JP4944586B2 - Optical system and optical apparatus having the same - Google Patents

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 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 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) Reference 6).

Further, as a solid material having an anomalous partial dispersion characteristic, there is known an optical system in which 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 7). .
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 Japanese Patent Laid-Open No. 2005-181392 JP 2006-145823 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 length of the lens 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.

  Solid materials having anomalous partial dispersion characteristics disclosed in Patent Documents 6 and 7 have a relatively low transmittance as compared with general optical materials.

  In order to prevent a decrease in the 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 and 7 is used as a lens or a layer having refractive power in an optical system, the thickness in the optical axis direction is reduced. However, it is important to correct chromatic aberration.

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

The optical system of the present invention, when the point of intersection of the optical axis and the paraxial chief ray is P, at least one of enlargement side or reduced side than the point P, the light input and morphism surface is made of solid material together with the refractive surface The first and second optical elements have anomalous partial dispersibility with respect to the g-line and F-line of the first and second optical elements, respectively, ΔθgF1, ΔθgF2, and the focal lengths of the first and second optical elements, respectively. , F2,
ΔθgF1> 0.0272
ΔθgF2 <−0.0278
f1 × f2 <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.

  The optical system of the present invention uses a refractive optical element (hereinafter, also simply referred to as “optical element”) in which a solid material that satisfies the conditions described later has a refractive action.

  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.

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

  The paraxial light beam is a paraxial light beam obtained when normal light having a focal length of 1 is incident on the optical system in parallel with the optical axis of the optical system. It is. In the following, it is assumed that the object is on the left side of the optical system, and light rays incident on the optical system from the object side travel from left to right. Also, the pupil paraxial ray 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 near paraxial ray passing through the intersection of the entrance pupil of the optical system and the optical axis. An axial ray. Hereinafter, the incident angle to the optical system is measured clockwise from the optical axis and positive in the counterclockwise direction. 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 with respect to the point P, first and second optical elements GNL1 and GL1 made of a solid material, both of which are light refracting surfaces and light refracting surfaces, are provided. Anomalous partial dispersibility of the first and second optical elements GNL1 and GL1 regarding the g-line and the F-line is denoted by ΔθgF1 and ΔθgF2, respectively.

  The focal lengths when the light incident / exit surfaces of the first and second optical elements GNL1 and GL1 are both in contact with air are denoted by f1 and f2, respectively.

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

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

  At this time, one or more of the following conditions are satisfied.

ΔθgF1> 0.0272 (1)
ΔθgF2 <−0.0278 (2)
Δθgd1> 0.038 (3)
Δθgd2 <−0.037 (4)
νd1 <60 (5)
νd2 <60 (6)
f1 × f2 <0 (7)
The anomalous partial dispersibility and Abbe number of the solid material of the optical element used in the optical system of the present example are as follows.

  The refractive indexes of the Fraunhofer line for g-line (435.8 nm), F-line (486.1 nm), d-line (587.6 nm), and C-line (656.3 nm) are Ng, NF, Nd, and NC, respectively. To do. 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.

  At least one refractive optical element GNL1 formed of a solid material satisfying the conditional expression (1) and one refractive optical element GL1 formed of a solid material satisfying the conditional expression (2) are used in the optical system. Thus, the chromatic aberration is corrected well over the entire visible wavelength range.

  By satisfying conditional expressions (3) and (4), it is easy to satisfactorily correct chromatic aberration between the short wavelength and the intermediate wavelength. Thus, chromatic aberration can be corrected more favorably in a wide wavelength range from a short wavelength to a long wavelength.

  By using a solid material that satisfies the conditional expressions (5) and (6), correction of chromatic aberration is facilitated.

  By configuring the first and second optical elements GNL1 and GL1 so as to satisfy the conditional expression (7), chromatic aberration is corrected well over a wide wavelength range.

  In the present embodiment, when the first and second optical elements GNL1 and GL1 are provided in the optical system, both are preferably provided in the same lens group. At this time, the first and second optical elements GNL1, GL1 may be joined to each other.

