JP2012047870A - Optical system and optical apparatus having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system capable of effectively reducing generation of flare and ghost due to reflection from a lens surface while favorably correcting chromatic aberration fluctuation when focusing.SOLUTION: This optical system comprises, in order from an object side towards an image side, a first lens group of positive refractive power, an aperture stop, and a second lens group, the first lens group includes a first 1a lens group of positive refractive power and a first 1b lens group of negative refractive power that moves on an optical axis in focusing, and the first 1b lens group comprises a first 1b positive lens of positive refractive power, and a first 1b negative lens of negative refractive power. When the Abbe number of a material of the first 1b positive lens and a partial dispersion ratio of the material thereof are νdbp and θgFbp respectively, the first 1b positive lens satisfies the following expression: 0.02<θgFbp-0.6438+0.0016821×νdbp<0.10, and both the first lens group and the second lens group include lens surfaces formed by a wet process.

Description

  The present invention relates to an optical system and an optical apparatus having the same, and is suitable for an optical apparatus such as a silver salt camera, a digital still camera, a digital video camera, and a TV camera.

  In recent years, one of the photographic optical systems used in imaging devices such as digital cameras and video cameras is easy to shoot long-distance objects (high photographic magnification), the entire system is small, and has high optical performance. There is a telephoto imaging optical system (telephoto lens). The telephoto lens can easily shoot a long-distance object at a high magnification. However, the telephoto lens has a large amount of chromatic aberration and particularly has a large variation in chromatic aberration during focusing, and it is difficult to obtain high optical performance. As a method for reducing the occurrence of chromatic aberration in an optical system, a method of using an abnormal partial dispersion material as a lens optical material is generally well known (see Patent Document 1).

  Patent Document 1 discloses a telephoto lens in which a chromatic aberration is reduced by using a material having an abnormal partial dispersion characteristic such as fluorite for the lens. In a telephoto lens, a plurality of lens surfaces having relatively close curvature radii are often arranged in an optical part (lens group) closer to the image side than the stop. In an optical system in which a plurality of lens surfaces with close curvature radii are arranged, an incident light beam is reflected by one lens surface and reaches the image surface when reflected by another reflecting surface, resulting in flare and ghost, The quality of the captured image may be degraded.

  Conventionally, in many optical systems, measures such as providing an antireflection film are provided on the surface of a lens made of glass, plastic, or the like in order to reduce a light amount loss due to reflection of incident light. For example, as an antireflection film for visible light, a multilayer film (so-called multicoat) in which a plurality of dielectric thin films are laminated is known. The multilayer film is generally formed by forming a metal oxide or fluoride on the lens surface by a method such as vacuum deposition. An optical system is known in which generation of ghost light due to reflection on a lens surface is reduced in a wide wavelength range (Patent Document 2).

  Patent Document 2 discloses an optical system in which two lens surfaces that cause ghosts are provided with an antireflection coating having antireflection properties that are complementary to each other. Further, as an antireflection structure on the lens surface, an optical system in which a fine concavo-convex structure having a wavelength of visible region (wavelength 400 nm to 700 nm) or less is formed on the lens surface and antireflection with good incident angle characteristics over a wide wavelength range is performed. Known (Patent Document 3).

JP-A-11-119092 JP-A-5-323226 JP 2005-62525 A

  In a telephoto lens using a low-dispersion material such as fluorite, when a total lens length is set long (approximately the same as the focal length), correction of various aberrations including chromatic aberration is relatively easy. However, in a telephoto lens, it is necessary to increase the refractive power of a lens made of a low dispersion material in order to shorten the total lens length. In general, when the curvature of the lens surface is increased (the curvature radius is decreased) in order to increase the refractive power of the lens, various aberrations such as spherical aberration, coma and astigmatism increase rapidly.

  In order to satisfactorily correct various aberrations such as chromatic aberration in a telephoto lens, it is effective to use an optical material having an abnormal partial dispersion and a low dispersion for a front lens having a large effective diameter. . However, this will increase the size of the entire system and increase the weight. Further, in the telephoto lens, since the front lens group is large and heavy, an inner focus method is often used in which focusing is not performed with the front lens group but with some lens groups in the lens group.

