JP2013061548A - Imaging optical system and optical instrument having refraction index distribution type lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adequately correct coma aberration, astigmatism, and field curvature as well while satisfactorily correcting color aberration by using a lens that is a radial type and a refraction index distribution type.SOLUTION: An imaging optical system comprises: an aperture stop AP; a front lens group G1 arranged closer to an object side than to the aperture stop; and a rear lens group G2 arranged closer to an image side to the aperture stop. The front lens group and the rear lens group include the refraction index distribution type lenses GR1 and GR2 which change refraction index according to a distance from an optical axis. One of the refraction index distribution type lenses of the front and rear lens groups has a refraction index distribution that decreases in refraction index as the distance from the optical axis increases. The other has a refraction index distribution that increases in refraction index as the distance from the optical axis increases.

Description

  The present invention relates to an image forming optical system using a gradient index lens, and more particularly to an optical system suitable for an optical apparatus such as a camera or an interchangeable lens.

  As the gradient index lens, there is a so-called radial gradient index lens in which the refractive index changes according to the distance (radius) from the optical axis. Since this radial type gradient index lens has a correction effect of chromatic aberration by appropriately giving a refractive index distribution for each wavelength, it is often used in an imaging optical system such as a photographing optical system.

  Patent Document 1 discloses a photographing optical system in which the number of lenses is reduced using a radial type gradient index lens. In particular, this photographing optical system corrects chromatic aberration between the g-line and the d-line.

Japanese Unexamined Patent Publication No. 01-097913

  In the radial type gradient index lens, an optical path difference is generated between the light beams incident on the radial refractive index distribution lens when passing through the gradient of the refractive index, and this appears as power. However, the radial type gradient index lens has a high incident angle dependency, and even if the light rays incident at the same distance from the optical axis are inclined with respect to the optical axis, Asymmetric imaging performance occurs above and below the optical axis, and coma, astigmatism, and field curvature occur.

  In particular, when a radial type gradient index lens is used in a wide angle optical system such as a photographing optical system, light rays are incident with a large inclination with respect to the optical axis of the gradient index lens. In addition, coma, astigmatism, and curvature of field are greatly generated.

  FIG. 3 shows a state in which coma aberration is generated in a light beam that is incident on a general radial type gradient index lens GR1 with an inclination with respect to its optical axis. The refractive index distribution lens GR1 is provided with a refractive index distribution so that the refractive index decreases from the optical axis toward the periphery (as the distance from the optical axis increases).

  Inside the lens GR1 having a refractive index distribution, the direction of the light beam is gradually changed to a higher refractive index. That is, in FIG. 3, the direction of the light beam is changed in a direction approaching the optical axis of the lens GR1. At this time, the influence received from the refractive index distribution differs between the upper light beam incident on the upper side of the optical axis of the lens GR1 and the lower light beam incident on the lower side.

  In the optical system shown in FIG. 3, parallel rays are incident obliquely from the lower side to the upper side of the optical axis. The upper ray traveling in the direction of decreasing the refractive index has a small amount of change in direction due to the influence of the refractive index distribution, and forms an image on the far side from the imaging position of the principal ray. On the other hand, the downward ray traveling in the direction in which the refractive index increases has a large amount of change in direction due to the influence of the refractive index distribution, and forms an image on the near side from the imaging position of the principal ray. In this way, coma aberration occurs in a light beam that is incident on a radial type gradient index lens with an inclination relative to the optical axis.

  The present invention provides an imaging optical system in which coma, astigmatism, and curvature of field are sufficiently corrected while chromatic aberration is satisfactorily corrected using a radial type gradient index lens.

An imaging optical system according to one aspect of the present invention includes an aperture stop, a front lens unit disposed on the object side of the aperture stop, and a rear lens unit disposed on the image side of the aperture stop. Each of the front lens group and the rear lens group includes a gradient index lens whose refractive index changes according to the distance from the optical axis. One of the refractive index distribution type lenses in the front and rear lens groups has a refractive index distribution in which the refractive index decreases as the distance from the optical axis increases, and the other has a distance from the optical axis. It has a refractive index distribution in which the refractive index increases as it increases.