  In view of aberration correction, it is preferable that at least one surface of the first and second optical elements GNL1 and GL1 has an aspherical shape.

  In view of aberration correction, it is preferable that at least one surface of the first and second optical elements GNL1, GL1 is in contact with air.

  As a specific example of the solid material (hereinafter, also referred to as “optical material”) that satisfies the conditional expression (1), there is a resin, for example. 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 (1). The solid material is not limited to these as long as it satisfies the conditional expression (1).

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 1) is obtained. Further, when ITO (Indium-Tin-Oxide) (Nd = 1.8571, νd = 5.69, θgF = 0.873) fine particles are dispersed in a synthetic resin at an appropriate volume ratio, the above conditional expression (2 ) Is obtained. The solid material is not limited to these as long as it satisfies the conditional expression (2).

  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 the glass material S-TIH53 manufactured by OHARA is as shown in FIG.

  And a high dispersion optical material with a smaller Abbe number tends to increase the partial dispersion ratio. In a general optical material, the partial dispersion ratio changes substantially 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.

  Compared with a general optical material, an optical material having a large partial dispersion ratio has a characteristic that a wavelength-dependent characteristic curve of a 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, it is possible to cancel the bending of the wavelength dependence characteristic curve of the chromatic aberration coefficient on the short wavelength side. 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 necessary to change the power of an appropriate glass surface in the optical system, but this 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 with a small partial dispersion ratio in addition to an optical material with 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. Become. 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.

  The refractive optical system part GNL using an optical material having a large partial dispersion ratio, the 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. The chromatic aberration correction of the optical system constituted by the refractive optical system part G using the material 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. The wavelength-dependent characteristic curve of the chromatic aberration coefficient of the refractive optical system portion G changes the overall inclination 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, when 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, the refractive optical system portion GNL is dependent on the wavelength dependence of the chromatic aberration coefficient of the refractive optical system portion G. Contributes at a constant rate at the same time as the curve component and slope component of the characteristic curve. For this reason, since it is impossible to cancel the bending component and the inclination component at the same time, it is difficult to correct chromatic aberration satisfactorily.

  On the other hand, when the refractive optical system portion GNL is made of a material having a partial dispersion ratio larger than that of a general optical material, the refractive optical system portion GNL is dependent on the wavelength dependence of the chromatic aberration coefficient of the main refractive optical system portion G. It contributes relatively greatly to the bending component of the entire characteristic curve. 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, the entire refractive index of the wavelength-dependent characteristic curve of the chromatic aberration coefficient of the refractive optical system part G is corrected by giving the refractive optical system part GL an appropriate power having a sign different from that of the refractive optical system part GNL. be able to. 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.

  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.

  In this way, by using the refractive optical system part GNL, the refractive optical system part GL, and the refractive optical system part G, it is relatively easy to simultaneously correct the inclination component and the bending component of the wavelength-dependent characteristic curve of the chromatic aberration coefficient. it can.

  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 the refractive optical system portion GNL and the refractive optical system portion 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 part GNL and the refractive optical system part GL, the refractive optical system part G can also obtain an achromatic effect without changing the power relatively large. There will be no major changes.

  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, it is preferable that at least one refractive optical system portion GNL, GL is provided on the enlargement side or the reduction side from the point P where the pupil paraxial ray intersects the optical axis. This will be described using the axial chromatic aberration coefficient and the lateral 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 apparent from the equations (a) and (b), the change of each aberration coefficient with respect to the power change of the lens surface becomes larger as the absolute value of the Abbe number is smaller (that is, the variance is larger). Therefore, if a high dispersion material having a small absolute value of the Abbe number is used, the amount of power change for obtaining the necessary 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 axial chromatic aberration coefficient and the lateral chromatic aberration coefficient is determined by the values of 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 correct these inclination components and bending components simultaneously. 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 other words, in order to reduce the thickness of the refractive optical system parts GNL and GL while obtaining a sufficient correction effect for chromatic aberration, the influence of the chromatic aberration coefficient on the bending component and the inclination component of the wavelength-dependent characteristic curve should be approximately the same. Is preferred. For this purpose, it is desirable that the values of the heights h and H from the optical axis in the refractive optical system parts GNL and GL are close to each other.

