JP4898307B2 - Optical system and optical apparatus having the same - Google Patents

Description

  The present invention relates to an optical system and an optical apparatus having the optical system, and is suitable for, for example, a silver salt film camera, a digital still camera, a video camera, a telescope, binoculars, a projector, and a copying machine.

  An optical system used in an imaging apparatus such as a digital camera or a video camera is required to have a short total lens length (optical total length, length from the first lens surface on the object side to the image plane).

  In general, as the entire optical system is miniaturized, various aberrations, particularly chromatic aberrations such as longitudinal chromatic aberration and lateral chromatic aberration, occur more frequently and optical performance tends to deteriorate. In particular, in a telephoto type optical system (telephoto lens) in which the total lens length is shortened, the chromatic aberration increases as the focal length is increased (longer).

  As a method for reducing the occurrence of chromatic aberration in an optical system, a method using an abnormal partial dispersion material as an optical material is generally well known.

  In a telephoto type optical system, chromatic aberration is corrected by a front lens group in which the paraxial-axis rays and pupil paraxial rays pass from the optical axis at relatively high positions. Specifically, a lens with a positive refractive power composed of a low-dispersion optical material (an optical member with a large Abbe number) having an anomalous partial dispersion such as fluorite and a negative refractive power composed of a high-dispersion optical material. Chromatic aberration is corrected using a lens.

  Conventionally, various telephoto type optical systems have been proposed (Patent Documents 1 to 3).

  On the other hand, a retrofocus type (wide angle lens) lens is known as a lens system that is advantageous for widening the angle of view (widening the angle of view), which is the opposite of the telephoto type optical system. This retrofocus lens has a short negative focal length and a long back focus by placing a negative refractive power lens group in front of the optical system and a positive refractive power lens group in the rear. ing.

  As a problem in correcting the aberration of the retrofocus lens, negative distortion (barrel distortion) is likely to occur due to the asymmetrical refractive power arrangement preceded by the negative refractive lens group. Can be mentioned.

  In order to correct the negative distortion, the negative lens material in the lens unit having a negative refractive power may be made of a high refractive index material. Lateral chromatic aberration is likely to occur.

  As a method of correcting this negative magnification chromatic aberration, the incident height of the pupil paraxial ray to the lens surface (distance from the optical axis) becomes relatively high, and there is an abnormality such as fluorite in the lens group behind the aperture stop. There is a method using a positive lens made of a low dispersion material having partial dispersion.

Conventionally, chromatic aberration is generally reduced by such a method, and various retrofocus type optical systems have been proposed. (Patent Documents 4 and 5)
Here, the paraxial-axis light beam is a paraxial light beam obtained by normalizing the focal length of the entire optical system to 1 and allowing light having a height of 1 from the optical axis to be incident in parallel with the optical axis of the optical system. It is. In the following, it is assumed that the object is on the left side of the optical system, and light rays incident on the optical system from the object side travel from left to right.

  The pupil paraxial ray normalizes the focal length of the entire optical system to 1, and passes through the intersection of the entrance pupil of the optical system and the optical axis among the rays incident at −45 ° with respect to the optical axis. This is a paraxial ray. Hereinafter, the incident angle to the optical system is measured clockwise from the optical axis and positive in the counterclockwise direction.

Also, an achromatic optical system using a liquid material that exhibits relatively high dispersion and relatively abnormal partial dispersion characteristics is known (Patent Documents 6 and 7).
Japanese Patent Publication No. 60-49883 Japanese Patent Publication No. 60-55805 JP-A-11-119092 Japanese Patent Application Laid-Open No. 06-082689 JP 2002-287031 A US Pat. No. 5,731,907 US Pat. No. 5,638,215

  In a telephoto type or retrofocus type optical system using fluorite or the like as an optical material, correction of chromatic aberration is easy when the overall lens length is set relatively long. However, if the total lens length is shortened, a large amount of chromatic aberration occurs, and it is difficult to correct this well.

  This is because the chromatic aberration generated in the front lens system is merely reduced by utilizing the low dispersion and abnormal partial dispersion of materials such as fluorite. In order to correct the chromatic aberration of the optical system that has deteriorated as the overall lens length is shortened, for example, in a lens system using a low dispersion glass with a large Abbe number such as fluorite, it is necessary to change the refractive power of the lens surface significantly. There is. For this reason, it is difficult to satisfactorily correct both chromatic aberration and various aberrations such as spherical aberration, coma aberration, and astigmatism generated by increasing the refractive power.

  Since the materials disclosed in Patent Documents 6 and 7 are liquids, a structure for sealing them is necessary, and when used as an optical material, the manufacture becomes difficult. In addition, characteristics such as refractive index and dispersion greatly change due to temperature change, and environmental resistance is not sufficient. Further, since an interface with air cannot be obtained, it is difficult to sufficiently correct chromatic aberration.

  An object of the present invention is to provide an optical system that can satisfactorily correct various aberrations including chromatic aberration, is easy to manufacture, and has excellent environmental resistance.

The optical system according to the present invention includes two refractive optical elements formed of a solid material having a refractive surface on both the light incident side and the light emitting side on either the front side or the rear side of the point where the optical axis and the paraxial light beam intersect. an optical system having j1 and j2,
The Abbe numbers of the materials of the two refractive optical elements j1 and j2 are νd1 and νd2, the abnormal partial dispersion of the materials of the two refractive optical elements j1 and j2 are ΔθgF1 and ΔθgF2, and the two refractive optical elements j1 and j2 When the focal length is f1 and f2,
0.012 <| ΔθgF1 |
0.012 <| ΔθgF2 |
40 <| νd1-νd2 |
0 <ΔθgF1 / f1 × ΔθgF2 / f2
It is characterized by satisfying the following conditions.

  According to the present invention, it is possible to obtain an optical system that is easy to manufacture and excellent in environmental resistance characteristics and having high optical performance.

  Examples of the optical system of the present invention will be described below.

  The optical system of each embodiment is used for an imaging apparatus such as a digital camera / video camera or a silver salt film camera, an observation apparatus such as a telescope or binoculars, an optical apparatus such as a copying machine or a projector.

  FIG. 1 is a lens cross-sectional view of the optical system according to the first embodiment. FIG. 2 is an aberration diagram when the optical system of Example 1 is focused on an object at infinity.

  FIG. 3 is a lens cross-sectional view of the optical system of Example 2. FIG. 4 is an aberration diagram when the optical system of Example 2 is focused on an object at infinity.

  FIG. 5 is a lens cross-sectional view of the optical system of Example 3. FIG. 6 is an aberration diagram when the optical system of Example 3 is focused on an object at infinity.

  FIG. 7 is a lens cross-sectional view of the optical system of Example 4. FIG. 8 is an aberration diagram when the optical system of Example 4 is focused on an object at infinity.

  FIG. 9 is a lens cross-sectional view of the optical system of Example 5. FIG. 10 is an aberration diagram when the optical system of Example 5 is focused on an object at infinity.