  The optical apparatus having the imaging optical system also constitutes another aspect of the present invention.

  According to the present invention, it is possible to satisfactorily correct chromatic aberration using a gradient index lens, and sufficiently correct coma, astigmatism and curvature of field that can occur in a gradient index lens, An imaging optical system having good imaging performance can be realized.

1 is an optical arrangement diagram of a zoom lens that is Embodiment 1 of the present invention. FIG. FIG. 3 is a diagram showing a refractive index distribution of a gradient index lens in Example 1. The figure which shows the image formation state of a general radial type gradient index lens. FIG. 4 is a longitudinal aberration diagram of the zoom lens of Example 1; FIG. 3 is a lateral aberration diagram of the zoom lens of Example 1; FIG. 6 is an optical arrangement diagram of a zoom lens that is Embodiment 2 of the present invention. FIG. 6 is a diagram showing a refractive index distribution of a gradient index lens in Example 2. FIG. 6 is a longitudinal aberration diagram of the zoom lens according to Example 2; FIG. 6 is a lateral aberration diagram of the zoom lens of Example 2. FIG. 6 is an optical arrangement diagram of a zoom lens that is Embodiment 3 of the present invention. FIG. 6 is a diagram showing a refractive index distribution of a refractive index distribution type lens in Example 3. FIG. 6 is a longitudinal aberration diagram of the zoom lens according to Example 3; FIG. 4 is a lateral aberration diagram of the zoom lens according to Example 3; The perspective view of the camera using the zoom lens of each Example.

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

FIG. 1A shows an optical arrangement at the wide-angle end of a zoom lens that is an imaging optical system that is Embodiment 1 of the present invention and that has a variable focal length. FIG. 1B shows an optical arrangement of the zoom lens at the telephoto end. Table 1 shows specific numerical examples (Numerical Example 1) corresponding to the present embodiment. E-XX represents “× 10 ^−XX ”.

  The zoom lens according to the present exemplary embodiment includes an aperture stop AP and a first lens group (front lens group) G1 that is one lens group disposed on the object side (left side in the drawing) of the aperture stop AP. The zoom lens according to the present exemplary embodiment includes a second lens group (rear lens group) G2 and a third lens group G3, which are a plurality of lens groups disposed on the image side (right side in the drawing) of the aperture stop AP. Have.

  Light rays (light beams) incident from each angle of view on the object side pass through the first lens group G1 having negative optical power and enter the aperture stop AP, and the light beam width is limited. Then, the light passes through the second lens group G2 and the third lens group G3 each having a positive optical power, and forms an image on the imaging surface IMG of an imaging element such as a CCD sensor.

  The first lens group G1 is a lens group closest to the aperture stop AP among the lens groups disposed on the object side of the aperture stop AP. The first lens group G1 is composed of one negative meniscus lens GR1 having a concave surface directed toward the object side. The negative meniscus lens GR1 is a radial type gradient index lens. The refractive index increases as the distance from the optical axis increases, and the wavelength dispersion of the refractive index increases as the distance from the optical axis increases. It has a decreasing radial refractive index profile. The first lens group G1 corrects chromatic aberration generated in the negative direction.

  The second lens group G1 is a lens group closest to the aperture stop AP among the lens groups disposed on the image side of the aperture stop AP. The second lens group G2 is composed of one positive meniscus lens GR2 having a convex surface directed toward the image side. The positive meniscus lens GR2 is a radial type gradient index lens. The refractive index decreases as the distance from the optical axis increases, and the wavelength dispersion of the refractive index increases as the distance from the optical axis increases. It has an increasing radial refractive index profile. Chromatic aberration generated in the positive direction is corrected by the second lens group G2.

  2A shows the refractive index distribution of the radial type refractive index distribution type lens GR1 in this embodiment, and FIG. 2B shows the refraction of the radial type refractive index distribution type lens GR2 in this example. Each rate distribution is shown. The horizontal axis is the distance (radial direction) from the optical axis, and the vertical axis is the refractive index for the C-line, d-line and F-line.

