JP2011107313A - Optical system and optical equipment using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical system which can obtain high optical performance over the whole of an object distance ranging from an infinity object to a close distance object. <P>SOLUTION: The optical system includes: a front group having lens parts arranged in order, from an object side to an image side, of a positive lens, a negative lens, an aperture diaphragm, a negative lens and a positive lens; and a rear group having lens parts arranged in order of a negative lens and a positive lens, wherein focusing is performed by changing the distance between the front group and the rear group, and the refractive index, Abbe number, partial dispersion ratio NdpR, νdpR and θgFpR of the material of at least one positive lens GpR among the positive lenses arranged more on the image side than the aperture diaphragm are suitably set respectively. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  Conventionally, a single-lens reflex camera has a structure in which a rotary reflecting mirror is provided behind the photographing lens to reflect the light beam from the photographing lens and guide it to the finder system. Therefore, a photographic lens used in a single-lens reflex camera is required to be a photographic lens that can easily obtain a long back focus to the extent that a rotary reflecting mirror is disposed on the image side and can easily obtain high optical performance. ing. Conventionally, a so-called Gaussian lens is known as a photographing lens having a standard angle of view that can achieve these requirements relatively easily (Patent Document 1).

  Gaussian lenses often focus by extending the entire lens system, and there is little aberration fluctuation with respect to fluctuations in object distance (shooting distance). For this reason, it is possible to shoot an object at a close range relatively easily with a simple structure. On the other hand, the Gaussian lens tends to have a relatively large axial chromatic aberration as the photographing magnification increases. Gaussian lenses have relatively small aberration fluctuations with respect to object distance fluctuations, but for example, when focusing to a macro shooting area of about -0.5 times, spherical aberration, coma aberration, and axial chromatic aberration are often generated. come. On the other hand, a lens group with a small refractive power is arranged on the image side of the Gaussian lens, and focusing is performed by changing the relative relationship of each lens group, thereby reducing aberration fluctuations due to fluctuations in object distance. Is known (Patent Document 2).

Japanese Patent Laid-Open No. 06-337348 JP 05-142474 A

  A Gaussian lens or a modified Gaussian lens obtained by deforming the Gaussian lens has a characteristic that aberration variation with respect to variation in object distance is relatively small. However, when the photographing distance is shortened and the photographing magnification is increased, for example, when the photographing magnification is about −0.5, fluctuations in various aberrations, particularly, spherical aberration, coma aberration, and axial chromatic aberration increase. For this reason, in order to obtain high optical performance over a wide range of object distances, including close-up objects with a large shooting magnification, in the Gaussian lens or a modified Gaussian lens modified from it, the material of each lens constituting the optical system is set appropriately. It becomes important to do. For example, it is important to use a lens made of a material in which the refractive index, Abbe number, partial dispersion ratio, and the like are appropriately selected.

  An object of the present invention is to provide an optical system capable of obtaining high optical performance over the entire object distance from an object at infinity to a close object. In particular, an object of the present invention is to provide an optical system in which aberration variation is small and high optical performance can be obtained even when the photographing distance is shortened and the maximum photographing magnification is increased.

The optical system of the present invention is arranged in the order of the front group having a lens unit arranged in the order of positive lens, negative lens, aperture stop, negative lens, and positive lens, negative lens, and positive lens in order from the object side to the image side. A rear group having a lens portion, focusing is performed by changing the distance between the front group and the rear group, and the material of at least one positive lens GpR among the positive lenses arranged on the image side from the aperture stop When the refractive index, Abbe number, and partial dispersion ratio are NdpR, νdpR, and θgFpR, respectively.
1.53 <NdpR <1.85
50 <νdpR <80
0.005 <θgFpR−0.6438 + 0.001682 × νdpR <0.080
It is characterized by satisfying the following conditional expression.

  According to the present invention, it is possible to obtain an optical system capable of obtaining high optical performance over the entire object distance from an object at infinity to a close object.