  Since the lens group used in the inner focus method is relatively small and light, high-speed focusing is easy. However, when the inner focus method is employed, aberration fluctuation, particularly chromatic aberration fluctuation, increases during focusing, and it becomes difficult to correct this. Also, in order to obtain high optical performance, while reducing various aberrations and preventing the generation of unnecessary light such as flares and ghosts, the lens surfaces that cause ghosts are selected, and configurations appropriate for these lens surfaces It is important to apply an antireflection film.

  However, in general, it is very difficult to select a lens surface that causes ghosts from a plurality of lens surfaces, and to prevent ghosts generated from these lens surfaces by applying an antireflection film to these lens surfaces. In order to form a fine concavo-convex structure having a wavelength equal to or smaller than the visible wavelength on the lens surface and to prevent reflection, it is important to apply the fine concavo-convex structure to an appropriate lens surface in the optical path. Even if a fine concavo-convex structure having a wavelength less than or equal to the wavelength in the visible range is applied to the lens surface, it is difficult to obtain an antireflection effect with good incident angle characteristics over the entire visible range.

  An object of the present invention is to provide an optical system capable of effectively correcting chromatic aberration fluctuations during focusing and effectively reducing flare and ghosting caused by reflection from the lens surface, and an optical apparatus having the optical system. To do.

The optical system according to the present invention includes, in order from the object side to the image side, a first lens group having a positive refractive power, an aperture stop, and a second lens group. The first lens group is a first lens group having a positive refractive power. And a negative-power 1b lens group that moves on the optical axis during focusing. The first-b lens group includes a positive-power 1b positive lens and a negative-power first-b negative lens. When the Abbe number and the partial dispersion ratio of the material of the 1b positive lens are νdbp and θgFbp, respectively,
0.02 <θgFbp−0.6438 + 0.0016821 × νdbp <0.10
And both the first lens group and the second lens group include a lens surface on which an antireflection film including at least one layer formed using a wet process is formed. Yes.

  According to the present invention, it is possible to obtain an optical system that can effectively reduce the occurrence of flare and ghost due to reflection from the lens surface while satisfactorily correcting chromatic aberration fluctuations during focusing.

Sectional drawing of the optical system of Example 1 of the present invention Aberration diagram when focusing on an object at infinity of the optical system of Example 1 of the present invention Sectional drawing of the optical system of Example 2 of the present invention Aberration diagram when focusing on an object at infinity of the optical system of Example 2 of the present invention Schematic sectional view of an antireflection film used in the present invention Refractive index profile of antireflection film used in the present invention Reflectivity characteristics of antireflection film used in the present invention Reflectivity characteristics of anti-reflective coatings using general dielectric multilayers (comparative example) Schematic diagram of essential parts of the optical apparatus of the present invention Illustration of average pitch

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The optical system according to the present invention includes, in order from the object side to the image side, a first lens unit having a positive refractive power, an aperture stop, and a second lens unit. The first lens group includes a 1a lens group having a positive refractive power and a 1b lens group having a negative refractive power that moves on the optical axis during focusing.

  Next, each embodiment of the present invention will be described. FIG. 1 is a lens cross-sectional view of an optical system according to Example 1 of the present invention. FIG. 2 is a diagram illustrating various aberrations when an object at infinity is focused in the optical system according to the first embodiment. FIG. 3 is a lens sectional view of Example 2 of the optical system of the present invention. FIG. 4 is a diagram of various aberrations when focusing on an object at infinity in Example 2.

  The optical system of each embodiment is a telephoto type (teletype). In the lens cross-sectional view, the left is the object side (front) and the right is the image side (rear). OL is an optical system, L1 is a first lens unit having a positive refractive power, and SP is an Fno stop (aperture stop) that regulates a light beam having an open number. L2 is the second lens group. L1a is a 1a lens group having positive refractive power, and L1b is a 1b lens group having negative refractive power that moves on the optical axis during focusing.

  IP is an image plane, and when used as a photographing optical system for a video camera or a digital still camera, on the imaging surface of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor, Corresponds to the film surface. In spherical aberration, the solid line is the d line, the two-dot chain line is the g line, and the dotted line is the C line. In the astigmatism diagram, the dotted line represents the d-line meridional image plane, and the solid line represents the d-line sagittal image plane. Lateral chromatic aberration is represented by the g-line.

