JP2012022105A - Optical system and optical equipment including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical system easily obtaining high optical performance by carrying out good corrections of various aberrations including chromatic aberration.SOLUTION: An optical system satisfying Lt/ft<1.0 when the whole optical length is Lt and focal distance is ft and including one or more refractive index distribution elements in an optical path has θgF(pmax), θgF(pmin), ΔθgFgi(p1) satisfy the suitably set conditions when the maximum value and the minimum value of partial distribution ratio regarding line g and line F in the medium of the refractive index distribution elements are respectively θgF(pmax), θgF(pmin), the position in the medium for taking a reference refractive ratio in the refractive ratio distribution in the refractive index distribution elements is a reference position P0 and equivalent abnormal dispersibility in a position p1 in the medium that is different from the reference position P0 is ΔθgFgi(p1).

Description

  The present invention relates to an optical system having a refractive index distribution element, and is suitable for optical equipment such as a silver salt photographic camera, a video camera, a digital still camera, a projector, a telescope, and an image reading device.

  2. Description of the Related Art Conventionally, as a long focal length photographing optical system, a so-called telephoto photographing optical system (telephoto lens) including a front lens group having a positive refractive power in order from an object side to an image side and a rear lens group having a negative refractive power. It has been known. In general, in a telephoto lens having a long focal length, the chromatic aberration such as axial chromatic aberration and lateral chromatic aberration tends to deteriorate as the overall system becomes smaller and the focal length increases.

  In recent years, a photographing optical system used in an optical apparatus such as a digital camera or a video camera is required to have high performance and be small and light as a whole. In order to satisfactorily correct chromatic aberrations such as longitudinal chromatic aberration and lateral chromatic aberration while reducing the size of the photographing optical system, it is difficult to use only existing optical materials such as glass. Conventionally, as a means for solving such a problem, a method of correcting aberration using a refractive index distribution element (refractive index distribution lens) in a part of an optical system is known (Patent Document 1). Patent Document 1 discloses an optical system using a refractive index distribution lens that has a large degree of freedom in correcting aberrations and easily corrects chromatic aberration as compared with a lens having a uniform refractive index of a medium.

JP 10-077853 A

  Patent Document 1 discloses an optical system in which chromatic aberration is well corrected including g-line using a radial type gradient index lens. In order to satisfactorily correct chromatic aberration by using a refractive index distribution lens, it is necessary to sufficiently consider the wavelength dispersion characteristic in the refractive action by the refractive index distribution. Here, the chromatic dispersion characteristics of the refractive action by the refractive index distribution are equivalently defined such as the focal length, the Abbe number of the material, and the partial dispersion ratio so that the refractive index distribution lens is treated as equivalent to the lens by the refractive action. In this case, it can be expressed by an equivalent Abbe number, an equivalent partial dispersion ratio, or the like. In addition to the three wavelengths of d-line, C-line, and F-line, the chromatic dispersion characteristics can be improved by taking into account the dispersion characteristics in the refractive action due to the refractive index distribution at four wavelengths including g-line. It becomes important to correct and obtain good optical performance in the visible light region.

  In addition, it is important to appropriately set the characteristics of the material for producing the gradient index lens in order to satisfactorily correct chromatic aberration and obtain high optical performance.

  The present invention relates to an optical system capable of satisfactorily correcting various aberrations including chromatic aberration and easily obtaining high optical performance by appropriately setting the refractive index distribution and materials of the refractive index distribution element, and an optical system having the same The purpose is to provide equipment.

The optical system of the present invention has an optical total length of Lt and a focal length of ft. Lt / ft <1.0
In the optical system having one or more refractive index distribution elements in the optical path, the maximum value and the minimum value of the partial dispersion ratio with respect to the g-line and the F-line in the medium of the refractive index distribution element are respectively θgF (pmax) , ΘgF (pmin), where the position in the medium that takes the reference refractive index of the refractive index distribution in the refractive index distribution element is the reference position P0, the equivalent anomalous dispersion at the position p1 in the medium different from the reference position P0 Is ΔθgFgi (p1) | θgF (pmax) −θgF (pmin) |> 0.02
0.0272 <| ΔθgFgi (p1) | <1.000
It satisfies the following conditional expression.

  According to the present invention, it is possible to obtain an optical system that can satisfactorily correct various aberrations including chromatic aberration and easily obtain high optical performance.

Lens sectional view of Numerical Example 1 Aberration diagram of Numerical Example 1 Lens sectional view of Numerical Example 2 Aberration diagram of Numerical Example 2 Lens sectional view of Numerical Example 3 Aberration diagram of Numerical Example 3 Lens sectional view of Numerical Example 4 Aberration diagram of Numerical Example 4 Lens sectional view of Numerical Example 5 Aberration diagram of Numerical Example 5 Lens sectional view at the wide-angle end in Numerical Example 6 (A) Aberration diagram at the wide-angle end of Numerical Example 6 (b) Aberration diagram at the intermediate position of Numerical Example 6 (c) Aberration diagram at the telephoto end of Numerical Example 6 Lens sectional view of Numerical Example 7 Aberration diagram of Numerical Example 7 Illustration of wavelength characteristics of chromatic aberration coefficient Schematic diagram of main parts of an imaging apparatus of the present invention

Hereinafter, the optical system of the present invention will be described. The optical system of the present invention has an optical total length of Lt and a focal length of ft. Lt / ft <1.0
This is a telephoto lens system that satisfies the above requirements. And it has one or more gradient index elements in the optical path.

  The optical system of the present invention has at least one refractive index distribution element (refractive index distribution lens) having a refractive index distribution in the medium, and specifies the wavelength characteristics of the refractive index distribution element. The optical system of each embodiment is used as an optical system of an optical apparatus such as a digital camera, a silver salt film camera, a digital video camera, a video camera, a telescope, binoculars, a copying machine, and a projector.

  The solid material constituting the gradient index element refers to a solid material in a state where it is applied to an optical system, and the state before being used in an optical system such as during manufacturing is in any state. good. For example, even if it is a liquid material at the time of manufacture, the solid material obtained by curing it corresponds to the solid material as referred to in the present invention.

  The optical system of the present invention corresponds to a so-called telephoto type telephoto lens in which the total optical length (distance from the first lens surface to the image plane) is smaller (shorter) than the focal length. When the focal length of the optical system is ft and the total optical length is Lt, the optical system of the present invention satisfies the following conditional expression.

Lt / ft <1.0 (0)
Preferably 0.45 <Lt / ft <0.95
It is an optical system that satisfies

  The refractive index distribution element of the optical system of the present invention has a refractive index difference depending on the position in the medium (the position in the optical axis direction or the direction perpendicular to the optical axis), thereby giving a phase difference to the incident light. The convergence and diverging effects of light rays such as the positive lens and negative lens of the medium are exhibited.

  Examples of the refractive index distribution in the medium include a radial refractive index distribution having a refractive index distribution in the medium in a direction perpendicular to the optical axis, and an axial refractive index distribution having a refractive index distribution in the medium in the optical axis direction. Etc. In the gradient index element, in addition to refraction at the interface (light incident / exit surface), it is possible to refract light rays in the medium. For this reason, there is a feature that the degree of freedom of aberration correction is larger than that of a lens of a homogeneous medium. Various methods for creating a refractive index profile in a medium have been proposed. For example, an ion exchange method, a sol-gel method, a three-dimensional printing technique, and the like can be given.

  In the ion exchange method, a refractive index distribution is obtained by immersing a medium containing ions capable of ion exchange in a solution and changing the composition ratio of the dopant of the medium by a diffusion action. In the sol-gel method, a sol containing silicon as a main component is prepared, a gel is obtained, and the solution is immersed in a solution to form a concentration distribution on the dopant to give the gel a desired refractive index distribution. A glass body is obtained. In the three-dimensional printing technique, a refractive index distribution is obtained by forming a plurality of layers having different refractive indexes, such as a medium in which the dopant concentration is changed, and providing a refractive index distribution. In these methods, a refractive index distribution is obtained by creating a distribution of a desired composition ratio in a plurality of materials having different refractive indexes in a medium.

  Considering the wavelength dispersion of the refractive index distribution, when there is a similar refractive index distribution for each wavelength, no chromatic aberration occurs as a refractive component in the medium. However, when creating a refractive index distribution by distributing the composition ratios of multiple materials as described above, the refractive index distribution change amount at each wavelength does not become zero, and there exists wavelength dispersion of the refractive index distribution. become. The wavelength dispersion characteristic in the refractive index distribution of the refractive index distribution element in the present invention satisfies the following conditional expression.

| ΘgF (pmax) −θgF (pmin) |> 0.02 (1)
0.0272 <| ΔθgFgi (p1) | <1.000 (2)
It is. Here, the refractive index at the wavelength λ at the position p in the medium is nλ (p), p0 is a position where the reference refractive index of the refractive index distribution is taken, and p1 is a position in the medium different from the position p0. Now, the partial dispersion ratio θgF relating to the g-line and the F ship of the material, the partial dispersion ratio θgd relating to the g-line and the d-line, and the Abbe number are as follows.

  The refractive indexes of the Fraunhofer line for g line (435.8 nm), F line (486.1 nm), d line (587.6 nm), and C line (656.3 nm) are ng, nF, nd, and nC, respectively. To do. At this time, the Abbe number νd for the d line, the partial dispersion ratio θgd for the g line and the d line, and the partial dispersion ratio θgF for the g line and the F line are as follows.