Sectional view of the optical system of Example 1 (A) (B) Infinity object of the optical system of Example 1 and aberration diagrams at a photographing magnification of −0.950 Sectional drawing of the optical system of Example 2 (A) (B) Infinity object of the optical system of Example 2 and aberration diagrams at a photographing magnification of −0.480 Sectional drawing of the optical system of Example 3 (A) (B) An aberration diagram of the optical system of Example 3 at infinity and an imaging magnification of −0.480. Schematic diagram of main parts of an imaging apparatus of the present invention

  Examples of the optical system of the present invention and an optical apparatus having the optical system will be described. The optical system of the present invention has a front group and a rear group in order from the object side to the image side. The front group includes a lens unit arranged in order of the positive lens, the negative lens, the aperture stop, the negative lens, and the positive lens in order from the object side to the image side. The rear group has a lens unit arranged in the order of a negative lens and a positive lens. Focusing is performed by changing the interval between the front group and the rear group.

  FIG. 1 is a lens cross-sectional view of an optical system according to Example 1 of the present invention. FIGS. 2A and 2B are aberration diagrams when the object distance of the optical system according to the first embodiment of the present invention is infinity and when the photographing magnification is −0.950. FIG. 3 is a lens sectional view of the optical system according to Example 2 of the present invention. FIGS. 4A and 4B are aberration diagrams when the object distance of the optical system according to Example 2 of the present invention is infinity and when the photographing magnification is −0.480. FIG. 5 is a lens cross-sectional view of the optical system according to Example 3 of the present invention. FIGS. 6A and 6B are aberration diagrams when the object distance of the optical system according to the third embodiment of the present invention is infinity and the photographing magnification is −0.480. FIG. 7 is a schematic view of the main part when the optical system of the present invention is applied to an optical apparatus such as a digital camera. The optical systems of Examples 1 and 2 in FIGS. 1 and 3 are Gaussian optical systems, and the optical system of Example 3 in FIG. 5 is a retrofocus optical system.

  The optical system of the present invention is used for optical devices such as digital cameras, video cameras, silver salt film cameras, telescopes, binocular observation devices, copying machines, and projectors. In the lens cross-sectional view, the left is the front (object side, enlargement side), and the right is the rear (image side, reduction side). When used in an image projection apparatus such as a projector, the left side is the screen side and the right side is the projected image side. LE is an optical system. LF is the front group and LR is the rear group. SP is an aperture stop (aperture) for adjusting the amount of light, and is disposed in the front group LF. IP is an image plane, and when used as a photographing optical system of a video camera or a digital still camera, a photosensitive surface corresponding to an imaging surface of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor is placed.

  In Example 1 of FIG. 1, when focusing from an infinitely distant object to a close object, the front group LF and the rear group LR are moved toward the object side at different speeds as indicated by arrows. In Embodiments 2 and 3 of FIGS. 3 and 5, the front group LF is moved to the object side, and the rear group LR is not moved. In each aberration diagram, in the spherical aberration, the solid line represents the d line (wavelength 587.6 nm), the two-dot chain line represents the g line (wavelength 435.8 nm), and the dotted line represents the F line (wavelength 486 nm). In astigmatism, the solid line represents the image plane ΔS of the d-line sagittal ray, and the dotted line represents the image plane ΔM of the d-line meridional ray. In lateral chromatic aberration, the two-dot chain line is the g-line. In the distortion aberration, it represents distortion in the d-line. Fno is the F number, and ω is the half angle of view.

  First, an optical function for reducing aberration fluctuations due to focusing in the optical system of the present invention will be described. In many cases, a Gauss type lens uses a material having a high refractive index for the positive lens in order to reduce the Petzval sum and correct the curvature of field well. Further, in order to correct the chromatic aberration of the entire system having a positive refractive power, in many cases, a low dispersion material is used for the positive lens and a high dispersion material is used for the negative lens. Currently, there are few high-refractive index, low-dispersion materials on the market that have a large partial dispersion ratio θgF, so the amount of axial chromatic aberration of g-line in the positive lens is insufficient, and the axial chromatic aberration correction in the negative lens. Since the effect is higher, the chromatic aberration of g-line tends to be overcorrected as a whole system. In the Gaussian lens disclosed in Patent Document 1, g-axis axial chromatic aberration is corrected by using a high dispersion material having a large partial dispersion ratio θgF for any of a plurality of positive lenses. With this method, good optical performance can be obtained in photographing an object at infinity. When focusing from an object at infinity to an object at a short distance, the incident height h to the on-axis light beam with a positive lens made of a high dispersion material changes. For this reason, the longitudinal chromatic aberration tends to fluctuate due to the fluctuation of the object distance.