  FIG. 11 is a lens cross-sectional view of the optical system according to Example 6. FIG. 12 is an aberration diagram when the optical system of Example 6 is focused on an object at infinity.

  FIG. 13 is a lens cross-sectional view of the optical system according to Example 7. FIG. 14 is an aberration diagram when the optical system of Example 7 is focused on an object at infinity.

  FIG. 15 is a lens cross-sectional view of the optical system according to Example 8. FIG. 16 is an aberration diagram when the optical system of Example 8 is focused on an object at infinity.

  FIG. 17 is a lens cross-sectional view of the optical system according to Example 9. FIG. 18 is an aberration diagram when the optical system according to Example 9 is focused on an object at infinity.

  FIG. 19 is a schematic diagram of a main part of an imaging apparatus including the optical system of the present invention.

  In the lens cross-sectional view, the left side is the front (the object side in a photographing optical system used for a camera, the screen side (enlarged side) in a projection optical system used for a liquid crystal projector, etc., and the right is the rear (the image side in a photographing optical system, This is the panel side (reduction side) in the projection optical system.

  In the lens cross-sectional view, OL is an optical system.

  Li is the i-th lens group, where i is the order of the lens group counted from the object side.

  Here, one lens group refers to a group of lens elements whose air spacing on the optical axis does not change during zooming, focusing, or image stabilization.

  Reference numerals j1 and j2 denote refractive optical elements (lenses) made of a solid material to be described later.

  The two refractive optical elements j1 and j2 are arranged in the same lens group.

  SP is an aperture stop. IP is the image plane. The image plane IP corresponds to an imaging plane of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor when used as a photographing optical system of a video camera or a digital still camera.

  Further, when used as a photographing optical system of a silver salt film camera, it corresponds to a film surface.

  Examples 1 to 5 in FIGS. 1, 3, 5, 7, and 9 are telephoto type optical systems (telephoto lenses).

  Examples 6 to 9 in FIGS. 11, 13, 15, and 17 are retrofocus type optical systems (wide-angle lenses).

  2, 4, 6, 8, 8, 10, 12, 14, 16, and 18, d, g, C, and F are d-line, g-line, C-line, and F-line, respectively. It is.

  ΔM and ΔS are a d-line meridional image plane and a d-line sagittal image plane.

  In FIGS. 2, 4, 6, 8, and 10, the chromatic aberration of magnification is represented by the g-line.

  In FIGS. 14, 16, and 18, the chromatic aberration of magnification is represented by the g-line, C-line, and F-line.

  Fno is the F number, and ω is the half angle of view.

  The optical system OL of each embodiment is made of a solid material (solid at room temperature and normal pressure) having a large difference in partial dispersion ratio from a normal glass material, and includes a plurality of refractive optical elements (optical members) having a refractive action (power). Used. That is, at least two of the refractive optical elements (optical members) having refractive power are formed of a solid material having a large difference in partial dispersion ratio from a normal glass material.

  Here, the refractive optical member means, for example, a refractive lens that generates power by refraction, and does not include a diffractive optical element that generates power by diffraction.

  Further, the solid material refers to a solid material in an environment where the optical system is used, and may be in any state before using the optical system at the time of manufacturing or the like. For example, even if it is a liquid material at the time of manufacture, what was hardened into a solid material corresponds to the solid material here.

  FIG. 20 is a schematic diagram of a paraxial refractive power arrangement for explaining the optical action of the optical systems of Examples 1 to 5. In FIG. 20, OL is a telephoto type optical system in which the total lens length (distance from the first lens surface to the image plane) is shorter than the focal length. Gp and Gn are a front group of positive refracting power and a rear group of negative refracting power, respectively, constituting the telephoto type optical system OL.

  j1 and j2 are refractive optical elements made of a material satisfying conditional expressions (1) to (4) described later introduced into one lens group of the front group Gp.

  In order to simplify the configuration, the lenses constituting the front group Gp and the rear group Gn are all thin single lenses, and are arranged on the optical axis with a lens interval of 0 in the front group Gp and the rear group Gn. And

  The refractive optical elements j1 and j2 are also thin single lenses, and are arranged on the optical axis La with a lens interval of 0 in the front group Gp. Q is a paraxial ray, R is a pupil paraxial ray, and P is an intersection of the pupil paraxial ray R and the optical axis La. IP is the image plane.

In FIG. 20, a point P is a point where the optical axis La and the pupil paraxial ray R intersect. In the optical system OL of FIG. 20, the maximum value h _Gp of the height from the optical axis La through which the paraxial beam Q passes the lens surface on the enlargement side from the point P is on the paraxial axis on the reduction side from the point P. This is an optical system in which the light beam Q is larger than the maximum height h _Gn from the optical axis passing through the lens surface.

  In the optical systems of Examples 1 to 5, the two refractive optical elements j1 and j2 are arranged in the lens group in front of the stop.

FIG. 21 is a schematic diagram of a paraxial refractive power arrangement for explaining the action of chromatic aberration correction in the optical systems of Examples 6 to 9. In FIG. 21, Gn and Gp are a negative refractive power front group and a positive refractive power rear group, respectively, constituting a retrofocus type optical system. In order to simplify the problem, the lenses constituting the front group Gn and the rear group Gp are all thin single lenses, and are arranged on the optical axis at the lens interval 0 in the front group Gn and the rear group Gp, respectively. To do. Q is a paraxial ray and R is a pupil paraxial ray. P is the intersection of the pupil paraxial ray R and the optical axis La, and usually coincides with the center of the aperture stop. h _n and h _p are incident heights of the paraxial axial ray Q on the lens surface. Hn and Hp are the incident heights of the pupil paraxial ray R to the lens surface.

The retrofocus type optical system in the present invention is such that the height h _{n of} the paraxial axial ray Q passing through the foremost lens surface is behind the intersection P and the paraxial axial ray Q passes through the lens surface. It refers to small optical system than the maximum value of the height h _p of the optical axis.

  In the optical systems of Examples 6 to 9, the two refractive optical elements j1 and j2 are disposed in the lens group behind the stop.

  The optical system of each embodiment has two refracting optical elements formed from a solid material whose light incident side and light emission side are both refractive surfaces at either the front side or the rear side from the point where the optical axis and the paraxial light beam intersect. Elements j1 and j2 are included.

Now, the refractive indexes of materials for g-line (wavelength 435.8 nm), F-line (486.1 nm), d-line (587.6 nm), and C-line (656.3 nm) are Ng, Nd, NF, and NC, respectively. . Then, Abbe number νd, partial dispersion ratio θgF, and abnormal partial dispersion ΔθgF,
νd = (Nd−1) / (NF−NC)
θgF = (Ng−NF) / (NF−NC)
ΔθgF = θgF − (− 1.665 × 10 ⁻⁷ × νd ³ + 5.213 × 10 ⁻⁵ × νd ² −5.656 × 10 ⁻³ × νd + 7.278 × 10 ⁻¹ )
Represent as The Abbe numbers of the materials of the two refractive optical elements j1 and j2 in the optical system OL are νd1 and νd2. The abnormal partial dispersibility of the materials of the two refractive optical elements j1 and j2 is assumed to be ΔθgF1 and ΔθgF2.

