JP2009169129A - Optical system and optical equipment having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical system with a short overall lens length, which is easy to manufacture, excels in environmental resistance, and has high optical performance. <P>SOLUTION: The optical system includes an aperture diaphragm, a front group with positive refractive power closer to the object side than the aperture diaphragm, and a rear group with positive refractive power closer to the image side than the aperture diaphragm. The front group has: at least a first optical element made of a first solid material; a negative lens LnF, the aperture diaphragm side lens face of which is concave; and a positive lens LpF closer to the object side than the negative lens LnF. The rear group has: at least a second optical element made of a second solid material; a negative lens LnR, the aperture diaphragm side lens face of which is concave; and a positive lens LpR closer to the image side than the negative lens LnR. The focal lengths fF and fR of the front group and the rear group respectively, the focal lengths f of the entire system, the refractive powers ϕF (1/mm) and ϕR (1/mm) of the first and the second optical elements of the first and the second solid materials respectively are appropriately set. <P>COPYRIGHT: (C)2009,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, as the size of an optical system is reduced, various aberrations, particularly chromatic aberrations such as longitudinal chromatic aberration and lateral chromatic aberration, are generated, and the optical performance is deteriorated.

  As small-sized optical systems, there are known Gauss type types in which the respective lenses are arranged substantially symmetrically with respect to the aperture stop, and modified Gauss type (substantially symmetrical type) optical systems such as an orthometer type and a xenator type. In these optical systems, a front group having a positive refractive power is disposed closer to the object side than the aperture stop, and a rear group having a positive refractive power is disposed closer to the image side than the aperture stop.

  These optical systems can easily correct spherical aberration, coma aberration, field curvature, and the like by adopting a symmetrical or substantially symmetrical refractive power arrangement with respect to the aperture stop. Further, since the F number can be made relatively small (bright) and the angle of view can be made relatively wide, it is often used for a standard lens of a single-lens reflex camera, a document reading lens, and the like.

  In a Gauss type or modified Gauss type optical system, an optical material having a relatively high refractive index is used to satisfactorily correct various aberrations such as spherical aberration, coma aberration, and astigmatism. However, since an optical material with a high refractive index generally has high dispersion, it is difficult to satisfactorily correct both axial chromatic aberration and lateral chromatic aberration at the same time.

  For such a problem, a method using an anomalous dispersion material such as fluorite is known as a method for satisfactorily correcting axial chromatic aberration and lateral chromatic aberration at the same time in an optical system such as a Gaussian type or a modified Gaussian type ( Patent Document 1).

Also, an optically achromatic material using a solid material made of a mixture or resin in which TiO ₂ fine particles and Indium-Tin Oxide (ITO) fine particles are dispersed in a transparent medium, which is a solid material having anomalous dispersion. The system is known. (Patent Documents 2 and 3)
Published Japanese Patent Laid-Open No. 2001-337271 Published JP 2007-025653 Published Japanese Patent Application Laid-Open No. 2005-352266

  In a Gauss type or deformed Gauss type optical system that is often used as a standard lens for a camera or the like, achromaticity is performed using an optical material represented by fluorite and the like having a relatively small dispersion. In this optical system, chromatic aberration can be easily corrected when the total lens length is set longer than the focal length.

  However, if the total lens length is made shorter than the focal length, a large amount of chromatic aberration occurs, and it is difficult to correct this well. This is because the chromatic aberration correction method merely reduces chromatic aberration generated in a lens system having a positive refractive power by utilizing the low dispersion characteristics and anomalous dispersion characteristics of materials such as fluorite.

  To correct chromatic aberration that has deteriorated due to the shortening of the overall lens length, for example, when using a low dispersion glass with a large Abbe number such as fluorite, the chromatic aberration will change greatly 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, glass materials having anomalous dispersion characteristics such as fluorite have a problem that they are very difficult to process, and a surface is easily damaged, and there are problems in that the use location for an optical system is limited.

  Further, the solid material having anomalous dispersion has a low transmittance as compared with a general optical material. In order to prevent a decrease in transmittance as the entire optical system, it is desirable that the optical element made of a solid material having anomalous dispersion has a small thickness in the optical axis direction. However, in order to satisfactorily correct chromatic aberration using an optical element made of a solid material having anomalous dispersion, an optical element having a certain thickness is required.

  As the thickness of the optical element made of a solid material increases in the optical path, the variation in optical characteristics increases with environmental changes, and the environmental resistance deteriorates. Further, when the thickness of the optical element made of a solid material is increased, molding becomes difficult and manufacture becomes difficult.

  For this reason, when an optical element made of a solid material having anomalous dispersion is used in an optical system as a lens or a layer having refractive power, the thickness in the optical axis direction is made as thin as possible and chromatic aberration is effectively reduced. It is important to configure so that correction can be performed.

  Thus, while shortening the overall lens length, various aberrations including chromatic aberration are corrected well, and an optical system having high optical performance, good environmental resistance, high transmittance, and easy manufacture is obtained. It is important to set each element appropriately.

  For example, it becomes important to use an optical element made of a solid material having anomalous dispersion in an appropriate state in the optical path.

  The present invention is an optical system that can properly correct various aberrations, particularly chromatic aberration, that occur when the overall lens length is shortened, while preventing a decrease in transmittance and a deterioration in environmental resistance. And an optical apparatus including the same.

The optical system of the present invention is an optical system in which an aperture stop, a front group having a positive refractive power on the object side of the aperture stop, and a rear group having a positive refractive power on the image side of the aperture stop are arranged. ,
The front group includes at least one first optical element made of a first solid material, the light incident surface and the light exit surface being both refractive surfaces,
The lens surface on the aperture stop side has a concave negative lens LnF, and the positive lens LpF is closer to the object side than the negative lens LnF.
The rear group includes at least one second optical element made of a second solid material, the light incident surface and the light exit surface being both refractive surfaces,
The lens surface on the aperture stop side has a concave negative lens LnR, and a positive lens LpR on the image side of the negative lens LnR.
The focal lengths of the front group and the rear group are fF and fR, respectively, and the focal length of the entire system is f,
The anomalous dispersibility of the first and second solid materials with respect to g-line and F-line is expressed as ΔθgFF, ΔθgFR,
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 φF (1 / mm) and φR (1 / mm), respectively,
0.8 <fF / f <5.0
0.4 <fR / f <3.0
0.3 <fF / fR <10.0
Satisfying the conditional expression
ΔθgFF <−0.0278 or ΔθgFF> 0.0272
Either of them and ΔθgFR <−0.0278 or ΔθgFR> 0.0272
Or φF (1 / mm) × ΔθgFF> 0
φR (1 / mm) × ΔθgFR> 0
It satisfies the following conditional expression.

  According to the present invention, an optical system that is easy to manufacture, excellent in environmental resistance, and has high optical performance and a short overall lens length can be obtained.

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

  In the optical system of the present invention, a front group having a positive refractive power is disposed closer to the object side than the aperture stop, and a rear group having a positive refractive power is disposed closer to the image side than the aperture stop.

  The optical system of the present invention corresponds to, for example, a Gaussian lens or a Xenota lens. The front group in the optical system includes at least one first optical element composed of a lens (layer) formed of a first solid material, both of a light incident surface and a light exit surface in the optical path, and a refractive surface. The lens surface has a concave negative lens LnF and a positive lens LpF on the object side of the negative lens LnF.