  The third lens group G3 is composed of one positive meniscus lens L3 having a convex surface directed toward the image side.

  By changing the interval between the first to third lens groups G1 to G3, a zoom lens (Numerical Example 1) having a zoom ratio of 1.5 times is configured. The distance between the first lens group G1 and the second lens group G2 at the telephoto end is narrower than the distance at the wide angle end.

  In this embodiment and other embodiments described later, when a radial type refractive index distribution is formed, it is given by a power series expansion formula as shown in the formula (1). The order of the power series expansion formula need not be particularly limited, but here it is assumed to be up to the 8th order for convenience.

Here, N _{00, λ} is a refractive index on the optical axis at the wavelength λ, and N _{10, λ} , N _{20, λ} , N _{30, λ} , N _{40, λ} are power series coefficients at the wavelength λ. r is the distance from the optical axis in the radial direction.

The refractive indexes N _{00, λ} on the optical axis and the power series coefficients N _{10, λ} , N _{20, λ} , N _{30, λ} , N _{40, λ} can be different values for each wavelength. The refractive index distributions N _C (r), N _d (r), and N _F (r) are given to the C line, d line, and F line, respectively.

Here, the gradient index lens needs to satisfy the expression (3) as an achromatic condition.

Where φ _S is the refractive power due to the surface shape of the gradient index lens, ν _d is the Abbe number with respect to the d-line on the optical axis, and φ _N is the power due to the refractive index distribution. Further, ν ₁₀ is the Abbe number of the refractive index distribution. Power phi _N due to the refractive index distribution is expressed by the following equation (4).

Here, d is the thickness of the gradient index lens.

The Abbe number ν ₁₀ of the refractive index distribution is expressed by the following equation (5).

From the equations (4) and (5), the term φ _N / ν ₁₀ of the refractive index distribution under the achromatic condition in the equation (3) can be expressed by the following equation (6).

That is, this is the difference between the power due to the refractive index distribution of the F line and the power due to the refractive index distribution of the C line.

As described above, the term φ _N / ν ₁₀ of the refractive index distribution under the achromatic condition depends on the refractive index distribution regardless of whether the refractive power φ _S depending on the surface shape of the gradient index lens is positive or negative. It is determined by the values of N10 _{, F−} N10, and _C irrespective of the power φN. For this reason, the refractive index distribution type lens can freely set the refractive index distribution while having a function capable of satisfactorily correcting the chromatic aberration of each lens group.

  In the present embodiment, the first lens group G1 having negative power is disposed immediately before the aperture stop AP, and the second lens group G2 having positive power is disposed immediately after the aperture stop AP. Further, two radial type gradient index lenses GR1 and GR2 whose refractive indexes change in opposite directions in the radial direction are disposed with the aperture stop AP interposed therebetween. Thereby, coma aberration, astigmatism and curvature of field generated in one of the gradient index lenses can be canceled by the other gradient index lens. Accordingly, it is possible to realize a zoom lens that sufficiently corrects coma, astigmatism, and field curvature that occur in the gradient index lens while satisfactorily correcting chromatic aberration using the gradient index lens.

  FIG. 3 shows a state in which coma aberration occurs due to the influence of the refractive index distribution on a light beam incident on a radial type gradient index lens with an inclination relative to the optical axis. However, in this embodiment, a radial type gradient index lens with refractive indexes changing in opposite directions in the radial direction is arranged in the lens groups before and after the aperture stop. Thereby, the coma generated in one of the gradient index lenses can be canceled by the coma generated in the other gradient index lens.

  That is, by including a radial type gradient index lens in the lens group before and after the aperture stop AP so that the upper ray and the lower ray are located on opposite sides of the optical axis, the coma aberration can be efficiently reduced. It can be corrected. Thereby, coma aberration can be favorably corrected in the entire zoom lens system.

