 includes, in order from the object side, a cemented lens in which a biconvex positive lens L21 and a negative meniscus lens L22 ′ having a concave surface facing the object side are cemented, and has a positive refractive power as a whole. is doing.

  The third lens group G3 includes a positive meniscus lens L31 having a concave surface directed toward the object side in the vicinity of the optical axis (lens center portion), and has a positive refractive power as a whole. Incidentally, the object side surface of the positive meniscus lens L31 having a concave surface facing the object side in the vicinity of the optical axis (lens center portion) has a configuration in which the negative refractive power gradually decreases from the lens center portion to the peripheral portion. ing. Further, the image-side surface of the positive meniscus lens L31 has a configuration in which the positive refractive power decreases from the center to the periphery of the lens.

  The aspheric surfaces are provided on both surfaces of the positive meniscus lens L31 having a convex surface facing the object side in the vicinity of the optical axis (lens center portion) of the third lens group G3.

  Next, numerical data of optical members constituting the image pickup apparatus according to the fifth embodiment of the present invention are shown below.

Numerical data 5
Focal length f: 6.45mm
Fno. (F number): 2.86
Image height (half the diagonal length of the effective imaging area): 3.60 mm
Half angle of view (ω): 29.54 °
r ₁ = -3.959 d ₁ = 0.200 n _d1 = 1.72916 ν _d1 = 54.68
r ₂ = -11.703 d ₂ = 1.376 n _d2 = 1.88300 ν _d2 = 40.76
r ₃ = -4.772 d ₃ = 0.600
r ₄ = ∞ (aperture) d ₄ = 0.500
r ₅ = 6.342 d ₅ = 2.822 n _d5 = 1.81600 ν _d5 = 46.62
r ₆ = -3.474 d ₆ = 0.200 n _d6 = 1.80810 ν _d6 = 22.76
r ₇ = −103.635 d ₇ = 1.072
r ₈ = −2.530 (aspherical surface) d ₈ = 2.000 n _d8 = 1.88300 ν _d8 = 40.76
r ₉ = -3.026 (aspherical surface) d ₉ = 2.863
r ₁₀ = ∞ d ₁₀ = 0.760 n _d10 = 1.54771 ν _d10 = 62.84
r ₁₁ = ∞ d ₁₁ = 0.600
r ₁₂ = ∞ d ₁₂ = 0.500 n _d12 = 1.51633 ν _d12 = 64.14
r ₁₃ = ∞ d ₁₃ = 0.560
r ₁₄ = ∞ (imaging surface)

Aspherical coefficients <br/> Face Number _{k A 4 A 6 A 8 A} 10
8 -1.0178 -2.7460 × 10 ^-3 1.2872 × 10 ^-3 -3.7565 × 10 ^-6 -1.0251 × 10 ^-8
9 -0.9585 9.1035 × 10 ^-5 1.6053 × 10 ^-4 2.3418 × 10 ^-5 3.8847 × 10 ^-8

Sixth Embodiment FIG. 11 shows a sixth embodiment of the imaging apparatus according to the present invention, and is a cross-sectional view along the optical axis showing the optical configuration. FIG. 12 is a diagram illustrating spherical aberration, astigmatism, distortion, and chromatic aberration of magnification when the imaging apparatus according to the sixth example is in focus at infinity.

  As shown in FIG. 11, the image pickup apparatus of the sixth embodiment has a photographing optical system and a CCD as an electronic image pickup element in order from the object side. In FIG. 11, I is the imaging surface of the CCD. Between the imaging optical system and the imaging surface I, a parallel plate-like optical low-pass filter LF and a CCD cover glass CG are provided.

  The photographing optical system includes a first lens group G1, an aperture stop S, a second lens group G2, and a third lens group G3 in order from the object side toward the imaging surface I.

  The first lens group G1 includes, in order from the object side, a cemented lens in which a negative meniscus lens L11 having a concave surface facing the object side and a positive meniscus lens L12 having a concave surface facing the object side are cemented. And has a positive refractive power as a whole.

  The second lens group G2 includes, in order from the object side, a cemented lens in which a biconvex positive lens L21 and a negative meniscus lens L22 ′ having a concave surface facing the object side are cemented, and has a positive refractive power as a whole. is doing.

  The third lens group G3 includes a positive meniscus lens L31 having a concave surface directed toward the object side in the vicinity of the optical axis (lens center portion), and has a positive refractive power as a whole. Incidentally, the object side surface of the positive meniscus lens L31 having a concave surface facing the object side in the vicinity of the optical axis (lens center portion) has a configuration in which the negative refractive power gradually decreases from the lens center portion to the peripheral portion. ing. Further, the image-side surface of the positive meniscus lens L31 has a configuration in which the positive refractive power decreases from the center to the periphery of the lens.