  In the rear group, the light incident surface and the light exit surface are both refracting surfaces in the optical path, at least one second optical element made of the second solid material, a negative lens LnR having a concave lens surface on the aperture stop side, a negative lens A positive lens LpR is provided on the image side of the lens LnR.

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

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

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

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

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

  FIG. 14 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 photographing lens system used in an imaging apparatus such as a video camera, a digital camera, or a silver salt film camera, an image reading lens used in an image reading apparatus, or a projection lens used in a projection apparatus. 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.

  When the optical system of each embodiment is used as an image reading lens, the left side is the read image side and the right side is the image sensor side.

  In the lens cross-sectional view, OL is an optical system. GpF is a front group of positive refractive power arranged on the object side of the aperture stop SP, and GpR is a rear group of positive refractive power arranged on the image side of the aperture stop SP.

  The aperture stop SP is disposed between the front group GpF and the rear group GpR. 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.

  GeF1 is a first optical element composed of a lens (layer) made of a first solid material with both light incident side and light emission side being refracting surfaces. Hereinafter, “GeF1” may be simply abbreviated as “GeF”.

  LnF is a negative lens having a concave surface on the aperture stop SP side. LpF is a positive lens disposed closer to the object side than the negative lens LnF.

GeR1 and GeR2 are second optical elements composed of lenses (layers) made of a second solid material, both of which are light refracting surfaces and light refracting surfaces. Hereinafter, “GeR1, GeR2” may be simply abbreviated as “GeR”. LnR is a negative lens having a concave surface on the aperture stop SP side. LpR is a positive lens disposed closer to the image side than the negative lens LnR.

  The specific lens configuration of each example is as follows in order from the object side to the image side.

  In Example 1 of FIG. 1, the front group GpF includes a positive lens LpF, a positive meniscus lens Gpa convex on the object side, a negative lens LnF having a concave surface on the aperture stop SP side, and a first optical element GeF1. Yes.

  The first optical element GeF1 is bonded to the lens surface on the aperture stop SP (image side) side of the negative lens LnF.

  The rear group GpR includes a second optical element GeR1, a negative lens Gpb having a concave surface on the aperture stop SP side, and a positive lens LpR.

  The second optical element GeR1 is cemented to the lens surface on the aperture stop SP (object side) side of the negative lens LnR.

  In Example 2 of FIG. 3, the front group GpF is the same as that of Example 1. The rear group GpR includes a second optical element GeR1, a negative lens LnR having a concave surface on the aperture stop SP side, a positive lens Gpb1 having a convex surface on the image side, a positive lens Gpb2 having a convex surface on the image side, and a positive lens. It consists of LpR.

  The second optical element GeR1 is cemented to the lens surface on the aperture stop SP side of the negative lens LnR.

  In Example 3 of FIG. 5, the front group GpF is the same as Example 1. The rear group GpR includes a second optical element GeR1, a negative lens LnR having a concave surface on the aperture stop SP side, a biconvex positive lens Gpb1, a biconcave negative lens Gnb1, a biconvex positive lens Gpb2, and a positive lens. It consists of LpR.

  The second optical element GeR1 is cemented to the lens surface on the aperture stop SP side (object side) of the negative lens LnR.

  In Example 4 of FIG. 7, the front group GpF is composed of a positive lens LpF, a positive lens Gpa having a convex surface on the object side, a first optical element GeF1, and a negative lens LnF having a concave surface on the aperture stop SP side. .

  The first optical element GeF1 is bonded to both lenses between the positive lens Gpa and the negative lens LnF.

  The rear group GpR includes a second optical element GeR1, a negative lens LnR having a concave surface on the aperture stop SP side, and a positive lens LpR. The second optical element GeR1 is cemented to the negative lens LnR and the lens surface on the aperture stop SP (object) side.

  In Example 5 of FIG. 9, the front group GpF includes a positive lens LpF having a convex surface on the object side, a negative lens LnF having a concave surface on the aperture stop SP side, a positive lens Gpa, and a first optical element GeF1. Yes.

  The first optical element GeF1 is cemented to the lens surface on the aperture stop SP side (image side) of the positive lens Gpa. The rear group GpR includes a second optical element GeR1, a second optical element GeR2, a biconcave negative lens Gnb, a biconvex positive lens Gpb, a negative lens LnR having a concave surface on the aperture stop SP side, and a positive lens LpR. It is made up.

  The negative lens Gnb and the positive lens Gpb are cemented. The two second optical elements GeR1 and GeR2 are joined, and further joined to the lens surface on the aperture stop SP side (object side) of the negative lens Gnb.

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

  In the optical system of each example, the focal lengths of the front group GpF and the rear group GpR are set to fF and fR, respectively. Let f be the focal length of the entire system.

  The anomalous dispersibility of the first and second solid materials with respect to g-line and F-line is assumed to be ΔθgFF and ΔθgFR respectively.

The refractive power when the light incident / exit surfaces of the first and second optical elements GeF and GeR are both in contact with air (that is, when arranged in the air) is φF (1 / mm) and φR (1 / mm), respectively. ). At this time,
0.8 <fF / f <5.0 (1)
0.4 <fR / f <3.0 (2)
0.3 <fF / fR <10.0 (3)
The following conditional expression is satisfied.

Furthermore, ΔθgFF <−0.0278 or ΔθgFF> 0.0272 (4)
Satisfied either one. Furthermore, ΔθgFR <−0.0278 or ΔθgFR> 0.0272 (5)
Satisfied either one. Furthermore, φF (1 / mm) × ΔθgFF> 0 (6)
φR (1 / mm) × ΔθgFR> 0 (7)
The following conditional expression is satisfied.

  When there are a plurality of first and second optical elements, it is sufficient that at least one of the first and second optical elements satisfies the conditional expressions (1) to (7). The same applies to the following description.

  In each embodiment, it is more preferable to satisfy one or more of the following (Condition A1) to (Condition A6).

(Condition A1)
The anomalous dispersibility of the first and second solid materials with respect to g-line and d-line is assumed to be ΔθgdF and ΔθgdR, respectively. At this time,
ΔθgFF × ΔθgdF> 0 (8)
ΔθgFR × ΔθgdR> 0 (9)
Satisfying the following conditional expressions,
ΔθgdF> 0.038 or ΔθgdF <−0.037 (10)
Or ΔθgdR> 0.038 or ΔθgdR <−0.037 (11)
It is to satisfy any one of.

(Condition A2)
The Abbe numbers of the first and second solid materials at the d-line are νdF and νdR, respectively. At this time,
νdF <60 (12)
νdR <60 (13)
The following conditional expression is satisfied.

(Condition A3)
Let L be the distance along the optical axis from the point where the most object-side lens surface intersects the optical axis to the point where the most image-side lens surface intersects the optical axis. DeF is the distance along the optical axis from the point where the image side surface of the first optical element GeF intersects the optical axis to the aperture stop SP. DeR is the distance along the optical axis from the point where the object-side surface of the second optical element GeR intersects the optical axis to the aperture stop SP. At this time,
DeF / L <0.4 (14)
DeR / L <0.4 (15)
The following conditional expression is satisfied.

  All signs related to distance are handled as positive. This is all the same in this specification.

(Condition A4)
The Abbe numbers of the first and second solid materials at the d-line are νdF and νdR, respectively. At this time,
0.05 <(ΔθgFF × φF / νdF) / (ΔθgFR × φR / νdR) <10
(16)
The following conditional expression is satisfied.