  Normally, a Gaussian lens has an optical arrangement close to symmetry with a diaphragm interposed therebetween, and performs focusing by moving the entire lens system in the optical axis direction. When the lens system is extended to the object side for photographing a close-range object, the incident height of the off-axis principal ray that passes through the lens on the image side from the aperture is reduced, but off-axis that passes through the lens group on the object side from the aperture The incident height of the chief ray is also reduced at the same time. As a result, the relationship of canceling off-axis aberrations before and after the stop is maintained regardless of the object distance, so that there is little variation in lateral chromatic aberration and field curvature due to the object distance. However, a lens system having a positive power as a whole moves forward when photographing a close-range object. For this reason, the incident height of the axial ray incident from the object side increases, and there is a tendency that the variation due to the object distance of spherical aberration, coma aberration, and axial chromatic aberration greatly occurs. In particular, as described above, in the case of axial chromatic aberration that tends to be overcorrected even when shooting an object at infinity, the tendency of overcorrection further increases and the optical performance deteriorates when shooting an object at a close distance.

  Therefore, in the macro lens disclosed in Patent Document 2, a weak power rear group having a positive lens and a negative lens is arranged on the image side of the Gaussian lens group. Then, focusing is performed by changing the relative distance between the lens groups. As a result, each aberration that varies due to the object distance variation in the Gaussian lens system is corrected by changing the relationship of the incident height of the on-axis light beam to each lens surface in the rear group, and the aberration variation due to the object distance variation is reduced. is doing. The reason why the power of the rear group is weakened is to reduce the influence on the lateral chromatic aberration and the off-axis aberration such as curvature of field, which are favorably corrected only by the Gauss type lens system. For this reason, with respect to spherical aberration and coma aberration, although an effect of reducing aberration fluctuation due to fluctuation of object distance is obtained, it is not necessarily sufficient for reducing fluctuation of axial chromatic aberration.

  Therefore, in the present invention, first, the portion that contributes most to the variation of longitudinal chromatic aberration in the Gaussian lens system is limited. When shooting an object at infinity in a Gaussian lens system, the point where the incident height of the on-axis light beam is the largest is the most positive lens on the object side. The height increases. Then, it was found that the incident height of the on-axis light beam to the lens on the front side of the stop becomes smaller due to the increase in the converging power. Therefore, if only the axial chromatic aberration at the time of photographing an object at infinity is improved, a method of arranging a material having an anomalous partial dispersion on the most positive lens on the object side can be considered. However, at the time of shooting an object at a close distance, the incident light beam on the lens closest to the object side changes in the direction of decreasing the incident height. For this reason, the tendency of occurrence of longitudinal chromatic aberration of the g-line in the abnormal partial dispersion material is weakened, and conversely, the distance is changed.

  Therefore, when using a material with anomalous partial dispersion for the positive lens on the image side where the incident height of the on-axis light beam is larger when shooting an object at close distance than when shooting an object at infinity, the axis is most effectively used. It was found that fluctuations in upper chromatic aberration can be reduced. Among the abnormal partial dispersion materials currently on the market, fluorite and the trade name FK01 are the most frequently used low refractive index low dispersion materials. Although these materials have high anomalous partial dispersibility, the refractive index is less than 1.5, and when used for a positive lens, the Petzval sum becomes large, which makes it difficult to correct field curvature well, which is not preferable.

  Therefore, in the optical system of the present invention, the use of a material having a refractive index of about 1.6 (a medium refractive index low dispersion material) as a positive lens material is slightly inferior in anomalous partial dispersion. The field curvature is corrected well. At this time, if this medium refractive index constant dispersion material is used for all the positive lenses, the Petzval sum is also increased, so that a positive lens made of a material having a high refractive index and low dispersion is used in part. In addition, since the material having anomalous partial dispersion is soft, the material is easily damaged, and is not suitable for use on the lens on the most object side exposed to the outside.

