JP2008203304A - Optical system and optical apparatus including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical system that can sufficiently correct a variety of aberrations including chromatic aberration, that can be easily fabricated, and that has an excellent resistance to the surrounding environment, and an optical apparatus including the optical system. <P>SOLUTION: In the optical system, when a point at which an optical axis and a pupil paraxial ray intersect is defined as P, the maximum value of heights from the optical axis where the paraxial marginal ray passes through the face of a lens on the enlargement side of the point P is greater than that from the optical axis where the paraxial marginal ray passes through the face of a lens on the reduction side of the point P. The optical system includes first and second optical elements, each of which is composed of a solid material having a refractive light incident surface and a refractive light exiting surface, on at least one of the enlargement side and the reduction side from the point P. The optical system satisfies conditions ΔθgF1>0.0272, ΔθgF2<-0.0278 and ϕ1×ϕ2<0 where ΔθgF1 and ΔθgF2 denote anomalous partial dispersion values of the solid material of the first and second optical elements for the g-line and F-line, respectively, and ϕ1 and ϕ2 denote refractive power of the first and second optical elements, respectively, when the light incident surfaces and the light exiting surfaces of the first and second optical elements are in contact with air. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical system, and is suitable for optical equipment such as a silver salt film camera, a digital still camera, a video camera, a digital video camera, a telescope, binoculars, a projector, and a copying machine.

  An optical system used in an optical apparatus such as a digital camera or a video camera has a short total lens length (optical total length, length from the first lens surface on the object side to the image plane), and the entire optical system is small. It has been demanded.

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

  There is known an optical system in which achromatic (correction of chromatic aberration) is performed using an abnormal partial dispersion material in a telephoto type optical system (Patent Documents 1 to 3).

  Further, as an optical material having a correction function for chromatic aberration, a liquid material that exhibits high dispersion and exhibits anomalous partial dispersion characteristics is known, and an optical system that is achromatic using the liquid material is known (Patent Literature). 4, 5).

  Further, an optical system is known in which a solid material made of a mixture in which Indium-Tin Oxide (ITO) fine particles are dispersed in a transparent medium is used as a solid material having an anomalous partial dispersion characteristic (Patent) References 6 and 7).

Further, as a solid material having an anomalous partial dispersion characteristic, there is known an optical system in which an achromatization is performed using a solid material made of a mixture or resin in which TiO ₂ fine particles are dispersed in a transparent medium (Patent Document 8, 9).
Japanese Patent Publication No. 60-49883 Japanese Patent Publication No. 60-55805 JP-A-11-119092 U.S. Pat. No. 4,913,535 US Pat. No. 5,731,907 JP 2005-181392 A JP 2005-215387 A JP 2006-145823 A JP 2006-349948 A

  In the telephoto type optical system disclosed in Patent Documents 1 to 3 using fluorite or the like as the optical material, correction of chromatic aberration is easy when the overall lens length is set relatively long. However, if the total lens length is shortened, a large amount of chromatic aberration occurs, and it is difficult to correct this well. This is because the chromatic aberration generated in the front lens system having a positive refractive power is merely reduced by utilizing the low dispersion and the anomalous partial dispersion of materials such as fluorite. If you try to correct chromatic aberration that has deteriorated as the overall lens length is shortened, for example, a lens using low-dispersion glass with a large Abbe number, such as fluorite, will have a significant change in chromatic aberration unless the refractive power of the lens surface is significantly changed. do not do. For this reason, it is difficult to achieve both correction of chromatic aberration and correction of various aberrations such as spherical aberration, coma aberration, and astigmatism caused by increasing the refractive power. In addition, a glass material having an abnormal partial dispersion characteristic such as fluorite has a problem that it is very difficult to process, and since the surface is easily damaged, there are cases where the use place for the optical system is limited.

Since the materials disclosed in Patent Documents 4 and 5 are liquids, a structure for sealing them is required, and when used as an optical material, the manufacture becomes difficult. In addition, characteristics such as refractive index and dispersion greatly change due to temperature change, and environmental resistance is not sufficient. Furthermore, since an interface with air cannot be obtained, it is difficult to obtain a sufficient chromatic aberration correcting action.

  The solid material having anomalous partial dispersion characteristics disclosed in Patent Documents 6, 7, 8, and 9 has a relatively low transmittance as compared with a general optical material.

  In order to prevent a decrease in transmittance of the entire optical system, it is desirable that the thickness of the solid material in the optical axis direction is thin. On the other hand, in order to satisfactorily correct chromatic aberration using a solid material, a certain thickness is required.

  However, as the thickness of the solid material increases in the optical path, the variation in optical characteristics under the environment increases, and the environmental resistance deteriorates. Further, since it is difficult to mold a thick solid material, it is not easy to manufacture.

  Therefore, when an optical element made of a solid material having anomalous partial dispersion disclosed in Patent Documents 6, 7, 8, and 9 is used as a lens or a layer having a refractive power in an optical system, It is important to correct chromatic aberration while reducing the thickness.

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

In the optical system of the present invention, when the point where the optical axis and the pupil paraxial ray intersect is P, the maximum value from the optical axis where the paraxial axial ray passes through the lens surface on the enlargement side from the point P. However, in the optical system in which the paraxial light beam is larger than the maximum value from the optical axis through which the paraxial light beam passes through the lens surface on the reduction side with respect to the point P, at least one of the enlargement side or the reduction side with respect to the point P, Both the light incident / exit surfaces are refracting surfaces and have first and second optical elements made of a solid material, and anomalous partial dispersibility with respect to g-line and F-line of the solid material of the first and second optical elements is expressed by ΔθgF1, ΔθgF2, when the refractive power when the light incident / exit surfaces of the first and second optical elements are both surfaces in contact with air is φ1 and φ2, respectively,
ΔθgF1> 0.0272
ΔθgF2 <−0.0278
φ1 × φ2 <0
It is characterized by satisfying the following conditions.