νd = (nd−1) / (nF−nC)
θgd = (ng−nd) / (nF−nC)
θgF = (ng−nF) / (nF−nC)
Accordingly, the refractive indexes of the g-line, the F-line, the d-line, and the C-line at the position P in the medium are sequentially set to ng (P), nF (P), nd (P), and nC (P). The Abbe number is νd (P). Then, the Abbe number νd (P) and the partial dispersion ratios θgd (P) and θgF (P) at the position P are as follows.

νd (p) = {nd (p) −1} / {nF (p) −nC (p)}
θgd (p) = {ng (p) −nd (p)} / {nF (p) −nC (p)}
θgF (p) = {ng (p) −nF (p)} / {nF (p) −nC (p)}
The anomalous dispersion Δθgd for the g-line and the d-line and the anomalous dispersion ΔθgF for the g-line and the F-line are as follows. The partial dispersion ratio of a general optical material changes almost in the same tendency with respect to the change in Abbe number. The standard values θgd0 and θgF0 of the partial dispersion ratio at this time are expressed as follows as a function of the Abbe number νd for the d-line.
θgd0 = −1.687 × 10 ⁻⁷ νd ³ + 5.702 × 10 ⁻⁵ νd ²
-6.603 × 10 ⁻³ νd + 1.462
θgF0 = −1.665 × 10 ⁻⁷ νd ³ + 5.213 × 10 ⁻⁵ νd ²
−5.656 × 10 ⁻³ νd + 0.7278
At this time, the anomalous dispersion means a difference from the standard value. That is, the anomalous dispersions Δθgd and ΔθgF are respectively
Δθgd = θgd−θgd0
ΔθgF = θgF−θgF0
It is expressed.

  Since the refractive index distribution element of the present invention has a refractive index distribution in the medium, the refractive index varies depending on the position p (the position in the optical axis direction or the direction perpendicular to the optical axis) in the medium. Therefore, the Abbe number and the partial dispersion ratio also change depending on the position p.

  In the conditional expression (1), pmax represents a position where the partial dispersion ratio θgF (p) regarding the g-line and the F-line takes the largest value in the medium. pmin represents a position where the partial dispersion ratio θgF (p) regarding the g line and the F line takes the smallest value in the medium. The equivalent partial dispersion ratios θgdgi and θgFgi and the equivalent Abbe number νdgi in the refraction of the medium in the present invention are as follows. In an optical element whose refractive index is uniform in the medium, the light beam is refracted at the interface between the medium and the atmosphere, and the light beam is not refracted in the medium. Since the refractive index of the medium changes depending on the wavelength, chromatic aberration occurs in the light beam refracted by the homogeneous optical element.

  The refracting action is a phenomenon caused by the phase difference of light beams. In a homogeneous optical element, the phase difference is given by changing the shape of the interface between the optical element and the atmosphere. When the optical element is disposed in the air, the refraction action can be considered from the difference in refractive index between the optical element and air. At this time, chromatic dispersion is caused by the difference in refractive action at each wavelength, and the Abbe number relating to the d-line serving as the index is the ratio of the refractive index difference from air when the refractive index of air is 1. It is represented.

  On the other hand, when the medium has a refractive index distribution element having a refractive index distribution, light rays are refracted in the medium in addition to refraction at the interface between the medium and the atmosphere. As described above, chromatic dispersion occurs in refraction at the interface between the medium and the atmosphere. Similarly, chromatic aberration also occurs in refraction in the medium due to chromatic dispersion of the refractive index distribution. The phase difference due to the refractive index distribution in the medium is caused by the difference between the refractive index at the reference position in the medium and the refractive index at the position where the light beam passes. For this reason, the chromatic dispersion in refraction in the medium is the ratio of the difference between the refractive index at the light passing position and the refractive index at the reference position.

  Here, the position where the refractive index serving as a reference in the medium is taken is generally a position on the optical axis in the radial refractive index distribution element. Further, in the axial refractive index distribution element, it is general that the position is closest to the light incident side or light exit side. In the present invention, the position where the refractive index serving as a reference for the radial gradient index element is taken is the position on the optical axis, and the position closest to the light incident side in the axial gradient index element. If the present invention is applicable, the position where the refractive index serving as a reference in the medium of the gradient index element is taken is not limited to the above.

  The chromatic dispersion obtained in this way can be treated equivalently as the chromatic dispersion of the virtual glass when the refraction in the medium is replaced with a virtual glass having a chromatic dispersion characteristic with equal chromatic aberration. That is, the chromatic dispersion in refraction in the medium can be replaced with a virtual refractive lens by using an equivalent Abbe number νdgi and an equivalent partial dispersion ratio θgFgi defined below.

  Let nλ (p0) be the refractive index of the reference position P0 at each wavelength when the medium has a refractive index distribution. At this time, the refractive index difference δnλ (p1) at the position p1 in the medium different from the position p0 is as follows. Furthermore, the equivalent Abbe number νdgi (p1) for the d line, the equivalent partial dispersion ratio θgFgi (p1) for the g line and the F line, and the equivalent partial dispersion ratio θgdgi (p1) for the g line and the d line are expressed as follows.

  Here, regarding the position p1, the refractive index differences in the g, F, d, and C lines are δng (p1), δnF (p1), δnd (p1), and δnC (p1). At the position p0, δng (p0), δnF (p0), δnd (p0), and δnC (p0).

δnλ (p1) = nλ (p1) −nλ (p0)
νdgi (p1) = δnd (p1) / {δnF (p1) −δnC (p1)}
θgFgi (p1) = {δng (p1) −δnF (p1)} / {δnF (p1) −δnC (p1)}
θgdgi (p1) = {δng (p1) −δnd (p1)} / {δnF (p1) −δnC (p1)}
In the refraction of the medium, the equivalent anomalous dispersion ΔθgFgi for the g-line and the F-line and the equivalent anomalous dispersion Δθgdgi for the g-line and the d-line are respectively expressed as follows.

Δθgdgi = θgdgi−θgdgi0
ΔθgFgi = θgFgi−θgFgi0
However, the standard values θgdgi0 and θgFgi0 of the equivalent partial dispersion ratio are functions of the equivalent Abbe number νdgi, and are expressed by the following equations.

θgdgi0 = −1.687 × 10 ⁻⁷ νdgi ³ + 5.702 × 10 ⁻⁵ νdgi ²
-6.603 × 10 ⁻³ νdgi + 1.462
θgFgi0 = −1.665 × 10 ⁻⁷ νdgi ³ + 5.213 × 10 ⁻⁵ νdgi ²
−5.656 × 10 ⁻³ νdgi + 0.7278
A refractive index distribution in which the refractive index changes in the direction perpendicular to the optical axis in the medium is defined as a radial refractive index distribution. At this time, the refractive index at the wavelength λ can be expressed by, for example, the following formula, where the distance r is perpendicular to the optical axis.

  The radial refractive indexes of the g, F, d, and C lines are sequentially set to ngR (r), nFR (r), ndR (r), and nCR (r). At this time, the radial Abbe number νdR for the d line, the partial dispersion ratio θgdR for the g line and the d line, and the radial partial dispersion ratio θgFR for the g line and the F line are expressed by the following equations.

νdR (r) = {ndR (r) −1} / {nFR (r) −nCR (r)}
θgdR (r) = {ngR (r) −ndR (r)} / {nFR (r) −nCR (r)}
θgFR (r) = {ngR (r) −nFR (r)} / {nFR (r) −nCR (r)}
In the radial refractive index distribution, the refractive index on the optical axis is the reference refractive index, and the refractive index difference δnλR (r) in the medium can be expressed by the following equation. The radial refractive index at the distance r at the wavelength λ and the standard value (r = 0) is nλR (r) and nλR (0). At this time, δnλR (r) = nλR (r) −nλR (0)
In addition, when r1 greater than 0 represents an equivalent Abbe number νdgiR (r1) and an equivalent partial dispersion ratio θgFgiR (r1) in the radial refractive index distribution, it is as follows.

The radial refractive index differences of the g, F, d, and C lines at the distance r1 are sequentially set as δngR (r1), δnFR (r1), δndR (r1), and δnCR (r1). At this time,
νdgiR (r1) = δndR (r1) / {δnFR (r1) −δnCR (r1)}
θgFgiR (r1) = {δngR (r1) −δnFR (r1)} / {δnFR (r1) −δnCR (r1)}
θgdgiR (r1) = {δngR (r1) −δndR (r1)} / {δnFR (r1) −δnCR (r1)}
The radial equivalent anomalous dispersion ΔθgFgiR for the g-line and the F-line and the radial equivalent anomalous dispersion ΔθgdgiR for the g-line and the d-line in the refractive index distribution of the medium are respectively expressed as follows.

ΔθgdgiR = θgdgiR−θgdgiR0
ΔθgFgiR = θgFgiR−θgFgiR0
However, the standard values θgdgiR0 and θgFgiR0 of the radial equivalent partial dispersion ratio are functions of the equivalent Abbe number νdgiR, and are expressed as follows.

θgdgiR0 = −1.687 × 10 ⁻⁷ νdgiR ³ + 5.702 × 10 ⁻⁵ νdgiR ² −6.603 × 10 ⁻³ νdgiR + 1.462
θgFgiR0 = −1.665 × 10 ⁻⁷ νdgiR ³ + 5.213 × 10 ⁻⁵ νdgiR ² −5.656 × 10 ⁻³ νdgiR + 0.7278
Assuming that the effective ray radius of the radial gradient index element is rea, radial partial dispersion ratios θgFR (rea) and θgFR for the g-line and the F-line on the distance rea from the optical axis and on the optical axis (distance 0) (standard value). (0) satisfies the following conditional expression.

| ΘgFR (rea) −θgFR (0) |> 0.02 (3)
Further, the equivalent refractive power φgiR of the radial refractive index distribution can be expressed as the following equation, where the thickness of the medium is dgi. The radial refractive index at the standard value at the wavelength λ is N0λR.