  Therefore, in the lens system of the present invention, a high refractive index and low dispersion material is disposed on the most positive lens on the object side. Further, as described above, the present inventor has a lower incidence of axial rays when photographing the closest object, so that the tendency of insufficient correction of g-line as chromatic aberration is weakened, and fluctuation of axial chromatic aberration is reduced. It has also been found that a correction effect can be further obtained. As a result, in the present invention, an optical system capable of satisfactorily correcting variations in all aberrations including spherical aberration and coma due to variations in object distance, regardless of the configuration in which the rear group is disposed on the image plane side of the lens system of Patent Document 2. I have a system. It was also confirmed that this configuration can be applied to a so-called retrofocus lens system in which a lens unit having a negative refractive power is arranged on the object side of a Gaussian lens system.

  In the optical system according to the present invention, the front group having a lens unit arranged in order of the positive lens, the negative lens, the stop, the negative lens, and the positive lens from the object side to the image side, and the negative lens and the positive lens are arranged in this order. A rear group having a lens portion is provided. Focusing is performed by changing the interval between the front group and the rear group. Here, the front lens group has a symmetrical lens structure with the stop interposed therebetween, so that off-axis aberrations such as field curvature and lateral chromatic aberration, and their distance variations are corrected well. Also, fluctuations in axial aberrations such as spherical aberration and coma that occur when the front group moves during focusing are corrected well by changing the incident height of axial rays on each surface of the rear group. .

In each embodiment, the refractive index, Abbe number, and partial dispersion ratio of the material of at least one positive lens GpR among the positive lenses disposed on the image side from the aperture stop SP are NdpR, νdpR, and θgFpR, respectively. At this time,
1.53 <NdpR <1.85 (1a)
50 <νdpR <80 (2a)
0.005 <θgFpR−0.6438 + 0.001682 × νdpR <0.080
... (3a)
The following conditional expression is satisfied. Here, the partial dispersion ratio θgF is defined as ng, nF, and nC for the refractive indexes of the material with respect to g-line, F-line, and C-line, respectively. At this time θgF = (ng−nF) / (nF−nC)
It is.

  Next, the technical meaning of the conditional expressions (1a) to (3a) will be described. If the lower limit of conditional expression (1a) is not reached, the Petzval sum increases in the positive direction and the field curvature increases. If the upper limit is exceeded, it will be difficult to obtain a good quality material. If the lower limit value of conditional expression (2a) is not reached, the variation of axial chromatic aberration with respect to the object distance increases. If the upper limit is exceeded, it will be difficult to obtain good quality materials. If the lower limit of conditional expression (3a) is not reached, the effect of generating g-line axial chromatic aberration is weakened, and the axial chromatic aberration is overcorrected in the entire system. On the other hand, if the value exceeds the upper limit, the effect of generating g-line axial chromatic aberration becomes too strong, and the axial chromatic aberration correction becomes insufficient as a whole system. More preferably, the conditional expressions (1a) to (3a) satisfy the conditional expressions (1b) to (3b).

1.55 <NdpR <1.65 (1b)
55 <νdpR <75 (2b)
0.010 <θgFpR−0.6438 + 0.001682 × νdpR <0.040
... (3b)
The optical system of the present invention is achieved by satisfying the above conditions. Further, in order to satisfactorily correct chromatic aberration and obtain high optical performance, it is preferable to satisfy one or more of the following conditions. The refractive index, Abbe number, and partial dispersion ratio of the material of at least one positive lens GpF among the positive lenses disposed on the object side from the stop SP of the front group LF are NdpF, νdpF, and θgFpF, respectively. Of the negative lenses arranged in the front group LF, the refractive index, Abbe number, and partial dispersion ratio of at least one negative lens GnF are NdnF, νdnF, and θgFnF, respectively. The focal length of the rear group LR is fR, and the focal length of the entire system is f.

At this time,
1.65 <NdpF <1.90 (4a)
30 <νdpF <60 (5a)
−0.020 <θgFpF−0.6438 + 0.001682 × νdpF <0.005
... (6a)
1.90 <NdnF + 0.0125νdnF <2.24 (7a)
−0.020 <θgFnF−0.6438 + 0.001682 × νdnF <0.003
... (8a)
| FR / f |> 40 (9a)
It is preferable to satisfy one or more of the following conditional expressions.