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

  Hereinafter, the optical system of the present invention and the optical apparatus having the same will be described.

  Let P be the point where the optical axis and the paraxial ray intersect. At this time, in the optical system of the present invention, the maximum value of the height from the optical axis through which the paraxial ray passes through the lens surface on the enlargement side from the point P, and the paraxial axis ray on the reduction side from the point P. This is a telephoto type optical system that is larger than the maximum height from the optical axis that passes through the lens surface.

  The present invention also relates to a refractive optical element in which a positive or negative refractive action is imparted to a solid material that satisfies the conditions described later in an optical system of a telephoto type (an optical system whose overall lens length is shorter than the focal length of the optical system). (Hereinafter, also simply referred to as “optical element”).

  The solid material of the refractive optical element used in the optical system of the present invention refers to a solid material in a state where the optical system is used, and what is the state before using the optical system at the time of manufacture or the like. May be. 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 here.

  FIG. 14 is a schematic diagram of a paraxial refractive power arrangement for explaining the optical action of the optical system of the present invention. In FIG. 14, OL is a telephoto type optical system in which the total lens length (distance from the first lens surface to the image plane) is shorter than the focal length. Gp and Gn are a front group of positive refracting power and a rear group of negative refracting power, respectively, constituting the telephoto type optical system OL. GNL1 and GL1 are first and second refractive optics made of solid materials (optical materials, hereinafter also referred to as “materials”), which are introduced into the front group Gp and satisfy the following conditional expressions (2) to (9). Elements (first and second optical elements). In order to simplify the configuration, the lenses constituting the front group Gp and the rear group Gn are all thin single lenses, and are arranged on the optical axis with a lens interval of 0 in the front group Gp and the rear group Gn. It is said. The first and second optical elements GNL1 and GL1 are also thin single lenses, and are arranged on the optical axis La with a lens interval of 0 in the front group Gp. Q is a paraxial ray. R is a pupil paraxial ray. The paraxial axial ray Q is a paraxial ray when the focal length of the entire optical system is normalized to 1 and light having a height of 1 is incident from the optical axis parallel to the optical axis of the optical system. In the following, it is assumed that the object is on the left side of the optical system, and light rays incident on the optical system from the object side travel from left to right. The pupil paraxial ray R normalizes the focal length of the entire optical system to 1, and among the rays incident at −45 ° with respect to the optical axis, the paraxial passing through the intersection of the entrance pupil of the optical system and the optical axis. Light rays. Hereinafter, the incident angle to the optical system is measured clockwise from the optical axis and positive in the counterclockwise direction. P is the intersection of the pupil paraxial ray R and the optical axis La. IP is the image plane.

The optical system OL in FIG. 14 is closer to the enlargement side (object side) than the point P, and the maximum value h _Gp of the height from the optical axis La through which the paraxial axial ray Q passes the lens surface is smaller than the point P. This is an optical system in which the paraxial light beam Q on the side (image side) is larger than the maximum height h _Gn from the optical axis passing through the lens surface. H _Gp and H _Gn are heights from the optical axis La when the pupil paraxial ray R is incident on the lens surfaces of the front group Gp and the rear group Gn.

  The characteristics of the optical system OL of the present embodiment are as follows.

  Let ft be the focal length of the entire lens system, and Lt be the total lens length (distance from the first lens surface to the image plane).

  Let P be the point where the optical axis La intersects the pupil paraxial ray R. On at least one of the enlargement side or the reduction side from the point P, first and second optical elements GNL1 and GL1 made of a solid material and having a light entrance / exit surface are both refractive surfaces.

  The anomalous partial dispersibility of the materials of the first and second optical elements GNL1 and GL1 with respect to the g-line and the F-line are denoted by ΔθgF1 and ΔθgF2, respectively.

  The refractive powers when the light incident / exit surfaces of the first and second optical elements GNL1 and GL1 are both surfaces in contact with air are φ1 and φ2, respectively.

  Anomalous partial dispersions regarding the g-line and d-line of the materials of the first and second optical elements GNL1 and GL1 are denoted by Δθgd1 and Δθgd2, respectively.

  The Abbe numbers of the materials of the first and second optical elements GNL1 and GL1 are νd1 and νd2, respectively.

  At this time, each embodiment satisfies one or more of the following conditions.

Lt / ft <1.0 (1)
ΔθgF1> 0.0272 (2)
ΔθgF2 <−0.0278 (3)
Δθgd1> 0.038 (4)
Δθgd2 <−0.037 (5)
νd1 <60 (6)
νd2 <60 (7)
φ1 × φ2 <0 (8)
(ΔθgF1 × φ1 / νd1) / (ΔθgF2 × φ2 / νd2) <1.5
(9)
The anomalous partial dispersibility and Abbe number of the material of the optical element used in the optical system of the present example are as follows.

  The refractive index of the Fraunhofer line for g-line (wavelength 435.8 nm), F-line (wavelength 486.1 nm), d-line (wavelength 587.6 nm), and C-line (wavelength 656.3 nm) is Ng, NF, respectively. Let Nd, NC. The Abbe number νd, 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)
The anomalous partial dispersibility Δθgd for g-line and d-line and the anomalous partial dispersibility ΔθgF for g-line and F-line are as follows.