(Condition A5)
DLnF is a distance along the optical axis from the point where the image side surface of the negative lens LnF intersects the optical axis to the aperture stop SP. DLnR is a distance along the optical axis from the point where the object side surface of the negative lens LnR intersects the optical axis to the aperture stop SP. At this time,
DLnF / L <0.4 (17)
DLnR / L <0.4 (18)
The following conditional expression is satisfied.

(Condition A6)
Let RnF be the radius of curvature of the image side surface of the negative lens LnF. Let RnR be the radius of curvature of the object side surface of the negative lens LnR. At this time,
0.0 <RnF / f <0.6 (19)
-0.6 <RnR / f <0.0 (20)
The following conditional expression is satisfied.

  Here, the first optical element GeF and the second optical element GeR (at least one when there are a plurality of optical elements) are refractive optical elements (hereinafter also simply referred to as “optical elements”) having a refractive action that satisfy the above-described conditions. is there.

  Further, here, the solid material in the refractive optical element means 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? Also good. For example, even if it is a liquid material at the time of manufacture, what was hardened into a solid material corresponds to the solid material here.

  The anomalous dispersions ΔθgF and Δθgd and the Abbe number νd of the solid material of the optical element used in the optical system OL of each 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. At this time, the Abbe number νd, the partial dispersion ratio θgd regarding the g line and the d line, and the partial dispersion ratio θgF regarding 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 dispersion Δθgd for the g-line and the d-line and the anomalous dispersion ΔθgF for the g-line and the F-line are as follows. Anomalous dispersibility refers to standard values θgd0 and θgF0 of partial dispersion ratios of θgd0 = −1.687 × 10 ⁻⁷ νd ³ + 5.702 × 10 ⁻⁵ νd ^2.
-6.603 × 10 ⁻³ νd + 1.462
θgF0 = −1.665 × 10 ⁻⁷ νd ³ + 5.213 × 10 ⁻⁵ νd ²
−5.656 × 10 ⁻³ νd + 0.7278
Is the difference from this standard curve.

That is, the anomalous dispersions Δθgd and ΔθgF are respectively
Δθgd = θgd−θgd0
ΔθgF = θgF−θgF0
It is expressed.

  In each example, the optical system OL includes, as a refractive optical element having refractive power, a first optical element GeF formed of a first solid material having relatively high dispersion and anomalous dispersion, on the object side of the aperture stop SP. At least one is used.

  In addition, at least one second optical element GeR formed of a second solid material having relatively high dispersion and anomalous dispersion is used on the object side of the aperture stop SP.

  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.

  Next, the technical meaning of each conditional expression described above will be described.

  It is assumed that the optical system of each embodiment is a Gauss type or modified Gauss type optical system that satisfies the conditional expressions (1) to (3).

  A first optical element GeF formed of a first solid material that satisfies the conditional expression (4) on the object side of the aperture stop SP and a second optical element that satisfies the conditional expression (5) on the image side of the aperture stop SP. Each of the second optical elements GeR formed of the solid material is used in the optical system OL. According to this, it becomes easy to satisfactorily correct chromatic aberration particularly on the short wavelength side in the visible range.

  At this time, the refractive powers (reciprocal of focal length) φF and φR in the air of the first and second optical elements GeF and GeR are configured to satisfy the conditional expressions (6) and (7). According to this, it becomes easy to correct chromatic aberration satisfactorily over a wide wavelength range.

  In each embodiment, it is more preferable to use the first and second solid materials that satisfy the conditional expression (8), the conditional expression (9), the conditional expression (10), and the conditional expression (11). According to this, it becomes easy to correct chromatic aberration satisfactorily over the entire visible wavelength range.

  In each embodiment, it is more preferable to use a relatively highly dispersed solid material that satisfies the conditional expressions (12) and (13) for the first and second optical elements GeF and GeR. According to this, chromatic aberration can be easily corrected.

  In each embodiment, the first and second optical elements GeF and GeR are preferably arranged so as to satisfy the conditional expressions (14) and (15). According to this, it becomes easy to correct chromatic aberration satisfactorily.

  In each embodiment, the refractive powers of the first and second optical elements GeF and GeR and the characteristics of the solid materials should satisfy the conditional expression (16). According to this, it becomes easy to satisfactorily correct chromatic aberration when the optical system OL of each embodiment is configured as a Gauss type or a modified Gauss type.

  In each embodiment, it is preferable that the negative lens LnF and the negative lens LnR have a configuration satisfying conditional expressions (17) and (18). According to this, it becomes easy to obtain a good chromatic aberration correction effect.

  In each embodiment, it is preferable that the radius of curvature RnF of the negative lens LnF and the radius of curvature RnR of the negative lens LnR satisfy the conditional expressions (19) and (20). This makes it easy to obtain a good chromatic aberration correction effect.

  As a specific example of the solid material (hereinafter, also referred to as “optical material”) that satisfies the conditional expressions (4) and (5), for example, there is a resin.

  Among the resins, in particular, UV curable resin 1 (refractive index Nd = 1.635, Abbe number νd = 22.7, partial dispersion ratio θgF = 0.69) and N-polyvinylcarbazole (Nd = 1.696, νd = 17.7. 7, θgF = 0.69) is an optical material satisfying conditional expressions (4) and (5).

  The optical materials applicable in each embodiment are not limited to these materials as long as conditional expressions (4) and (5) are 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) There is. Further examples include CrO ₃ (Nd = 2.2178, νd = 13.4), BaTiO ₃ (Nd = 2.4362, νd = 11.3), and the like.

Among these inorganic oxides, 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 4) and (5) can be obtained.

  When fine particles of ITO (Indium-Tin-Oxide) (Nd = 1.8571, νd = 5.69, θgF = 0.290) are dispersed in a synthetic resin at an appropriate volume ratio, the above conditional expression (4 ) And (5) are obtained.

  For example, an optical material satisfying the conditional expressions (4) and (5) can be obtained by dispersing the fine particles and the like in the UV curable resin 2 described later at an appropriate volume ratio.

  The optical material applicable in each embodiment is not limited to these fine particle dispersed materials as long as the conditional expressions (4) and (5) are satisfied.

  In each embodiment, an optical material having anomalous dispersion is disposed on the object side of the aperture stop and on the image side of the aperture stop, respectively, compared to a general optical material, thereby performing excellent chromatic aberration correction. ing.

  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 a refractive index on the long wavelength side, and the Abbe number in the d line, the partial dispersion ratio in the g line and the F line, and the partial dispersion ratio in the g line and the d line are Each takes a positive value.

  For this reason, the dispersion characteristic curve (refractive index characteristic with respect to wavelength) has a downward convex shape. Further, as the wavelength becomes shorter, the change in refractive index with respect to the change in wavelength increases.

  For example, the refractive index wavelength of trade name S-BSL7 (Nd = 1.516, νd = 64.1), trade name S-TIH53 (Nd = 1.847, νd = 23.8) of OHARA Co., Ltd. The characteristics are as shown in FIG.

  Further, as the high-dispersion optical material having a smaller Abbe number, the values of the partial dispersion ratio θgF regarding the g-line and the F-line and the partial dispersion ratio θgd regarding the g-line and the d-line tend to increase.

  In a general optical material, the partial dispersion ratio changes almost linearly in the low dispersion region with respect to the Abbe number, and the degree of change tends to increase as the dispersion becomes higher. What deviates from such a curve change is an optical material having anomalous 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 the wavelength characteristic curve of the chromatic aberration coefficient is bent relatively large on the short wavelength side.