φgiR = -2N0λR × dgi
A refractive index distribution in which the refractive index changes in the optical axis direction in the medium is referred to as an axial refractive index distribution. The refractive index at the wavelength λ of the axial refractive index distribution can be expressed by the following formula, where the distance t in the optical axis direction from the point closest to the light incident side in the medium.

  At this time, the axial Abbe number νdA for the d line, the axial partial dispersion ratio θgdA for the g line and the d line, and the axial partial dispersion ratio θgFA for the g line and the F line are set. The axial Abbe number νdA (t), the axial partial dispersion ratio θgdA (t), and the axial partial dispersion ratio θgFA (t) at the distance t in the optical axis direction are expressed by the following equations.

Here, the axial refractive indexes of the g, F, d, and C lines at the distance t in the optical axis direction are sequentially set to ngA (t), nFA (t), ndA (t), and nCA (t). At this time, νdA (t) = {ndA (t) −1} / {nFA (r) −nCA (t)}
θgdA (t) = {ngA (t) −ndA (t)} / {nFA (t) −nCA (t)}
θgFA (t) = {ngA (t) −nFA (t)} / {nFA (t) −nCA (t)}
In the axial refractive index distribution, the refractive index difference δnλA (t) in the medium can be expressed by the following equation. The axial refractive indexes at the distance t at the wavelength λ and the standard value (t = 0) are nλA (t) and nλA (0). At this time, δnλA (t) = nλA (t) −nλA (0)
Further, when the equivalent Abbe number νdgiA (t1) and the equivalent partial dispersion ratio θgdgiA (t1) in the axial refractive index distribution are represented by t1 larger than 0, the following is obtained. The axial refractive index differences in the g, F, d, and C lines at the distance t1 are assumed to be δndA (t1), δnFA (t1), δnCA (t1), and δnCA (t1). At this time, νdgiA (t1) = δndA (t1) / {δnFA (t1) −δnCA (t1)}
θgFgiA (t1) = {δngA (t1) −δnFA (t1)} / {δnFA (t1) −δnCA (t1)}
θgdgiA (t1) = {δngA (t1) −δndA (t1)} / {δnFA (t1) −δnCA (t1)}
In the refraction of the medium, the axial equivalent anomalous dispersion ΔθgFgiA for the g-line and the F-line and the axial equivalent anomalous dispersion ΔθgdgiA for the g-line and the d-line are respectively expressed as follows.

ΔθgdgiA = θgdgiA−θgdgiA0
ΔθgFgiA = θgFgiA−θgFgiA0
However, the standard values θgdgiA0 and θgFgiA0 of the equivalent partial dispersion ratio are functions of the equivalent Abbe number νdgiA, and are defined as follows.

θgdgiA0 = −1.687 × 10 ⁻⁷ νdgiA ³ + 5.702 × 10 ⁻⁵ νdgiA ² −6.603 × 10 ⁻³ νdgiA + 1.462
θgFgiA0 = −1.665 × 10 ⁻⁷ νdgiA ³ + 5.213 × 10 ⁻⁵ νdgiA ² −5.656 × 10 ⁻³ νdgiA + 0.7278
In the medium, when the most light incident side point in the optical axis direction is tobj and the most light emission side point is tig, the axial partial dispersion ratios θgFA (tobj) and θgFA (timg) with respect to g-line and F-line are as follows. Satisfies the conditional expression.

| ΘgFA (tobj) −θgFA (timg) |> 0.02 (4)
Further, the equivalent refractive power φgiA of the axial refractive index distribution can be expressed as the following equation. The axial refractive indexes at the point tobj and the point tigg at the wavelength λ are NλA (tobj) and NλA (timg).
φgiA = {NλA (timg) −1} ÷ rA1− {NλA (tobj) −1} ÷ rA2
However, rA1 is a radius of curvature on the object side of the axial gradient index element, and rA2 is a radius of curvature on the image side.

  As a method of creating an optical element having a refractive index distribution (refractive index distribution element), a case where the medium constituting the optical element is made of a mixture of a solid material and one or more optical materials is considered. In order to create a refractive index distribution, for example, the composition ratio of a solid material and one or more optical materials may be distributed in a medium. When the anomalous dispersibility of the solid material and the optical material with respect to g-line and F-line is ΔθgFs and ΔθgFm, respectively, it is desirable to satisfy the following conditional expressions.

| ΔθgFs−ΔθgFm |> 0.027 (5)
At this time, the Abbe number regarding the d-line of the solid material and the partial dispersion ratio regarding the g-line and the F-line are set to νds and θgFs, respectively. Similarly, the Abbe number for the d-line of the solid material and the partial dispersion ratio for the g-line and the F-line are νdm and θgFm, respectively. Further, it is desirable that the wavelength dispersion characteristic of the gradient index element of the present invention satisfies the following conditional expression. Let νdgiR (r) be the radial equivalent Abbe number at a distance r from the optical axis. Let νdgiA (t) be the axial equivalent Abbe number at a distance t in the optical axis direction. Let the equivalent anomalous dispersion at the position p1 be Δθgdgi (p1). The largest equivalent partial dispersion ratio in the medium is defined as θgFgi (pmaxgi). The smallest equivalent partial dispersion ratio in the medium is defined as θgFgi (pmingi).

| Δθgdgi (p1) |> 0.0250 (6)
| ΘgFgi (pmaxgi) −θgFgi (pmingi) | <0.1 (7)
0 <νdgiR (r) <80 (8)
0 <νdgiA (t) <200 (9)
Next, the technical meaning of each conditional expression described above will be described. Each of the conditional expressions described above defines the wavelength dispersion characteristics of the refractive index distribution in the refractive index distribution element included in the optical system of the present invention. When chromatic dispersion characteristics satisfying conditional expressions (1) and (2) are satisfied, it becomes easy to satisfactorily correct various aberrations of the optical system, particularly chromatic aberration.

  Here, means for satisfactorily correcting the short wavelength region of visible light in the optical system will be described. In a general optical material, the wavelength dispersion has a substantially uniform tendency with respect to the Abbe number as described above. In the present invention, the characteristic is expressed as the standard value θgF0 of the partial dispersion ratio and It is expressed as θgd0 or the like. When correcting aberrations at four wavelengths of g-line in addition to d-line, F-line, and C-line, the absolute values of the above-mentioned anomalous dispersions ΔθgF and Δθgd are large, an optical material having anomalous dispersion is used, etc. Means are conceivable.

  The same applies to the chromatic dispersion of the refractive action due to the refractive index distribution. By using an optical element whose equivalent partial dispersion ratio has anomalous dispersion, it can be used well in a wide wavelength range including the short wavelength range of visible light. It becomes possible to correct chromatic aberration. That is, in the refraction action by the refractive index distribution, the equivalent anomalous dispersion ΔθgFgi takes a positive value when the refractive index change of the g-line is larger than the refractive index changes of other wavelengths, and the conditional expression (2) If the numerical range is satisfied, it is easy to satisfactorily correct chromatic aberration. Further, when the change in the refractive index of the g-line is not significantly different from the change in the refractive index at other wavelengths, the equivalent anomalous dispersion ΔθgFgi takes a negative value and satisfies the numerical range of the conditional expression (2). Thus, it is easy to correct chromatic aberration satisfactorily.

  When the conditional expression (1) is satisfied, the anomalous dispersion having the refractive action by the refractive index distribution becomes more remarkable. This means that the ratio of the refractive index change of the g-line with respect to other wavelengths changes greatly in the medium. Thus, when the partial dispersion θgF (p) at the position p with respect to the g-line and the F-line varies greatly depending on the position in the medium, it becomes easy to satisfactorily correct the secondary spectrum.

  When the refractive index distribution element has a radial refractive index distribution, it is easy to satisfactorily correct chromatic aberration if the partial dispersion ratios θgFR (rea) and θgFR (0) satisfy the conditional expression (3). When the refractive index distribution element has an axial refractive index distribution, it is easy to satisfactorily correct chromatic aberration if the partial dispersion ratios θgFA (tobj) and θgFA (timg) satisfy the conditional expression (4).

  As a method for producing the above gradient index element, there is a method in which a solid material and one or more optical materials are mixed and their composition ratio is changed in a medium. At this time, when a solid material and an optical material that satisfy the conditional expression (5) are selected, it is easy to realize a refractive index distribution that satisfies the conditional expressions (1) and (2).

For example, when the following inorganic oxide fine particles are mixed in a solid material and the mixing ratio is changed in the medium, the above conditional expressions (1) and (2) are satisfied. Examples of the inorganic oxide include TiO ₂ (nd = 2.304, νd = 13.8), Nb ₂ O ₅ (nd = 2.367, νd = 14.0), ITO (nd = 1.8571, νd). = 5.69). Further examples include CrO ₃ (nd = 2.2178, νd = 13.4), BaTiO ₃ (nd = 2.4362, νd = 11.3), and the like.

Among these inorganic oxides, TiO ₂ fine particles and ITO (Indium-Tin-Oxide) fine particles are dispersed in a solid material at an appropriate volume ratio, and when the composition ratio is changed, refraction satisfying the above conditional expression A rate distribution element is obtained. Considering the scattering of the material, the particle size of these fine particles mixed with the solid material is preferably about 100 nm or less, and a dispersant or the like may be added to suppress aggregation. In addition, if the said conditional expression is satisfied, it will not be limited to these manufacturing methods and materials. In the mixture in which the fine particles are dispersed, the refractive index N (λ) at the wavelength λ can be easily calculated by the following equation derived from the well-known Drude equation.