  Next, the technical meaning of each conditional expression described above will be described. If the lower limit of conditional expression (4a) is not reached, the Petzval sum increases in the positive direction, and the field curvature increases. If the upper limit is exceeded, it will be difficult to obtain good quality materials. If the lower limit of conditional expression (5a) is not reached, the variation of axial chromatic aberration with respect to the object distance becomes large. If the upper limit is exceeded, it will be difficult to obtain good quality materials. If the lower limit of conditional expression (6a) is not reached, the axial chromatic aberration of the g-line will be insufficient, and the axial chromatic aberration will be overcorrected as a whole system. If the upper limit is exceeded, the variation of axial chromatic aberration with respect to the object distance becomes large. More preferably, the numerical ranges of the conditional expressions (4a) to (6a) satisfy the conditional expressions (4b) to (6b).

1.65 <NdpF <1.88 (4b)
31 <νdpF <58 (5b)
−0.010 <θgFpF−0.6438 + 0.001682 × νdpF <0.004
... (6b)
When the refractive index NdnF is small when the lower limit value of conditional expression (7a) is not reached, spherical aberration, coma aberration, and field curvature are insufficiently corrected. When the Abbe number νdnF is small, the longitudinal chromatic aberration and the lateral chromatic aberration are overcorrected. When the upper limit value is exceeded and the refractive index NdnF is large, spherical aberration, coma aberration, and field curvature are overcorrected, and when the Abbe number νdnF is small, axial chromatic aberration and lateral chromatic aberration are undercorrected. If the lower limit of conditional expression (8a) is not reached, it will be difficult to obtain a good material. If the upper limit is exceeded, the axial chromatic aberration of the g line is overcorrected. More preferably, the numerical ranges of the conditional expressions (7a) and (8a) satisfy the conditional expressions (7b) and (8b).

2.00 <NdnF + 0.0125νdnF <2.22 (7b)
−0.010 <θgFnF−0.6438 + 0.001682 × νdnF <0.000
... (8b)
If the lower limit of conditional expression (9a) is not reached, the power of the rear group LR becomes too large, and many off-axis aberrations such as lateral chromatic aberration and field curvature corrected in the front group occur, which is not good. More preferably, the numerical value of conditional expression (9a) satisfies conditional expression (9b).

| FR / f |> 5.0 (9b)
In the optical system of each embodiment, when focusing from an object at infinity to a close object, the front group LF is moved to the object side, and the rear group LR is fixed or moved to the object side. When the rear lens group LR moves to the image side, the incident height of the axial ray on each lens surface of the rear lens group LR changes too much, so that the spherical aberration and the coma aberration at the time of shooting an object at a close distance are corrected well. It becomes difficult.

Hereinafter, a detailed lens configuration in each example will be described.
Example 1
In order from the object side to the image side, the front lens group LF includes a positive lens FFP1 having a convex surface facing the object side, a positive lens FFP2 having a convex surface facing the object side, a negative lens FFN having a concave surface facing the image side, and an aperture stop SP. is doing. Further, the lens includes a negative lens FRN having a concave surface facing the object side and a cemented lens obtained by cementing a positive lens FRP1 having a convex surface facing the image side, and a positive lens FRP2. The rear group LR includes a negative lens RN having a concave surface facing the image side and a positive lens RP having both lens surfaces convex. The optical system of Example 1 is a Gaussian lens system.

  Here, the positive lens FRP2 satisfies the conditional expressions (1a) to (3a), the Petzval sum of the entire system is reduced, the field curvature is corrected well, and the variation of axial chromatic aberration with respect to the object distance is improved. It is suppressed. Further, the positive lens FFP1 satisfies the conditional expressions (4a) to (6a), the Petzval sum of the entire system is reduced, the field curvature is corrected well, and the variation of the longitudinal chromatic aberration with respect to the object distance is improved. It is suppressed. Further, the negative lens FFN and the negative lens FRN both satisfy the conditional expressions (7a) and (8a), and the axial chromatic aberration is corrected well. The rear lens group LR satisfies the conditional expression (9a), and corrects the variation of spherical aberration and coma with respect to the object distance without affecting the off-axis aberrations such as field curvature and lateral chromatic aberration. . Further, the rear group LR moves to the object side at the time of focusing, and the spherical aberration and the coma aberration in the front group LF are changed by changing the incident height of the axial ray on each surface of the rear group LR. It is corrected to.