  When the power of the lens surface of an optical material having a large partial dispersion ratio is changed in order to control chromatic aberration, the inclination of the wavelength characteristic 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 on the short wavelength side of the wavelength characteristic of the chromatic aberration coefficient, which has been relatively difficult to correct.

  On the other hand, in an optical material having a small partial dispersion ratio, the bending on the short wavelength side in the wavelength characteristic curve of the chromatic aberration coefficient is relatively 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 lens surface power is changed with an optical material with a small partial dispersion ratio in order to control chromatic aberration, the wavelength characteristic of the chromatic aberration coefficient is relatively linear with respect to the wavelength around the position of the design reference wavelength. The tilt changes while keeping. In addition, since the chromatic aberration coefficient is relatively linear with respect to the wavelength as compared with the general glass material, the bending on the short wavelength side can be canceled.

  In other words, it is effective to use an optical element having anomalous dispersion for correcting the short wavelength side bend in the wavelength characteristic of the chromatic aberration coefficient, which is difficult to correct with a general glass material in an optical system. The chromatic aberration correction effect can be obtained by either an optical material having a partial dispersion ratio larger than that of a general glass material or an optical material having a partial dispersion ratio smaller than that of a general glass material, although there is a difference in action. According to this, 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.

  12 and 13 schematically show the wavelength characteristics of the longitudinal chromatic aberration coefficient Ltot and the lateral chromatic aberration coefficient Ttot in a Gaussian type or modified Gaussian type optical system, respectively. Next, with reference to these drawings, it will be described that the present embodiment can simultaneously correct axial chromatic aberration and lateral chromatic aberration in the entire visible wavelength range.

  The characteristics of the wavelength characteristics of the axial chromatic aberration coefficient L of the Gaussian type or the modified Gaussian type are the axial chromatic aberration coefficient LF in the front group on the object side of the aperture stop, and the rear group on the image side of the aperture stop. The tendency of the axial chromatic aberration coefficient LR is similar. That is, in FIG. 12, it is convex upward and has a bend on the short wavelength side.

  The axial chromatic aberration coefficient Ltot in the entire optical system is the sum of the axial chromatic aberration coefficient LF in the front group and the axial chromatic aberration coefficient LR in the rear group. For this reason, in a Gauss type or modified Gauss type optical system, the axial chromatic aberration coefficient Ltot is convex upward and has a tendency to bend on the short wavelength side.

  In the lateral chromatic aberration coefficient Ttot, the lateral chromatic aberration coefficient TF in the front group and the lateral chromatic aberration coefficient TR in the rear group have symmetrical wavelength characteristics. That is, in FIG. 3, the lateral chromatic aberration coefficient TF in the front group shows a monotone increasing tendency with respect to the wavelength, and the lateral chromatic aberration coefficient TR in the rear group has a monotonically decreasing tendency with respect to the wavelength.

  For this reason, the lateral chromatic aberration coefficient Ttot in the entire optical system is the sum of the lateral chromatic aberration coefficient TF in the front group and the lateral chromatic aberration coefficient TR in the rear group. For this reason, it is easy to obtain the feature that they are mutually canceled and well corrected in a wide wavelength range.

  In an optical system using only a general glass material, it is necessary to change the power and refractive index of the optical material relatively large in order to correct the short wavelength side bending of the axial chromatic aberration with the chromatic aberration of magnification corrected well. . At this time, various aberrations such as spherical aberration and coma are also likely to fluctuate greatly. For this reason, it is difficult to achieve both correction of various aberrations and simultaneous correction of axial chromatic aberration and lateral chromatic aberration.

  At this time, a certain degree of chromatic aberration correction effect can be obtained by disposing an optical material having anomalous dispersion on either the object side or the image side near the aperture stop. At this time, in order to obtain a further chromatic aberration correction effect, it is necessary to greatly change the refractive power of the optical material having anomalous dispersion. However, if it is arranged only in either the front group or the rear group, the balance of axial chromatic aberration and chromatic aberration of magnification as the entire optical system is deteriorated, and it is difficult to obtain a sufficient effect. is there. Further, when the refractive power is increased, the thickness of the optical material in the optical axis direction increases. As a result, when the optical material is a resin premised on molding, environmental fluctuations become large, and molding becomes more difficult.

  In the Gauss type or modified Gauss type optical system, the first optical element GeF having anomalous dispersion disposed in the front group on the object side from the aperture stop and the anomalous dispersion disposed in the rear group on the image side from the aperture stop. It is preferable to use both of the second optical elements GeR having the property. According to this, axial chromatic aberration and lateral chromatic aberration can be corrected relatively well simultaneously. Further, since the chromatic aberration correction effect can be obtained without relatively increasing the thickness of the optical material in the optical axis direction, the environment resistance is good and the molding becomes easy. Furthermore, from the viewpoint of correcting chromatic aberration independently, it is preferable that both the first optical element GeF and the second optical element GeR have a relatively small Abbe number, that is, are made of a highly dispersed material.

  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)
The paraxial light beam is a paraxial light beam obtained by normalizing the focal length of the entire optical system to 1, and allowing light having a height of 1 from the optical axis to be incident in parallel with the optical axis of the optical system. is there. In addition, the pupil paraxial ray is the intersection of the entrance pupil of the optical system OL and the optical axis among the rays incident at −45 ° with respect to the optical axis by normalizing the focal length of the entire optical system OL to 1. Is a paraxial ray passing through.

  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 ν decreases (that is, the variance increases). Therefore, if a high dispersion material having a small absolute value of the Abbe number ν is used, the amount of power change for obtaining the necessary chromatic aberration can be small.

  This means that 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.

  It can also be seen from the equations (a) and (b) that the amount of change in the axial chromatic aberration coefficient ΔL and the magnification chromatic aberration coefficient ΔT is determined by the values of the heights h and H. Next, based on this, an appropriate arrangement location of the first and second optical elements GeF and GeR will be described.

  In order to correct chromatic aberration satisfactorily, it is necessary to correct simultaneously the inclination component and the bending component of the wavelength characteristic of the chromatic aberration coefficient. 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 anomalous dispersion constituting the first and second optical elements GeF and GeR needs to be relatively thin when used as a lens. This is because such an optical material generally has a relatively low transmittance. Further, if the thickness is thinner, the performance change with respect to the environmental change is small, so that the environmental resistance is improved and the molding becomes easier.

  That is, in order to reduce the thickness of the first and second optical elements GeF and GeR while obtaining a sufficient correction effect of chromatic aberration, the correction amount of the bending component and the inclination component of the wavelength characteristic curve of the chromatic aberration coefficient is appropriately adjusted. It is preferable to do.

  Since this correction amount is affected by the heights h and H from the equations (a) and (b), it changes depending on the position in the optical system where the first and second optical elements GeF and GeR are arranged. That is, in order to satisfactorily correct chromatic aberration and reduce the power change of the first and second optical elements GeF and GeR at that time, a place where the first and second optical elements GeF and GeR are arranged in the optical system. It is important to select appropriately.

  Appropriate arrangement positions of the first and second optical elements GeF and GeR vary depending on the aberration structure of the optical system. The aberration structure varies depending on the type of optical system.

  Considering the sign relationship between the aberration coefficients ΔL and ΔT, each sign is determined by the sign of the height h and the height H from the expressions (a) and (b). In general, the sign of the height h does not change before and after the aperture stop. The height H is reversed before and after the aperture stop.