  The sign of the value of the height H is different between the enlargement side and the reduction side of the point P. That is, when the refractive optical system portions GNL and GL are arranged on the enlargement side and the reduction side of the point P, the values that the heights h and H can take are greatly different. Accordingly, it is preferable in terms of chromatic aberration correction that the refractive optical system parts GNL and GL are arranged at least one by one on the enlargement side or reduction side of the point P. At this time, in order to cancel the bending component and the inclination component of the wavelength dependence characteristic curve of the chromatic aberration coefficient, the product of the focal length (f1) of the refractive optical system portion GNL and the focal length (f2) of the GL is a conditional expression (7 ) As long as it is negative.

  The maximum height from the optical axis when the ray on the paraxial axis passes through the lens surface on the enlargement side from the intersection point P of the optical axis and the pupil paraxial ray, and the ray on the paraxial axis on the reduction side from the intersection point P. An optical system that is larger than the maximum height from the optical axis when passing through the lens surface is a telephoto type optical system. In the telephoto type optical system, if the GNL and the GL are arranged on the enlargement side from the P, the axial chromatic aberration and the lateral chromatic aberration can be favorably corrected.

  On the other hand, the maximum value from the optical axis when the paraxial light beam passes through the lens surface on the enlargement side from the intersection point P is when the paraxial light beam passes through the lens surface on the reduction side from the intersection point P. An optical system smaller than the maximum height from the optical axis is a retrofocus type optical system. In the retrofocus type optical system, if GNL and GL are arranged on the reduction side from P, axial chromatic aberration and lateral chromatic aberration can be corrected satisfactorily.

  If the refractive optical system parts GNL and GL are arranged relatively apart from each other in the optical axis direction, the values of the heights h and H on the respective lens surfaces are greatly different. At this time, the values of the aberration coefficients ΔL and ΔT on the respective lens surfaces are greatly different. For this reason, the influence of the chromatic aberration coefficient of the entire optical system on the inclination component and the bending component of the wavelength-dependent characteristic curve is also greatly different.

  Conversely, when the refractive optical system parts GNL and GL are arranged close to each other in the optical system, the values of the heights h and H are relatively close to each lens surface. At this time, the influence of the chromatic aberration coefficient of the entire optical system on the bending component and the inclination component of the wavelength-dependent characteristic curve is almost the same, and the chromatic aberration can be corrected satisfactorily.

  Accordingly, it is preferable that the refractive optical system parts GNL and GL are arranged close to each other, for example, bonded. In addition, since the heights h and H do not change to the same extent in the same lens group in the optical system, it is more preferable to arrange the refractive optical system parts GNL and GL in the same lens group.

  In general, during zooming, focusing, and image position correction, the state of light incident on each lens group changes due to the movement of the lens group, and the aberration generated in each lens group changes accordingly. Therefore, in order to satisfactorily correct the aberration of the entire optical system in all use states, it is necessary to provide 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.

  In addition, when the refractive optical elements GNL and GL are thin, fluctuations in the environment are reduced, and furthermore, fluctuations in the environment are canceled when the condition (7) is satisfied, 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 necessary for aberration correction that these partial dispersion ratios have 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.

  In other words, it is important that the material of the refractive optical system partial GNL is an optical material having a large partial dispersion ratio compared to a general optical material, and that the partial dispersion ratio is not too far compared with a general optical material.

  If the numerical range of the anomalous partial dispersibility ΔθgF1 in the conditional expression (1) is set to the following range, a better chromatic aberration correction effect can be expected.

0.0272 <ΔθgF1 <0.2832 (1a)
Further, from the viewpoint of aberration correction, it is more desirable to set the numerical range of (1a) to the range shown below.

0.0342 <ΔθgF1 <0.2832 (1b)
By setting the numerical range of the anomalous partial dispersibility ΔθgF2 in the conditional expression (2) to the following range, a further excellent chromatic aberration correction effect can be expected.