N (λ) = [1 + V {N _m ² (λ) −1} + (1-V) {N ₀ ² (λ) −1}] ^1/2
Here, λ is an arbitrary wavelength, N _m is a refractive index of dispersed fine particles, N ₀ is a refractive index of a medium in which the fine particles are dispersed, such as a polymer, and V is a fraction of a total volume of fine particles with respect to the volume of the medium. Rate. Table 9 shows the refractive index at each wavelength of the medium and the fine particles, the Abbe number νd with respect to the d line, the partial dispersion ratio θgF with respect to the g line and the F line, and the partial dispersion ratio θgd with respect to the g line and the d line.

  In order to satisfactorily reduce chromatic aberration in the visible wavelength band according to the present invention, in addition to satisfying the numerical range of conditional expression (1), the equivalent partial dispersion ratio of g-line and d-line is set to conditional expression (6 ) Is preferably satisfied. When the conditional expression (6) is not satisfied, the chromatic aberration reduction effect in the entire visible range cannot be obtained.

  In the gradient index element of the present invention, if the equivalent anomalous dispersion characteristic varies depending on the passing height of the light beam, it becomes difficult to correct the color spherical aberration, the color coma aberration, and the color image plane characteristic. Therefore, it is preferable to satisfy the numerical range of conditional expression (7).

  In the present invention, a relatively large chromatic aberration is generated in the gradient index element to reduce the chromatic aberration of the entire optical system. Therefore, when the equivalent Abbe number of the gradient index element is low dispersion, the effect of the present invention cannot be obtained unless a large change in refractive power is given. If a large refractive power is applied to the refractive power distribution element, it is difficult to correct chromatic aberration and other aberrations at the same time. Therefore, it is desirable that the equivalent Abbe number has a relatively high dispersion characteristic. That is, it is preferable to satisfy the numerical ranges of conditional expressions (8) to (9).

  In the gradient index element of the optical system of the present invention, the composition ratio of the solid material serving as the medium and the optical material serving as the dispersion is changed depending on the position p in the medium. According to this, the wavelength dispersion characteristic changes depending on the position p in the medium. At this time, the absolute value of the equivalent anomalous dispersion ΔθgFgi (p) of the equivalent partial dispersion ratio relating to refraction in the medium tends to increase as the amount of change in the partial dispersion ratio θgF (p) increases with respect to the position p in the medium. It is in. The larger the absolute value of the equivalent anomalous dispersion ΔθgFgi (p) at the position p, the easier it is to obtain the chromatic aberration correction effect described below.

  In each embodiment, good chromatic aberration correction is facilitated by using a refractive index distribution element having a large or small equivalent partial dispersion ratio as compared with a partial dispersion ratio of a general optical material. In the wavelength dispersion characteristic at the refractive index of the optical material, the Abbe number and the equivalent Abbe number represent the slope of the dispersion characteristic curve, and the partial dispersion ratio and the equivalent partial dispersion ratio represent the degree of bending of the dispersion characteristic curve. In particular, the partial dispersion ratio θgF and the equivalent partial dispersion ratio θgFgi for the g-line and the F-line represent the curve of the dispersion characteristic curve in the short wavelength region in visible light.

  When a graded index element is made of an optical material having general characteristics, it is as follows. In the visible light region, the refractive index distribution on the short wavelength side has a larger change than the refractive index distribution on the long wavelength side, and the equivalent partial dispersion ratio θgFgi, g line and d line for the d line and the equivalent Abbe number νdgi, g line and F line Each equivalent partial dispersion ratio θgdgi for the line takes a positive value. For this reason, as the dispersion characteristic curve (refractive index characteristic with respect to wavelength) becomes shorter, the change in the refractive index distribution with respect to the change in wavelength increases. In an optical material having general characteristics, the partial dispersion ratio changes almost linearly in the low dispersion region with respect to the Abbe number, and the degree of change tends to increase as the dispersion increases. What deviates from such a distribution is an optical material having anomalous dispersion.

  An optical system part GNL using a refractive index distribution element with a large equivalent partial dispersion ratio, an optical system part GL using a refractive index distribution element with a small equivalent partial dispersion ratio, and a refractive index whose partial dispersion ratio is a general value. The chromatic aberration of the optical system constituted by the refractive optical system portion G using the distribution element will be described.

  In FIG. 15, a wavelength characteristic curve of a chromatic aberration coefficient (hereinafter also referred to as a chromatic aberration coefficient curve) in a state in which the chromatic aberration is corrected to some extent by using the refractive optical system portion G as a partial system is indicated by a broken line G. The corrected curve (solid line GE) shows a chromatic aberration coefficient curve when the chromatic aberration is corrected by introducing the optical system parts GNL and GL into the refractive optical system part G.

  In general, a chromatic aberration coefficient curve in an optical system in which chromatic aberration is corrected often balances chromatic aberration in a state in which a bend is left on the short wavelength side as shown by a broken line G. It is difficult to correct chromatic aberration better using only the material. When the optical system part GNL is introduced to such a refractive optical system part G and appropriate power is given, the inclination of the chromatic aberration coefficient changes around the design reference wavelength. At this time, since the equivalent partial dispersion ratio of the optical system portion GNL is larger than that of a general optical material, the change of the chromatic aberration coefficient curve on the short wavelength side becomes larger. At this time, if the inclination of the chromatic aberration coefficient curve generated in the optical system portion GNL is appropriately corrected, the bending in the short wavelength region of the refractive optical system portion G is canceled, and the chromatic aberration is improved in a wide wavelength region such as the curve GE. It can be corrected.

  The optical system portion GL is composed of an optical system having a smaller equivalent partial dispersion ratio than a general optical material. For this reason, the chromatic aberration coefficient curve is relatively linear. At this time, if the power of the refractive optical system portion G is relaxed and appropriate power is given to the optical system portion GL, the bending of the chromatic aberration coefficient curve in the short wavelength region can be relaxed. According to this, it is possible to correct chromatic aberration satisfactorily in a region including a short wavelength region in visible light.

  The optical element (refractive index distribution element) of the present invention corrects various aberrations including chromatic aberration in combination with a general optical material. For this reason, it is necessary for aberration correction that the equivalent partial dispersion ratio has anomalous dispersion, but if the anomalous dispersion is too large, it becomes difficult to correct chromatic aberration.

  When a lens (an optical element) having characteristics significantly different from those of general optical materials is used, the change in wavelength-dependent characteristics of the chromatic aberration coefficient is particularly large. In order to correct the large change and correct the chromatic aberration, it is necessary to greatly change the power of other lenses. At this time, if the power is greatly changed, the spherical aberration, the coma aberration, the astigmatism, and the like are greatly affected, so that it is difficult to correct the aberration. For this reason, if the numerical range of the conditional expression (1) regarding the wavelength dispersion of the refractive index distribution element is set to the following range, chromatic aberration can be corrected more satisfactorily.

0.020 <| θgF (pmax) −θgF (pmin) | <0.800 (1a)
Further, from the viewpoint of aberration correction, it is more desirable to set the numerical range of (1a) to the range shown below.
0.030 <| θgF (pmax) −θgF (pmin) | <0.750 (1b)
More preferably, the numerical range of (1b) is set to the following range.
0.040 <| θgF (pmax) −θgF (pmin) | <0.700 (1c)
If the numerical range of the conditional expression (2) regarding the equivalent partial dispersion ratio of the g-line and the F-line in the refraction of the medium of the gradient index element is set to the following range, chromatic aberration can be corrected more satisfactorily. .

0.0272 <| ΔθgFgi (p1) | <0.980 (2a)
Further, from the viewpoint of aberration correction, it is more desirable to set the numerical range of (2a) to the range shown below.
0.050 <| ΔθgFgi (p1) | <0.900 (2b)
More preferably, the numerical range of (2b) is set to the following range.
0.080 <| ΔθgFgi (p1) | <0.800 (2c)
If the equivalent partial dispersion ratio of the g-line and d-line in the refraction of the medium of the gradient index element satisfies the following numerical range, chromatic aberration can be corrected more satisfactorily.
0.025 <| Δθgdgi (p1) | <1.000 (6a)
More preferably, the numerical range of (6a) is set to the following range.
0.050 <| Δθgdgi (p1) | <0.900 (6b)
More preferably, the numerical range of (6b) is set to the following range.
0.080 <| Δθgdgi (p1) | <0.800 (6c)
If the equivalent partial dispersion ratio of the g-line and the F-line in the refraction of the medium of the gradient index element is in the following numerical range, it becomes possible to correct chromatic aberration more satisfactorily.

| ΘgFgi (pmaxgi) −θgFgi (pmingi) | <0.09 (7a)
More preferably, the numerical range of (7a) is set to the range shown below.
| ΘgFgi (pmaxgi) −θgFgi (pmingi) | <0.08 (7b)
If the numerical range of the conditional expression (3) regarding the partial dispersion ratio of the g-line and the F-line regarding the radial refractive index distribution is set to the following range, chromatic aberration can be corrected more satisfactorily.
0.020 <| θgFR (rea) −θgFR (0) | <0.800 (3a)
More preferably, the numerical range of (3a) is set to the following range.
0.024 <| θgFR (rea) −θgFR (0) | <0.750 (3b)
More preferably, the numerical range of (3b) is set to the range shown below.
0.028 <| θgFR (rea) −θgFR (0) | <0.700 (3c)
If the equivalent Abbe number of the d-line in the radial refractive index distribution is in the following numerical range, chromatic aberration can be corrected more satisfactorily.