(Example 2)
The lens configuration of Example 2 is the same as that of Example 1. The second embodiment is different from the first embodiment in that the rear group LR is fixed when focused. When focusing, moving the rear group LR to the object side as in the first embodiment has selectivity of the axial ray height h on each lens surface of the rear group LR, and more appropriately corrects the variation with respect to the object distance. be able to. However, in the second embodiment, the mechanical holding mechanism is simplified by fixing the rear group LR.

(Example 3)
In order from the object side to the image side, the front lens group LF has a convex meniscus lens FFN with a convex object side surface, a biconvex positive lens FFP1, a positive lens FFP2 with a convex surface facing the object side, and a concave surface facing the image side. And a negative lens FFN2 and an aperture stop SP. Further, the lens includes a cemented lens obtained by cementing the negative lens FRN and the positive lens FRP1, and a positive lens FRP2. The rear group LR includes a negative lens RN having a concave surface facing the image side, and a positive lens RP having convex both lens surfaces. The optical system in Example 3 is a retrofocus lens system. Both positive lenses FRP1 and FRP2 satisfy the conditional expressions (1a) to (3a), and the variation of axial chromatic aberration with respect to the object distance is improved while reducing the Petzval sum of the entire system and correcting the curvature of field well. It is suppressed to. The positive lens FFP2 satisfies the conditional expressions (4a) to (6a), reduces the Petzval sum of the entire system, corrects the curvature of field well, and suppresses the fluctuation of the longitudinal chromatic aberration with respect to the object distance. ing. Further, the negative lens FFN2 satisfies the conditional expressions (7a) and (8a), and the axial chromatic aberration is corrected well. The rear lens group LR satisfies the conditional expression (9a), and its power is sufficiently weak so that the fluctuation of the spherical aberration and the coma aberration with respect to the object distance is good without affecting off-axis aberrations such as field curvature and lateral chromatic aberration. It is corrected to. The rear group LR is fixed at the time of focusing, and the variation of spherical aberration and coma aberration in the front group LF is corrected by changing the incident height of the axial ray on each lens surface of the rear group LR. The holding structure is simplified.

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

  Lens data of Numerical Examples 1 to 3 corresponding to Numerical Examples 1 to 3 are shown. In these numerical examples, i indicates the order of the surfaces from the object side. ri is the radius of curvature of the i-th lens surface from the object side. di represents the distance between the upper surfaces of the axes in the i-th reference state from the object side, and ndi, νdi, and θgFi represent the refractive index, Abbe number, and partial dispersion ratio of the i-th optical member at the d-line. The effective beam diameter is also shown. In addition to specs such as focal length and F-number, the angle of view is the half angle of view of the entire system, the image height is the maximum image height that determines the half angle of view, and the total lens length is the distance from the first lens surface to the final lens surface. , BF indicate the length (back focus) from the final lens surface to the image plane. Further, the part where the distance d between the optical surfaces is (variable) changes during focusing, and the surface distance corresponding to the photographing magnification is shown in the attached table. The shooting magnification 1 / ∞ represents shooting at an infinite object distance. Table 1 shows the calculation results of the conditional expressions based on the lens data of Numerical Examples 1 to 3 described below.

(Numerical example 1)

Unit mm

Surface data surface number rd nd νd θgF Effective diameter
1 39.096 4.51 1.77250 49.6 0.5520 33.26
2 181.579 0.15 31.94
3 21.011 3.57 1.60 300 65.4 0.5401 26.29
4 32.983 1.27 24.45
5 52.555 1.30 1.65412 39.7 0.5737 23.88
6 14.422 13.76 19.45
7 (Aperture) ∞ 3.24 13.24
8 -13.801 1.30 1.65412 39.7 0.5737 13.41
9 -139.302 4.91 1.77250 49.6 0.5520 16.27
10 -18.079 0.15 18.91
11 67.358 3.48 1.56907 71.3 0.5451 22.47
12 -54.087 (variable) 23.02
13 -555.436 1.60 1.67270 32.1 0.5988 24.04
14 43.700 1.43 24.78
15 119.406 3.16 1.77250 49.6 0.5520 25.03
16 -68.054 (variable) 25.53
Image plane ∞