  4A shows longitudinal aberrations at the wide-angle end of the zoom lens of the present embodiment, and FIG. 4B shows longitudinal aberrations at the telephoto end of the zoom lens. As shown in these drawings, the zoom lens of the present embodiment corrects axial chromatic aberration well and also corrects astigmatism well.

  FIG. 5A shows lateral aberrations at the wide-angle end of the zoom lens of the present embodiment, and FIG. 5B shows lateral aberrations at the telephoto end of the zoom lens. As can be seen from these drawings, the zoom lens of the present embodiment corrects lateral chromatic aberration well at each image height, and also corrects coma aberration and field curvature at each wavelength.

  FIG. 6A shows an optical arrangement at the wide-angle end of a zoom lens that is an imaging optical system that is Embodiment 2 of the present invention and that has a variable focal length. Table 2 shows specific numerical examples (numerical example 2) corresponding to the present embodiment.

  The zoom lens according to the present exemplary embodiment includes an aperture stop AP, and a first lens group G1 and a second lens group (front lens group) that are a plurality of lens groups disposed on the object side (left side in the drawing) of the aperture stop AP. ) G2. The zoom lens according to the present exemplary embodiment includes a third lens group G3, a fourth lens group (rear lens group) G4, which are a plurality of lens groups arranged on the image side (right side in the drawing) of the aperture stop AP. A fifth lens group G5 is included.

  The first lens group G1 includes three lenses, and has positive optical power as a whole. The second lens group G2 includes three lenses, and has a negative optical power as a whole. The second lens group G2 is a lens group closest to the aperture stop AP among the lens groups disposed on the object side of the aperture stop AP.

  The third lens group G3 includes three lenses, and has positive optical power as a whole. The third lens group G3 is a lens group closest to the aperture stop AP among the lens groups arranged on the image side of the aperture stop AP.

  The fourth lens group G4 and the fifth lens group G5 are each composed of a single lens, and the entire group has positive optical power. The aperture stop AP disposed between the second lens group G2 and the third lens group G3 moves together with the third lens group G3 during zooming.

  In the present embodiment, one of the three lenses constituting the second lens group G2 disposed immediately before the aperture stop AP is a radial type gradient index lens GL1. One of the three lenses constituting the third lens group G3 disposed immediately after the aperture stop AP is a radial type gradient index lens GL2.

  By changing the interval between the first to fifth lens groups G1 to G5, a zoom lens (Numerical Example 2) having a focal length f = 4.0 to 80 mm and a wide angle and high magnification (20 ×) is configured. . The distance between the second lens group G2 and the third lens group G3 at the telephoto end is narrower than the distance at the wide angle end.

  FIG. 7A shows the refractive index distribution of the radial type refractive index distribution type lens GL1 in this embodiment, and FIG. 7B shows the refraction of the radial type refractive index distribution type lens GL2 in this example. Each rate distribution is shown. The horizontal axis is the distance (radial direction) from the optical axis, and the vertical axis is the refractive index for the C-line, d-line and F-line.

  As shown in FIG. 7A, the gradient index lens GL1 has a radial type refractive index distribution in which the refractive index decreases from the optical axis toward the periphery (as the distance from the optical axis increases). . On the other hand, the refractive index distribution type lens GL2 has a radial type refractive index distribution in which the refractive index increases from the optical axis toward the periphery.

  As described above, the gradient index lens GL1 and the gradient index lens GL2 are respectively included in the lens groups before and after the aperture stop AP, and the refractive indexes change in opposite directions in the radial direction. Thereby, the coma generated in one of the gradient index lenses can be canceled by the coma generated in the other gradient index lens. In particular, at the telephoto end, the positions of the two gradient index lenses GL1 and GL2 are moved to the object side as compared with the wide angle end, and the sensitivity of the refractive index distribution is increased. For this reason, the two gradient index lenses GL1 and GL2 are placed close to the aperture stop AP to facilitate correction of coma.

  Further, as described above, the refractive index distribution type lens GL1 has a refractive index distribution in which the refractive index decreases as it goes from the optical axis toward the peripheral portion, and the wavelength dispersion of the refractive index also decreases. That is, the amount of change in the refractive index from the optical axis to the peripheral portion is made larger for the F line than for the C line.