0 <νdgiR (r) <60 (8a)
More preferably, the numerical range of (8a) is set to the following range.
0 <νdgiR (r) <40 (8b)
If the partial dispersion ratio of the g-line and the F-line with respect to the axial refractive index distribution is set within the following range, chromatic aberration can be corrected more satisfactorily.
0.020 <| θgFA (tobj) −θgFA (timg) | <0.800 (4a)
More preferably, the numerical range of (4a) is set to the following range.
0.030 <| θgFA (tobj) −θgFA (timg) | <0.750 (4b)
More preferably, the numerical range of (4b) is set to the range shown below.
0.050 <| θgFA (tobj) −θgFA (timg) | <0.700 (4c)
If the equivalent Abbe number of the d line in the axial refractive index distribution is in the following numerical range, chromatic aberration can be corrected more satisfactorily.

0 <νdgiA (t) <100 (9a)
More preferably, the numerical range of (9a) is set to the range shown below.
0 <νdgiA (t) <60 (9b)
More preferably, the numerical range of (9b) is set to the following range.
0 <νdgiA (t) <40 (9c)
In each embodiment, a refractive index distribution element that satisfies the conditional expressions (1) and (2) is applied in the optical system.

  An optical element composed of these refractive index distribution elements may have an aspheric refracting surface, which makes it easy to correct chromatic aberration flare such as chromatic spherical aberration. In addition, if a boundary surface is formed by these refractive index distribution elements, an atmosphere such as air, or an optical material having a large refractive index difference, the chromatic aberration can be changed relatively greatly by a slight change in the curvature of the boundary surface. Correction of chromatic aberration becomes easy.

The optical system of the present invention is an optical system that satisfies the following conditional expression (10), and examples thereof include a telephoto type optical system used for a telephoto lens and an optical system such as a telephoto zoom lens. In the present invention, the refractive power of the entire optical system is set to φt. Let the equivalent radial refractive power of the gradient index element be φgiR. In this case, it is desirable to satisfy the following conditional expression.
0.001 <| φgiR / φt | <0.4 (10)
If the lower limit of conditional expression (10) is not reached, it is difficult to sufficiently obtain the chromatic aberration correction effect of the gradient index element. When the value exceeds the upper limit, the influence of various aberrations other than chromatic aberration generated in the gradient index element becomes large, and it is difficult to satisfactorily correct the various aberrations as the entire optical system. If conditional expression (10) is preferably set to the following numerical range, chromatic aberration can be corrected more satisfactorily.

0.003 <| φgiR / φt | <0.39 (10a)
More preferably, the numerical range of (10a) is set to the following range.
0.005 <| φgiR / φt | <0.38 (10b)
In addition, the equivalent axial refractive power of the gradient index element is φgiA. In this case, it is desirable to satisfy the following conditional expression.

0.001 <| φgiA / φt | <0.4 (11)
If the lower limit of conditional expression (11) is not reached, it is difficult to sufficiently obtain the chromatic aberration correction effect of the gradient index element. When the value exceeds the upper limit, the influence of various aberrations other than chromatic aberration generated in the gradient index element becomes large, and it is difficult to satisfactorily correct the various aberrations as the entire optical system. If conditional expression (11) is preferably set to the following numerical range, chromatic aberration can be corrected more satisfactorily.
0.003 <| φgiA / φt | <0.39 (11a)
More preferably, the numerical range of (11a) is set to the range shown below.
0.005 <| φgiA / φt | <0.38 (11b)
Specific examples of the optical system using the optical element of the present invention will be described below.

  FIG. 1 is a lens cross-sectional view of an optical system according to Example 1 of the present invention. 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 at the wide-angle end (short focal length end) of the optical system according to Example 6 of the present invention. FIGS. 12A, 12B, and 12C are aberration diagrams when the optical system of Example 6 is focused on an object at infinity at the wide-angle end, the intermediate zoom position, and the telephoto end (long focal length end), respectively. It is. FIG. 13 is a lens cross-sectional view of the optical system according to Example 7 of the present invention. FIG. 14 is an aberration diagram when the optical system of Example 7 is focused on an object at infinity.

  The optical system of each embodiment is a photographic lens system used in an imaging apparatus such as a video camera, a digital camera, or a silver salt film camera. In the lens cross-sectional view, the left side is the object side (front), and the right side is the image side (rear). When the optical system of each embodiment is used as a projection lens such as a projector, the left side is a screen and the right side is a projected image. In the lens cross-sectional view, OL is an optical system. i indicates the order of the lens groups from the object side, and Li is the i-th lens group. SP is an aperture stop. IP is an image plane. When used as a photographing lens for a video camera or a digital still camera, the imaging surface of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor is used. A photosensitive surface corresponding to the film surface is placed. Ggij (j = 1, 2, 3,...) Represents a lens having a refractive index distribution.

  The optical system of each embodiment includes one or more lenses having the refractive index distribution described above. In the aberration diagrams, d, g, C, and F are d-line, g-line, C-line, and F-line, respectively. ΔM and ΔS are a meridional image plane and a sagittal image plane. Lateral chromatic aberration is represented by the g-line. ω is a half angle of view, and Fno is an F number.

  1 includes a first lens unit L1 having a positive refractive power that does not move during focusing, a second lens unit L2 having a negative refractive power that moves for focusing, and a focus. The third lens unit L3 has a positive refractive power that does not move. The optical system OL is a reduction type imaging optical system that forms an inverted one-time image.

The optical system of Example 1 is a telephoto lens having a focal length of 392 mm and a telephoto ratio (a value obtained by dividing the length along the optical axis direction from the first lens surface to the image plane by the focal length) 0.71. In Example 1, a refractive index distribution lens Ggi1 in which TiO ₂ fine particles are dispersed in the UV curable resin 1 by changing the composition ratio is used for the first lens unit L1. The refractive index distribution lens included in the first lens group is a radial refractive index distribution lens whose refractive index changes in a direction perpendicular to the optical axis. The volume ratio of the TiO ₂ fine particles to the UV curable resin 1 is a mixture in which the maximum is 8.05% and the minimum is 0.87%. The composition ratio of the TiO ₂ fine particles decreases in the radial direction from the optical axis of the gradient index lens Ggi1. For this reason, in the gradient index lens Ggi1, the partial dispersion ratio θgF regarding the g-line and the F-line takes the maximum value on the optical axis and becomes the minimum value at the effective diameter position (outermost position). The equivalent partial dispersion ratio for the g-line and the F-line has a minimum value on the optical axis and a maximum value at the effective diameter position.

  In the gradient index lens Ggi1 applied to the first embodiment, the refractive power of the medium has a positive refractive power, and the equivalent partial dispersion ratio in the g-line and the F-line is larger than that of a general optical material. . The optical system OL of Example 1 has a telephoto type power arrangement in which the combined refractive power of the object side lens units L1 and L2 is positive and the refractive power of the image side lens unit L3 is negative. In the first embodiment, the refractive index distribution lens Ggi1 of the present invention is attached to the first lens unit L1 in front of the aperture stop SP, on the object side of the aperture stop SP, where the paraxial axial ray passing position is relatively high. Arrangement corrects various aberrations, particularly chromatic aberrations.

  The optical system OL of Embodiment 2 of the present invention shown in FIG. 3 includes a first lens unit L1 having a positive refractive power that does not move during focusing, a second lens unit L2 having a negative refractive power that moves for focusing, and a focus. The third lens unit L3 has a positive refractive power that does not move. The optical system OL is a reduction type imaging optical system that forms an inverted one-time image.

The optical system of Example 2 is a telephoto lens having a focal length of 392 mm and a telephoto ratio of 0.71. In Example 2, a refractive index distribution lens Ggi1 in which TiO ₂ fine particles are dispersed in the UV curable resin 1 by changing the composition ratio is used for the first lens unit L1. This refractive index distribution lens Ggi1 is a radial refractive index distribution lens whose refractive index changes in a direction perpendicular to the optical axis. The volume ratio of the TiO ₂ fine particles to the UV curable resin 1 is a mixture in which the maximum is 8.05% and the minimum is 0.00%. The composition ratio of the TiO ₂ fine particles decreases in the radial direction from the optical axis of the gradient index lens Ggi1. For this reason, in the gradient index lens 1Ggi1, the partial dispersion ratio θgF regarding the g-line and the F-line takes the maximum value on the optical axis and becomes the minimum value at the effective diameter position. The equivalent partial dispersion ratio for the g-line and the F-line has a minimum value on the optical axis and a maximum value at the effective diameter position.

  In the gradient index lens Ggi1 applied to the second embodiment, the refractive power of the medium has a positive refractive power, and the equivalent partial dispersion ratio in the g-line and the F-line is larger than that of a general optical material. . The optical system OL of Example 2 has a telephoto type power arrangement in which the combined refractive power of the object side lens units L1 and L2 is positive and the refractive power of the image side lens unit L3 is negative. In the second embodiment, the refractive index distribution lens Ggi1 of the present invention is provided on the first lens unit L1 in front of the aperture stop SP, on the object side of the aperture stop SP, where the paraxial axial ray passing position is relatively high. Arrangement corrects various aberrations, particularly chromatic aberrations.

  The optical system OL according to the third embodiment of the present invention shown in FIG. 5 includes a first lens unit L1 having a positive refractive power and a second lens unit L2 having a negative refractive power with the widest air gap therebetween. The optical system OL is a reduction type imaging optical system that forms an inverted one-time image. The optical system OL of Example 3 is a telephoto lens having a focal length of 200 mm and a telephoto ratio of 0.90. In Example 3, a refractive index distribution lens Ggi1 in which ITO fine particles are dispersed in the acrylic resin 1 by changing the composition ratio is used for the first lens unit L1.