Generally, the partial dispersion ratios θgd and θgF of a solid material used for a lens system are set to θgd = −1.687 × 10 ⁻⁷ νd ³ + 5.702 × 10 ⁻⁵ νd ^2.
-6.603 × 10 ⁻³ νd + 1.462
θgF = −1.665 × 10 ⁻⁷ νd ³ + 5.213 × 10 ⁻⁵ νd ²
−5.656 × 10 ⁻³ νd + 0.7278
Approximate as

At this time, the abnormal partial dispersions Δθgd and ΔθgF are
Δθgd = θgd − (− 1.687 × 10 ⁻⁷ νd ³ + 5.702 × 10 ⁻⁵ νd ²
-6.603 × 10 ⁻³ νd + 1.462)
ΔθgF = θgF − (− 1.665 × 10 ⁻⁷ νd ³ + 5.213 × 10 ⁻⁵ νd ²
−5.656 × 10 ⁻³ νd + 0.7278)
It is.

  The optical system OL of the present embodiment is formed of a first optical element GNL1 formed of a solid material having a high dispersion and a high partial dispersion ratio as a refractive optical element having refractive power, and a solid material having a high dispersion and a low partial dispersion ratio. At least one second optical element GL1 is used.

  Here, the refractive optical element means a refractive lens that generates power (refractive power) by a refractive action, and does not include a diffractive optical element that generates power by a diffractive action.

  The optical system of each example is a telephoto type optical system that satisfies the conditional expression (1).

  In each example, the refractive optical element GNL1 formed of a solid material having anomalous partial dispersion satisfying conditional expression (2) and a solid material having an abnormal partial dispersion satisfying conditional expression (3) are used. It is preferable to use at least one refractive optical element GL1 in the optical system. According to this, chromatic aberration can be corrected satisfactorily over the entire visible wavelength range.

  Moreover, it is preferable to use a solid material having an anomalous partial dispersibility that satisfies the conditional expressions (4) and (5). According to this, it becomes easy to satisfactorily correct chromatic aberration between a short wavelength (wavelength 400 nm) and an intermediate wavelength (wavelength 550 nm). Further, according to this, chromatic aberration can be corrected more favorably in a wide wavelength range from a short wavelength to a long wavelength (wavelength 700 nm).

  In addition, it is preferable to use a solid material having an Abbe number satisfying the conditional expressions (6) and (7). This facilitates correction of chromatic aberration.

  The first and second optical elements GNL1 and GL1 are preferably configured to have a refractive power that satisfies the conditional expression (8). According to this, chromatic aberration can be favorably corrected over a wide wavelength range.

  Further, it is preferable to configure each element of the first and second optical elements GNL1, GL1 so as to satisfy the conditional expression (9). According to this, it is possible to satisfactorily correct chromatic aberration that frequently occurs in a telephoto type optical system.

  In each embodiment, when the first and second optical elements GNL1 and GL1 are provided in the optical system, it is preferable to provide both on the enlargement side from the point P where the optical axis La and the pupil paraxial ray R intersect.

  A specific example of the solid material (optical material) that satisfies the conditional expression (2) is, for example, a resin. Among various resins, UV curable resin (Nd = 1.635, νd = 22.7, θgF = 0.69) and N-polyvinylcarbazole (Nd = 1.696, νd = 17.7, θgF = 0. 69) is an optical material satisfying conditional expression (2). Note that the present invention is not limited to these as long as the conditional expression (2) is satisfied.

Further, as an optical material having characteristics different from those of general glass materials, there is a mixture in which the following inorganic oxide nanoparticles are dispersed in a synthetic resin. That is, 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) CrO ₃ (Nd = 2.2178, νd = 13.4), BaTiO ₃ (Nd = 2.4362, νd = 11.3), and the like.

Among these inorganic oxides, when TiO ₂ (Nd = 2.304, νd = 13.8, θgF = 0.87) fine particles are dispersed in a synthetic resin at an appropriate volume ratio, the above conditional expression ( An optical material satisfying 2) is obtained.

  When fine particles of ITO (Indium-Tin-Oxide) (Nd = 1.8571, νd = 5.69, θgF = 0.873) are dispersed in a synthetic resin at an appropriate volume ratio, the above conditional expression (3 ) Is obtained. Note that the present invention is not limited to these as long as the conditional expression (3) is satisfied.

  In each embodiment, chromatic aberration is corrected favorably by using an optical material having a large partial dispersion ratio and an optical material having a small partial dispersion ratio compared to a general optical material.

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

  In general, an optical material has a refractive index on the short wavelength side higher than that on the long wavelength side, and the Abbe number and the partial dispersion ratio have positive values.

  For this reason, the dispersion characteristic curve is convex downward, and the change in the refractive index with respect to the change in wavelength increases as the wavelength becomes shorter. For example, the wavelength characteristic of the refractive index of a glass material having the trade name S-TIH53 of OHARA Corporation is as shown in FIG.

  And the higher dispersion optical material having a smaller Abbe number tends to increase the partial dispersion ratio regarding the g-line and the F-line and the partial dispersion ratio regarding the g-line and the d-line.

  In a general optical material, the partial dispersion ratio changes almost linearly with respect to the Abbe number. What deviates from this linear change is an optical material having anomalous partial dispersion, and generally includes fluorite and the like.

  An optical material having a large partial dispersion ratio as compared with a general optical material has a characteristic that the wavelength-dependent characteristic curve of the chromatic aberration coefficient is greatly bent on the short wavelength side.

  When the power of the lens surface of an optical material having a large partial dispersion ratio is changed so as to control chromatic aberration, the inclination of the wavelength dependence characteristic curve of the chromatic aberration coefficient changes as a whole around the position of the design reference wavelength. This change is particularly large on a short wavelength side in a material having a large partial dispersion ratio. As a result, the overall inclination changes while greatly changing the amount of bending on the short wavelength side.