−0.4278 <ΔθgF2 <−0.0528 (2a)
More preferably, the numerical range of the formula (2a) is set to the range shown below.

−0.4278 <ΔθgF2 <−0.0778 (2b)
When the numerical range of the anomalous partial dispersibility Δθgd1 in the conditional expression (3) is set to the following range, a better chromatic aberration correction effect can be expected.

0.038 <Δθgd1 <0.347 (3a)
More preferably, the numerical range of the expression (3a) is set to the following range.

0.051 <Δθgd1 <0.347 (3b)
By setting the numerical range of the anomalous partial dispersibility Δθgd2 in the conditional expression (4) to the following range, a better chromatic aberration correction effect can be expected.

−0.5620 <Δθgd2 <−0.062 (4a)
More preferably, the numerical range of the equation (4a) is set to the range shown below.

−0.5620 <Δθgd2 <−0.112 (4b)
When the numerical ranges of the Abbe numbers νd1 and νd2 in the conditional expressions (5) and (6) are set to the following ranges, a further excellent chromatic aberration correction effect can be expected.

νd1 <50 (5a)
νd2 <50 (6a)
More preferably, the numerical ranges of (5a) and (6a) are set to the ranges shown below.

νd1 <45 (5b)
νd2 <45 (6b)
More preferably, the numerical ranges of the conditional expressions (5b) and (6b) are set to the ranges shown below.

νd1 <40 (5c)
νd2 <40 (6c)
In each embodiment, the optical elements GNL1 and GL1 made of an optical material satisfying the conditional expressions (1) and (2) are applied to the lens in the optical system and the refractive layer provided on the lens surface. If the refracting surface made of this optical material is aspherical, chromatic aberration flare such as chromatic spherical aberration can be corrected. In addition, if an interface is formed between these optical elements and an atmosphere such as air, or an interface is formed with an optical material having a relatively low refractive index, the chromatic aberration is relatively large due to a slight change in the curvature of the interface. This is preferable because it can be changed.

Next, an embodiment in which an optical element formed from an optical material that satisfies the conditional expressions (1) to (7) described above is applied to a specific optical system will be described. Here, as an optical material satisfying the conditional expressions (1), (3), and (5), 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 (2), (4), and (6), a mixture in which ITO fine particles are dispersed in the UV curable resin 2 and N-polyvinylcarbazole is used.

  FIG. 1 is a cross-sectional view at the wide-angle end (short focal length) when the zoom lens as the optical system of Example 1 is used.

  2A, 2B, and 2C are aberration diagrams when focusing on an object at infinity at the wide-angle end, the intermediate zoom position, and the telephoto end (long focal length) of the zoom lens of Embodiment 1, respectively. is there.

  FIG. 3 is a lens cross-sectional view of the optical system according to the second embodiment of the present invention, and FIG. 4 is an aberration diagram when focusing on an object at infinity according to the second embodiment of the optical system of the present invention.

  FIG. 5 is a lens cross-sectional view of the optical system according to the third embodiment of the present invention. FIG. 6 is an aberration diagram when focusing on an object at infinity according to the third embodiment of the optical system of the present invention.

  FIG. 7 is a lens cross-sectional view of Embodiment 4 of the optical system of the present invention, and FIG. 8 is an aberration diagram when focusing on an infinite object of Embodiment 4 of the optical system of the present invention.

  FIG. 9 is a lens cross-sectional view of Example 5 of the optical system of the present invention, and FIG. 10 is an aberration diagram when focusing on an infinite object of Example 5 of the optical system of the present invention.

  FIG. 11 is a lens cross-sectional view of Embodiment 6 of the optical system of the present invention, and FIG. 12 is an aberration diagram when focusing on an infinite object in Embodiment 6 of the optical system of the present invention.

  13 is a lens cross-sectional view of Embodiment 7 of the optical system of the present invention, and FIG. 14 is an aberration diagram when focusing on an infinite object of Embodiment 7 of the optical system of the present invention.