  The optical system of each embodiment is an imaging optical system used in an imaging apparatus such as a digital camera / video camera or a silver salt film camera. In addition, the optical system of each embodiment is used for an optical apparatus such as a telescope, a binocular observation device, and a projector.

In each embodiment, the 1b lens unit L1b includes a 1b positive lens having a positive refractive power and a 1b negative lens having a negative refractive power. The Abbe number and partial dispersion ratio of the material of the 1b positive lens are νdbp and θgFbp, respectively. At this time,
0.02 <θgFbp−0.6438 + 0.0016821 × νdbp <0.10
... (1)
Is satisfied. Each of the first lens group L1 and the second lens group L2 includes a lens surface on which an antireflection film including at least one layer formed using a wet process is formed.

  The partial dispersion ratio and Abbe number of the lens material used in the optical system of this example are as follows. The refractive index of the Fraunhofer line for g-line (wavelength 435.8 nm), F-line (wavelength 486.1 nm), d-line (wavelength 587.6 nm), and C-line (wavelength 656.3 nm) is Ng, NF, respectively. Let Nd, NC. The partial dispersion ratio θgF for the Abbe number νd, g-line and F-line is as follows.

νd = (Nd−1) / (NF−NC)
θgF = (Ng−NF) / (NF−NC)
Conditional expression (1) is that an optical material having a large positive value of anomalous partial dispersion near the g-line is used for the 1b positive lens in the 1b lens group L1b. In the telephoto optical system, axial chromatic aberration and lateral chromatic aberration can be reduced by using an optical material having a high value of anomalous partial dispersion on the object side of the stop SP. Further, by adopting a configuration that satisfies the conditional expression (1), the burden of correcting the chromatic aberration of the first lens unit L1a can be reduced, and the refractive power of the positive lens in the first lens unit L1 can be reduced. As a result, the overall length of the lens is shortened and the weight is reduced.

If the upper limit value 0.10 of the conditional expression (1) is exceeded, chromatic aberration correction becomes excessive. On the other hand, if the lower limit of 0.02 is not reached, correction of chromatic aberration will be insufficient, and aberrations will worsen. From the viewpoint of further aberration reduction, the conditional expression (1) is
0.02 <θgFbp−0.6438 + 0.0016821 × νdbp <0.04
... (1a)
It is even better to set the range.

In each embodiment, the first lens unit L1 may include two or more lens units. The 1b lens group L1b may have two or more lenses. In each embodiment, it is more preferable to satisfy one or more of the following conditions. The 1a lens unit L1a has a 1a positive lens having a positive refractive power, and the Abbe number and partial dispersion ratio of the material of the 1a positive lens are νdap and θgFap, respectively. Among the negative lenses included in the first lens unit L1, the most object-side first n negative lens has a material specific gravity of SG1n. The first n negative lens has an Abbe number and a partial dispersion ratio of νd1n and θgF1n, respectively. In the optical system, the focal length of the first lens closest to the object is fG1, and the air distance from the first lens to the second lens adjacent to the first lens is d2. At this time, it is preferable to satisfy one or more of the following conditions.

νdbp <23 (2)
70 <νdap (3)
0.02 <θgFap−0.6438 + 0.0016821 × νdap (4)
2.40 <SG1n <4.75 (5)
θgF1n−0.6438 + 0.001682 × νd1n <0 (6)
5 <fG1 / d2 <20 (7)
Next, the technical meaning of each conditional expression described above will be described.

  In each embodiment, since the 1b lens unit L1b is a lens unit having negative refractive power, it is better to use a high dispersion material for the 1b positive lens in order to satisfactorily erase the lens group. . For this reason, in the 1b lens group L1b, it is preferable for correcting chromatic aberration that the 1b positive lens satisfying the conditional expression (1) simultaneously satisfies the conditional expression (2).