  On the other hand, the refractive index distribution type lens GL2 has a refractive index distribution in which the refractive index increases as it goes from the optical axis to the periphery as described above, and the wavelength dispersion of the refractive index also increases. That is, the amount of change in the refractive index from the optical axis to the peripheral portion is made larger for the F line than for the C line.

  As described above, when the refractive index change amount from the optical axis to the peripheral portion in one of the two gradient index lenses sandwiching the aperture stop AP is larger in the F line than in the C line, the other is the same. In addition, the amount of change in the refractive index from the optical axis to the peripheral portion is larger for the F-line than for the C-line. Thereby, it is possible to easily correct the curvature of field of the color. As a result, not only can coma generated due to the influence of the refractive index distribution be corrected, but also the color field curvature can be corrected well, so that advanced chromatic aberration correction is possible.

  FIG. 8A shows longitudinal aberrations at the wide-angle end of the zoom lens of the present embodiment, and FIG. 8B shows longitudinal aberrations at the telephoto end of the zoom lens. As can be seen from these drawings, the zoom lens of the present embodiment corrects axial chromatic aberration well at the wide-angle end and telephoto end, and also corrects astigmatism well. 9A shows lateral aberrations at the wide-angle end of the zoom lens of the present embodiment, and FIG. 9B shows lateral aberrations at the telephoto end of the zoom lens. As can be seen from these figures, the zoom lens of the present embodiment corrects the coma aberration and the field curvature at each wavelength while correcting the lateral chromatic aberration at the wide-angle end and the telephoto end.

  In the present embodiment, since the zoom ratio is increased by moving the third lens group G3 from the first lens group G1 to the object side at the telephoto end, the sensitivity of these lens groups G1 to G3 is increased. It is high. As described above, the distance between the second lens group G2 and the third lens group G3 at the telephoto end is narrower than the distance at the wide-angle end. Further, since the radial type gradient index lens is used for the second lens group G2 and the third lens group G3, the power difference of each wavelength is enlarged to affect the imaging performance.

  Therefore, at the telephoto end, the distance between the second lens group G2 including the radial type gradient index lens and the third lens group G3 is made the narrowest from the wide-angle end to the telephoto end, and the second lens group G2 The third lens group G3 is provided with a reverse refractive index distribution and a refractive index wavelength dispersion distribution. Accordingly, it is possible to easily form an aberration canceling relationship, and to easily correct coma aberration and field curvature of each wavelength.

  In Numerical Example 2 shown in Table 2, the surface numbers 6, 7, 15, and 20 are aspheric surfaces and have a shape expressed by the following expression (7).

Where R is the radius of curvature and K is the conic constant. A, B, C, and D are fourth-order, sixth-order, eighth-order, and tenth-order aspheric coefficients, respectively.

  FIG. 10A shows an optical arrangement at the wide-angle end of a zoom lens that is an imaging optical system that is Embodiment 3 of the present invention and has a variable focal length. Table 3 shows a specific numerical example (Numerical Example 3) corresponding to the present embodiment.

  The zoom lens according to the present exemplary embodiment includes an aperture stop AP and a first lens group (front lens group) G1 that is one lens group disposed on the object side (left side in the drawing) of the aperture stop AP. The first lens group G1 includes a first lens L1 and a second lens L2 in order from the object order. The zoom lens according to the present exemplary embodiment includes a second lens group (rear lens group) G2 and a third lens group G3, which are a plurality of lens groups disposed on the image side (right side in the drawing) of the aperture stop AP. Have. The second lens group G2 includes a third lens L3 and a fourth lens L4 in order from the object order. The third lens group G3 includes a fifth lens L5. 2 is an optical filter such as an infrared cut filter and a low-pass filter, and 3 is an image sensor such as a CMOS sensor or a CCD sensor.

  The first lens L1 is a negative meniscus lens having a concave surface directed to the image side, and its incident surface is formed as a spherical surface, and its exit surface is formed as an aspheric surface. The second lens L2 is a meniscus lens having a concave surface directed to the image side, and both the entrance surface and the exit surface are formed as spherical surfaces. The first lens group G1 including the first lens L1 and the second lens L2 has negative optical power as a whole.