  FIG. 15 is a schematic view of a main part of a camera (imaging device) provided with the optical system of the present invention.

  The optical system of each embodiment is a photographic lens system used in an imaging apparatus such as a video camera, a digital camera, or a silver salt film camera. In the lens cross-sectional view, the left side is the subject 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. G is an optical block corresponding to an optical filter, a face plate, a quartz low-pass filter, an infrared cut filter, or the like.

  IP is an image plane. When used as a photographing lens for a video camera or a digital still camera, the imaging surface of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor is used. A photosensitive surface corresponding to the film surface is placed.

  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, in order from the object side to the image side, a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a third lens unit having a positive refractive power. L3 is a zoom lens having a four-group configuration having a zoom ratio of about 12 and comprising a fourth lens unit L4 having a positive refractive power.

  The arrows indicate the movement trajectory of each lens unit during zooming from the wide-angle end to the telephoto end.

  During zooming, the lens groups are moved so that the distance between the lens groups changes.

  In this embodiment, a lens made of a mixture of UV curable resin and ITO fine particles is used as a part of the optical system. In FIG. 1, GNL 1 is a lens (layer) formed of the UV curable resin 1. GL1 is a lens (layer) formed of a mixture in which ITO fine particles are dispersed in the UV curable resin 2 by a volume ratio of 14.2%.

In the first embodiment, among the lens groups constituting the zoom lens, UV curing is applied to the first lens unit L1 on the object side that does not move at the time of focusing when the passing position of the paraxial light beam from the optical axis is relatively high. A lens GNL1 made of resin 1 and a lens GL1 made of a mixture of ITO fine particles are introduced. The lens GNL1 and the lens GL1 are in close contact with each other and are joined between the lenses.

  The lens (layer) GNL1 formed of the UV curable resin 1 has a positive refractive power, and the lens (layer) GL1 formed of a mixture of ITO fine particles has a negative refractive power. As a result, in zooming from the wide-angle end to the telephoto end, axial chromatic aberration and lateral chromatic aberration are corrected well, and the entire optical system is made compact.

  The optical systems of Examples 2 to 6 in FIGS. 3, 5, 7, 9, and 11 are telephoto imaging lenses. Here, the telephoto photographic lens means a lens system in which the total lens length is shorter than the focal length.

The optical system of Example 2 in FIG. 3 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 a positive lens unit L2. This is a super-telephoto lens having a focal length of 300 mm and comprising a third lens unit L3 having a refractive power.

  In this example, a lens GNL1 made of UV curable resin 1 is used as a part of the optical system, and a lens GL1 made of a mixture obtained by dispersing 14.2% by volume of ITO fine particles in UV curable resin 2 is used. It is. In FIG. 3, GNL 1 is a lens (layer) formed of the UV curable resin 1. GL1 is a lens (layer) formed of a mixture of ITO.

  In the optical system of the second embodiment, a lens (layer) GNL1 having a positive power made of UV curable resin 1 and ITO fine particles are disposed on the object side where the passing position of the paraxial light beam from the optical axis is relatively high. A lens (layer) GL1 having a negative power made of a mixture is 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 0.681 is obtained.

  The optical system of Example 3 in FIG. 5 includes a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power that moves in the optical axis direction for focusing, and a third lens unit having a positive refractive power. This is a super telephoto lens having a focal length of 300 mm, which is composed of the lens unit L3.

In this example, a lens GNL1 made of a mixture in which 20% by volume of TiO ₂ fine particles are dispersed in a UV curable resin 2 in a part of the optical system, and 20% by volume of ITO fine particles in a UV curable resin 2 are dispersed. This is an example using a lens GL1 made of a mixed material. In FIG. 5, GNL1 is a lens (layer) formed of a mixture of TiO ₂ . GL1 is a lens (layer) formed of a mixture of ITO. In the optical system of Example 3, TiO ₂ fine particles are mixed on the object side where the passing position of the paraxial light beam from the optical axis is relatively high. A lens (layer) GNL1 having a positive power consisting of a body and a lens (layer) GL1 having a negative power consisting of a mixture of ITO fine particles are introduced. As a result, axial chromatic aberration and lateral chromatic aberration are corrected well, and a compact super telephoto lens with a telephoto ratio of 0.680 is obtained.