More preferably, the numerical range of the conditional expression (2) is 18 <νdbp <23 (2a)
It is good to set to. By doing so, it is possible to reduce the variation of chromatic aberration during focusing. Since the 1a lens unit L1a is a lens unit having a positive refractive power, it is possible to improve axial chromatic aberration and lateral chromatic aberration by using an optical material having high anomalous partial dispersion and low dispersion for the 1a positive lens. Can be improved. For this reason, it is preferable that the material of at least one 1a positive lens in the 1a lens group L1a satisfies the conditional expressions (3) and (4). More preferably, the numerical ranges of conditional expressions (3) and (4) are set to 90 <νdap (3a)
0.04 <θgFap−0.6438 + 0.0016821 × νdap (4a)
It is good to set to.

  As the focal length of the optical system becomes longer, the ratio of the weight of the first n negative lens located closest to the object side to the weight of the entire optical system tends to increase. Therefore, it is preferable that the specific gravity SG1n of the optical material of the first n negative lens located closest to the object side among the negative lenses included in the first lens unit L1 satisfies the conditional expression (5). If the specific gravity of the material of the first n negative lens is selected so as to satisfy the conditional expression (5), an increase in weight can be suppressed.

  In general, when considering secondary achromatism, the larger the difference between the partial dispersion of the optical material used for the positive lens and the partial dispersion of the optical material used for the negative lens, the greater the effect. Therefore, it is preferable to use a material that satisfies the conditional expression (6) for the first n negative lens closest to the object among the negative lenses in the first lens unit L1. Further, the focal length of the first lens closest to the object side is fG1, and the ratio of the air distance d2 between the first lens and the second second lens counted from the object side satisfies the conditional expression (7). good.

When the upper limit value of conditional expression (7) is exceeded, the effective diameter of the second lens increases and the weight increases. On the other hand, if the value is below the lower limit value, the correction ability of various aberrations (particularly axial chromatic aberration and spherical aberration) by the second lens is lowered, and the optical performance is deteriorated. Conditional expression (7) is more preferably
6 <fG1 / d2 <14 (7a)
It is good to set to the range.

  By setting the optical system so as to satisfy at least one of the conditional expressions (2) to (7), the overall length of the lens is shortened and the weight is reduced, and high optical performance with various aberrations suppressed is obtained. It is done. In the optical systems of the respective embodiments, at least one of the optical surfaces of the first lens unit L1 and the second lens unit L2 includes at least one layer formed by using a wet process. Is formed.

  As for the antireflection film, it is known that the lower the refractive index of the thin film used for the outermost layer, the higher the performance of the antireflection film having excellent incident angle characteristics and wavelength band characteristics. In a general vapor deposition method, it is difficult to form a dielectric thin film having a refractive index lower than that of magnesium fluoride (about 1.38). However, since a film having a lower density can be formed by the wet coating method, a thin film having a refractive index lower than 1.38 can be easily formed. As a result, a high antireflection effect can be obtained.

  In addition, as a reflection preventing means different from those obtained by laminating a plurality of thin films made of a homogeneous material such as a dielectric multilayer film or Japanese Patent Application Laid-Open No. 2005-284040, fine irregularities having a pitch below the visible wavelength range An antireflection structure using a shape is effective. This method is very excellent because it is equivalent to a film whose refractive index continuously changes in a pseudo manner by making it a shape whose space occupancy changes continuously (for example, a shape like a pyramid). The incident angle characteristic and the wavelength band characteristic can be obtained.

  As an example of the manufacturing method, a sol solution containing aluminum oxide is applied by a wet process, dried and sintered. Subsequently, when the obtained film is immersed in warm water, a structure in which the average pitch is 400 nm or less and the space occupancy continuously changes over a thickness of 200 nm or more can be formed (for example, JP-A-2005-2005). 234447). In the optical system of each embodiment, a low-refractive index film or an antireflection structure made of fine unevenness is formed on at least one of the optical surfaces using a wet process. This realizes a high-quality optical system that suppresses the occurrence of flare and ghost.

  In the first and second embodiments, the first lens unit L1a includes, in order from the object side to the image side, a first lens having a positive refractive power, a positive second lens, a negative third lens, a positive fourth lens, It is composed of a negative fifth meniscus lens having a convex surface facing the object side. The 1b lens group L1b is composed of a cemented lens in which, from the object side, a sixth lens having a positive refractive power and a negative seventh lens are cemented. The second lens unit L2, in order from the object side to the image side, hereinafter, a cemented lens in which the eighth lens having a negative refractive power and a positive ninth lens are cemented, and a positive tenth lens and a negative eleventh lens are cemented. The cemented lens is composed of a negative twelfth lens. Furthermore, it is composed of a cemented lens in which a positive thirteenth lens, a positive fourteenth lens, and a negative fifteenth lens are cemented.