  The third lens L3 is a biconvex lens, and its entrance surface is formed as an aspherical surface and the exit surface is formed as a spherical surface. The fourth lens L4 is a biconcave lens, and both its entrance surface and exit surface are formed as spherical surfaces. The second lens group G2 including the third lens L3 and the fourth lens L4 has a positive optical power as a whole.

  The fifth lens L5 is a biconvex lens, and both its entrance surface and exit surface are formed as spherical surfaces. The third lens group G3 including the fifth lens L5 has a positive optical power as a whole.

  With the above configuration, a zoom lens (Numerical Example 3) having a wide angle of view with an angle of view 2ω = 83.4 deg (corresponding to a focal length of 24 mm in terms of 35 mm film) and a double zoom ratio is configured.

In this embodiment, the second lens L2 included in the first lens group G1 and the fourth lens L4 included in the second lens group G2 are radial type gradient index lenses. Specifically, the second lens L2 uses PMMA (Nd = 1.492, νd = 57.2), which is an optical resin, as a base material, and titania TiO ₂ that is a metal oxide in nanoparticles mixed therewith. (Nd = 2.761, νd = 9.5) is used. That is, it is formed of a nanocomposite material in which nanoparticles having an Abbe number lower than that of the base material are mixed in the base material.

  On the optical axis, about 14% (η = 0.14) of titania nanoparticles are mixed with PMMA as a base material, and the concentration of titania nanoparticles is gradually decreased as the distance from the optical axis increases. The concentration of nanoparticles is reduced to about 3% (η = 0.03). That is, the concentration of the nanoparticles is lower in the peripheral part than on the optical axis.

  The fourth lens L4 is the base material (Nd = 1.847, νd = 23.8) itself on the optical axis. However, the concentration of nanoparticles (Nd = 2.219, νd = 20.0) is gradually increased as the distance from the optical axis increases, and the concentration of nanoparticles increases to about 10% (η = 0.10) in the periphery. I am letting. That is, the concentration of the nanoparticles is higher in the periphery than on the optical axis. Thereby, a concentration gradient of nanoparticles is formed in the radial direction of the second lens L2, and a radial type refractive index distribution is given.

  FIG. 11A shows the refractive index distribution of the radial type refractive index distribution type lens L2 in this embodiment, and FIG. 11B shows the refractive index of the radial type refractive index distribution type lens L4 in this example. Each rate distribution is shown. The horizontal axis is the distance (radial direction) from the optical axis, and the vertical axis is the refractive index for C-line, d-line, F-line and g-line.

  The refractive index distributions for the C-line, d-line, F-line, and g-line shown in FIG. 11A are all distributions that have the highest refractive index on the optical axis and decrease in refractive index as they move away from the optical axis. is there. On the other hand, the refractive index distributions for the C-line, d-line, F-line, and g-line shown in FIG. 11B all have the lowest refractive index on the optical axis, and the refractive index increases as the distance from the optical axis increases. Distribution.

  Table 3 shows the refractive index distribution coefficients of the second lens L2 and the fourth lens L4. As the expression for the refractive index distribution, only the 0th order and second order terms are used in the power series expansion expression shown in the expression (1). Therefore, the refractive index distribution in the present embodiment is expressed by a quadratic function with respect to the distance r from the optical axis.

  In the zoom lens of this embodiment, radial type gradient index lenses L2 and L4 are arranged in the lens groups G1 and G2 immediately before and after the aperture stop AP, respectively, and one of these two gradient index lenses. Has a refractive index distribution in which the refractive index decreases as the distance from the optical axis increases. The other has a refractive index distribution in which the refractive index increases as the distance from the optical axis increases. Thereby, it is possible to correct coma and curvature of field while correcting chromatic aberration satisfactorily.