  In a Gauss type or modified Gauss type optical system, it is preferable to correct axial chromatic aberration while minimizing the influence on well-corrected lateral chromatic aberration. That is, it is effective to arrange the first and second optical elements GeF and GeR at a location where the height H near the aperture stop is small.

  In addition, since the height H has a different sign on the object side and the image side with respect to the aperture stop, the first and second optical elements GeF and GeR are used before and after the aperture stop, thereby affecting the lateral chromatic aberration of each other. Can be countered. According to this, it is possible to correct axial chromatic aberration relatively well while maintaining a state in which lateral chromatic aberration is corrected relatively well.

Accordingly, in the Gauss type or modified Gauss type optical system as in each embodiment, the first optical element GeF is disposed on the object side with respect to the aperture stop, and the second optical element GeR is disposed on the image side with respect to the aperture stop. Good to do. This makes it easy to correct axial chromatic aberration and lateral chromatic aberration at the same time and relatively well.
At this time, in order to reduce the thickness of each of the first and second optical elements GeF and GeR, it is preferable to satisfy the conditional expression (16). Further, the product of the refractive power (φF, φR) of each of the first and second optical elements and the anomalous dispersion (ΔθgFF, ΔθgFR) related to the g-line and F-line is expressed by conditional expressions (6) and (7). If it is positive, the wavelength characteristic of the chromatic aberration coefficient can be easily corrected. These are due to the wavelength-dependent characteristics of chromatic aberration possessed by a Gauss type or modified Gauss type optical system.

  The first and second optical elements are combined with a general optical material to correct various aberrations including chromatic aberration. For this reason, 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 anomalous dispersion is too strong.

  When a lens made of a material having characteristics far from those of general optical materials is used, the curve of the wavelength characteristic curve of the chromatic aberration coefficient on the lens surface is particularly large. In order to correct the large bending component, the power of the other lens is also greatly changed. At this time, spherical aberration, coma aberration, astigmatism, etc. are greatly affected, making it difficult to correct aberrations.

  By setting the numerical range of the anomalous dispersion ΔθgFF of the conditional expression (4) relating to the first solid material constituting the first optical element GeF to the following range, a further excellent chromatic aberration correction effect can be expected.

0.0272 <ΔθgFF <0.2832, or −0.4278 <ΔθgFF <−0.0528 (4a)
It is.

  Further, from the viewpoint of aberration correction, it is more desirable to set the numerical range of (4a) to the range shown below.

0.0342 <ΔθgFF <0.2832, or −0.4278 <ΔθgFF <−0.0778 (4b)
It is.

  By setting the numerical range of the anomalous dispersion ΔθgFR of the conditional expression (5) relating to the second solid material constituting the second optical element GeR to the following range, a further excellent chromatic aberration correction effect can be expected.

0.0272 <ΔθgFR <0.2832, or −0.4278 <ΔθgFR <−0.0528 (5a)
It is.

  Further, from the viewpoint of aberration correction, it is more desirable to set the numerical range of (5a) to the range shown below.

0.0342 <ΔθgFR <0.2832, or −0.4278 <ΔθgFR <−0.0778 (5b)
It is.

  With respect to the first solid material, by setting the numerical range of the anomalous dispersion ΔθgdF of the conditional expression (10) to the following range, a further excellent correction effect of chromatic aberration can be expected.

0.038 <ΔθgdF <0.347, or −0.562 <ΔθgdF <−0.062 (10a)
It is.

  More preferably, the numerical range of the expression (10a) is set to the range shown below.

0.051 <ΔθgdF <0.347, or −0.562 <ΔθgdF <−0.112 (10b)
It is.

  With respect to the second solid material, by setting the numerical range of the anomalous dispersion ΔθgdR in the conditional expression (11) to the following range, a further excellent correction effect of chromatic aberration can be expected.

0.038 <ΔθgdR <0.347, or −0.562 <ΔθgdR <−0.062 (11a)
It is.

  More preferably, the numerical range of the expression (11a) is set to the following range.

0.051 <ΔθgdR <0.347, or −0.562 <ΔθgdR <−0.112 (11b)
It is.

  If the numerical ranges of the Abbe numbers νdF and νdR in the conditional expressions (12) and (13) are set to the following ranges, a better chromatic aberration correction effect can be expected.

νdF <50 (12a)
νdR <50 (13a)
More preferably, the numerical ranges of (12a) and (13a) are set to the following ranges.

νdF <45 (12b)
νdR <45 (13b)
More desirably, the numerical ranges of the conditional expressions (12b) and (13b) are set to the ranges shown below.

νdF <40 (12c)
νdR <40 (13c)
In each embodiment, the first optical element GeF and the second optical element GeR made of an optical material satisfying the conditional expressions (4) and (5) are provided on the lens in the optical system or on the lens surface with a refractive power. Has been applied.

  A refracting surface made of these optical materials is preferably aspherical, and according to this, chromatic aberration flare such as chromatic spherical aberration can be corrected more satisfactorily.

  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.

  As described above, according to each embodiment, it is possible to satisfactorily correct various aberrations including chromatic aberration, and an optical system that is easy to manufacture and excellent in environmental resistance can be obtained.

  Conditional expressions (8) to (20) are not necessarily satisfied, and are more preferable conditions for obtaining the optical system targeted by the present invention.

  Example 1 in FIG. 1 is a Gauss-type optical system (photographing with an angle of view of 46 ° and an F number of 1.96) comprising a front group GpF having positive refractive power, an aperture stop SP, and a rear group GpR having positive refractive power. Lens).

  The optical system of Example 1 has a focal length of 51 mm when the numerical value of Numerical Example 1 described later is expressed in mm.

In FIG. 1, GeF1 is a first optical element composed of a lens (layer) formed of a UV curable resin 1 (first solid material) disposed on the object side of the aperture stop SP. GeR1 is a second optical element comprising a lens (layer) formed of a mixture (second solid material) in which 20% by volume of TiO ₂ fine particles are dispersed in a UV curable resin 2 disposed on the image side of the aperture stop SP. It is an element.

  The first optical element GeF1 is joined to the surface on the aperture stop SP side of the negative lens LnF having a concave shape on the surface on the aperture stop SP side. In the second optical element GeR1, the surface on the aperture stop SP side is joined to the surface on the aperture stop SP side of the negative lens LnR having a concave shape.

  The first optical element GeF1 has a negative refracting power when it is joined to the negative lens LnF, but is positively refracted when disposed in the air (when the light incident surface is a surface in contact with air). It acts as a force.

The same applies to the second optical element GeR1. That is,
0 <φF
0 <φR
It is.

  In the optical system of Example 1, the first optical element GeF1 having a positive power made of the UV curable resin 1 and the fine particles are located in the vicinity of the aperture stop SP whose height from the optical axis through which the paraxial ray passes is relatively low. The second optical element GeR1 having a positive power composed of the above mixture is disposed.

  Thereby, axial chromatic aberration and lateral chromatic aberration are corrected satisfactorily.

  Example 2 in FIG. 3 is a Gauss type optical system having an angle of view of 46 ° and an F number of 1.52, which includes a front group GpF having a positive refractive power, an aperture stop SP, and a rear group GpR having a positive refractive power. .

  The optical system of Example 2 has a focal length of 51 mm when the numerical value of Numerical Example 2 described later is expressed in mm.