  The aspheric surfaces are provided on both surfaces of the positive meniscus lens L31 having a convex surface facing the object side in the vicinity of the optical axis (lens center portion) of the third lens group G3.

  Next, numerical data of optical members constituting the image pickup apparatus according to the sixth embodiment of the present invention are shown below.

Numerical data 6
Focal length f: 6.45mm
Fno. (F number): 2.85
Image height (half the diagonal length of the effective imaging area): 3.60 mm
Half angle of view (ω): 29.58 °
r ₁ = -3.040 d ₁ = 0.200 n _d1 = 1.72916 ν _d1 = 54.68
r ₂ = -3.991 d ₂ = 1.000 n _d2 = 1.81600 ν _d2 = 46.62
r ₃ = -3.546 d ₃ = 0.300
r ₄ = ∞ (aperture) d ₄ = 0.300
r ₅ = 5.934 d ₅ = 3.554 n _d5 = 1.81600 ν _d5 = 46.62
r ₆ = -2.929 d ₆ = 0.200 n _d6 = 1.84666 ν _d6 = 23.78
r ₇ = -22.274 d ₇ = 1.094
r ₈ = -2.362 (aspherical surface) d ₈ = 2.000 n _d8 = 1.88300 ν _d8 = 40.76
r ₉ = -2.981 (aspherical surface) d ₉ = 2.237
r ₁₀ = ∞ d ₁₀ = 0.760 n _d10 = 1.54771 ν _d10 = 62.84
r ₁₁ = ∞ d ₁₁ = 0.600
r ₁₂ = ∞ d ₁₂ = 0.500 n _d12 = 1.51633 ν _d12 = 64.14
r ₁₃ = ∞ d ₁₃ = 0.560
r ₁₄ = ∞ (imaging surface)

Aspherical coefficients <br/> Face Number _{k A 4 A 6 A 8 A} 10
8 -1.0080 -1.9452 × 10 ^-3 1.0616 × 10 ^-3 -1.4687 × 10 ^-6 -2.5137 × 10 ^-8
9 -1.9622 -4.0818 × 10 ^-3 4.1040 × 10 ^-4 2.9955 × 10 ^-6 2.1571 × 10 ^-7

Next, Table 1 shows values corresponding to the conditional expressions in the above embodiments.
Table 1

  As described above, the electronic imaging apparatus using the imaging optical system of the present invention described above is an imaging in which an object image is formed by an imaging optical system such as an imaging optical system, and the image is received by a solid-state imaging device such as a CCD. The present invention can be used for devices such as digital cameras and video cameras, personal computers that are examples of information processing devices, telephones, especially mobile phones that are convenient to carry. The embodiment is illustrated below.

  FIGS. 13 to 15 are conceptual diagrams of a configuration in which the photographing optical system of the present invention is incorporated in the photographing optical system 41 of the digital camera. FIG. 13 is a front perspective view showing the appearance of the digital camera 40, and FIG. FIG. 15 is a cross-sectional view showing the configuration of the digital camera 40. The digital camera shown in FIG. 13 has a configuration in which the imaging optical path is bent in the long side direction of the viewfinder, and the observer's eyes in FIG.

  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 button 45, a flash 46, a liquid crystal display monitor 47, and the like. When the shutter button 45 disposed at the upper part is pressed, photographing is performed through the photographing optical system 41, for example, the photographing optical system of the first embodiment in conjunction therewith. Then, the object image formed by the photographing optical system 41 is formed on the imaging surface of the CCD 49 through a filter such as a low-pass filter or an infrared cut filter.

  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 unit 52 may be provided separately from the processing unit 51, or may be configured to perform recording and writing electronically using a flexible disk, a memory card, an MO, or the like.

  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 in this manner is effective in reducing the camera thickness. In addition, since the photographic optical system 41 can secure an appropriate angle of view, has good aberrations, is bright, and can be provided with a filter or the like, high performance can be realized and the photographic optical system 41 can be reduced in number of optical members. Therefore, downsizing and cost reduction can be realized.

  Note that the imaging optical path of the digital camera 40 of this embodiment may be configured to bend in the short side direction of the viewfinder. In that case, a strobe (or flash) may be arranged further upward from the entrance surface of the photographic lens, so that the layout can reduce the influence of shadows that occur when a person takes a stroboscope.

  In the example of FIG. 15, a parallel plane plate is disposed as the cover member 50, but a lens having power may be used.