  This refractive index distribution lens Ggi1 is a radial refractive index distribution lens whose refractive index changes in a direction perpendicular to the optical axis. The volume ratio of ITO fine particles to the acrylic resin 1 is a mixture in which a maximum of 12.06% and a minimum of 0.00% are dispersed. The composition ratio of the ITO fine particles increases in the radial direction from the optical axis of the gradient index lens Ggi1. For this reason, in the gradient index lens Ggi11, the partial dispersion ratio θgF regarding the g-line and the F-line takes the maximum value on the optical axis and becomes the minimum value at the effective diameter position. The equivalent partial dispersion ratio for the g-line and the F-line has a maximum value on the optical axis and a minimum value at the effective diameter position.

  The refractive index distribution lens Ggi1 applied to the third embodiment has a negative refractive power in the medium, and the equivalent partial dispersion ratio in the g-line and the F-line is smaller than that of a general optical material. . The optical system OL of Example 3 has a telephoto type power arrangement in which the refractive power of the lens unit L1 on the object side is positive and the refractive power of the lens unit L2 on the image side is negative. In Example 3, the refractive index distribution lens Ggi1 of the present invention is disposed in the first lens unit L1 in which the paraxial axial ray passing position is relatively high at the aperture stop SP position, thereby causing various aberrations, particularly chromatic aberration. Corrected well.

7 includes a first lens unit L1 having a positive refractive power that does not move during focusing, a second lens unit L2 having a negative refractive power that moves for focusing, and a focus. The third lens unit L3 has a positive refractive power that does not move. The optical system OL is a reduction type imaging optical system that forms an inverted one-time image. The optical system OL of Example 4 is a telephoto lens having a focal length of 294 mm and a telephoto ratio of 0.815. In Example 4, a refractive index distribution lens Ggi1 in which TiO ₂ fine particles are dispersed in the UV curable resin 1 while changing the composition ratio is used for the first lens unit L1.

This refractive index distribution lens Ggi1 is a radial refractive index distribution lens whose refractive index changes in a direction perpendicular to the optical axis. The volume ratio of the TiO ₂ fine particles to the UV curable resin 1 is a mixture in which the maximum is 1.00% and the minimum is 0.24%. The composition ratio of the TiO ₂ fine particles decreases in the radial direction from the optical axis of the gradient index lens Ggi1. For this reason, in the gradient index lens Ggi1, the partial dispersion ratio θgF regarding the g-line and the F-line takes the maximum value on the optical axis and becomes the minimum value at the effective diameter position. The equivalent partial dispersion ratio for the g-line and the F-line has a minimum value on the optical axis and a maximum value at the effective diameter position.

  In the gradient index lens Ggi1 applied to the fourth embodiment, the refractive power of the medium has a positive refractive power, and the equivalent partial dispersion ratio in the g-line and the F-line is larger than that of a general optical material. . The optical system OL of Example 4 has a telephoto type power arrangement in which the combined refractive power of the object side lens units L1 and L2 is positive and the refractive power of the image side lens unit L3 is negative. In Example 4, the refractive index distribution lens Ggi1 of the present invention is disposed on the first lens unit L1 in front of the aperture stop SP, on the object side of the aperture stop SP, in which the paraxial axial ray passing position is relatively high. Arrangement corrects various aberrations, particularly chromatic aberrations.

The optical system OL according to the fifth embodiment of the present invention shown in FIG. 9 includes a first lens unit L1 having a positive refractive power that does not move during focusing, a second lens unit L2 having a negative refractive power that moves for focusing, and a focus. The third lens unit L3 has a positive refractive power that does not move. The optical system OL is a reduction type imaging optical system that forms an inverted one-time image. The optical system OL of Example 5 is a telephoto lens having a focal length of 294 mm and a telephoto ratio of 0.816. In Example 5, a refractive index distribution lens Ggi1 in which TiO ₂ fine particles are dispersed in the inorganic glass 1 by changing the composition ratio is used for the first lens unit L1. This inorganic glass 1 is an optical material having an anomalous dispersion having a partial dispersion ratio larger than that of a normal glass material. If the refractive index distribution is created by dispersing fine particles with anomalous dispersion in such an optical material having anomalous dispersion, the equivalent partial dispersion ratio is anomalous dispersion rather than being dispersed in a material having general dispersion characteristics. It is easy to express sexual characteristics.

This refractive index distribution lens Ggi1 is a radial refractive index distribution lens whose refractive index changes in a direction perpendicular to the optical axis. The volume ratio of TiO ₂ fine particles to the inorganic glass 1 is a mixture in which the maximum is 10.00% and the minimum is 0.70%. The composition ratio of the TiO ₂ fine particles decreases in the radial direction from the optical axis of the gradient index lens Ggi1. For this reason, in the gradient index lens Ggi1, the partial dispersion ratio θgF regarding the g-line and the F-line takes the maximum value on the optical axis and becomes the minimum value at the effective diameter position. The equivalent partial dispersion ratio for the g-line and the F-line has a minimum value on the optical axis and a maximum value at the effective diameter position.

  In the gradient index lens Ggi1 applied to the fifth embodiment, the refractive power of the medium has a positive refractive power, and the equivalent partial dispersion ratio in the g-line and the F-line is larger than that of a general optical material. . The optical system OL of Example 5 has a telephoto power arrangement in which the combined refractive power of the object side lens units L1 and L2 is positive and the refractive power of the image side lens unit L3 is negative. In the fifth embodiment, the refractive index distribution lens Ggi1 of the present invention is attached to the first lens unit L1 in front of the aperture stop SP, in which the paraxial axial ray passing position is relatively higher on the object side than the aperture stop SP. Arrangement corrects various aberrations, particularly chromatic aberrations.

  The optical system OL of Embodiment 6 of the present invention shown in FIG. 11 includes, in order from the object side to the image side, a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a positive refractive power. The third lens unit L3 includes a fourth lens unit L4 having a positive refractive power. The optical system OL of the present embodiment is a zoom lens having a four-group configuration with a zoom ratio of about 15.4 times. The arrows in FIG. 11 indicate the movement trajectory of each lens unit during zooming from the wide-angle end to the telephoto end. During zooming, the lens groups move so that the distance between the lens groups changes. The fourth lens unit L4 moves in the optical axis direction for focusing. This optical system is a reduction type imaging optical system that forms an inverted image once.

  In Example 6, the gradient index lens Ggi1 is applied to the first lens unit L1. In the gradient index lens Ggi1, ITO fine particles are dispersed in the UV curable resin 1 while changing the composition ratio. The refractive index distribution lens Ggi1 is a radial refractive index distribution lens whose refractive index changes in a direction perpendicular to the optical axis. In the gradient index lens Ggi1, the volume ratio of the ITO fine particles to the UV curable resin 1 is dispersed by 3.14% at the maximum and 0.0% by the minimum. The composition ratio of the ITO fine particles increases in the radial direction from the optical axis. For this reason, in the gradient index lens Ggi1, the partial dispersion ratio θgF regarding the g-line and the F-line takes the maximum value on the optical axis and becomes the minimum value at the effective diameter position. The equivalent partial dispersion ratio for the g-line and the F-line has a maximum value on the optical axis and a minimum value at the effective diameter position.

  The refractive index distribution lens Ggi1 applied to Example 6 has a curved surface shape, is tightly bonded between two optical elements, and has refractive power at the boundary between the atmosphere and the refractive index distribution lens Ggi1. The refractive power of the medium has a negative refractive power. The equivalent partial dispersion ratio for g-line and F-line is small compared to general optical materials. In the sixth embodiment, among the lens groups constituting the zoom lens, the object-side first lens beam on the object side with respect to the aperture stop SP and the passing position from the optical axis of the paraxial-axis light beam is relatively high at the telephoto end. A refractive index distribution lens Ggi1 is arranged in one lens unit L1. As a result, various aberrations, particularly chromatic aberration, are corrected well.

  The optical system OL of Embodiment 7 of the present invention shown in FIG. 13 includes a first lens unit L1 having a positive refractive power that does not move during focusing, a second lens unit L2 having a negative refractive power that moves for focusing, and a focus. The third lens unit L3 has a negative refractive power that does not move. This optical system is a reduced type imaging optical system that forms an inverted one-time image. The optical system OL of Example 7 is a telephoto lens having a focal length of 294 mm and a telephoto ratio of 0.816. In Example 7, a refractive index distribution lens Ggi1 in which ITO fine particles are dispersed in the UV curable resin 2 while changing the composition ratio is used for the first lens unit L1.

  The refractive index distribution lens Ggi1 is an axial refractive index distribution lens whose refractive index changes in the optical axis direction. The volume ratio of ITO fine particles to the UV curable resin 1 is a mixture in which the maximum is 9.00% and the minimum is 3.33%. The composition ratio of the ITO fine particles decreases from the object side to the image side in the optical axis direction of the gradient index lens Ggi1. In the gradient index lens Ggi1, the partial dispersion ratio θgF for the g-line and the F-line takes the minimum value on the most object side and the maximum value on the most image side. The equivalent partial dispersion ratio for the g-line and the F-line takes the minimum value on the most object side and the maximum value on the most image side. Further, the refractive power of the medium has a positive refractive power, and the equivalent partial dispersion ratio in the g-line and the F-line is larger than that of a general optical material.

  The optical system OL of Example 7 has a telephoto type power arrangement in which the refractive power of the lens unit L on the object side from the stop SP is positive and the combined refractive power of the lens units L2 and L3 on the image side is negative. Yes. In the seventh embodiment, the refractive index distribution lens Ggi1 of the present invention is attached to the first lens unit L1 in front of the aperture stop SP, where the paraxial axial ray passing position is relatively higher on the object side than the aperture stop SP. Arrangement corrects various aberrations, particularly chromatic aberrations.