  7 includes a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power moving in the optical axis direction for focusing, and a third lens unit having a positive refractive power. This is a super telephoto lens having a focal length of 300 mm, which is composed of the lens unit L3.

  In this example, a lens GNL1 made of N-polyvinylcarbazole and GL1 made of a mixture in which ITO fine particles are dispersed in a volume ratio of 5% in the UV curable resin 2 are used as a part of the optical system. In FIG. 7, GNL1 is a lens (layer) formed of N-polyvinylcarbazole. GL1 is a lens (layer) formed of a mixture of ITO.

In the optical system of Example 4, a lens (layer) GNL1 having a positive power made of a mixture of TiO ₂ fine particles is disposed on the object side where the passing position of the paraxial light beam from the optical axis is relatively high, and ITO. A lens (layer) GL1 having a negative power made of a mixture of fine particles is introduced. Thereby, axial chromatic aberration and lateral chromatic aberration are corrected well, and a compact super telephoto lens with a telephoto ratio of 0.731 is obtained.

  9 includes a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power moving in the optical axis direction for focusing, and a third lens having a positive refractive power. This is a super telephoto lens having a focal length of 300 mm and composed of the group L3.

In this example, a lens GNL1 made of a mixture obtained by dispersing 3% by volume of TiO ₂ fine particles in UV curable resin 2 in a part of the optical system, and 10% by volume of ITO fine particles in N-polyvinylcarbazole are dispersed. It is an example using GL1 which consists of the made mixture. In FIG. 9, GNL1 is a lens (layer) formed of a mixture of TiO ₂ . GL1 is a lens (layer) formed of a mixture of ITO.

In the optical system of Example 5, a lens (layer) GNL1 having a positive power made of a mixture of TiO ₂ fine particles is disposed on the object side where the passing position of the paraxial light beam from the optical axis is relatively high, and ITO. A lens (layer) GL1 having a negative power made of a mixture of fine particles is introduced. As a result, axial chromatic aberration and lateral chromatic aberration are corrected well, and a compact super telephoto lens with 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, a second lens unit L2 having a negative refractive power that moves in the optical axis direction for focusing, and a third lens having a positive refractive power. This is a super telephoto lens having a focal length of 300 mm and composed of the group L3.

  In this example, a lens GNL1 made of UV curable resin 1 and GL1 made of a mixture in which ITO fine particles are dispersed in a volume ratio of 5% in UV curable resin 2 are used as part of the optical system. In FIG. 11, GNL 1 is a lens (layer) formed of the UV coin resin 1. GL1 is a lens (layer) formed of a mixture of ITO.

  In the optical system of Example 6, a lens (layer) GNL1 having a positive power made of UV curable resin and ITO fine particles are mixed on the object side where the passing position of the paraxial light beam from the optical axis is relatively high. A lens (layer) GL1 having a negative power composed of a body is introduced. As a result, axial chromatic aberration and lateral chromatic aberration are corrected well, and a compact super telephoto lens with a telephoto ratio of 0.737 is obtained.

  The optical system of Example 7 in FIG. 13 is a wide-angle (retro focus type) photographing lens. Here, the wide-angle photographic lens means a lens system whose focal length is shorter than the entire lens length.

  The optical system of Example 7 in FIG. 13 includes a first lens unit L1 having a negative refractive power that moves in the optical axis direction for focusing, a second lens unit L2 having a negative refractive power, and a third lens having a positive refractive power. This is a wide-angle lens having a focal length of 24.5 mm and made up of the group L3.

In this example, a lens GNL1 made of UV curable resin 1 and GL1 made of a mixture in which ITO fine particles are dispersed in a volume ratio of 5% in UV curable resin 2 are used as part of the optical system. In FIG. 13 , GNL 1 is a lens (layer) formed of the UV coin resin 1. GL1 is a lens (layer) formed of a mixture of ITO.