  By utilizing this property, it is possible to cancel the bending on the short wavelength side of the wavelength dependence characteristic curve of the chromatic aberration coefficient.

  However, it is difficult to simultaneously correct the slope of the wavelength-dependent characteristic curve of the remaining chromatic aberration coefficient. Further, by correcting the short wavelength side curvature, the long wavelength side chromatic aberration is relatively deteriorated. In order to perform correction on the long wavelength side, it is preferable to change the power of an appropriate glass surface in the optical system, but it is not preferable for correcting various aberrations other than chromatic aberration.

  On the other hand, in an optical material having a small partial dispersion ratio, the curve on the short wavelength side in the wavelength dependence characteristic curve of the chromatic aberration coefficient is small.

  For this reason, compared with a general optical material, it has the characteristic that a chromatic aberration coefficient changes more linearly with respect to a change in wavelength.

  When the power of the lens surface is changed with an optical material with a small partial dispersion ratio so as to control chromatic aberration, the wavelength-dependent characteristic curve of the chromatic aberration coefficient is relatively linear with respect to the wavelength with the position of the design reference wavelength as the center of rotation. The inclination changes while maintaining the sex. From this, the inclination of the wavelength-dependent characteristic curve of the chromatic aberration coefficient can be corrected.

  Therefore, by using an optical material having a small partial dispersion ratio in addition to an optical material having a large partial dispersion ratio, it is possible to simultaneously correct the short wavelength side curve and the overall inclination of the wavelength dependence characteristic curve of the chromatic aberration coefficient.

  That is, the chromatic aberration of the entire optical system can be corrected well in a wide wavelength region from the g line to the C line.

  Next, a refractive optical system part GNL using an optical material having a large partial dispersion ratio, a refractive optical system part GL using an optical material having a small partial dispersion ratio, and a general optical whose partial dispersion ratio is a general value. Correction of chromatic aberration in a telephoto lens composed of a refractive optical system portion G using materials will be described.

  First, a relatively high dispersion optical material is selected for the negative lens constituting the refractive optical system part G from a state in which the chromatic aberration is corrected to some extent by using the refractive optical system part G as a partial system. At this time, the entire inclination of the wavelength-dependent characteristic curve of the chromatic aberration coefficient of the refractive optical system portion G changes while being bent larger than the original state on the short wavelength side.

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

  However, it is assumed that the refractive optical system portion GNL is made of a general optical material having a uniform partial dispersion ratio with respect to the Abbe number. In this case, the refractive optical system part GNL contributes at a constant rate simultaneously with the bending component and the inclination component of the wavelength-dependent characteristic curve of the chromatic aberration coefficient of the refractive optical system part G. For this reason, it is difficult to cancel these bending components and inclination components simultaneously.

  In contrast, it is assumed that the refractive optical system portion GNL is made of a material having a partial dispersion ratio larger than that of a general optical material. In this case, the refractive optical system part GNL mainly contributes to the bending component of the entire wavelength-dependent characteristic curve of the chromatic aberration coefficient of the main refractive optical system part G. For this reason, the bending component can be canceled mainly. As a result, the overall slope of the dependency characteristic curve of the chromatic aberration coefficient wavelength can be changed while increasing the linearity as compared with the original state.

  In this state, further, by giving the refractive optical system part GL an appropriate power (refractive power) having a sign different from that of the refractive optical system part GNL, the entire wavelength-dependent characteristic curve of the chromatic aberration coefficient of the refractive optical system part G is obtained. The inclination can be corrected.

  However, when the refractive optical system part GL is made of a general optical material, the refractive optical system part GL has a relatively large curve in the opposite direction to the curve of the wavelength-dependent characteristic curve of the chromatic aberration of the refractive optical system part G. Have.

  Therefore, the inclination component of the wavelength dependence characteristic curve of the chromatic aberration coefficient can be canceled as a whole optical system, but a bending component that deteriorates the chromatic aberration is generated.

  In order to correct the bending component of the wavelength dependent characteristic curve of the chromatic aberration coefficient generated at this time, it is necessary to change the power of the refractive optical system portion GNL made of a material having a large partial dispersion ratio. However, if the power is changed more, the thickness of the lens in the optical axis direction increases, which is not preferable.

  On the other hand, when the refractive optical system part GL is made of an optical material having a small partial dispersion ratio, the wavelength-dependent characteristic curve of the chromatic aberration coefficient of the refractive optical system part GL is relatively linear. That is, when the power of the refractive optical system portion GL is changed to control chromatic aberration, the inclination can be changed with the design reference wavelength as the rotation center while maintaining relatively linearity. For this reason, chromatic aberration can be favorably corrected.

  In this way, by using both the refractive optical system part GNL and the refractive optical system part GL as the main refractive optical system part G, it is relatively easy to simultaneously correct the slope component and the curved component of the wavelength-dependent characteristic curve of the chromatic aberration coefficient. be able to.

  When achromatic is performed using only one of the refractive optical system part GNL and the refractive optical system part GL, neither GNL or GL nor the refractive optical system part G changes the power of the lens surface relatively large. It is difficult to obtain a sufficient effect.

  That is, by using both refractive optical system parts GNL and GL, each refractive power can be relatively small, and as a result, the thickness of the solid material in the optical axis direction can be reduced. Further, by using both the refractive optical system parts GNL and GL, the refractive optical system part G can also obtain an achromatic effect without changing the power relatively large, so that various aberrations other than chromatic aberration do not change greatly. It will be over.