  In the following, specific numerical data is shown for numerical examples corresponding to the respective examples. In each numerical example, i indicates the surface number counted from the object side, for example, Ri is the radius of curvature of the i-th optical surface (i-th surface), and Di is the i-th surface and the (i + 1) -th surface. Is the on-axis spacing between Ndi and νdi represent the refractive index and Abbe number of the material of the i-th optical member with respect to the d-line, respectively. When the i-th optical member is a refractive index distribution lens, it is expressed as Ngi and νdgi, and the wavelength dispersion of the refractive index distribution is described separately. 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, B, When C, D, E... Are the aspheric coefficients of the respective orders,

Represented by Note that “E ± XX” in each numerical value means “× 10 ^{± XX} ”. Table 1-a shows the correspondence between conditional expression (0), conditional expression (1) to conditional expression (10), and each example. The material characteristics of the refractive index distribution of each example are shown in Table 1-a. Table 1-b shows the refractive index of the optical material used in the gradient index lens of the present invention, the Abbe number, the partial dispersion ratio, and the like for the d-line, g-line, C-line, and F-line. Moreover, it shows in Table 1-a about the material characteristic of the refractive index distribution of each Example. In the embodiment of the present invention, the refractive index distribution is approximated by the following equation.

The approximate expression of the refractive index distribution is not limited to the above expression, and any approximate expression can be used. In each numerical example, as a refractive index distribution characteristic, a coefficient of an approximate expression of a refractive index distribution in d line, g line, C line, F line, and e line (546.1 nm) is described.

(Numerical example 1)
Surface data surface number rd nd νd Effective diameter
1 129.772 6.45 1.85026 32.3 95.35
2 266.122 3.75 Ngi νdgi 94.79
3 * 285.266 9.52 1.51633 64.1 93.62
4 -463.735 1.03 92.41
5 84.422 9.64 1.51633 64.1 82.72
6 290.490 3.69 81.33
7 -1311.268 3.00 1.84666 23.8 81.09
8 121.786 13.54 75.93
9 70.407 9.00 1.51823 58.9 68.85
10 389.159 0.15 67.87
11 67.059 4.00 1.84666 23.8 62.00
12 44.629 (variable) 55.87
13 350.423 4.00 1.62041 60.3 47.88
14 92.021 (variable) 45.44
15 (Aperture) ∞ 18.79 38.86
16 105.523 1.50 1.88300 40.8 34.67
17 53.252 4.80 1.53172 48.8 34.16
18 -185.409 0.15 34.09
19 29.081 5.38 1.51742 52.4 32.90
20 140.883 1.50 1.84666 23.8 32.22
21 32.112 11.30 30.04
22 -109.675 1.80 1.88300 40.8 29.57
23 73.404 1.74 29.96
24 146.084 8.50 1.72825 28.5 30.53
25 -23.906 1.50 1.69350 53.2 30.99
26 614.184 41.55 32.49
27 102.407 6.00 1.62588 35.7 49.48
28 -209.813 64.82 49.53
Image plane ∞

Aspheric data 3rd surface
K = 4.50679e-001 B = 2.43864e-009 C6 = 2.08439e-013 D = -2.88363e-016

Various data focal length 392.00
F number 4.12
Angle of View 3.15
Statue height 21.64
Total lens length 279.32
BF 64.82

Object distance infinity 3500 20000
d12 19.82 65.01 22.12
d14 22.19 7.00 19.90

Refractive index distribution characteristic second surface g line F line e line d line C line
Nr0 1.70689 1.68248 1.66534 1.65774 1.64896
Nr2 -6.5550e-05 -5.8659e-05 -5.4049e-05 -5.2117e-05 -4.9940e-05
Nr4 -1.4459e-09 -1.1583e-09 -9.8420e-10 -9.1570e-10 -8.4154e-10

(Numerical example 2)
Surface data surface number rd nd νd Effective diameter
1 128.451 6.94 1.84666 23.9 95.15
2 156.124 12.56 1.51823 58.9 93.37
3 -442.862 1.10 92.53
4 87.145 9.73 1.51823 58.9 84.45
5 254.667 3.80 82.82
6 * -3540.011 3.38 Ngi νdgi 82.60
7 -972.205 4.50 1.84666 23.9 81.00
8 124.599 18.79 75.56
9 70.393 9.00 1.51742 52.4 67.74
10 404.946 0.15 66.73
11 69.299 4.00 1.84666 23.9 61.62
12 46.162 (variable) 55.94
13 259.328 3.92 1.48749 70.2 48.00
14 87.025 (variable) 45.64
15 (Aperture) ∞ 10.87 36.74
16 111.588 1.50 1.84666 23.9 33.31
17 39.069 5.66 1.60342 38.0 32.74
18 -237.446 0.15 32.70
19 30.846 5.63 1.51742 52.4 32.00
20 170.638 1.50 1.88300 40.8 31.09
21 40.557 9.70 29.58
22 -356.827 1.80 1.88300 40.8 28.79
23 66.858 2.36 28.69
24 134.079 7.28 1.69895 30.1 29.26
25 -26.473 2.30 1.65100 56.2 29.48
26 81.609 31.68 30.12
27 91.787 6.00 1.59551 39.2 42.78
28 -336.666 64.82 42.92
Image plane ∞

Aspheric data 6th surface
K = 1.96971e + 003 B = -1.08101e-008 C = 2.94558e-012 D = -9.50457e-017

Various data focal length 392.00
F number 4.12
Angle of View 3.16
Statue height 21.64
Total lens length 279.32
BF 64.82

Object distance infinity 3500 20000
d12 20.66 43.21 23.99
d14 29.55 7.00 26.22

Refractive index distribution characteristic 6th surface g-line F-line e-line d-line C-line
Nr0 1.70689 1.68248 1.66534 1.65774 1.64896
Nr2 -9.4392e-05 -8.4470e-05 -7.7831e-05 -7.5049e-05 -7.1914e-05
Nr4 -2.9983e-09 -2.4019e-09 -2.0408e-09 -1.8988e-09 -1.7450e-09

(Numerical Example 3)
Surface data surface number rd nd νd Effective diameter
1 (Aperture) ∞ 1.00 1.51633 64.1 34.67
2 ∞ 0.34 Ngi νdgi 34.92
3 ∞ 1.00 1.51633 64.1 34.88
4 ∞ 0.50 34.74
5 74.315 3.48 1.62041 60.3 34.69
6 -645.547 2.04 34.51
7 -245.117 1.62 1.80518 25.4 34.32
8 -7464.930 109.88 34.32
9 -38.621 1.50 1.51742 52.4 33.96
10 564.424 0.20 35.83
11 147.671 3.47 1.88300 40.8 36.39
12 -193.683 54.98 36.62
Image plane ∞

Various data Object distance Infinity focal length 200.00
F number 5.77
Angle of View 6.18
Statue height 21.64
Total lens length 180.00
BF 54.98

Refractive index distribution characteristic second surface g line F line e line d line C line
Nr0 1.50279 1.49774 1.49374 1.49171 1.48917
Nr2 1.9572e-04 1.7818e-04 1.6006e-04 1.4837e-04 1.2844e-04
Nr4 -1.2065e-08 -1.0079e-08 -8.1943e-09 -7.0728e-09 -5.3389e-09

(Numerical example 4)
Surface data surface number rd nd νd Effective diameter
1 115.069 9.56 1.48749 70.2 71.20
2 -255.189 14.61 70.91
3 * 155.575 9.00 Ngi νdgi 61.72
4 698.100 2.57 58.88
5 -363.361 5.15 1.80518 25.4 58.41
6 195.114 10.58 56.29
7 59.814 7.57 1.67790 55.3 53.01
8 559.784 0.15 51.99
9 50.120 3.00 1.80518 25.4 47.35
10 37.982 11.26 43.62
11 (Aperture) ∞ (Variable) 40.48
12 -11061.726 3.76 1.84666 23.8 38.00
13 -72.439 2.00 1.88300 40.8 37.58
14 81.708 (variable) 35.61
15 138.393 1.60 1.72825 28.5 31.98
16 26.489 8.40 1.67003 47.2 30.83
17 -71.380 1.59 30.53
18 106.560 7.95 1.84666 23.8 28.00
19 -43.405 1.68 1.85026 32.3 26.24
20 34.693 9.29 24.90
21 -29.813 1.50 1.72000 50.2 25.89
22 -79.285 0.15 27.63
23 155.486 5.67 1.67270 32.1 29.00
24 -42.355 3.92 1.84666 23.8 29.70
25 -53.707 94.08 31.19
Image plane ∞

Aspheric data 3rd surface
K = -2.34972e + 000 B = -1.42570e-007 C = -5.02286e-011 D = -1.04328e-014

Various data focal length 294.00
F number 4.14
Angle of View 4.21
Statue height 21.64
Total lens length 239.85
BF 94.08

Object distance infinity 1500 15000
d11 4.02 17.44 5.07
d14 20.79 7.37 19.74

Refractive index distribution characteristic third surface g-line F-line e-line d-line C-line
Nr0 1.55916 1.55091 1.54450 1.54138 1.53762
Nr2 -1.7455e-05 -1.5472e-05 -1.4166e-05 -1.3623e-05 -1.3015e-05
Nr4 -9.9702e-11 -7.8578e-11 -6.6045e-11 -6.1170e-11 -5.5931e-11