Let the focal lengths of the two refractive optical elements j1 and j2 be f1 and f2. At this time, 0.012 <| ΔθgF1 | (1)
0.012 <| ΔθgF2 | (2)
40 <| νd1−νd2 | (3)
0 <(ΔθgF1 / f1) × (ΔθgF2 / f2) (4)
Is satisfied.

  In each embodiment, refracting optical members made of a plurality of solid materials satisfying conditional expressions (1) and (2) are used in the optical path, so that chromatic aberration can be corrected well over a wide wavelength band of g-line to C-line. ing.

  Further, by using a high-dispersion solid material and a low-dispersion solid material that satisfy the conditional expression (3), the thickness and weight of the refractive optical elements j1 and j2 are reduced.

  Conditional expression (4) is a conditional expression for aligning the achromatic directions of the refractive optical elements j1 and j2. By satisfying conditional expression (4), chromatic aberration can be corrected satisfactorily over a wide wavelength band between g-line and C-line as a whole while each refracting optical element j1, j2 supplements each other's chromatic aberration correction capability. Yes. If this conditional expression (4) is not satisfied, the respective chromatic aberration correction capabilities cancel each other, making it difficult to perform chromatic aberration correction well.

  In each embodiment, refractive optical elements j1 and j2 satisfying conditional expressions (1), (2), (3), and (4) are arranged in the same lens group. Chromatic aberration is favorably corrected over a wide wavelength band of g-line to C-line by intensively arranging the refractive optical elements j1 and j2 in a lens group having a high achromatic effect.

  Three or more refractive optical elements that satisfy the conditional expressions (1) to (4) may be provided in the same lens group.

  In each embodiment, it is more preferable to set the numerical ranges of conditional expressions (1) to (4) as follows.

0.0125 <| ΔθgF1 | (1a)
0.0125 <| ΔθgF2 | (2a)
45 <| νd1−νd2 | (3a)
1 × 10 ⁻⁹ <(ΔθgF1 / f1) × (ΔθgF2 / f2) (4a)
It is preferable that at least one of the plurality of refractive optical elements satisfying the conditional expressions (1), (2), (3), and (4) satisfies the following conditional expression (5).

0.001 <| ΔθgF | / νd <0.007 (5)
By using at least one refractive optical element made of a solid material that satisfies the conditional expression (5), the thickness of the refractive optical element in the optical axis direction is suppressed while obtaining a sufficient achromatic effect. When a solid material lower than the lower limit of conditional expression (5) is used, it is difficult to obtain a sufficient achromatic effect while suppressing the thickness. Also, when a solid material exceeding the upper limit of conditional expression (5) is used, the anomalous dispersion is too strong, making it difficult to balance the achromaticity with other optical members of the optical system, thereby deteriorating chromatic aberration. End up.

  In addition, a favorable achromatic effect can be acquired, suppressing thickness further by making the range of conditional expression (5) into the following ranges.

0.002 <| ΔθgF | / νd <0.007 (5a)
Examples of solid materials satisfying the conditional expressions (1) and (2) (hereinafter also referred to as “optical materials”) include glass materials and fluorite having low dispersion and abnormal partial dispersion, and resins and inorganic oxide nanoparticles. There is a mixture dispersed in a synthetic resin. Among various resins, UV curable resin (Nd = 1.635, νd = 22.7, θgF = 0.69) and N-polyvinylcarbazole (Nd = 1.696, νd = 17.7, θgF = 0. 69) is an optical material satisfying conditional expressions (1) and (2). The resin is not limited to these as long as it satisfies the conditional expressions (1) and (2).

Moreover, as an optical material having characteristics different from those of general glass materials, there is a mixture in which the following inorganic oxide nanoparticles are dispersed in a synthetic resin (transparent medium) . Here, as the inorganic fine particles, TiO ₂ (Nd = 2.757, νd = 9.53), Nb ₂ O ₅ (Nd = 2.367, νd = 14.0), ITO (Nd = 1.8581, νd = 5.53), Cr ₂ O ₂ (Nd = 2.2178, νd = 13.4), BaTiO ₂ (Nd = 2.4362, νd = 11.3), and other inorganic oxides.

Among these inorganic oxides, TiO ₂ fine particles (Nd = 2.757, νd = 9.53, θgF = 0.76) and ITO fine particles (Nd = 1.8581, νd = 5.53, θgF = When 0.29) is dispersed in a synthetic resin at an appropriate volume ratio, an optical material satisfying the conditional expressions (1) and (2) can be obtained.

TiO ₂ is a material used in various applications, and is used as an evaporation material for forming an optical thin film such as an antireflection film in the optical field. In addition, photocatalysts, white pigments and the like, and TiO ₂ fine particles are used as cosmetic materials.

  ITO is a material constituting a transparent electrode, and is usually used for an infrared shielding element and an ultraviolet shielding element for other uses such as a liquid crystal display element and an EL element.

In each example, the average diameter of the TiO ₂ fine particles or ITO fine particles dispersed in the resin is preferably about 2 nm to 50 nm in consideration of the influence of scattering, and a dispersant may be added to suppress aggregation.

A medium material for dispersing TiO ₂ or ITO is preferably a polymer, and high mass productivity can be obtained by photopolymerization molding or thermal polymerization molding using a mold or the like.

In addition, as a characteristic of the optical constant of the polymer, a polymer having a relatively large partial dispersion ratio or a polymer having a relatively small Abbe number, or a polymer satisfying both, is preferable. N-polyvinylcarbazole, styrene, polymethyl methacrylate (acrylic) ), Etc. are applicable. In examples described later, a UV curable resin and N-polyvinylcarbazole are used as a host polymer in which TiO ₂ fine particles are dispersed. However, each embodiment is not limited to these optical materials.

  The dispersion characteristic N (λ) of the mixture in which the nanoparticles are dispersed can be easily calculated by the following equation derived from the well-known Drude equation.

That is, the refractive index N (λ) at the wavelength λ is
N (λ) = [1 + V {N _TI ² (λ) −1} + (1-V) {N _P ² (λ) −1}] ^1/2
It is.

Here, lambda any _wavelength, the _{N TI} is the refractive index, _{N P} of TiO ₂ or ITO refractive index of the polymer, V is a fraction of the total volume of TiO ₂ or ITO particles to the polymer volume.