  At this time, from the viewpoint of correcting chromatic aberration independently, it is preferable that both the refractive optical system portion GNL and the refractive optical system portion GL have a small Abbe number, that is, are made of a highly dispersed material. Further, in the telephoto type optical system, it is preferable that at least one refractive optical system portion GNL, GL is provided on the enlargement side from the point P where the pupil paraxial ray intersects the optical axis.

  Next, this will be described using an axial chromatic aberration coefficient and a magnification chromatic aberration coefficient on the lens surface.

  Let Δψ be the power change at the surface of the refractive lens, ν be the Abbe number, and h and H be the heights from the optical axis through which the paraxial ray and the pupil paraxial ray pass through the lens surface. At this time, the axial chromatic aberration coefficient change ΔL and the magnification chromatic aberration coefficient change ΔT on the lens surface can be expressed as follows.

ΔL = h ² · Δψ / ν (a)
ΔT = h · H · Δψ / ν (b)
As is clear from the equations (a) and (b), the change in the aberration coefficients ΔL and ΔT with respect to the lens surface power change increases as the absolute value of the Abbe number decreases (that is, the variance increases). Therefore, if a high dispersion material with a small absolute value of the Abbe number is used, the amount of power change for obtaining the required chromatic aberration can be small.

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

  On the other hand, when a low dispersion material is used, the amount of power change for obtaining the necessary chromatic aberration increases, and accordingly, various aberrations such as spherical aberration change greatly, and the independence of chromatic aberration correction is weakened. Therefore, it is important for aberration correction that at least one lens surface of the lenses constituting the optical system is a refractive lens surface formed of a high dispersion material.

  It can also be seen from the equations (a) and (b) that the amount of change in the longitudinal chromatic aberration coefficient ΔL and the magnification chromatic aberration coefficient ΔT is determined by the heights h and H. From this, the position where the refractive optical system parts GNL and GL are suitable to be arranged in the optical system will be described.

  In order to correct chromatic aberration satisfactorily, it is necessary to simultaneously correct the inclination component and the bending component of the wavelength dependent characteristic of the chromatic aberration coefficient. However, if the power change Δψ is reduced, a sufficient chromatic aberration correction effect cannot be obtained. Conversely, when the power change Δψ is increased, the thickness of the optical element as a lens increases.

  The optical material having the anomalous partial dispersion characteristic that constitutes the refractive optical system parts GNL and GL generally has a low transmittance. Therefore, when used as a lens, it is necessary to make the thickness relatively thin. In addition, the smaller the thickness, the smaller the performance change with respect to the environmental change, and thus the environmental resistance is improved.

  That is, in order to reduce the thickness of the refractive optical system parts GNL and GL while obtaining a sufficient correction effect of chromatic aberration, the correction amount of the bending component and the inclination component of the wavelength dependent characteristic curve of the chromatic aberration coefficient should be adjusted appropriately. Is preferred. Since this correction amount is affected by the heights h and H from the equations (a) and (b), it varies depending on the position in the optical system where the refractive optical system portions GNL and GL are arranged. In other words, in order to correct chromatic aberration satisfactorily and reduce the power change of the refractive optical system parts GNL and GL at that time, it is important to appropriately select a place where the refractive optical system parts GNL and GL are arranged. is there.

  The position at which the refractive optical system portions GNL and GL are arranged can satisfactorily correct the chromatic aberration and reduce the power change, depending on the aberration structure of the optical system. The aberration structure varies depending on the type of optical system.

  In the telephoto type optical system of each embodiment, the refractive optical system parts GNL and GL are preferably arranged on the enlargement side from the point P. According to this, axial chromatic aberration and lateral chromatic aberration can be corrected satisfactorily. Further, in order to correct axial chromatic aberration and lateral chromatic aberration at the same time and to better correct the bending component and the inclination component of the wavelength-dependent characteristic curve of the chromatic aberration coefficient, the optical characteristics of the refractive optical system parts GNL and GL are conditional expressions (9 ) Is preferably satisfied.

  At this time, the product φ1 × φ2 of the refractive power (φ1) of the refractive optical system part GNL and the refractive power (φ2) of the GL is required to cancel the bending component and the inclination component of the wavelength-dependent characteristic curve of the chromatic aberration coefficient. It is good to make it negative as shown in equation (8). These are due to the wavelength-dependent characteristics of chromatic aberration possessed by the telephoto type optical system.

Particularly preferably,
φ1> 0
φ2 <0
It is good to do.

  Generally, when a lens group moves during zooming, focusing, or image position correction, the state of light incident on each lens group changes.

  Along with this, the aberration generated in each lens group changes. Therefore, in order to satisfactorily correct the aberration of the entire optical system in all use states, it is preferable to give an aberration coefficient that is continuous in all use states for each lens group. If the refractive optical elements GNL and GL are arranged in the same lens group, a desired aberration can be easily obtained.

  Moreover, when the refractive optical elements GNL and GL are thin, fluctuations in the environment are reduced. Further, when the conditional expression (8) is satisfied, fluctuations in the environment of the refractive optical elements GNL and GL cancel each other, so that the environmental resistance is improved.

  The refractive optical system portions GNL and GL are combined with a general optical material to correct various aberrations including chromatic aberration. Therefore, it is preferable for aberration correction that the partial dispersion ratio has characteristics different from those of general optical materials, but it is not good if the abnormal partial dispersion is too strong.

  When a lens made of a material having a characteristic far from that of a general optical material is used, the bending of the wavelength-dependent characteristic of the chromatic aberration coefficient on the lens surface is particularly large. In order to correct the large bending component, the power of other lenses must be increased. At this time, spherical aberration, coma aberration, astigmatism, etc. are greatly affected, making it difficult to correct aberrations.

  That is, it is preferable that the material of the refractive optical system partial GNL is an optical material having a partial dispersion ratio larger than that of a general optical material, and the partial dispersion ratio is not too far compared with that of a general optical material.