  In this embodiment, focusing is performed by moving the 1b lens unit L1b in the optical axis direction. Further, by moving some of the lens units in the second lens unit L2 in the direction perpendicular to the optical axis, image shift due to camera shake during shooting is prevented. By selecting the optical material so as to satisfy the conditional expressions (1) to (7) in both Example 1 and Example 2, the overall length of the lens can be shortened and the weight can be reduced, and various aberrations can be suppressed. Image performance is achieved.

In the optical system OL of each embodiment, the radius of curvature of the lens surface is r, and the focal length of the optical system is f. At this time,
| R | / f <0.5
The lens surface that satisfies the following condition has a first optical part in which five or more lens surfaces are continuously arranged on the optical path. The first optical part includes at least one lens surface provided with an antireflection film. In Examples 1 and 2, the 18th lens surface to the 22nd lens surface correspond.

  The second lens unit L2 includes, in order from the object side to the image side, a cemented lens in which a positive lens and a negative lens are cemented, and a second optical part in which one negative lens is continuously arranged on the optical path. The second optical part includes at least one lens surface provided with an antireflection film including at least one layer formed using a wet process.

  An antireflection film is applied to the lens surface of one negative lens in the second lens unit L2. The sign of the radius of curvature of the lens surface provided with the antireflection film is the same as the sign of the cemented lens surface and the radius of curvature of the cemented lens. In Examples 1 and 2, the lens surface of the negative lens corresponds to the 21st lens surface in the numerical example described later, and the cemented lens surface of the cemented lens corresponds to the 19th lens surface.

  Next, an antireflection film including a layer formed by using a wet process, which is used in the optical systems of Example 1 and Example 2, will be described. In this embodiment, the layer formed using the wet process forms the outermost surface of the antireflection film, contains aluminum or aluminum oxide, and has a plurality of fine concavo-convex structures with an average pitch of 400 nm or less. Here, the average pitch is as follows.

  If the used wavelength is not a single wavelength but covers a certain range, the average pitch may be set to be equal to or shorter than the shortest wavelength in the used wavelength range. Here, the case of the visible range is applied, and the average pitch is set to 400 nm or less. This is because if an average pitch larger than the shortest wavelength used is used, harmful light due to diffraction or scattering is generated.

  Here, the average pitch will be described with reference to FIG. FIGS. 10A and 10B are views of a fine concavo-convex structure having a wavelength not longer than the use wavelength as viewed from above. The fine concavo-convex shape is typically round. FIG. 10A shows an example in which fine irregularities are periodically arranged in a triangular lattice shape. In this case, the average pitch is equal to the interval between one minute unevenness and one adjacent minute unevenness. FIG. 10B shows an example in which fine irregularities are arranged aperiodically.

In such a case, the average pitch is
(1) Select six fine irregularities in ascending order from one fine irregularity, calculate the average value of the intervals,
(2) What is necessary is just to define by calculating (1) regarding all the fine unevenness | corrugations, and calculating the average value. However, since it is practically difficult to measure all the fine concavo-convex structures provided on the optical surface, one or several points on the optical surface are observed with a scanning electron microscope, and the values calculated within a certain area are used. You may substitute. And it is a film | membrane whose refractive index in wavelength 550nm is 1.45 or less.

  In the optical systems of Example 1 and Example 2, lens surfaces having a similar radius of curvature are adjacent to each other from the 18th lens surface to the 22nd lens surface (hereinafter simply referred to as “i-th surface”) of the second lens unit L2. Has been placed. Therefore, after the incident light beam is reflected by the lens surface, it is easy to reach the image plane when it is reflected again, and the antireflection film made of ordinary dielectric multilayer film prevents the generation of harmful light such as flare and ghost. Is a difficult configuration. Therefore, an average formed by using a wet process as shown in FIG. 5 on the 18th surface, 20th surface, 21st surface, and 22nd surface shown in the lens cross-sectional views of the optical system of FIGS. An antireflection film having a fine uneven shape with a pitch of 400 nm or less is formed.