Focal length 50.20
F number 2.90
Angle of view 23.32
Statue height 21.64
Total lens length 84.64
BF 40.01

Magnification 1 / ∞ -0.012 -0.290 -0.480 -0.950
d12 0.80 1.25 4.74 7.26 12.13
d16 0.00 0.16 10.94 18.25 37.82

Entrance pupil position 31.55
Exit pupil position -20.62
Front principal point position 40.19
Rear principal point position -10.19

Lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 51.81 37.65 37.00 -7.40
2 13 542.44 6.19 26.22 23.15

Single lens Data lens Start surface Focal length
1 1 63.62
2 3 86.31
3 5 -30.80
4 8 -23.52
5 9 26.43
6 11 53.27
7 13 -60.16
8 15 56.53

(Numerical example 2)

Unit mm

Surface data surface number rd nd νd θgF Effective diameter
1 56.164 5.39 1.69680 55.5 0.5434 41.73
2 1622.472 0.15 40.59
3 29.388 7.15 1.60 300 65.4 0.5401 33.12
4 50.623 1.46 27.57
5 122.946 2.00 1.65412 39.7 0.5737 26.97
6 21.398 14.96 23.74
7 (Aperture) ∞ 4.41 22.14
8 -22.541 2.00 1.65412 39.7 0.5737 22.48
9 -100.349 3.22 1.71999 50.2 0.5521 24.87
10 -33.277 0.15 25.74
11 -25747.812 4.43 1.56907 71.3 0.5451 27.19
12 -33.334 (variable) 27.78
13 -126.966 1.60 1.61340 44.3 0.5633 28.97
14 83.775 1.05 29.62
15 199.853 2.99 1.83481 42.7 0.5642 29.77
16 -109.271 0 30.00
Image plane ∞

Focal length 90.40
F number 2.90
Angle of View 17.90
Statue height 29.20
Total lens length 117.18
BF 65.43

Magnification 1 / ∞ -0.021 -0.290 -0.480
d12 0.80 2.57 25.28 41.33

Entrance pupil position 41.50
Exit pupil position -19.28
Front principal point position 35.43
Rear principal point position -24.97

Lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 87.36 45.31 32.91 -21.64
2 13 -15320.31 5.64 -449.64 -467.02

Single lens Data lens Start surface Focal length
1 1 83.38
2 3 103.13
3 5 -39.92
4 8 -44.90
5 9 67.79
6 11 58.65
7 13 -82.05
8 15 85.00

(Numerical Example 3)

Unit mm

Surface data surface number rd nd νd θgF Effective diameter
1 56.502 1.80 1.77250 49.6 0.5520 31.70
2 17.704 22.37 26.58
3 60.168 5.35 1.59282 68.6 0.5446 24.83
4 -31.916 0.15 24.57
5 25.115 3.03 1.85026 32.3 0.5929 20.51
6 61.775 2.41 19.48
7 -169.332 1.10 1.65412 39.7 0.5737 18.38
8 22.845 11.69 17.26
9 (Aperture) ∞ 1.43 16.41
10 474.312 1.10 1.84666 23.8 0.6205 16.50
11 28.564 3.72 1.59282 68.6 0.5446 16.66
12 -42.085 0.15 17.12
13 67.981 2.54 1.59282 68.6 0.5446 17.64
14 -111.242 (variable) 17.96
15 858.813 1.20 1.51633 64.1 0.5353 19.13
16 34.051 1.34 19.57
17 472.914 2.16 1.84666 23.8 0.6205 19.58
18 -111.924 0 20.20
Image plane ∞

Focal length 35.20
F number 2.90
Angle of view 31.58
Statue height 21.64
Total lens length 102.44
BF 40.10

Magnification 1 / ∞ -0.008 -0.290 -0.480
d14 0.80 0.99 7.54 11.95

Entrance pupil position 24.54
Exit pupil position -10.95
Front principal point position 35.47
Rear principal point position 4.90

Lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 28.60 56.85 33.81 6.93
2 15 -203.67 4.70 -3.46 -6.90

Single lens Data lens Start surface Focal length
1 1 -34.06
2 3 35.96
3 5 47.95
4 7 -30.70
5 10 -35.94
6 11 29.28
7 13 71.56
8 15 -68.70
9 17 107.08

  Next, an embodiment in which the optical system shown in Embodiments 1 to 3 is applied to an optical apparatus such as a digital single lens reflex camera will be described with reference to FIG. FIG. 7 is a schematic diagram of a main part of a single-lens reflex camera. In FIG. 7, reference numeral 10 denotes a photographic lens having the optical systems of Examples 1 to 3. The optical system 1 is held by a lens barrel 2 that is a holding member. Reference numeral 20 denotes a camera body, which includes a quick return mirror 3 that reflects the light beam from the photographing lens 10 upward and a focusing screen 4 that is disposed at an image forming position of the photographing lens 10. Further, it has a penta roof prism 5 for converting an inverted image formed on the focusing screen 4 into an erect image, an eyepiece 6 for enlarging the erect image, and the like. Reference numeral 7 denotes a photosensitive surface, on which a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor, or a silver salt film is disposed. At the time of photographing, the quick return mirror 3 is retracted from the optical path and an image is formed on the photosensitive surface 7 by the photographing lens 10.

LE: Optical system, SP: Aperture, IP: Imaging surface, LF: Front group, LR: Rear group

Claims (8)

In order from the object side to the image side, a front group having a lens unit arranged in the order of a positive lens, a negative lens, an aperture stop, a negative lens, and a positive lens, and a rear group having a lens unit arranged in the order of a negative lens and a positive lens And focusing by changing the distance between the front group and the rear group, and the refractive index, Abbe number, and portion of the material of at least one positive lens GpR among the positive lenses arranged on the image side from the aperture stop When the dispersion ratios are NdpR, νdpR, and θgFpR, respectively.
1.53 <NdpR <1.85
50 <νdpR <80
0.005 <θgFpR−0.6438 + 0.001682 × νdpR <0.080
An optical system characterized by satisfying the following conditional expression: When the refractive index, Abbe number, and partial dispersion ratio of the material of at least one positive lens GpF among the positive lenses disposed on the object side from the stop of the front group are NdpF, νdpF, and θgFpF, respectively.
1.65 <NdpF <1.90
30 <νdpF <60
−0.020 <θgFpF−0.6438 + 0.001682 × νdpF <0.005
The optical system according to claim 1, wherein the following conditional expression is satisfied. When the refractive index, Abbe number, and partial dispersion ratio of the material of at least one negative lens GnF among the negative lenses arranged in the front group are NdnF, νdnF, and θgFnF, respectively.
1.90 <NdnF + 0.0125νdnF <2.24
−0.020 <θgFnF−0.6438 + 0.001682 × νdnF <0.003
The optical system according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the rear group is fR and the focal length of the entire system is f,
| FR / f |> 40
The optical system according to claim 1, wherein the following conditional expression is satisfied.   5. The focus according to claim 1, wherein the front group moves toward the object side and the rear group moves immovably or moves toward the object side when focusing from an object at infinity to a close object. The optical system described in 1.   In order from the object side to the image side, the front group includes a positive lens having a convex surface facing the object side, a positive lens having a convex surface facing the object side, a negative lens having a concave surface facing the image side, an aperture stop, and a concave surface facing the object side. The rear lens group is composed of a negative lens having a concave surface facing the image side and a positive lens having both convex surfaces. 6. The optical system according to claim 1, wherein the optical system is configured.   In order from the object side to the image side, the front group has a negative meniscus lens with a convex object side surface, a biconvex positive lens, a positive lens with a convex surface on the object side, and a negative lens with a concave surface on the image side. The rear lens group is composed of a lens, an aperture stop, a cemented lens obtained by cementing a negative lens and a positive lens, and a positive lens, and the rear group is composed of a negative lens having a concave surface facing the image side and a positive lens having both convex surfaces. The optical system according to claim 1, wherein:   An optical apparatus comprising the optical system according to claim 1.