In FIG. 3, GeF1 is a lens (layer) formed of a mixture (first solid material) in which TiO ₂ fine particles are dispersed in a volume ratio of 3% in a UV curable resin 2 disposed on the object side of the aperture stop SP. It is the 1st optical element which consists of. GeR1 is a second optical element comprising a lens (layer) formed of a mixture (second solid material) in which ITO is dispersed 20% by volume in a UV curable resin 2 disposed on the image side of the aperture stop SP. is there.

  The first optical element GeF1 is joined to the surface on the aperture stop SP side of the negative lens LnF having a concave shape on the surface on the aperture stop SP side. In the second optical element GeR1, the surface on the aperture stop SP side is joined to the surface on the aperture stop SP side of the negative lens LnR having a concave shape.

  The first optical element GeF1 acts as a negative refracting power when it is joined to the negative lens LnF, but acts as a positive refracting power when it is placed in the air.

  The second optical element GeR1 acts as a negative refractive power in a state where it is joined to the negative lens LnR. Further, it also acts as a negative refractive power when placed in the air.

That is, 0 <φF
φR <0
It is.

In the optical system according to the second embodiment, the first optical element GeF1 having a positive power made of a mixture of TiO ₂ fine particles is provided in the vicinity of the aperture stop SP whose height from the optical axis through which the paraxial ray passes is relatively low. The second optical element GeR1 having a negative power made of a mixture of ITO fine particles is disposed.

  Thereby, axial chromatic aberration and lateral chromatic aberration are corrected satisfactorily.

  Example 3 in FIG. 5 is a Dauss type optical system having a field angle of 45.4 ° and an F number of 1.30, which includes a front group GpF having a positive refractive power, an aperture stop SP, and a rear group GpR having a positive refractive power. . The optical system of Example 3 has a focal length of 52 mm when the numerical value of Numerical Example 3 described later is expressed in mm.

  In FIG. 5, GeF1 is a lens (first solid material) formed of a mixture (first solid material) in which ITO fine particles are dispersed in a volume ratio of 14.2% in the UV curable resin 2 disposed on the object side of the aperture stop SP. A first optical element comprising a layer). GeR1 is a second optical element comprising a lens (layer) formed of a mixture (second solid material) in which ITO is dispersed 20% by volume in a UV curable resin 2 disposed on the image side of the aperture stop SP. is there.

  The first optical element GeF1 is joined to the surface on the aperture stop SP side of the negative lens LnF having a concave shape on the surface on the aperture stop SP side. In the second optical element GeR1, the surface on the aperture stop SP side is joined to the surface on the aperture stop SP side of the negative lens LnR having a concave shape.

  The first optical element GeF1 acts as a negative refractive power in a state where it is joined to the negative lens LnF. It also acts as a negative refractive power when placed in air.

  The same applies to the second optical element GeR1.

That is,
φF <0
φR <0
It is.

  In the optical system of Example 3, a first optical element GeF1 having a negative power made of a mixture of ITO fine particles is provided in the vicinity of the aperture stop SP whose height from the optical axis through which the paraxial ray passes is relatively low, A second optical element GeR1 having a negative power made of a mixture of ITO fine particles is disposed.

  Thereby, axial chromatic aberration and lateral chromatic aberration are corrected satisfactorily. Moreover, spherical aberration, chromatic aberration, and the like are favorably corrected by making the object-side surface of the second optical element GeR1 an aspherical shape.

  Example 4 in FIG. 7 includes a front group GpF having a positive refractive power, an aperture stop SP, and a rear group GpR having a positive refractive power, an angle of view of 40 °, an F number of 3.16, a magnification of −0.11 times, It is an optical system for xenota type image reading.

  The optical system of Example 4 has a focal length of 100 mm when the numerical value of Numerical Example 4 described later is expressed in mm.

  In FIG. 7, GeF1 is obtained from a lens (layer) formed of a mixture (first solid material) in which ITO fine particles are dispersed at a volume ratio of 5% in a UV curable resin 2 disposed on the object side of the aperture stop SP. It is the 1st optical element which consists of. GeR1 is a second optical element composed of a lens (layer) formed of N-polyvinylcarbazole (second solid material) disposed on the image side of the aperture stop SP.

  The first optical element GeF1 is joined between the positive lens Gpa and the negative lens LnF having a concave surface on the aperture stop SP side.

  The second optical element GeR1 is joined to the surface on the aperture stop SP side of the negative lens LnR having a concave shape on the surface on the aperture stop SP side.

  The first optical element GeF1 acts as a positive refractive power in the bonded state, but acts as a negative refractive power when it is placed in the air.

  The second optical element GeR1 acts as a negative refractive power in the joined state, but acts as a positive refractive power when arranged in the air.

That is,
φF <0
0 <φR
It is.

  In the optical system of Example 4, the first optical element GeF1 having a negative power made of a mixture of ITO fine particles is disposed in the vicinity of the aperture stop SP whose height from the optical axis through which the paraxial ray passes is relatively low. is doing. Furthermore, a second optical element GeR1 having a positive power made of N-polyvinylcarbazole is disposed.

  Thereby, axial chromatic aberration and lateral chromatic aberration are corrected satisfactorily.

  Example 5 of FIG. 9 is an optical system having a front angle GpF having a positive refractive power, an aperture stop SP, and a rear group GpR having a positive refractive power and an angle of view of 64.7 ° and an F number of 4.32.

  The optical system of Example 5 has a focal length of 55 mm when the numerical value of Numerical Example 5 described later is expressed in mm.

  In FIG. 9, GeF1 is a first optical element composed of a lens (layer) formed of N-polyvinylcarbazole (first solid material) disposed on the object side of the aperture stop SP. GeR1 is a second optical element b1 composed of a lens (layer) formed of a mixture (second solid material) in which ITO is dispersed at a volume ratio of 5% in a UV curable resin 2 disposed on the image side of the aperture stop SP. It is. GeR2 is a second optical element b2 made of a lens (layer) formed of UV curable resin 1 (second solid material).

  The first optical element GeF1 is bonded to the surface on the aperture stop SP side of the positive lens Gpa disposed on the object side of the aperture stop SP.

  The second optical element b1 is joined to the second optical element b2, and the second optical element b2 is joined to the negative lens Gnb having concave lens surfaces arranged on the image side of the aperture stop SP.

  The negative lens Gnb and the positive lens Gpb constitute a cemented lens that is cemented.

  The first optical element GeF1 acts as a negative refracting power when it is joined to the positive lens Gpa, and acts as a positive refracting power when it is placed in the air.

  The second optical element b1 acts as a negative refracting power when it is joined to the second optical element b2, and also acts as a negative refracting power φR1 when it is placed in the air.

  The second optical element b2 acts as a positive refracting power in the joined state, and also acts as a positive refracting power φR2 when it is disposed in the air.

That is,
0 <φF
φR1 <0
0 <φR2
It is.

  In the optical system of Example 5, the first optical element GeF1 made of N-polyvinylcarbazole having a positive power is disposed in the vicinity of the aperture stop SP whose height from the optical axis through which the paraxial ray passes is relatively low. ing.

  Further, a second optical element GeR1 having a negative power made of a mixture of ITO fine particles in the vicinity of the aperture stop SP whose height from the optical axis through which the paraxial ray passes is relatively low, and a positive made of the UV curable resin 1. The second optical element GeR2 having the following power is arranged.

  Thereby, axial chromatic aberration and lateral chromatic aberration are corrected satisfactorily.