  An example of the manufacturing method of the antireflection film shown in FIG. 5 is shown below. The fine concavo-convex shape provided on the outermost surface can be formed as follows. Step (1) A solution containing aluminum oxide is applied to the lens surface using a sol-gel method to form a film, and then dried and sintered. Step (2) Subsequently, the obtained film is immersed in warm water to develop a fine uneven shape. The thickness of the fine concavo-convex shape can be adjusted by the thickness of the coating applied first, the time of immersion in warm water, or the like. In Example 1 and Example 2, the thickness was adjusted to 220 nm.

  When the refractive index of the obtained fine concavo-convex shape was analyzed using spectroscopic ellipsometry, as shown in FIG. 6, a structure in which the refractive index continuously changed from 1.4 to 1.0 at a wavelength of 550 nm over 220 nm was obtained. I found out that Since the materials of the above lenses (18th surface, 20th surface, 21st surface, 22nd surface) have a high refractive index of 1.713 to 1.883, as shown schematically in FIG. 5 and FIG. The performance improvement is achieved by introducing the intermediate layer 103 between the lens 102 and the lens 101.

Table 1 shows the refractive index and film thickness of the intermediate layer for each lens (18th surface, 20th surface, 21st surface, 22nd surface) of Example 1 and Example 2. A manufacturing method is not limited as long as the intermediate layer satisfies a desired refractive index and film thickness. A dry process for forming a dielectric by vacuum deposition or the like may be used, or a wet process may be used. In the case of the wet process, for example, a method of applying a solution containing silica (SiO ₂ ) and titania (TiO ₂ ) to the lens surface using a sol-gel method can be used. According to this method, a desired refractive index can be easily realized by changing the mixing ratio of silica and titania.

  As an example, FIG. 6 shows the refractive index structure of the antireflection film formed on the 21st surface of Example 1, and FIG. 7 shows the reflectance characteristics. Other aspects are not described. By adopting the film configuration described in Table 1, substantially equivalent reflectance characteristics can be realized. For comparison, FIG. 8 shows the reflectance characteristics of an antireflection film using a dielectric multilayer film composed of six layers formed on the 21st surface of Example 1 by a general vapor deposition method.

  As can be seen by comparing FIG. 7 and FIG. 8, the antireflection film formed by using the wet process used in the present invention has not only a low reflectance as an absolute value but also an extremely excellent wavelength band characteristic and incident angle characteristic. Excellent anti-reflection performance. Therefore, the optical system of the present invention realizes a high-quality optical system that suppresses the occurrence of flare, ghost, and the like.

  Moreover, although the antireflection film formed using the wet process was provided on the four surfaces in both Example 1 and Example 2, the present invention is not limited to this, and it is possible to suppress ghost by providing it on at least one surface. An effect is obtained. For example, when providing an antireflection film using a wet process on only one surface, it is preferable to provide it on the 21st surface in the case of the optical system of this embodiment. This is because the 19th surface is a cemented lens surface, so the degree of freedom in design of the antireflection film is poor, and large reflected light is generated, and the surface has the same sign of curvature as the 21st surface. Therefore, it is easy to be a combination that generates a ghost.

  Further, in this embodiment, the antireflection film including at least one layer formed by the wet process is provided on the lenses of the second lens group. However, the present invention is not limited to this, and the first a lens group is not limited thereto. You may apply to the lens surface of L1a and 1b lens group L1b. In this embodiment, an example of an antireflection film having a fine uneven shape is shown, but the present invention is not limited to this, and is an antireflection film in which a uniform low refractive index film is provided on the outermost layer by a wet process. Also good.

As described above, in the optical system of each embodiment, the variation of chromatic aberration at the time of focusing is favorably corrected by appropriately selecting an optical material. The formation of a high-performance antireflection film using a wet process on at least one surface of the optical system effectively suppresses generation of harmful light such as flare and ghost.

  Next, an embodiment of a single lens reflex camera system (optical apparatus) using the optical system OL of the present invention will be described with reference to FIG.