  Furthermore, the refractive index distribution type lens L2 included in the lens group G1 immediately before the aperture stop AP has a refractive index distribution in which the wavelength dispersion of the refractive index decreases as the distance from the optical axis increases. On the other hand, the refractive index distribution type lens L4 included in the lens group G2 immediately after the aperture stop AP has a refractive index distribution in which the wavelength dispersion of the refractive index increases as the distance from the optical axis increases. Thereby, coma aberration and curvature of field at each wavelength can be corrected well.

  FIG. 12A shows longitudinal aberrations at the wide-angle end of the zoom lens of the present embodiment, and FIG. 12B shows longitudinal aberrations at the telephoto end of the zoom lens. As can be seen from these figures, the zoom lens of the present embodiment corrects axial chromatic aberration and astigmatism well. FIG. 13A shows lateral aberrations at the wide-angle end of the zoom lens of the present embodiment, and FIG. 13B shows lateral aberrations at the telephoto end of the zoom lens. As can be seen from these figures, the zoom lens of the present embodiment corrects the coma aberration and the field curvature at each wavelength while correcting the lateral chromatic aberration at the wide-angle end and the telephoto end.

  In each of the embodiments (aberration diagrams) described above, the case of correcting chromatic aberration in the C-line, d-line, and F-line has been described. However, correction of chromatic aberration in other spectral lines such as g-line and infrared rays is also performed. Can do.

  In each embodiment, the zoom lens having a variable focal length has been described. However, the present invention also includes a single focus lens having a fixed focal length.

  FIG. 14 shows a digital still camera (optical apparatus) using the zoom lens described in the first to third embodiments as a photographing optical system. Reference numeral 20 denotes a camera body, 21 denotes a photographic optical system (zoom lenses of Examples 1 to 3), 22 denotes a built-in camera body 20 such as a CCD sensor or a CMOS sensor that receives a subject image formed by the photographic optical system 21. An imaging element (photoelectric conversion element).

  Reference numeral 23 denotes a memory for recording information corresponding to the subject image photoelectrically converted by the image sensor 22, and reference numeral 24 denotes a finder configured by a liquid crystal display panel or the like for observing the subject image formed on the image sensor 22.

  Thus, by applying the zoom lenses of Examples 1 to 3 to an optical device, an optical device having high optical performance can be realized. Optical devices include not only digital still cameras but also various optical devices such as video cameras and interchangeable lenses.

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

  Providing an imaging optical system suitable for photographic optical systems that can achieve both correction of chromatic aberration using a gradient index lens and correction of coma, astigmatism and curvature of field generated by a gradient index lens it can.

GR1, GR2, GL1, GL2 Gradient index lens AP Aperture stop

Claims (5)

An aperture stop,
A front lens group disposed closer to the object side than the aperture stop, and
A rear lens group disposed on the image side of the aperture stop,
Each of the front lens group and the rear lens group includes a gradient index lens whose refractive index changes according to the distance from the optical axis,
One of the refractive index distribution type lenses of the front and rear lens groups has a refractive index distribution in which the refractive index decreases as the distance from the optical axis increases, and the other from the optical axis. An imaging optical system having a refractive index distribution in which the refractive index increases as the distance increases. Having one or a plurality of lens groups on each of the object side and the image side of the aperture stop;
The imaging according to claim 1, wherein the front lens group and the rear lens group including the gradient index lens are lens groups closest to the aperture stop on the object side and the image side, respectively. Optical system. The front lens group has negative optical power;
The gradient index lens included in the front lens group has a refractive index distribution in which the wavelength dispersion of the refractive index decreases as the distance from the optical axis increases,
The refractive index distribution type lens included in the rear lens group has a refractive index distribution in which the wavelength dispersion of the refractive index increases as the distance from the optical axis increases. The imaging optical system described in 1. The focal length of the imaging optical system is variable by changing the interval between the front lens group and the rear lens group,
The imaging according to any one of claims 1 to 3, wherein a distance between the front lens group and the rear lens group at a telephoto end is narrower than the distance at a wide-angle end. Optical system.   An optical apparatus comprising the imaging optical system according to any one of claims 1 to 4.