  Hereinafter, specific numerical data will be shown for numerical examples 1 to 5 corresponding to the first to fifth 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 Abbe number of the material of the i-th optical member (excluding the first and second optical elements) with respect to the d-line, respectively.

  The refractive index and Abbe number for the d-line of the material of the first optical element GeF1 are separately indicated as NGeF1 and νGeF1. Further, the refractive index and Abbe number of the material of the second optical element GeRj with respect to the d-line are separately represented by NGeRj and νGeRj (j = 1, 2). The unit of angle of view is “degree”.

  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,

It expresses by.

Note that “E ± XX” in each aspheric coefficient and the numerical values in the table means “× 10 ^{± XX} ”.

  Corresponding to the refractive index, the Abbe number, the partial dispersion ratio, and the power of the materials of the first and second optical elements GeF1, GeR1, and GeR2 used in each numerical example with respect to the d-line, g-line, C-line, and F-line. The numerical values are shown in Table 1.

Table 1 also shows related conditional expressions. Table 2 shows the refractive index, Abbe number, and partial dispersion ratio of the UV curable resin 2 and the d-line, g-line, C-line, and F-line of ITO and TiO ₂ . Table 3 shows numerical values corresponding to the conditional expression (16) of the first and second optical elements GeF1, GeR1, and GeR2 in each numerical example. Table 4 shows numerical values corresponding to the conditional expressions (1) to (3), the conditional expressions (14) and (15), and the conditional expressions (17) to (20).

(Numerical example 1)
Focal length 51.00
F number 1.96
Angle of view 45.97
Statue height 21.64
Total lens length 35.37
Back focus 37.50

R1 = 38.463 D1 = 3.19 N1 = 1.7190 ν1 = 53.0
R2 = 287.736 D2 = 0.15
R3 = 23.857 D3 = 2.67 N2 = 1.8619 ν2 = 42.5
R4 = 37.690 D4 = 1.43
R5 = 66.719 D5 = 3.21 N3 = 1.7002 ν3 = 28.5
R6 = 14.246 D6 = 0.90 NGeF1 1.6355 νGeF1 22.7
R7 = 17.200 D7 = 4.86
R8 = ∞ (aperture stop) D8 = 5.45
R9 = -20.310 D9 = 0.54 NGeR1 1.7088 νGeR1 21.6
R10-17.207 D10 2.50 N4 = 1.7508 ν4 = 26.1
R11261.185 D11 6.29 N5 = 1.8083 ν5 = 47.0
R12-27.283 D12 0.15
R13152.024 D13 2.62 N6 = 1.8595 ν6 = 42.7
R14-66.561

(Numerical example 2)
Focal length 51.00
F number 1.52
Angle of view 45.98
Statue height 21.64
Total lens length 48.42
Back focus 37.50

R1 = 49.896 D1 = 3.59 N1 = 1.8500 ν1 = 43.4
R2 = 267.058 D2 = 0.29
R3 = 29.633 D3 = 3.24 N2 = 1.8834 ν2 = 39.6
R4 = 46.536 D4 = 2.32
R5 = 70.831 D5 = 2.29 N3 = 1.6864 ν3 = 30.3
R6 = 17.430 D6 = 1.02 NGeF1 1.5532 νGeF1 39.8
R7 = 20.371 D7 = 6.08
R8 = ∞ (aperture stop) D8 = 11.48
R9 = -18.999 D9 = 0.07 NGeR1 1.5963 νGeR1 13.9
R10-21.067 D10 3.00 N4 = 1.8500 ν4 = 23.0
R11-200.021 D11 7.46 N5 = 1.8848 ν5 = 41.0
R12-30.580 D12 0.17
R13-102.791 D13 4.17 N6 = 1.8496 ν6 = 43.4
R14-37.839 D14 0.15
R15 78.385 D15 3.10 N7 = 1.8786 ν7 = 41.4
R16608.715

(Numerical Example 3)
Focal length 51.70
F number 1.30
Angle of view 45.42
Statue height 21.64
Total lens length 61.88
Back focus 37.50

R1 = 60.702 D1 = 4.16 N1 = 1.7800 ν1 = 50.0
R2 = 527.517 D2 = 0.15
R3 = 35.174 D3 = 6.00 N2 = 1.8850 ν2 = 41.0
R4 = 48.933 D4 = 1.43
R5 = 80.331 D5 = 2.50 N3 = 1.6247 ν3 = 34.1
R6 = 23.347 D6 = 0.08 NGeF1 1.5648 νGeF1 20.0
R7 = 22.759 D7 = 8.36
R8 = ∞ (Aperture stop) D8 = 11.01
R9 = -25.141 (aspherical surface) D9 = 0.05 NGeR1 1.5963 νGeR1 13.9
R10-26.336 D10 2.28 N4 = 1.6546 ν4 = 31.5
R11103.553 D11 8.50 N5 = 1.8850 ν5 = 41.0
R12-32.918 D12 1.37
R13-26.579 D13 1.20 N6 = 1.6950 ν6 = 28.8
R14137.806 D14 6.76 N7 = 1.8850 ν7 = 41.0
R15-43.483 D15 0.15
R16179.221 (Aspherical) D16 8.00 N8 = 1.7800 ν8 = 50.0
R17-61.836

Aspheric coefficient k B C D E
9th surface -2.768E-02 8.760E-07 -4.854E-09 3.641E-11 -3.199E-14
16th surface-1.326E + 01 -1.717E-06 5.764E-10 -1.267E-12 7.932E-16

(Numerical example 4)
Focal length 100.00
F number 3.16
Angle of view 39.80
Statue height 36.20
Total lens length 71.11
Back focus 50.40

R1 = 58.623 D1 = 5.67 N1 = 1.8770 ν1 = 34.9
R2 = 124.818 D2 = 8.74
R3 = 28.587 D3 = 9.89 N2 = 1.8240 ν2 = 45.5
R4 = 66.759 D4 = 0.10 NGeF1 1.5425 νGeF1 29.1
R5 = 58.129 D5 = 1.20 N3 = 1.8500 ν3 = 23.0
R6 = 21.035 D6 = 10.93
R7 = ∞ (Aperture stop) D7 = 15.92
R8 = -22.443 D8 = 0.50 NGeR1 1.6959 νGeR1 17.7
R9 = -21.545 D9 = 5.00 N4 = 1.8500 ν4 = 23.0
R10-30.039 D10 0.15
R11-261.062 D11 13.00 N5 = 1.7794 ν5 = 50.0
R12-47.514


(Numerical example 5)
Focal length 55.00
F number 4.32
Angle of View 64.72
Statue height 34.85
Total lens length 32.33
Back focus 40.72

R1 = 19.446 D1 = 5.80 N1 = 1.8774 ν1 = 35.2
R2 = 66.062 D2 = 2.55 N2 = 1.7962 ν2 = 24.5
R3 = 15.487 D3 = 0.96
R4 = 30.638 D4 = 1.95 N3 = 1.5093 ν3 = 68.1
R5 = 73.107 D5 = 0.12 NGeF1 1.6959 νGeF1 17.7
R6 = 111.539 D6 = 2.69
R7 = ∞ (Aperture stop) D7 = 2.33
R8 = −37.625 D8 = 0.05 NGeR1 1.5425 νGeR1 29.1
R9 = -47.897 D9 = 0.16 NGeR2 1.6355 νGeR2 22.7
R10-34.950 D10 1.20 N4 = 1.8251 ν4 = 45.3
R11 23.692 D11 4.07 N5 = 1.8022 ν5 = 47.6
R12-21.426 D12 1.12
R13-13.897 D13 2.50 N6 = 1.6846 ν6 = 29.4
R14-102.677 D14 6.83 N7 = 1.8850 ν7 = 41.0
R15-22.371

  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. 14, reference numeral 20 denotes a camera body. Reference numeral 21 denotes a photographing optical system configured by any one of the optical systems described in the first to fifth 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 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. FIG. 9 is an aberration diagram of Numerical Example 4. 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. It is explanatory drawing regarding the wavelength characteristic of the refractive index of a general glass material. It is explanatory drawing regarding the wavelength characteristic of the axial chromatic aberration coefficient in this invention. It is explanatory drawing regarding the wavelength characteristic of the magnification chromatic aberration coefficient in this invention. It is a principal part schematic of the imaging device of this invention.