  Further, when the thickness of the resin or inorganic fine particle dispersed material is increased, the influence of curing shrinkage at the time of molding becomes large, and it becomes difficult to obtain surface accuracy in production. Further, since the thickness in the optical axis direction is thick, the degree of optical change under an environment such as high humidity is increased. Accordingly, it is preferable that the following condition is satisfied, where Dmax (mm) is the maximum thickness of a lens formed of a resin or an inorganic fine particle dispersed material that satisfies the conditional expressions (1) and (2). In a positive (convex) lens, the maximum thickness Dmax is the center thickness, and in a negative (concave) lens, the maximum thickness Dmax is the thickness of the lens periphery.

Dmax ≦ 5.0 (6)
If the range of conditional expression (6) is set to the following range, it becomes easier to manufacture and it is easy to obtain desired optical performance.

Dmax ≦ 4.0 (6a)
More preferably, the following range is used.

Dmax ≦ 3.0 (6b)
More preferably, the following range is used.

Dmax ≦ 2.0 (6c)
In each example, as an optical material satisfying the conditional expressions (1), (2), and (3), an optical material having low dispersion and anomalous partial dispersion and the aforementioned UV curable resin, N-polyvinylcarbazole, TiO ₂ , A combination of ITO fine particle dispersion materials is used. However, the present invention is not limited to this.

  As an optical material satisfying the conditional expressions (1), (2), (3), when the absolute value of the temperature change of the refractive index of the d-line at 0 ° C. to 40 ° C. is | dn / dT | It is preferable to satisfy the conditions.

| Dn / dT | <2.5 × 10 ⁻⁴ (1 / ° C.) (7)
Here, if the range of the conditional expression (7) is deviated, it becomes difficult to maintain good optical performance in the temperature range of 0 ° C to 40 ° C.

  In each embodiment, a plurality of refractive optical elements made of an optical material satisfying the conditional expressions (1), (2), (3), and (4) are provided on the lens in the optical system or the surface of the lens. It is applied to a certain layer (surface).

  In each embodiment, at least one of the refractive surfaces of the refractive optical element made of this optical material may be aspherical. According to this, chromatic aberration flare such as chromatic spherical aberration can be corrected satisfactorily.

  Next, aberration correction when a refractive optical element having a power made of an optical material having a large difference in partial dispersion ratio from a normal glass material is used in an optical system will be described.

  In the wavelength dependence characteristic (dispersion characteristic) of the refractive index of the optical material, the Abbe number νd represents the overall slope of the dispersion characteristic curve, and the partial dispersion ratio θgF represents the degree of bending of the dispersion characteristic curve.

  In general, an optical material has a refractive index on the short wavelength side higher than that on the long wavelength side (Abbe number νd is a positive value), and the dispersion characteristic curve is convex downward (a partial dispersion ratio θgF is a positive value). ), The change in the refractive index with respect to the change in wavelength increases as the wavelength becomes shorter. Further, the optical dispersion material having a small Abbe number νd and a large dispersion has a larger partial dispersion ratio θgF, and the dispersion characteristic curve tends to be convex downward.

  The wavelength-dependent characteristic curve of the chromatic aberration coefficient of the lens surface using an optical material having a large partial dispersion ratio θgF shows a larger curvature on the short wavelength side than when an optical material having a small partial dispersion ratio θgF is used.

  On the other hand, the wavelength-dependent characteristic curve of the chromatic aberration coefficient of the lens surface using an optical material having a small partial dispersion ratio θgF shows a shape closer to a straight line over the entire wavelength region.

  The partial dispersion ratio θgF of a general optical material such as a glass material changes almost uniformly with respect to the Abbe number νd, and the change of the partial dispersion ratio θgF with respect to the Abbe number νd can be expressed by the following equation.

θgF (νd) = − 1.665 × 10 ⁻⁷ × νd ³ + 5.213 × 10 ⁻⁵ × νd ²
−5.656 × 10 ⁻³ × νd + 7.278 × 10 ⁻¹ (a)
In general, the change of the partial dispersion ratio θgF with respect to the Abbe number νd is represented by a straight line, but the actual distribution of the glass material has a curved line, and the characteristic represented by the curved line as described above is better. An optical material having characteristics deviating from this curve is an optical material exhibiting abnormal partial dispersion. Therefore, the anomalous partial dispersion ΔθgF of an optical material having a partial dispersion ratio of θgF is expressed by the following equation.

ΔθgF = θgF − (− 1.665 × 10 ⁻⁷ × νd ³ + 5.213 × 10 ⁻⁵ × νd ² −5.656 × 10 ⁻³ × νd + 7.278 × 10 ⁻¹ ) (b)
When an optical material having a positive value of the anomalous partial dispersion ΔθgF is used as a lens, the wavelength-dependent characteristic curve of the chromatic aberration coefficient is larger on the short wavelength side than a general glass material.

  When an optical material having a negative anomalous partial dispersion ΔθgF is used as a lens, the wavelength-dependent characteristic curve of the chromatic aberration coefficient is less bent on the short wavelength side than the general glass material (high linearity). ).

  Correction of chromatic aberration in the optical system is performed by combining several optical materials. However, it is difficult to satisfactorily correct the chromatic aberration over the entire wavelength band even if only a normal glass material having the characteristics represented by the curve of the above formula (a) is used.

  The partial dispersion ratio θgF represents the curve on the short wavelength side (g-line to F-line) of the wavelength-dependent characteristic curve of the chromatic aberration coefficient when an optical material is used as a lens. The Abbe number νd represents the inclination of the F line to the C line.

  Therefore, the uniform change of the partial dispersion ratio θgF with respect to the Abbe number νd means that the ratio of the bending of the g-line to the F-line with respect to the inclination of the F-line to the C-line is constant. For this reason, if the lens power is changed in order to correct the inclination component of the chromatic aberration of the F-line to C-line, the bending of the g-line to F-line also changes at a constant rate. For this reason, it is difficult to correct the inclination component and the bending component of chromatic aberration at the same time even if only ordinary glass materials are combined.

  However, when a material having anomalous partial dispersion is used as a lens, the ratio of the bending component and the inclination component of the chromatic aberration coefficient is different from that of a normal glass material. For this reason, when such an optical material having anomalous partial dispersion is used as a lens, the degree of freedom in correcting chromatic aberration is greatly increased, and chromatic aberration can be corrected well over the entire wavelength range (F-line to C-line). it can.

  Next, the achromatic action when an optical material having abnormal partial dispersion is used in the optical system will be described. Here, the abnormal partial dispersion ΔθgF takes a positive value, that is, a refractive optical element GNL using a material having a large partial dispersion ratio θgF and a refractive optical element G having a normal partial dispersion ratio θgF are shown in FIG. The achromatic action of the telephoto lens shown will be described as an example.

  The following concept is the same for the wide-angle lens shown in FIG.

  The telephoto lens shown in FIG. 20 includes a front group having a positive refractive power and a rear group having a negative refractive power in order from the object side to the image side.

  The telephoto lens shown in FIG. 20 is a lens system in which the total lens length is shorter than the focal length.