In the optical system of Example 7, the third lens unit L3 on the image side from the point P where the optical axis and the paraxial ray of the pupil cross each other has a lens (layer) GNL1 having a positive power made of UV curable resin, and ITO fine particles. A lens (layer) GL1 having a negative power made of a mixture is introduced. As a result, a wide-angle lens in which the longitudinal chromatic aberration and the lateral chromatic aberration are corrected well is obtained.

Hereinafter, specific numerical data will be shown for numerical examples 1 to 7 corresponding to the first to seventh 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 the axial distance between the i-th surface and the (i + 1) -th surface, and Ni and νi are the i-th lens (layer made of resin, TiO ₂ fine particle dispersion material or ITO fine particle dispersion material) with respect to the d line, respectively. ) Represents the refractive index and Abbe number of the optical member material. 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} ”.

  Five planes (surfaces with a radius of curvature ∞) closest to the image side in Numerical Example 1 correspond to insertion filters, optical low-pass filters, infrared cut filters, and the like.

Table 1 shows the refractive index, Abbe number, and partial dispersion ratio of the refractive optical system parts GNL1 and GL1 used in each numerical example for the d-line, g-line, C-line, and F-line. 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 the respective focal lengths fGNLj and fGLj 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. 15, 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 cross-sectional view at the wide-angle end of the optical system according to Numerical Example 1. FIG. FIG. 6 is an aberration diagram of Numerical Example 1. FIG. 6 is an aberration diagram of Numerical Example 1. 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. 10 is an optical system sectional view of an optical system according to Numerical Example 7. FIG. 10 is an aberration diagram of the optical system according to Numerical Example 7. FIG. It is a principal part schematic of the imaging device of this invention. It is a figure of the refractive index wavelength characteristic of a common optical element.

Explanation of symbols

OL optical system GNL1 optical element GL1 optical element L1 first lens group L2 second lens group L3 third lens group L4 fourth lens group SP aperture stop IP image surface d d line g g line G CCD force plate, low pass filter, etc. Glass block ΔM Meridional image surface ΔS Sagittal image surface

Claims (9)

When the point where the optical axis and the paraxial ray intersect with each other is P, the first and second optical elements made of a solid material are both refractive surfaces and refractive surfaces on at least one of the enlargement side or the reduction side from the point P. Anomalous partial dispersibility with respect to g-line and F-line of the first and second optical elements is defined as ΔθgF1, ΔθgF2, and the light incident / exit surfaces of the first and second optical elements are in contact with air, respectively. When the focal lengths are f1 and f2, respectively,
ΔθgF1> 0.0272
ΔθgF2 <−0.0278
f1 × f2 <0
An optical system that satisfies the following conditional expression: When the anomalous partial dispersions for the g-line and d-line of the first and second optical elements are 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. The first, at least one surface of the second optical element, an optical system of any one of claims 1 to 3, characterized in that an aspheric shape. The first, at least one surface of the second optical element is any one optical system of claim 1, characterized in that in contact with the air 4. The optical system includes, in order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, an aperture stop, a third lens group having a positive refractive power, and a positive refractive power. 2. The zoom lens according to claim 1, wherein the zoom lens is configured such that an interval between the lens groups changes during zooming, and the first and second optical elements are included in the first lens group. 6. The optical system according to any one of items 1 to 5 . The optical system includes a first lens group having positive refractive power that does not move during focusing from the object side to the image side, an aperture stop, and a second lens group having negative refractive power that moves in the optical axis direction for focusing. , a third lens group stationary positive refractive power during focusing, the first and second optical elements are one of claims 1, characterized in that included in the first lens group 5 Item 1 optical system. The optical system includes a first lens group having a negative refractive power that moves in the direction of the optical axis for focusing in order from the object side to the image plane, a second lens group having a negative refractive power that does not move during focusing , and an aperture stop. , a third lens group stationary positive refractive power during focusing, the first and second optical elements are one of claims 1, characterized in that included in the third lens group 5 Item 1 optical system. An optical apparatus characterized by comprising an optical system of any one of claims 1 to 8.