(Numerical example 5)
Surface data surface number rd nd νd Effective diameter
1 ∞ 2.49 Ngi νdgi 71.22
2 ∞ 0.15 71.21
3 169.088 9.88 1.48749 70.2 71.12
4 -164.055 2.67 70.78
5 116.718 6.00 1.51823 58.9 65.55
6 771.172 3.68 64.55
7 -188.064 3.40 1.84666 23.8 64.38
8 408.814 16.48 62.82
9 69.724 7.65 1.51823 58.9 57.26
10 963.130 10.16 56.36
11 60.148 3.00 1.56732 42.8 46.25
12 41.614 9.88 42.98
13 (Aperture) ∞ (Variable) 40.51
14 214.371 3.72 1.76182 26.5 38.00
15 -112.398 2.00 1.88300 40.8 37.52
16 81.708 (variable) 35.75
17 151.080 2.97 1.76182 26.5 30.83
18 32.447 6.85 1.63930 44.9 29.64
19 -74.283 0.15 29.37
20 48.267 5.47 1.88300 40.8 28.01
21 -48.458 2.36 1.80400 46.6 27.52
22 29.012 4.73 24.69
23 -43.819 1.50 1.77250 49.6 24.69
24 270.763 4.94 25.64
25 77.740 7.00 1.62588 35.7 29.00
26 -29.938 4.00 1.88300 40.8 29.32
27 -65.055 90.04 31.12
Image plane ∞

Various data focal length 294.00
F number 4.14
Angle of View 4.21
Statue height 21.64
Total lens length 240.00
BF 90.04

Object distance infinity 1500 15000
d13 4.00 25.49 5.62
d16 24.83 3.35 23.22

Refractive index distribution characteristic first surface g line F line e line d line C line
Nr0 2.14068 2.08990 2.05376 2.03742 2.01840
Nr2 -8.7907e-05 -7.8129e-05 -7.1639e-05 -6.8980e-05 -6.6004e-05
Nr4 -1.9551e-09 -1.5700e-09 -1.3364e-09 -1.2464e-09 -1.1492e-09

(Numerical example 6)
Surface data surface number rd nd νd Effective diameter
1 78.356 2.00 1.85026 32.3 29.23
2 33.025 1.33 Ngi νdgi 28.28
3 33.877 5.29 1.49700 81.5 28.20
4 -227.700 0.15 28.12
5 32.264 3.24 1.74100 52.6 27.66
6 138.108 (variable) 27.28
7 46.808 0.90 1.83481 42.7 16.44
8 8.163 3.99 12.76
9 -26.774 0.75 1.55880 62.5 12.72
10 24.197 0.78 12.70
11 15.522 1.77 1.92286 18.9 13.12
12 35.584 (variable) 12.86
13 (Aperture) ∞ (Variable) 6.74
14 * 7.096 3.00 1.55880 62.5 9.00
15 -177.293 1.69 8.60
16 27.393 0.70 1.85026 32.3 8.10
17 6.763 0.90 7.90
18 20.783 1.70 1.75500 52.3 8.10
19 -1818.569 (variable) 8.40
20 ∞ (variable) 7.66
21 16.975 2.62 1.73400 51.5 9.13
22 -11.713 0.80 1.67270 32.1 9.06
23 92.710 (variable) 8.89
Image plane ∞

Aspheric data 14th surface
K = -4.42169e-001 B = -5.95459e-005 C = -4.50730e-007 D = -1.01817e-008 E = 2.38618e-010

Various data Zoom ratio 14.97
Wide angle Intermediate position Telephoto focal length 6.15 26.41 92.07
F number 2.88 3.78 3.49
Angle of view 30.32 7.72 2.20
Image height 3.60 3.60 3.60
Total lens length 80.78 86.56 89.56
BF 11.66 17.22 6.89

d 6 0.80 20.42 34.13
d12 28.38 8.97 1.36
d13 4.24 1.20 1.20
d19 1.10 1.10 1.10
d20 3.00 6.04 13.28
d23 11.66 17.22 6.89

Zoom lens group data group Start surface Focal length Lens construction length
1 1 50.18 12.00
2 7 -10.60 8.19
3 14 23.21 7.99
4 21 24.09 3.42

Refractive index distribution characteristic second surface g line F line e line d line C line
Nr0 1.53706 1.53133 1.52658 1.52415 1.52117
Nr2 7.1550e-05 6.4788e-05 5.7810e-05 5.3288e-05 4.5532e-05
Nr4 -1.5399e-09 -1.2760e-09 -1.0264e-09 -8.7763e-10 -6.4732e-10

(Numerical example 7)

Surface data surface number rd nd νd Effective diameter
1 175.015 9.48 1.48749 70.2 71.27
2 -155.858 2.20 Ngi νdgi 71.05
3 -155.858 0.15 70.90
4 114.104 6.39 1.48749 70.2 66.81
5 956.586 5.68 65.84
6 -176.476 3.40 1.85280 39.0 64.27
7 576.433 17.87 62.91
8 69.911 8.11 1.48749 70.2 56.98
9 10584.932 6.64 56.03
10 59.073 5.71 1.67300 38.1 47.86
11 41.604 9.80 42.77
12 (Aperture) ∞ (Variable) 40.30
13 287.551 3.84 1.80518 25.4 37.91
14 -92.454 2.00 1.88300 40.8 37.46
15 81.708 (variable) 35.65
16 157.218 2.58 1.69895 30.1 31.56
17 29.858 7.42 1.63854 55.4 30.41
18 -78.410 0.34 30.12
19 38.741 6.30 1.85026 32.3 28.00
20 -70.523 1.50 1.78590 44.2 26.98
21 26.073 4.62 24.31
22 -53.104 1.50 1.86400 40.6 24.31
23 124.067 5.85 25.04
24 70.561 7.00 1.57501 41.5 29.00
25 -31.751 4.00 1.88300 40.8 29.37
26 -58.305 90.54 31.18
Image plane ∞

Various data focal length 294.00
F number 4.14
Angle of View 4.21
Statue height 21.64
Total lens length 239.86
BF 90.54

Object distance infinity 1500 15000
d12 4.00 24.75 5.56
d15 22.94 2.19 21.38

Refractive index distribution characteristic second surface g line F line e line d line C line
Nr0 1.70038 1.67900 1.66231 1.65388 1.64278
Nr2 -2.4868e-03 -2.2802e-03 -2.0151e-03 -1.8221e-03 -1.4641e-03
Nr4 -1.8595e-06 -1.5806e-06 -1.2442e-06 -1.0207e-06 -6.6130e-07

  Next, an embodiment of a digital still camera (optical apparatus) using the optical system shown in each example as a photographing optical system will be described with reference to FIG. In FIG. 16, reference numeral 20 denotes a camera body. Reference numeral 21 denotes a photographing optical system constituted by any one of the optical systems described in each embodiment. 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 a subject image photoelectrically converted by the solid-state imaging device 22. Reference numeral 24 denotes a finder for observing a subject image formed on the solid-state image sensor 22, which includes a liquid crystal display panel or the like. In this way, by applying the optical system of the present invention to a digital still camera, it is possible to realize an optical apparatus having a small size and high optical performance.

Ggij Refractive index distribution lens L1 First lens group L2 Second lens group L3 Third lens group L4 Fourth lens group SP Aperture stop IP image surface d d line g g line CC line FF line ΔM meridional image surface ΔS sagittal image surface

Claims (8)

When the total optical length is Lt and the focal length is ft, Lt / ft <1.0
In the optical system having one or more refractive index distribution elements in the optical path, the maximum value and the minimum value of the partial dispersion ratio with respect to the g-line and the F-line in the medium of the refractive index distribution element are respectively θgF (pmax) , ΘgF (pmin), where the position in the medium that takes the reference refractive index of the refractive index distribution in the refractive index distribution element is the reference position P0, the equivalent anomalous dispersion at the position p1 in the medium different from the reference position P0 Is ΔθgFgi (p1) | θgF (pmax) −θgF (pmin) |> 0.02
0.0272 <| ΔθgFgi (p1) | <1.000
An optical system that satisfies the following conditional expression:   The optical system according to claim 1, wherein the refractive index distribution element has a refractive index distribution in a direction perpendicular to the optical axis. When the effective ray radius of the refractive index distribution element is rea and the partial dispersion ratios regarding the g-line and the F-line at a distance rea in the vertical direction from the optical axis and a distance 0 are θgFR (rea) and θgFR (0), respectively.
| ΘgFR (rea) −θgFR (0) |> 0.02
The optical system according to claim 1, wherein the following conditional expression is satisfied.   The optical system according to claim 1, wherein the refractive index distribution element has a refractive index distribution in an optical axis direction. The most light incident side point in the refractive index distribution element in the optical axis direction is tobj, the most light exit side point is tig, and the g-line and F-line at the point tobj and the point tig in the optical axis direction of the refractive index distribution element. When the partial dispersion ratios for θgFA (tobj) and θgFA (timg) are
| ΘgFA (tobj) −θgFA (timg) |> 0.02
The optical system according to claim 1, wherein the following conditional expression is satisfied.   The optical system includes, in order from the object side to the image side, a first lens group having positive refractive power that does not move during focusing, a second lens group having negative refractive power that moves in the optical axis direction for focusing, and during focusing. 6. The optical system according to claim 1, wherein the refractive index distribution element is included in the first lens group. .   The optical system includes, in order from the object side to the image side, a first lens group having a positive refractive power and a second lens group having a negative refractive power with the widest air gap interposed therebetween. 6. The optical system according to claim 1, wherein the optical system is included in the first lens group.   An optical apparatus comprising the optical system according to claim 1.