  First, a material having a relatively large partial dispersion ratio θgF is selected for the negative lens constituting the refractive optical element G from a state in which the chromatic aberration is corrected to some extent as the refractive optical element G as a partial system.

  Here, in general, a material having a large partial dispersion ratio θgF has a large dispersion at the same time, and therefore, the overall inclination of the wavelength-dependent characteristic curve of the chromatic aberration coefficient of the refractive optical element G changes while bending more than the original state.

  In this state, an appropriate power is given to the refractive optical element GNL, and at the same time, a material having a relatively large dispersion is selected for the positive lens constituting the refractive optical element G.

  However, when the refractive optical element GNL is formed of a general optical material having a uniform partial dispersion ratio with respect to the Abbe number, the refractive optical element GNL has a wavelength-dependent characteristic curve of the aberration coefficient of the refractive optical element G. Contributes to the bending component and the inclination component at a constant rate at the same time. As a result, neither of these components can be canceled simultaneously.

  On the other hand, when the refractive optical element GNL is made of a material having a large partial dispersion ratio θgF as compared with a general material, the refractive optical element GNL mainly includes the entire wavelength-dependent characteristic curve of chromatic aberration of the refractive optical element G. Contributes to bending components. For this reason, it is possible to cancel only the bending component.

  As a result, the refractive optical element GNL mainly cancels the bending component of the entire wavelength-dependent characteristic curve of the chromatic aberration of the refractive optical element G, and the positive lens constituting the refractive optical element G mainly cancels the tilt component independently and simultaneously. Can do.

  Further, it is preferable that the absolute value of the Abbe number νd of the refractive optical element GNL is small, that is, the dispersion is large, because chromatic aberration can be independently corrected. This will be described using the axial chromatic aberration coefficient and the lateral chromatic aberration coefficient of the lens surface.

  If the power change of the surface of the refractive lens is Δψ and the Abbe number of the material is ν, the change in axial chromatic aberration coefficient ΔL and the change in magnification chromatic aberration coefficient ΔT on the lens surface can be expressed as follows.

ΔL ∝ Δψ / ν (c)
ΔT ∝ Δψ / ν (d)
As is clear from the equations (c) and (d), the aberration coefficient changes ΔL and ΔT with respect to the lens surface power change Δψ increase as the absolute value of the Abbe number ν decreases (that is, the dispersion increases).

  Therefore, if a material having a large dispersion with a small absolute value of the Abbe number ν is used, the amount of power change for obtaining the necessary chromatic aberration can be small.

  This means that chromatic aberration can be controlled without greatly affecting spherical aberration, coma aberration, astigmatism, etc. in terms of aberration theory, and the independence of chromatic aberration correction is enhanced.

  On the other hand, if a material with small dispersion (large Abbe number ν) is used, the power change for obtaining the necessary chromatic aberration becomes large. Along with this, various aberrations such as spherical aberration change greatly, and the independence of chromatic aberration correction is weakened. Therefore, it is important for aberration correction that at least one lens surface of the lenses constituting the optical system is a surface made of a refractive lens made of a high dispersion material. The Abbe number νd of the highly dispersed material desirably satisfies the following conditions.

νd <30 (8)
By setting the range of conditional expression (8) to the following range, it is possible to obtain a good achromatic effect while further suppressing the thickness.

νd <25 (8a)
Next, the effect when a refractive optical element having power made of an optical material having a large difference in partial dispersion ratio θgF from a normal glass material is used in the optical system will be described.

  By using an optical material having anomalous partial dispersion as a lens, chromatic aberration can be corrected well over the entire wavelength range. However, in order to correct chromatic aberration satisfactorily, a certain amount of power must be applied to a lens made of an optical material having anomalous partial dispersion.

  When a highly dispersed resin or fine particle dispersed material is used, the power is smaller than when a low dispersed material such as fluorite is used. However, when used in an optical system having a lens having a large effective diameter such as a telephoto lens, the absolute thickness of the lens becomes thick. The resin and the fine particle dispersed material are preferably subjected to photopolymerization molding or thermal polymerization molding. However, if the absolute thickness of the lens is large, the resin is hardened and contracted by curing, which makes it difficult to mold. In addition, if lenses made of resin or fine particle dispersed material are used at a plurality of locations in the optical system, the molding cost is increased by that amount, which is also not preferable in terms of environmental resistance.

  When only a low dispersion material such as fluorite is used, since the refractive index of the material is low, it is necessary to greatly change the refractive power of the lens surface in order to increase the power. For this reason, it is difficult to satisfactorily correct both chromatic aberration and various aberrations such as spherical aberration, coma aberration, and astigmatism generated by increasing the refractive power. In addition, when a plurality of lenses are used to disperse power, the specific gravity is large and the weight of the optical system is increased.

  Therefore, in order to make an optical system that is advantageous in terms of manufacturing and weight while using an optical material having anomalous partial dispersibility as a lens and correcting chromatic aberration well over the entire wavelength range, the thickness of the lens must be reduced. It is important to suppress.

For this reason, in each embodiment, a lens made of a high dispersion material such as a resin having an abnormal partial dispersion or a fine particle dispersion material and a low dispersion material such as fluorite is combined in the optical path. By using in combination in this way, it is possible to satisfactorily correct chromatic aberration over the entire wavelength range while suppressing the thicknesses of the high dispersion material and the low dispersion material.

  In the optical system, in order to satisfactorily correct both the longitudinal chromatic aberration and the lateral chromatic aberration, it is preferable that the lens made of an anomalous partial dispersive material is concentrated on the object side or the image side from the stop.

  This is because the correction direction of the lateral chromatic aberration is reversed on the object side or the image side from the stop, and the simultaneous chromatic aberration and lateral chromatic aberration cannot be obtained.

  Furthermore, the position where the achromatic effect is high in many optical systems is limited. Now, a group of lens elements whose air spacing on the optical axis does not change during zooming (magnification), focus (focusing), or during image stabilization is defined as one lens group. At this time, a lens made of a material having an anomalous partial dispersibility can be arranged in a concentrated manner in a lens group having a high achromatic effect, whereby a further excellent chromatic aberration correction effect can be obtained.

  Next, when two lenses made of optical materials having a plurality (two) of abnormal partial dispersions ΔθgF1 and ΔθgF2 are used in the optical system, the focal lengths f1 and f2 of the lenses and the abnormal partial dispersions ΔθgF1 and ΔθgF2 The relationship will be described.

  The power of the refractive lens surface of the refractive optical element J is assumed to be ψ. The relationship among the power ψ, Abbe number νd, and anomalous partial dispersion ΔθgF for obtaining a good chromatic aberration correction effect can be expressed as follows.

ψ ∝ νd / ΔθgF (e)
Here, the anomalous partial dispersion ΔθgF is a difference in partial dispersion ratio θgF at the same Abbe number between the refractive optical element GNL represented by the above-described formula (b) and a general glass material.