  In FIG. 9, 10 is a single-lens reflex camera body, and 11 is an interchangeable lens equipped with an optical system according to the present invention. Reference numeral 12 denotes a recording unit such as a film or an image sensor for recording a subject image obtained through the interchangeable lens 11, and reference numeral 13 denotes a finder optical system for observing the subject image from the interchangeable lens 11. Reference numeral 14 denotes a rotating quick return mirror for switching and transmitting to the recording means 12 for receiving the subject image from the interchangeable lens 11 and the finder optical system 13. When observing the subject image with the finder, the subject image formed on the focusing plate 15 via the quick return mirror 14 is made into an erect image with the pentaprism 16 and then magnified and observed with the eyepiece optical system 17. At the time of shooting, the quick return mirror 14 rotates in the direction of the arrow, and the subject image is formed and recorded on the recording means 12. Reference numeral 18 denotes a submirror, and 19 denotes a focus detection device.

  Thus, by applying the imaging optical system of the present invention to an imaging apparatus such as a single-lens reflex camera interchangeable lens, an imaging apparatus having high optical performance can be realized. The present invention can be similarly applied to an SLR (Single Lens Reflex) camera having no quick return mirror.

  As mentioned above, although the preferable Example of this invention was described, this invention is not limited to these Examples, A various deformation | transformation and change are possible within the range of the summary.

  Hereinafter, specific numerical data for numerical examples 1 and 2 corresponding to the first and second embodiments will be described. In each numerical example, i indicates the order counted from the object side. ri is the radius of curvature of the i-th optical surface, di is the axial distance between the i-th surface and the (i + 1) -th surface, and ndi and νdi are the i-th surface and (i + 1) -th surface for the d-line, respectively. The refractive index and Abbe number of the medium in between are shown. θgFi is a partial dispersion ratio of the medium between the i-th surface and the (i + 1) -th surface, and is shown for only some lenses. The specific gravity is shown only for some lenses.

  BF is a back focus. In each numerical example, the last two optical surfaces are glass blocks such as face plates and filters. Table 2 shows the relationship between the above conditional expressions (1) to (7) and various numerical values in the numerical examples. Table 2 also shows the correspondence with the lenses shown in each claim.

[Numerical Example 1]
Lens data (r and d units: mm)
Surface number rd nd νd θgF Specific gravity
1 285.181 10.70 1.48749 70.2 0.530
2 -365.280 45.00
3 77.200 19.00 1.43387 95.1 0.537
4 -201.628 0.12
5 -211.919 3.10 1.65412 39.7 0.574 3.02
6 185.490 0.74
7 68.270 9.50 1.43387 95.1 0.537
8 241.309 4.51
9 49.323 5.00 1.51633 64.1
10 36.974 18.45
11 -366.928 4.05 1.92286 18.9 0.649
12 -98.774 2.40 1.74950 35.3
13 101.913 29.58
14 (Aperture) ∞ 5.56
15 153.525 1.33 1.84666 23.8
16 52.297 5.67 1.65 160 58.5
17 -178.690 10.22
18 80.489 3.59 1.84666 23.8
19 -117.581 1.80 1.72916 54.7
20 38.409 5.45
21 -114.990 1.70 1.83400 37.2
22 105.792 4.62
23 83.144 3.75 1.80518 25.4
24 -362.882 3.23
25 118.635 5.83 1.74950 35.3
26 -68.316 1.61 1.92286 18.9
27 -658.596 6.39
28 ∞ 2.00 1.51633 64.1
29 ∞ 59.36
Image plane ∞

Each data
Focal length 294.99mm
F number 2.9
Angle of view 4.19 °
Image height 21.64mm
Total lens length 274.25mm
BF 59.36mm