Explanation of symbols

LF Axial chromatic aberration coefficient LR in the front group arranged on the object side from the aperture stop LR Axial chromatic aberration coefficient Ltot in the rear group arranged on the image side from the aperture stop Object on the axial chromatic aberration coefficient TF of the entire optical system Lateral chromatic aberration coefficient TR in the front group arranged on the side, lateral chromatic aberration coefficient Ttot in the rear group arranged on the image side from the aperture stop, lateral chromatic aberration coefficient OL of the entire optical system, optical system GpF, arranged on the object side from the aperture stop Front group GpR with positive refractive power Rear group GeF, GeF1 first optical element GeR, GeR1, GeR2 arranged on the image side from the aperture stop Second optical element LnF, LnR Negative lens LpF, LpR Positive lens SP Aperture stop IP Image plane La Optical axis L Point where the most image side lens surface intersects the optical axis from the point where the most object side lens surface intersects the optical axis
A distance DeF along the optical axis to the distance DeR along the optical axis from the point where the image side surface of the first optical element GeF intersects the optical axis La to the aperture stop SP The surface on the object side of the second optical element GeR is the optical axis Distance DLnF along the optical axis from the point intersecting La to the aperture stop SP DLnF Distance along the optical axis from the point where the image side of the negative lens LnF intersects the optical axis La to the aperture stop SP DLnR On the object side of the negative lens LnR Distance along the optical axis from the point where the surface intersects the optical axis La to the aperture stop SP along the optical axis dd line g g line ΔM meridional image plane ΔS sagittal image plane

Claims (15)

In an optical system in which an aperture stop, a front group of positive refractive power on the object side of the aperture stop, and a rear group of positive refractive power on the image side of the aperture stop are arranged,
The front group includes at least one first optical element made of a first solid material, the light incident surface and the light exit surface being both refractive surfaces,
The lens surface on the aperture stop side has a concave negative lens LnF, and the positive lens LpF is closer to the object side than the negative lens LnF.
The rear group includes at least one second optical element made of a second solid material, the light incident surface and the light exit surface being both refractive surfaces,
The lens surface on the aperture stop side has a concave negative lens LnR, and a positive lens LpR on the image side of the negative lens LnR.
The focal lengths of the front group and the rear group are fF and fR, respectively, and the focal length of the entire system is f,
The anomalous dispersibility of the first and second solid materials with respect to g-line and F-line is expressed as ΔθgFF, ΔθgFR,
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 φF (1 / mm) and φR (1 / mm), respectively,
0.8 <fF / f <5.0
0.4 <fR / f <3.0
0.3 <fF / fR <10.0
Satisfying the conditional expression
ΔθgFF <−0.0278 or ΔθgFF> 0.0272
Either of them and ΔθgFR <−0.0278 or ΔθgFR> 0.0272
Or φF (1 / mm) × ΔθgFF> 0
φR (1 / mm) × ΔθgFR> 0
An optical system that satisfies the following conditional expression: When the anomalous dispersion for the g-line and d-line of the first and second solid materials is ΔθgdF and ΔθgdR, respectively.
ΔθgFF × ΔθgdF> 0
ΔθgFR × ΔθgdR> 0
Satisfying the following conditional expressions,
ΔθgdF> 0.038 or ΔθgdF <−0.037
Either of them and ΔθgdR> 0.038 or ΔθgdR <−0.037
The optical system according to claim 1, wherein either one of the above is satisfied. When the Abbe numbers at the d-line of the first and second solid materials are νdF and νdR, respectively.
νdF <60
νdR <60
The optical system according to claim 1, wherein the following conditional expression is satisfied. The distance along the optical axis from the point where the lens surface closest to the object side intersects with the optical axis to the point where the lens surface closest to the image side intersects with the optical axis is L, and the image side surface of the first optical element intersects with the optical axis. When the distance along the optical axis from the point to the aperture stop is DeF, and the distance along the optical axis from the point where the object-side surface of the second optical element intersects the optical axis is DeR,
DeF / L <0.4
DeR / L <0.4
The optical system according to claim 1, 2 or 3, wherein the following conditional expression is satisfied. When the Abbe numbers at the d-line of the first and second solid materials are νdF and νdR, respectively.
0.05 <(ΔθgFF × φF / νdF) / (ΔθgFR × φR / νdR) <10
5. The optical system according to claim 1, wherein the following conditional expression is satisfied. The distance along the optical axis from the point where the image side surface of the negative lens LnF intersects the optical axis to the aperture stop is DLnF, and from the point where the object side surface of the negative lens LnR intersects the optical axis to the aperture stop When the distance along the optical axis is DLnR,
DLnF / L <0.4
DLnR / L <0.4
The optical system according to claim 1, wherein the following conditional expression is satisfied. When the radius of curvature of the image side surface of the negative lens LnF is RnF and the radius of curvature of the object side surface of the negative lens LnR is RnR,
0.0 <RnF / f <0.6
−0.6 <RnR / f <0.0
The optical system according to claim 1, wherein the following conditional expression is satisfied.   The optical system according to any one of claims 1 to 7, wherein the at least one first optical element is cemented to a lens surface of the negative lens LnF on the aperture stop side.   9. The optical system according to claim 1, wherein the at least one second optical element is cemented to a lens surface of the negative lens LnR on the aperture stop side. 10.   The optical system according to any one of claims 1 to 9, wherein a meniscus positive lens convex on the object side is disposed between the positive lens LpF and the negative lens LnF.   11. The positive lens having at least one image-side lens surface having a convex shape is disposed between the negative lens LnR and the positive lens LpR. Optical system.   A positive lens Gpa having a convex object-side lens surface is disposed between the positive lens LpF and the negative lens LnF, and the at least one first optical element includes the positive lens Gpa and the negative lens. The optical system according to claim 1, wherein the optical system is disposed between the optical system and LnF.   A positive lens Gpa having a convex object-side lens surface is disposed on the image side of the negative lens LnF, and the at least one first optical element is cemented to the image-side lens surface of the positive lens Gpa. The optical system according to claim 1, wherein the optical system is an optical system.   On the object side of the negative lens LnR, a cemented lens in which a negative lens Gnb whose concave surfaces are concave and a positive lens Gpb whose convex surfaces are convex is disposed, and the at least one second optical element is disposed. The optical system according to claim 1, wherein the optical system is cemented to an object side lens surface of the negative lens Gnb.   An optical apparatus comprising: the optical system according to claim 1; and a photoelectric conversion element that receives an image formed by the optical system.