  Since the Abbe number is always positive in the optical material, the sign of the power ψ, that is, the sign of the focal length f for obtaining a good chromatic aberration correction effect is determined by the sign of the anomalous partial dispersion ΔθgF. The direction of chromatic aberration to be corrected is determined on the object side or the image side from the stop.

  Therefore, for example, consider a case where an optical material j1 having a positive anomalous partial dispersion ΔθgF1 on the object side with respect to the stop is used in a positive lens (f1> 0). Here, when an optical material j2 having a positive anomalous partial dispersion ΔθgF2 is disposed, it must be used as a positive lens (f2> 0). Conversely, when an optical material j2 having a negative anomalous partial dispersion ΔθgF2 is disposed, it must be used as a negative lens (f2 <0). The above-described conditional expression (4) shows this relationship.

  If this conditional expression (4) is not satisfied, the achromatic effects will be canceled by the refractive optical elements j1 and j2 made of a plurality of anomalous partially dispersive materials.

  As is clear from the equation (e), the power ψ of the refractive optical element J decreases as the Abbe number νd decreases (high dispersion) and the abnormal partial dispersion ΔθgF increases.

  In the optical system, as the lens power decreases, the thickness of the lens along the optical axis (the lens center thickness along the optical axis for positive lenses and the lens peripheral thickness along the optical axis for negative lenses) decreases.

  Therefore, in order to reduce the thickness of the lens, it is sufficient that the absolute value of ΔθgF / νd is large. However, the refractive optical element GNL is used in combination with a general optical material. For this reason, the partial dispersion ratio of the material used for the refractive optical element GNL needs to be different from that of a general optical material, but it should not be too far away. This condition is shown by conditional expression (5).

  In the case of a solid material that falls below the lower limit of conditional expression (5), it is difficult to obtain a sufficient achromatic effect while suppressing the thickness. In the case of a solid material exceeding the upper limit of conditional expression (5), the anomalous dispersibility is too strong, making it difficult to balance achromaticity with other optical members of the optical system, and worsen chromatic aberration. .

  Next, features of each embodiment will be described.

  The optical system OL of Numerical Example 1 in FIG. 1 is a telephoto lens having a focal length of 300 mm. In the first lens unit L1 constituting the telephoto lens OL, a positive lens j1 made of a product name S-FPL53 (manufactured by OHARA Co., Ltd.) having an anomalous partial dispersion and a positive lens j2 made of an UV curable resin having an anomalous partial dispersion are provided. Used.

  In the optical system of Numerical Example 1, the first lens unit L1 on the object side where the passing position of the paraxial light beam from the optical axis is relatively high includes the positive lens j1 made of the product name S-FPL53 and the UV curable resin. The axial chromatic aberration is mainly corrected by using the positive lens j2.

  The optical system of Numerical Example 1 is very compact with a telephoto ratio of 0.677.

  The second lens unit L2 of the optical system of Numerical Example 1 is a focus unit, and moves to the image side for focusing when the object distance is shortened. The fourth lens unit L4 is an anti-vibration lens unit that moves so as to have a component perpendicular to the optical axis, thereby displacing the image position.

  The maximum thickness of the positive lens j2 is 2.00 mm, and the center thickness of the positive lens j1 is 10.9 mm. By using the lens j1 made of product name S-FPL53 and the lens j2 made of UV curable resin in the same lens group on the object side from the stop SP, good optical performance can be obtained while suppressing both thickness and weight.

  The optical system OL of Numerical Example 2 in FIG. 3 is a telephoto lens having a focal length of 300 mm. In the first lens unit L1 constituting the telephoto lens OL, a positive lens j1 made of a product name S-FPL51 (manufactured by OHARA Inc.) having an anomalous partial dispersion and a positive lens j2 made of a UV curable resin are used.

  In the optical system of Numerical Example 2, the first lens unit L1 on the object side where the passing position of the paraxial light beam from the optical axis is relatively high includes the positive lens j1 made of the product name S-FPL51 and the UV curable resin. The axial chromatic aberration is mainly corrected by using the positive lens j2.

  The optical system of Numerical Example 2 is very compact with a telephoto ratio of 0.677.

  The second lens unit L2 of the optical system of Numerical Example 2 is a focus unit, and moves to the image side for focusing when the object distance is shortened. The fourth lens unit L4 is an anti-vibration lens unit.

  The maximum thickness of the positive lens j2 is 2.00 mm, and the center thickness of the positive lens j1 is 9.9 mm. By using the positive lens j1 made of the product name S-FPL51 and the positive lens j2 made of UV curable resin in the same lens group on the object side from the stop SP, good optical performance can be obtained while suppressing the thickness and weight of both. Yes. In Numerical Example 2, a positive lens made of the product name S-FPL51 (center thickness: 7.2 mm) is used for the second positive lens j3 counted from the image side in the same first lens unit L1 (center thickness: 7.2 mm). Chromatic aberration is corrected.

  The optical system OL of Numerical Example 3 in FIG. 5 is a telephoto lens having a focal length of 300 mm. A fine particle dispersion material in which a positive lens j1 made of a product name S-FPL51 (manufactured by OHARA Co., Ltd.) having an abnormal partial dispersion and 10% TiO2 fine particles are dispersed in a UV curable resin in the first lens unit L1 constituting the telephoto lens OL. A positive lens j2 is used.

In the optical system of Numerical Example 3, the positive lens j1 made of the product name S-FPL51 and the TiO ₂ fine particles 10 are added to the first lens unit L1 on the object side where the passing position of the paraxial light beam from the optical axis is relatively high. A positive lens j2 made of a% -UV curable resin fine particle dispersed material is used. This mainly corrects axial chromatic aberration.

  The optical system of Numerical Example 3 is very compact with a telephoto ratio of 0.677.

  The second lens unit L2 of the optical system of Numerical Example 3 is a focus unit, and moves to the image side for focusing when the object distance is shortened. The fourth lens unit L4 is an anti-vibration lens unit.

  The maximum thickness of the positive lens j2 is 1.36 mm, and the center thickness of the positive lens j1 is 9.3 mm. By using the positive lens j1 made of the product name S-FPL51 and the positive lens j2 made of TiO2 fine particle 10% -UV cured resin fine particle dispersed material in the same lens group on the object side from the stop SP, both thickness and weight are suppressed. Good optical performance is obtained.

  The optical system OL of Numerical Example 4 in FIG. 7 is a telephoto lens having a focal length of 300 mm. In the first lens unit L1 constituting the telephoto lens OL, a positive lens j1 made of an anomalous partial dispersion product name K-GFK70 (manufactured by Sumita Optical Glass Co., Ltd.) and 9% of ITO fine particles were dispersed in N-polyvinylcarbazole. A negative lens j2 made of a fine particle dispersed material is used.