  Here, without providing the cover member, the surface disposed closest to the object side in the optical system of the present invention can also be used as the cover member. In this example, the most object side surface is the entrance surface of the first lens group G1.

  Next, a personal computer which is an example of an information processing apparatus as an imaging apparatus of the present invention is shown in FIGS. 16 is a front perspective view with the cover of the personal computer 300 opened, FIG. 17 is a sectional view of the photographing optical system 303 of the personal computer 300, and FIG. 18 is a side view of FIG.

  As shown in FIGS. 16 to 18, a personal computer 300 includes a keyboard 301 for an operator to input information from the outside, an information processing unit and a recording unit (not shown), and a monitor 302 for displaying information to the operator. 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. This photographic optical system 303 has, on the photographic optical path 304, an objective lens 112 made up of, for example, the photographic optical system of the first embodiment according to the present invention, and an image sensor chip 162 that receives an image. These are built in the personal computer 300.

  Here, a cover glass CG is additionally attached on the image pickup device chip 162 to be integrally formed as the image pickup unit 160, and can be fitted and attached to the rear end of the lens frame 113 of the objective lens 112 with one touch. Therefore, the center alignment of the objective lens 112 and the image sensor chip 162 and the adjustment of the surface interval are unnecessary, and the assembly is simple. Further, a cover glass 114 for protecting the objective lens 112 is disposed at the tip (not shown) of the lens frame 113. The driving mechanism of the photographing optical system in the lens frame 113 is not shown.

  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 displayed on the monitor 302 as an electronic image. FIG. 16 shows an image 305 taken by the operator as an example. 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. 19 shows a telephone which is an example of an information processing apparatus using the imaging apparatus of the present invention, particularly a portable telephone which is convenient to carry. 19A is a front view of the mobile phone 400, FIG. 19B is a side view, and FIG. 19C is a cross-sectional view of the photographing optical system 405.

  As shown in FIGS. 19A to 19C, the mobile phone 400 includes a microphone unit 401 that inputs an operator's voice as information, a speaker unit 402 that outputs the voice of the other party, and the operator receives information. An input dial 403 for input, a monitor 404 for displaying information such as a photographed image and 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 image information And processing means (not shown) for processing 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 photographic optical system 405 includes an objective lens 112 that is arranged on a photographic optical path 407 according to the present invention, for example, the optical path bending zoom optical system of the first embodiment, and an image sensor chip 162 that receives an object image. is doing. These are built in the mobile phone 400.

  Here, a cover glass CG is additionally attached on the image pickup device chip 162 to be integrally formed as the image pickup unit 160, and can be fitted and attached to the rear end of the lens frame 113 of the objective lens 112 with one touch. Therefore, the center alignment of the objective lens 112 and the image sensor chip 162 and the adjustment of the surface interval are unnecessary, and the assembly is simple. Further, a cover glass 114 for protecting the objective lens 112 is disposed at the tip (not shown) of the lens frame 113. The driving mechanism of the photographing optical system in the lens frame 113 is not shown.

  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.

  In the present invention, the image processing unit may be provided integrally with the electronic imaging device, or may be provided as an image processing device separately from the electronic imaging device.

It is sectional drawing which follows the optical axis which shows the optical structure of the imaging device which concerns on 1st Example of this invention. 4 shows spherical aberration, astigmatism, distortion, and lateral chromatic aberration when the imaging apparatus according to the first embodiment is focused at infinity. It is sectional drawing which follows the optical axis which shows the optical structure of the imaging device which concerns on 2nd Example of this invention. FIG. 6 shows spherical aberration, astigmatism, distortion, and lateral chromatic aberration, respectively, when the imaging apparatus according to the second embodiment is focused on infinity. It is sectional drawing which follows the optical axis which shows the optical structure of the imaging device which concerns on 3rd Example of this invention. FIG. 6 shows spherical aberration, astigmatism, distortion, and lateral chromatic aberration, respectively, when the imaging apparatus according to the third example is focused at infinity. It is sectional drawing which follows the optical axis which shows the optical structure of the imaging device which concerns on 4th Example of this invention. 4 shows spherical aberration, astigmatism, distortion, and lateral chromatic aberration, respectively, when the imaging apparatus according to the fourth example is focused on infinity. It is sectional drawing which follows the optical axis which shows the optical structure of the imaging device which concerns on 5th Example of this invention. 10 shows spherical aberration, astigmatism, distortion, and lateral chromatic aberration, respectively, when the imaging apparatus according to the fifth example is focused at infinity. It is sectional drawing which follows the optical axis which shows the optical structure of the imaging device which concerns on 6th Example of this invention. The spherical aberration, the astigmatism, the distortion aberration, and the lateral chromatic aberration at the time of focusing on infinity of the imaging apparatus according to the sixth example are respectively shown. It is a front perspective view which shows the external appearance of the electronic camera to which the optical system of this invention is applied. FIG. 14 is a rear perspective view of the electronic camera of FIG. 13. It is sectional drawing which shows the structure of the electronic camera of FIG. It is the front perspective view which opened the cover of the personal computer in which the optical system of 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. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view, a side view, and a sectional view of a photographing optical system of a mobile phone in which the optical system of the present invention is incorporated as an objective optical system.