  If the numerical range of the anomalous partial dispersibility ΔθgF1 in the conditional expression (2) is set to the following range, a better chromatic aberration correction effect can be expected.

0.0272 <ΔθgF1 <0.2832 (2a)
Further, from the viewpoint of aberration correction, it is more desirable to set the numerical range of the conditional expression (2a) to the range shown below.

0.0342 <ΔθgF1 <0.2832 (2b)
If the numerical range of the anomalous partial dispersibility ΔθgF2 in the conditional expression (3) is set to the following range, a better chromatic aberration correction effect can be expected.

−0.4278 <ΔθgF2 <−0.0528 (3a)
More desirably, the numerical range of the conditional expression (3a) is set to the following range.

−0.4278 <ΔθgF2 <−0.0778 (3b)
If the numerical range of the anomalous partial dispersibility Δθgd1 in conditional expression (4) is set to the following range, a better chromatic aberration correction effect can be expected.

0.038 <Δθgd1 <0.347 (4a)
More preferably, the numerical range of the equation (4a) is set to the range shown below.

0.051 <Δθgd1 <0.347 (4b)
If the numerical range of the anomalous partial dispersibility Δθgd2 in the conditional expression (5) is set to the following range, a better chromatic aberration correction effect can be expected.

−0.5620 <Δθgd2 <−0.062 (5a)
More preferably, the numerical range of the equation (5a) is set to the range shown below.

−0.5620 <Δθgd2 <−0.112 (5b)
If the numerical ranges of the Abbe numbers νd1 and νd2 in the conditional expressions (6) and (7) are set to the following ranges, a better chromatic aberration correction effect can be expected.

νd1 <50 (6a)
νd2 <50 (7a)
More preferably, the numerical ranges of (6a) and (7a) are set to the ranges shown below.

νd1 <45 (6b)
νd2 <45 (7b)
More preferably, the numerical ranges of the conditional expressions (6b) and (7b) are set to the ranges shown below.

νd1 <40 (6c)
νd2 <40 (7c)
In each embodiment, the optical elements GNL1 and GL1 made of an optical material satisfying the conditional expressions (2) and (3) are applied to the lens in the optical system and the refractive power layer provided on the lens surface. It is more preferable that the refracting surface made of this optical material has an aspherical shape. According to this, chromatic aberration flare such as chromatic spherical aberration can be corrected. It is more preferable to form an interface between these optical elements and an atmosphere such as air, or to form an interface with an optical material having a relatively low refractive index. This is preferable because the chromatic aberration can be changed relatively large by a slight change in the curvature of the interface.

Next, each example in which an optical element formed of an optical material satisfying one or more of the conditional expressions (2) to (9) described above is applied to an optical system satisfying the conditional expression (1) will be described. Here, as an optical material satisfying the conditional expressions (2), (4), and (6), a UV curable resin 1, N-polyvinylcarbazole, and a mixture in which TiO ₂ fine particles are dispersed in the UV curable resin 2 are used. . As an optical material that satisfies the conditional expressions (3), (5), and (7), a mixture in which ITO fine particles are dispersed in the UV curable resin 2 and N-polyvinylcarbazole is used.

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

  FIG. 3 is a lens cross-sectional view of the optical system of Example 2, and 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, and 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, and 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, and FIG. 10 is an aberration diagram when the optical system of Example 5 is focused on an object at infinity.

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

  FIG. 13 is a schematic diagram of a main part of a camera (imaging device) including the optical system of the present invention.

  The optical system of each embodiment is a telephoto photographic lens system, and is used in an imaging apparatus such as a video camera, a digital camera, and 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, 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, and when used as a photographing lens of a video camera or a digital still camera, an imaging plane of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor is placed. In the case of a silver salt film camera, a photosensitive surface corresponding to the film surface is placed.

  In the aberration diagrams, d and g are d-line and g-line, ΔM and ΔS are meridional image surface, sagittal image surface, and lateral chromatic aberration are represented by g-line. ω is a half angle of view, and Fno is an F number.

  The optical system of Example 1 in FIG. 1 includes a first lens unit L1 having a positive refractive power that does not move during focusing, a second lens unit L2 that has a negative refractive power that moves in the optical axis direction for focusing, and does not move during focusing. The third lens unit L3 has a positive refractive power. The optical system of Example 1 is a telephoto lens having a focal length of 400 mm.

  Here, the first and second optical elements are included in the first lens group.

  In this embodiment, a lens (first optical element) GNL1 made of UV curable resin 1 as part of an optical system and a lens made of a mixture in which ITO fine particles are dispersed by 14.2% by volume in UV curable resin 2. This is an example using (second optical element) GL1.

  In FIG. 1, GNL 1 is a lens (layer) having a positive refractive power (power) formed of the UV curable resin 1. GL1 is a lens (layer) having a negative refractive power formed of a mixture of ITO.

  In the optical system of Example 1, the lens (layer) GNL1 and the lens (layer) GL1 are disposed on the object side surface of the first lens unit L1 where the passing position of the paraxial light beam from the optical axis is relatively high. Has been introduced. Further, these lenses GNL1, GL1 are in close contact with each other, and the contact surfaces thereof are aspherical and are joined between the lenses. As a result, axial chromatic aberration and lateral chromatic aberration are corrected well, and a very compact telephoto lens with a telephoto ratio of 0.764 is obtained.

  The optical system of Example 2 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 that has a negative refractive power that moves in the optical axis direction for focusing, and does not move during focusing. The third lens unit L3 has a positive refractive power. The optical system of Example 2 is a telephoto lens having a focal length of 300 mm.