  In the optical system of Numerical Example 4, the first lens unit L1 on the object side where the passing position of the paraxial light beam from the optical axis is relatively high, the positive lens j1 made of the trade name K-GFK70 and the ITO fine particles 9%. A negative lens j2 made of a dispersion material of -N-polyvinylcarbazole fine particles is used. This mainly corrects axial chromatic aberration.

  The optical system of Numerical Example 4 is very compact with a telephoto ratio of 0.677.

  The second lens unit L2 of the optical system of Numerical Example 4 is a focus unit, and moves to the image side for focusing when the object distance is shortened. The fourth lens unit L4 is an anti-vibration lens unit.

  The maximum thickness of the negative lens j2 is 0.98 mm, and the center thickness of the positive lens j1 is 9.1 mm. By using a positive lens made of the trade name K-GFK70 and a negative lens made of ITO fine particle 9% -N-polyvinylcarbazole fine particle dispersed material in the same lens group on the object side from the stop SP, both thickness and weight are suppressed. Good optical performance is obtained.

  The optical system OL of Numerical Example 5 in FIG. 9 is a telephoto lens having a focal length of 300 mm. Fine particle dispersion in which a positive lens j1 made of a product name S-FPL52 (manufactured by OHARA Inc.) having an anomalous partial dispersion and 5% of ITO fine particles are dispersed in N-polyvinylcarbazole in the first lens unit L1 constituting the telephoto lens OL. A negative lens j2 made of a material is used.

  In the optical system of Numerical Example 5, the positive lens j1 made of the product name S-FPL52 and the ITO fine particle 5% are included in the first lens unit L1 on the object side where the passing position of the paraxial light beam from the optical axis is relatively high. A negative lens j2 made of a dispersion material of -N-polyvinylcarbazole fine particles is used. This mainly corrects axial chromatic aberration.

  The optical system of Numerical Example 5 is very compact with a telephoto ratio of 0.677.

  The second lens unit L2 of the optical system of Numerical Example 5 is a focus unit, and moves to the image side for focusing when the object distance is shortened. The fourth lens unit L4 is an anti-vibration lens unit.

  The maximum thickness of the negative lens j2 is 0.30 mm, and the center thickness of the positive lens j1 is 10.8 mm. By using the positive lens j1 made of the trade name S-FPL52 and the negative lens j2 made of the ITO fine particle 5% -N-polyvinylcarbazole fine particle dispersion material in the same lens group on the object side from the stop SP, the thickness and weight of both can be reduced. Good optical performance is obtained while suppressing.

  In Numerical Example 5, the product name S-FPL51 is used with a center thickness of 11.8 mm for the third positive lens j3 counted from the object side in the same first lens unit L1, and the chromatic aberration is corrected more favorably. Yes.

  The optical system OL of Numerical Example 6 in FIG. 11 is a wide-angle lens having a focal length of 14 mm. A positive lens j1 made of a trade name K-GFK70 (manufactured by Sumita Optical Glass Co., Ltd.) having anomalous partial dispersion on the image side of the aperture stop SP of the second lens unit L2 constituting the wide-angle lens OL, and a positive made of a UV curable resin. The lens j2 is used.

  The second lens unit L2 of the optical system of Numerical Example 6 is a focus unit, and moves to the object side for focusing when the object distance is shortened.

  In the optical system of Numerical Example 6, a positive lens made of the product name K-GFK70 on the image side from the stop SP of the second lens unit L2 on the image side where the passing position of the paraxial light beam from the optical axis is relatively high. A positive lens j2 made of j1 and UV curable resin is used to mainly correct lateral chromatic aberration.

  The maximum thickness of the positive lens j2 is 1.76 mm, and the center thickness of the positive lens j1 is 2.8 mm. By using a positive lens j1 made of product name K-GFK70 and a positive lens j2 made of UV curable resin on the image side of the stop SP in the same lens group, good optical performance can be obtained while suppressing the thickness and weight of both. ing.

  The optical system OL of Numerical Example 7 in FIG. 13 is a wide-angle lens having a focal length of 14 mm. It consists of a positive lens j1 made of a product name K-GFK70 (manufactured by Sumita Optical Glass Co., Ltd.) having anomalous partial dispersion on the image side of the stop SP of the second lens unit L2 constituting the wide-angle lens OL and N-polyvinylcarbazole. A positive lens j2 is used.

  The second lens unit L2 of the optical system according to Numerical Example 7 is a focus unit, and moves to the object side for focusing when the object distance is shortened.

  In the optical system of Numerical Example 7, a positive lens made of the product name K-GFK70 on the image side from the stop SP of the second lens unit L2 on the image side where the passing position of the paraxial light beam from the optical axis is relatively high. A positive lens j2 made of j1 and N-polyvinylcarbazole is used. This mainly corrects lateral chromatic aberration.

  The maximum thickness of the positive lens j2 is 1.18 mm, and the center thickness of the positive lens j1 is 3.5 mm. By using a positive lens j1 made of the trade name K-GFK70 and a positive lens j2 made of N-polyvinylcarbazole on the image side of the stop SP in the same lens group, good optical performance can be achieved while suppressing both thickness and weight. It has gained.

  The optical system OL of Numerical Example 8 in FIG. 15 is a wide-angle lens with a focal length of 14 mm. A positive lens j1 made of a trade name S-FPL53 (manufactured by OHARA Co., Ltd.) having an anomalous partial dispersion on the image side of the aperture stop SP of the second lens unit L2 constituting the wide-angle lens OL, and 4% of TiO2 fine particles are UV cured resin. A positive lens j2 made of a fine particle dispersed material is used.

  The second lens unit L2 of the optical system of Numerical Example 8 is a focus unit, and moves to the object side for focusing when the object distance is shortened.

In the optical system of Numerical Example 8, a positive lens made of the product name S-FPL53 on the image side from the stop SP of the second lens unit L2 on the image side where the passing position of the paraxial ray from the optical axis is relatively high. The positive lens j2 made of j1 and TiO ₂ fine particles 4% -UV cured resin fine particle dispersed material is used. This mainly corrects lateral chromatic aberration.

The maximum thickness of the positive lens j2 is 0.97 mm, and the center thickness of the positive lens j1 is 3.5 mm. By using the positive lens j1 made of the trade name S-FPL53 and the positive lens j2 made of TiO ₂ fine particles 4% -UV cured resin fine particle dispersed material on the image side of the stop SP in the same lens group, both thickness and weight are used. Good performance is obtained while suppressing

  The optical system OL of Numerical Example 9 in FIG. 17 is a wide-angle lens with a focal length of 14 mm. Fine particle dispersion in which a positive lens j1 made of a product name K-GFK70 having an anomalous partial dispersion and 9% of ITO fine particles are dispersed in N-polyvinylcarbazole on the image side of the aperture stop SP of the second lens unit L2 constituting the wide-angle lens OL. A negative lens j2 made of a material is used.

  The second lens unit L2 of the optical system in Numerical Example 9 is a focus unit, and moves to the object side for focusing when the object distance is shortened.