Explanation of symbols

S Brightness stop
LF Parallel plate-shaped optical low-pass filter CG Cover glass I Imaging surface G1 First lens group G2 Second lens group G3 Third lens group L11 Negative meniscus lens L12 with a concave surface facing the object side Positive with a concave surface facing the object side Meniscus lens L21 Biconvex positive lens L22 Biconcave negative lens L22 ′ Negative meniscus lens L31 with a concave surface facing the object side Positive meniscus lens 40 with a concave surface facing the object side in the vicinity of the optical axis (lens center portion) Digital camera 41 Imaging optics System 42 Optical path for photographing 43 Viewfinder optical system 44 Optical path for viewfinder 45 Shutter button 46 Flash 47 Liquid crystal display monitor 49 CCD
50 cover member 51 processing means 52 recording means 53 finder objective optical system 55 Porro prism 57 field frame 59 eyepiece optical system 103 control system 160 imaging unit 162 imaging element chip 166 terminal 300 personal computer 301 keyboard 302 monitor 303 imaging optical system 304 imaging optical path 305 Image 400 Mobile phone 401 Microphone unit 402 Speaker unit 403 Input dial 404 Monitor 405 Imaging optical system 406 Antenna 407 Imaging optical path E Observer eyeball

Claims (19)

An electronic imaging apparatus comprising: an imaging optical system; and an imaging element that converts a subject image formed on an imaging surface by the imaging optical system into an electrical signal,
The photographing optical system includes, in order from the object side, a first lens group having a positive refractive power, an aperture stop, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. With
The lens surfaces of the exit surface of the first lens group and the entrance surface of the second lens group both have a convex surface facing the aperture stop side,
The first lens group includes, in order from the object side, a negative meniscus lens and a positive meniscus lens, and the lens surfaces of the negative meniscus lens and the positive meniscus lens are each convex on the aperture stop side on the optical axis. the are towards,
An electronic imaging device characterized by satisfying the following conditional expression :
0.15 ≦ T1 / IH ≦ 0.90
0.5 <R2 / R3 <1.2
0 ≦ D23 / D14 <0.2
However, T1 is the optical on-axis distance to the surface on the most image side from the surface on the most object side of the first lens group, the diagonal of the effective image pickup area of the electronic image pickup device IH is a maximum photographing image height half the length der length Ri, R2 is the paraxial curvature radius of the image side surface of the negative meniscus lens of the first lens group, R3 is near the object side surface of the positive meniscus lens of the first lens group D23 is the air space on the optical axis from the image side surface of the negative meniscus lens of the first lens group to the object side surface of the positive meniscus lens, and D14 is the negative radius of the first lens group. Ru length der on the optical axis from the object side surface of the meniscus lens to the image side surface of the positive meniscus lens. Claim 1, wherein the first lens group, the second lens group, said lens having a refractive power of the third lens group, characterized by being composed of a lens material with all 1.7 or more refractive index The electronic imaging device described in 1. The first lens group, the electronic imaging equipment according to claim 1 or 2, characterized in that it is composed of one cemented lens. The second lens group, in order from the object side, is composed of two lenses, a positive lens and a negative lens with a convex surface facing the object side,
The third lens group includes a positive meniscus lens component having a concave surface facing the object side;
The object side surface of the positive meniscus lens component of the third lens group has an aspheric surface whose negative refractive power decreases as it moves away from the optical axis, and the image side surface of the positive meniscus lens component of the third lens group 4. The electronic imaging apparatus according to claim 1, further comprising an aspheric surface whose positive refractive power decreases as the distance from the axis increases . 5.
However, the lens component is a lens having only two air contact surfaces on the most object surface side and the most image side surface, and is constituted by a single lens or a cemented lens. Any one of the first lens group, the second lens group, and the third lens group includes a cemented lens having a glass lens and an auxiliary lens combined with the glass lens,
The electronic imaging apparatus according to claim 1, wherein the following conditional expression is satisfied .
0.05 ≦ DC ≦ 0.3 (mm)
Ndc ≧ 1.65
| Νdm−νdc |> 6
Where DC is the thickness on the optical axis of the auxiliary lens alone combined with the glass lens, and Ndc is the refractive index with respect to the d-line (587.56 nm) of the auxiliary lens combined with the glass lens. Νdm is the Abbe number of the glass lens, and νdc is the Abbe number of the auxiliary lens combined with the glass lens . The first lens group is the cemented lens;