[Numerical Example 2]
Lens data (r and d units: mm)
Surface number rd nd νd θgF Specific gravity
1 251.287 16.40 1.48749 70.2 0.530
2 -569.439 47.74
3 134.398 21.28 1.43387 95.1 0.537
4 -239.479 0.24
5 -237.555 4.00 1.61340 44.3 0.563 3.29
6 178.770 17.18
7 76.688 14.20 1.43387 95.1 0.537
8 318.525 1.03
9 60.263 6.00 1.51633 64.1
10 47.352 22.04
11 -1630.821 4.00 1.92286 18.9 0.649
12 -301.810 3.20 1.65412 39.7
13 149.471 45.57
14 (Aperture) ∞ 8.36
15 327.772 2.18 1.72047 34.7
16 40.638 10.87 1.72916 54.7
17 -927.465 10.02
18 103.249 5.93 1.84666 23.8
19 -133.810 1.71 1.71300 53.9
20 45.777 5.62
21 -155.221 1.67 1.88300 40.8
22 121.068 6.32
23 137.098 3.35 1.74950 35.3
24 -256.865 5.53
25 85.030 7.34 1.65412 39.7
26 -133.787 2.00 1.92286 18.9
27-3193.452 21.53
28 ∞ 2.20 1.51633 64.1
29 ∞ 67.53
Image plane ∞

Each data
Focal length 390.06mm
F number 2.90
Angle of view 3.17 °
Image height 21.64mm
Lens total length 365.05mm
BF 39.00mm

L1 first lens group, L2 second lens group, L1a 1a lens group, L1b 1b lens group, SP stop

Claims (13)

In order from the object side to the image side, the lens unit includes a first lens unit having a positive refractive power, an aperture stop, and a second lens unit. The first lens unit has an optical axis for focusing with the first a lens unit having a positive refractive power. A first-b lens group having a negative refractive power that moves upward, the first-b lens group including a first-b positive lens having a positive refractive power and a first-b negative lens having a negative refractive power; When the Abbe number and the partial dispersion ratio of the lens material are νdbp and θgFbp, respectively.
0.02 <θgFbp−0.6438 + 0.0016821 × νdbp <0.10
And both the first lens group and the second lens group include a lens surface on which an antireflection film including at least one layer formed using a wet process is formed. Optical system. The material of the 1b positive lens is:
νdbp <23
The optical system according to claim 1, wherein the following conditional expression is satisfied. The 1a lens group includes a 1a positive lens having a positive refractive power, and the Abbe number and partial dispersion ratio of the material of the 1a positive lens are νdap and θgFap, respectively.
70 <νdap
0.02 <θgFap−0.6438 + 0.0016821 × νdap
The optical system according to claim 1, wherein the following conditional expression is satisfied. When the radius of curvature of the lens surface is r and the focal length of the optical system is f,
| R | / f <0.5
The lens surface that satisfies the following condition has a first optical part in which five or more lens surfaces are continuously arranged on the optical path, and the first optical part includes at least one lens surface to which the antireflection film is applied. The optical system according to claim 1, wherein the optical system is an optical system.   The second lens group includes, in order from the object side to the image side, a cemented lens in which a positive lens and a negative lens are cemented, and a second optical part in which one negative lens is continuously arranged on the optical path. The optical system according to any one of claims 1 to 4, wherein the optical part includes at least one lens surface on which the antireflection film is applied.   The lens surface of the one negative lens is provided with the antireflection film, and the sign of the radius of curvature of the lens surface provided with the antireflection film is the sign of the cemented lens surface of the cemented lens and the sign of the radius of curvature. The optical system according to claim 5, which is the same.   The layer formed using the wet process forms the outermost surface of the antireflection film, contains aluminum or aluminum oxide, and has a plurality of fine concavo-convex structures having an average pitch of 400 nm or less. The optical system according to any one of claims 1 to 6.   The layer formed by using the wet process forms an outermost surface of the antireflection film, and is a film having a refractive index of 1.45 or less at a wavelength of 550 nm. 2. The optical system according to item 1. When the specific gravity of the material of the first n negative lens closest to the object among the negative lenses included in the first lens group is SG1n,
2.40 <SG1n <4.75
The optical system according to claim 1, wherein the following condition is satisfied. The first n negative lens has an Abbe number and a partial dispersion ratio of νd1n and θgF1n, respectively.
θgF1n−0.6438 + 0.001682 × νd1n <0
The optical system according to claim 9, wherein the following condition is satisfied. When the focal length of the first lens closest to the object side in the optical system is fG1, and the air distance from the first lens to the second lens adjacent to the first lens is d2,
5 <fG1 / d2 <20
The optical system according to claim 1, wherein the following condition is satisfied.   The optical system according to claim 1, wherein the optical system is an imaging optical system.   An optical apparatus comprising the optical system according to claim 1.