  In the optical system of Numerical Example 9, the above-described positive lens j1 and the above-described negative lens are disposed on the image side of the aperture SP of the second lens unit L2 on the image side where the passing position of the paraxial ray from the optical axis is relatively high. The lens j2 is used to mainly correct lateral chromatic aberration.

  The maximum thickness of the negative lens j2 is 0.35 mm, and the center thickness of the positive lens j1 is 4.3 mm. By using the positive lens j1 made of the trade name K-GFK70 and the positive lens j2 made of the ITO fine particle 9% -N-polyvinylcarbazole fine particle dispersed material on the image side of the stop SP in the same lens group, both thickness and weight are used. Good optical performance is obtained while suppressing

  Hereinafter, specific numerical data of Numerical Examples 1 to 9 will be shown. In each numerical example, i represents the surface number counted from the object side. Ri is the radius of curvature of the i-th optical surface (i-th surface), Di is the axial distance between the i-th surface and the (i + 1) -th surface, and Ni and νi are the i-th (conditional expression) for the d-line, respectively. The refractive index and the Abbe number of the material of the optical member of the lens (layer) formed of the anomalous partial dispersion material satisfying the above (excluding the lens (layer)). Refractive indexes and Abbe numbers of the lenses j1 and j2 formed of an anomalous partial dispersive material with respect to the d-line are separately indicated as Nj1, Nj2, νj1, and νj2. f is a focal length, Fno is an F number, and ω is a half angle of view.

  Further, the aspherical shape is such that X is the amount of displacement from the surface vertex in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic constant, Let C, D, E ... be the aspheric coefficients of each order,

It is represented by

Note that “E ± XX” in each aspheric coefficient means “× 10 ^{± XX} ”.

In Numerical Examples 3 and 8, lenses made of a solid material dispersed in a TiO ₂ fine particle volume ratio of 10% and 4%, respectively, in a UV curable resin as a host polymer are used. The refractive index of the TiO ₂ fine particle-dispersed material is calculated using the value calculated using the aforementioned Drude equation. In Numerical Examples 4, 5, and 9, lenses made of a solid material in which ITO fine particles are dispersed by 9%, 5%, and 9% by volume in N-polyvinylcarbazole, which is a host polymer, are used. The refractive index of the ITO fine particle dispersed material is calculated using the value calculated using the aforementioned Drude equation.

Table 1 shows optical constant values of optical materials used in Examples 1 to 9 described later and values corresponding to conditional expressions (1), (2), (3), (4), (5), and (6). It is shown in 1. Table 2 shows the optical constant values of each of the UV curable resin, N-polyvinylcarbazole, TiO ₂ and ITO fine particles constituting the fine particle dispersed material.

  Next, an embodiment of a digital still camera (imaging device) using the optical system of the present invention as a photographing optical system will be described with reference to FIG.

In FIG. 19, reference numeral 20 denotes a camera body. Reference numeral 21 denotes a photographing optical system constituted by the optical system of the present invention. Reference numeral 22 denotes a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor that receives a subject image formed by the photographing optical system 21 and is built in the camera body. A memory 23 records information corresponding to the subject image photoelectrically converted by the image sensor 22. Reference numeral 24 is a finder for observing a subject image formed on the solid-state imaging element 22 ( on the photoelectric conversion element) , which is constituted by a liquid crystal display panel or the like.

  Thus, by applying the optical system of the present invention to an image sensor such as a digital still camera, a small-sized image pickup apparatus having high optical performance is realized.

Optical sectional view of the optical system of Example 1 Aberration diagram of optical system of Example 1 Optical sectional view of the optical system of Example 2 Aberration diagram of optical system of Example 2 Optical sectional view of the optical system of Example 3 Aberration diagram of optical system of Example 3 Optical sectional view of the optical system of Example 4 Aberration diagram of optical system of Example 4 Optical sectional view of the optical system of Example 5 Aberration diagram of optical system of Example 5 Optical sectional view of the optical system of Example 6 Aberration diagram of optical system of Example 6 Optical sectional view of the optical system of Example 7 Aberration diagram of optical system of Example 7 Optical sectional view of the optical system of Example 8 Aberration diagram of optical system of Example 8 Optical sectional view of the optical system of Example 9 Aberration diagram of optical system of Example 9 Schematic diagram of main parts of an imaging apparatus of the present invention Explanatory drawing of the paraxial refractive power arrangement of the optical system of the present invention Explanatory drawing of the paraxial refractive power arrangement of the optical system of the present invention

Explanation of symbols

OL optical system j1 refractive optical element j2 refractive optical element L1 first lens group L2 second lens group L3 third lens group L4 fourth lens group L5 fifth lens group SP aperture IP image surface d d line g g line C C line FF line ΔS Sagittal image surface ΔM Meridional image surface

Claims (8)

An optical system having two refracting optical elements j1 and j2 formed of a solid material in which the light incident side and the light exit side are both refractive surfaces at either the front side or the rear side of the point where the optical axis and the paraxial ray of the pupil intersect. Because
The Abbe numbers of the materials of the two refractive optical elements j1 and j2 are νd1 and νd2, the abnormal partial dispersion of the materials of the two refractive optical elements j1 and j2 are ΔθgF1 and ΔθgF2, and the two refractive optical elements j1 and j2 When the focal length is f1 and f2,
0.012 <| ΔθgF1 |
0.012 <| ΔθgF2 |
40 <| νd1-νd2 |
0 <ΔθgF1 / f1 × ΔθgF2 / f2
An optical system characterized by satisfying the following conditions.   The optical system according to claim 1, wherein the two refractive optical elements j1 and j2 are disposed in the same lens group. When the anomalous partial dispersion is ΔθgF and the Abbe number is νd, at least one of the two refractive optical elements is:
0.001 <| ΔθgF | / νd <0.007
The optical system according to claim 1, wherein the following condition is satisfied.   In the optical system, the maximum value of the height from the optical axis through which the light on the paraxial axis passes through the lens surface in front of the point where the optical axis and the pupil paraxial ray intersect is the optical axis and the pupil paraxial ray. An optical system that is larger than the maximum value of the height from the optical axis through which the paraxial light beam passes through the lens surface behind the crossing point, and the two refractive optical elements are in front of the stop The optical system according to claim 1, wherein the optical system is disposed in the lens group.   In the optical system, the height from the optical axis of the paraxial beam passing through the foremost lens surface is behind the intersection of the optical axis and the pupil paraxial beam, and the paraxial beam passes through the lens surface. 2. An optical system having a height smaller than a maximum value from the optical axis, wherein the two refractive optical elements are arranged in a lens group behind the stop. Or the optical system of 3.   The optical system according to any one of claims 1 to 5, wherein at least one of the two refractive optical elements is made of a mixture in which inorganic fine particles are dispersed in a transparent medium.   The optical system according to claim 1, wherein an image is formed on the photoelectric conversion element.   An optical apparatus comprising the optical system according to claim 1.