Wherein said auxiliary lens combined to the glass lens and the glass lens is a refractive power opposite sign alone, which have different Abbe numbers respectively, each lens shape is characterized in that it is a meniscus shape Item 6. The electronic imaging device according to Item 5. The image side lens surface of the lens arranged closest to the image plane of the second lens group is concave with respect to the image side;
A double-sided air lens between the second lens group and the third lens group;
The electronic imaging apparatus according to claim 1, wherein the following conditional expression is satisfied .
1.4 ≦ | r2R | /IH≦18.0
Where r2R is the paraxial radius of curvature of the image side lens surface of the lens disposed closest to the image plane of the second lens group, and IH is the maximum photographed image height, which is a pair of effective imaging areas of the image sensor. It is half the length of the corner. The electronic imaging apparatus according to claim 1, wherein the following conditional expression is satisfied .
0.8 ≦ fg2 / fall ≦ 5.5
Here, fg2 is the focal length of the second lens group, and fall is the focal length of the entire photographing optical system. Between the second lens group and the third lens group, a double-sided air lens having a convex surface,
The electronic imaging apparatus according to claim 1, wherein the following conditional expression is satisfied.
r2R / r3F ≦ −1
Where r2R is the paraxial radius of curvature of the image side lens surface of the lens arranged closest to the image side of the second lens group, and r3F is the object side of the lens arranged closest to the object side of the third lens group. This is the paraxial radius of curvature of the lens surface. An image side lens surface of a lens disposed closest to the image side of the second lens group is a concave surface;
An object side lens surface of a lens disposed closest to the object side of the third lens group is a concave surface, and an image side lens surface of a lens disposed closest to the image side is a convex surface. The electronic imaging device according to claim 1 . The electronic imaging apparatus according to claim 10 , wherein the following conditional expression is satisfied.
0.3 ≦ | r3F | /IH≦2.5
Where r3F is the paraxial radius of curvature of the object side lens surface of the lens disposed closest to the object side in the third lens group, and IH is the maximum photographed image height, which is the diagonal of the effective image pickup area of the image sensor. It is half the length . The third lens group is composed of a single positive meniscus lens having an aspheric surface in which the positive power around the lens becomes gentle with respect to the lens center and the object side surface is concave on the object side. electronic imaging equipment according to any one of claims 1 to 11, characterized in that it is. The electronic imaging apparatus according to claim 1, wherein the following conditional expression is satisfied.
0.6 ≦ | r1F | /IH≦4.0
Where r1F is the paraxial radius of curvature of the object-side lens surface of the lens disposed closest to the object side in the first lens group, and IH is the maximum captured image height, which is the diagonal of the effective imaging area of the image sensor. It is half the length . Claims wherein the second lens unit, in order from the object side, is a first lens having a positive refractive power, characterized in that it is constituted by a second lens having a concave surface on the image side has a negative refractive power The electronic imaging device according to any one of 1 to 3 . 15. The electronic imaging apparatus according to claim 14, wherein the second lens group includes a cemented lens of the first lens having the positive refractive power and the second lens having the negative refractive power. Place. The electronic imaging apparatus according to claim 1, wherein the following conditional expression is satisfied .
｜ IH / EP | ≦ 0.455
However, IH is the maximum photographed image height, which is half the diagonal length of the effective imaging region of the image sensor, and EP is the distance from the position of the exit pupil of the photographing optical system to the imaging plane. . The electron according to any one of claims 1 to 3 , wherein each of the first lens group, the second lens group, and the third lens group is configured by two or less lenses. imaging equipment. The electronic imaging apparatus according to claim 1, wherein the following conditional expression is satisfied .
2.5 <TL / IH <4.1
However, TL is the distance on the optical axis from the incident surface of the first lens group to the imaging surface, and IH is the maximum captured image height, which is half the diagonal length of the effective imaging region of the image sensor. is there. The electronic imaging apparatus according to claim 1, wherein the following conditional expression is satisfied .
0.03 <TS / TL <0.4
Where TS is the total length of the air gap on the optical axis from the entrance surface of the first lens group to the exit surface of the third lens group, and TL is from the entrance surface of the first lens group. This is the distance on the optical axis to the imaging surface.

Images