  In this embodiment, a lens (first optical element) GNL1 made of UV curable resin 1 as part of an optical system and a lens made of a mixture in which ITO fine particles are dispersed by 14.2% by volume in UV curable resin 2. This is an example using (second optical element) GL1. In FIG. 3, GNL 1 is a lens (layer) having a positive refractive power formed of the UV curable resin 1. GL1 is a lens (layer) having a negative refractive power formed of a mixture of ITO.

  In the optical system of Example 2, the lens (layer) GNL1 and the lens (layer) GL1 are disposed on the object side surface of the first lens unit L1 where the passing position of the paraxial light beam from the optical axis is relatively high. Has been introduced. Further, these lenses GNL1, GL1 are used in close contact with each other, and the contact surfaces thereof are aspherical. As a result, axial chromatic aberration and lateral chromatic aberration are corrected well, and a very compact super telephoto lens with a telephoto ratio of 0.669 is obtained.

  The optical system of Example 3 in FIG. 5 includes a first lens unit L1 having a positive refractive power that does not move during focusing, a second lens unit L2 that has a negative refractive power that moves in the optical axis direction for focusing, and does not move during focusing. The third lens unit L3 having a positive refractive power. The optical system of Example 3 is a telephoto lens having a focal length of 300 mm.

In this embodiment, a lens (first optical element) GNL1 made of a mixture obtained by dispersing 20% by volume of TiO ₂ fine particles in the UV curable resin 2 is provided in a part of the optical system. Further, this is an example using a lens (second optical element) GL1 made of a mixture in which ITO fine particles are dispersed in the UV curable resin 2 by 20% by volume.

In FIG. 5, GNL1 is a lens (layer) having a positive refractive power formed of a mixture of TiO ₂ . GL1 is a lens (layer) having a negative refractive power formed of a mixture of ITO. In the optical system of Example 3, the first lens group in which the passing position of the paraxial light beam from the optical axis is relatively high. A lens (layer) GNL1 and a lens (layer) GL1 are introduced on the object side surface of L1. As a result, axial chromatic aberration and lateral chromatic aberration are corrected well, and a telephoto lens with a telephoto ratio of 0.669 is obtained.

  The optical system of Example 4 in FIG. 7 includes a first lens unit L1 having positive refractive power that does not move during focusing, a second lens unit L2 having negative refractive power that moves in the optical axis direction for focusing, and does not move during focusing. The third lens unit L3 having a positive refractive power. The optical system of Example 4 is a telephoto lens having a focal length of 300 mm.

  In this example, a lens (first optical element) GNL1 made of N-polyvinylcarbazole as a part of the optical system and a lens (first optical element) made by dispersing 5% by volume of ITO fine particles in the UV curable resin 2 (the first optical element). This is an example using two optical elements GL1.

  In FIG. 7, GNL1 is a lens (layer) having a positive refractive power formed of N-polyvinylcarbazole. GL1 is a lens (layer) having a negative refractive power formed of a mixture of ITO.

  In the optical system of Example 4, the lens (layer) GNL1 and the lens (layer) GL1 are disposed on the object side surface of the first lens unit L1 where the paraxial axial ray passes from the optical axis. Has been introduced. As a result, axial chromatic aberration and lateral chromatic aberration are corrected well, and a telephoto lens having a telephoto ratio of 0.720 is obtained.

  The optical system of Example 5 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 that has a negative refractive power that moves in the optical axis direction for focusing, and does not move during focusing. The third lens unit L3 has a positive refractive power. The optical system of Example 5 is a telephoto lens having a focal length of 300 mm.

In this embodiment, a lens (first optical element) GNL1 made of a mixture in which 3% by volume of TiO ₂ fine particles are dispersed in a UV curable resin 2 is provided in a part of the optical system. Furthermore, this is an example using a lens (second optical element) GL1 made of a mixture in which ITO fine particles are dispersed in N-polyvinylcarbazole at a volume ratio of 10%.

In FIG. 9, GNL1 is a lens (layer) having a positive refractive power formed of a mixture of TiO ₂ . GL1 is a lens (layer) having a negative refractive power formed of a mixture of ITO.

  In the optical system of Example 5, the lens (layer) GNL1 and the lens (layer) GL1 are arranged on the object side surface of the first lens unit L1 where the paraxial axial ray passes from the optical axis. Has been introduced. Thus, the axial chromatic aberration and the lateral chromatic aberration are corrected well, and a telephoto lens having a telephoto ratio of 0.748 is obtained.

  The optical system of Example 6 in FIG. 11 includes a first lens unit L1 having a positive refractive power that does not move during focusing, a second lens unit L2 that has a negative refractive power that moves in the optical axis direction for focusing, and does not move during focusing. The third lens unit L3 has a positive refractive power. The optical system of Example 6 is a telephoto lens having a focal length of 300 mm.

  In this embodiment, a lens (first optical element) GNL1 made of UV curable resin 1 as a part of the optical system and a lens (first optical element) made by dispersing 5% by volume of ITO fine particles in UV curable resin 2 (first optical element). This is an example using two optical elements GL1.

  In FIG. 11, GNL 1 is a lens (layer) having a positive refractive power formed of the UV coin resin 1. GL1 is a lens (layer) having a negative refractive power formed of a mixture of ITO.

  In the optical system of Example 6, the lens (layer) GNL1 and the lens (layer) GL1 are disposed on the object side surface of the first lens unit L1 where the passing position of the paraxial light beam from the optical axis is relatively high. Has been introduced. As a result, axial chromatic aberration and lateral chromatic aberration are corrected satisfactorily, and a telephoto lens with a telephoto ratio of 0.737 is obtained.

Hereinafter, specific numerical data will be shown for numerical examples 1 to 6 corresponding to the first to sixth embodiments. In each numerical example, i indicates the number of the surface counted from the object side, and Ri is the radius of curvature of the i-th optical surface (i-th surface). Di is an axial distance between the i-th surface and the (i + 1) -th surface. Ni and νi represent the refractive index and the Abbe number of the optical member material of the i-th (excluding the lens (layer) formed of resin, TiO ₂ fine particle dispersion material or ITO fine particle dispersion material) with respect to the d line. The refractive index and Abbe number for the d-line of the lens GNLj formed of resin or TiO ₂ fine particle dispersion material are separately indicated as NGNLj, νGNLj (j = 1, 2,...). Further, the refractive index and Abbe number for the d-line of the lens GLj formed of a resin or ITO fine particle dispersion material are separately indicated as NGLj, νGLj (j = 1, 2,...). f is the focal length of the optical system, Fno is the F number, and ω is the half angle of view.

  Further, the aspherical shape is such that X is the amount of displacement from the surface vertex in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, r is the paraxial radius of curvature, k is the conic constant, B, When C, D, E... Are the aspheric coefficients of the respective orders,

Represented by

“E ± XX” in Table 3 and each aspheric coefficient means “× 10 ^{± XX} ”.

Refractive indexes of the refractive optical system parts GNL1 and GL1 used for each numerical example with respect to d-line, g-line, C-line, and F-line, and Abbe number, partial dispersion ratio, power, and numerical values corresponding to conditional expression (1) Is shown in Table 1. Table 2 shows the refractive index, Abbe number, and partial dispersion ratio of the UV effect resin 2 and ITO and TiO ₂ with respect to the d-line, g-line, C-line, and F-line. Table 3 shows numerical values corresponding to the conditional expression (9) of the refractive optical elements GNLj and GLj in each numerical example.

  Next, an embodiment of a digital still camera using the optical system shown in each example as a photographing optical system will be described with reference to FIG.

  In FIG. 13, 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 the first to seventh embodiments. 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.

2 is an optical system sectional view of an optical system according to Numerical Example 1. FIG. FIG. 6 is an aberration diagram of Numerical Example 1. 6 is an optical system cross-sectional view of an optical system according to Numerical Example 2. FIG. FIG. 6 is an aberration diagram of Numerical Example 2. 6 is an optical system cross-sectional view of an optical system according to Numerical Example 3. FIG. FIG. 10 is an aberration diagram of Numerical Example 3. 10 is an optical system cross-sectional view of an optical system according to Numerical Example 4. FIG. 10 is an aberration diagram of the optical system according to Numerical Example 4. FIG. 10 is an optical system sectional view of an optical system according to Numerical Example 5. FIG. FIG. 10 is an aberration diagram of Numerical Example 5. 10 is an optical system sectional view of an optical system according to Numerical Example 6. FIG. 10 is an aberration diagram of the optical system according to Numerical Example 6. FIG. It is a principal part schematic of the imaging device of this invention. It is explanatory drawing of paraxial refractive power arrangement | positioning of the optical system of this invention. It is a figure of the wavelength characteristic of the refractive index of a common optical element.

Explanation of symbols

OL optical system Gp front group Gn rear group Q paraxial on-axis ray R pupil paraxial ray GNL1 first optical element GL1 second optical element L1 first lens group L2 second lens group L3 third lens group SP aperture stop IP image Surface d d line g g line ΔM meridional image surface ΔS sagittal image surface

Claims (9)

When the point where the optical axis and the pupil paraxial ray intersect is P, the maximum height from the optical axis through which the paraxial ray passes through the lens surface on the enlargement side from the point P is reduced from the point P. In the optical system in which the paraxial beam on the side is larger than the maximum height from the optical axis passing through the lens surface, the light incident / exit surface is refracted at least on the enlargement side or the reduction side from the point P. The first and second optical elements made of a solid material on the surface have anomalous partial dispersibility with respect to g-line and F-line of the solid material of the first and second optical elements, respectively, ΔθgF1, ΔθgF2, When the refractive power when the light incident / exit surfaces of the two optical elements are both surfaces in contact with air is φ1 and φ2, respectively,
ΔθgF1> 0.0272
ΔθgF2 <−0.0278
φ1 × φ2 <0
An optical system characterized by satisfying the following conditions. When the focal length of the entire optical system is ft and the total lens length is Lt,
Lt / ft <1.0
The optical system according to claim 1, wherein the following conditional expression is satisfied. When the anomalous partial dispersibility for the g-line and d-line of the solid material of the first and second optical elements is Δθgd1 and Δθgd2, respectively.
Δθgd1> 0.038
Δθgd2 <−0.037
The optical system according to claim 1, wherein the following conditional expression is satisfied. When the Abbe numbers of the solid materials of the first and second optical elements are νd1 and νd2, respectively,
νd1 <60
νd2 <60
The optical system according to claim 1, wherein the following conditional expression is satisfied.   5. The optical system according to claim 1, wherein both the first optical element and the second optical element are located on an enlargement side with respect to the point P. 6. The φ1 and φ2 are
φ1> 0
φ2 <0
The optical system according to claim 1, wherein the following conditional expression is satisfied. When the Abbe numbers of the solid materials of the first and second optical elements are νd1 and νd2, respectively,
(Φ1 × ΔθgF1 ÷ νd1) / (φ2 × ΔθgF2 ÷ νd2) <1.5
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, 8. The lens unit according to claim 1, wherein the first lens unit includes a third lens unit having positive refractive power that does not move, and the first and second optical elements are included in the first lens unit. The optical system according to item. An optical apparatus comprising the optical system according to claim 1.

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