JP2007079361A - Imaging optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging optical system equipped with a mechanism achieving variable power, where at least chromatic aberration and distortion aberration are excellently corrected, and which has high resolving power and wide image size. <P>SOLUTION: In the imaging optical system, a front group F1 having positive or negative refractive power, an aperture stop S, and a rear group F2 having positive refractive power are arranged in order from an object side, and the imaging optical system has an aberration variation compensating function for negating the variation of the caused aberration by widening an air distance d8 on an optical axis between the front group F1 and the rear group F2 when imaging magnification is increased from a low-magnification side (1-POS) to a high-magnification side (4-POS) by moving both the front group F1 and the rear group F2 to the object side. Assuming that the focal distance of the front group F1 is fF1, the focal distance of the rear group F2 is fF2, and the focal distance of the entire system of the optical system on the lowest-magnification side is fAm, the imaging optical system satisfies following expressions, 40<¾fF1¾/fF2<60, 25<¾fF1¾/fAm<45 and 0.5<fF2/fAm<1.1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging optical system having a mechanism capable of scaling by changing the distance between an object plane and an image plane, and is particularly suitable for a line CCD camera used for a pattern inspection, an image recognition apparatus, a shape measurement apparatus, and the like. The present invention relates to an imaging optical system.

  In recent years, pattern inspection, image recognition apparatuses, shape measurement apparatuses, and the like have been required to have higher performance with respect to imaging optical systems to be used with higher definition of imaging elements (devices). Specifically, the resolution of the optical system has been increased to enable higher resolution by increasing the image size as the device becomes larger, greatly reducing distortion, correcting chromatic aberration at a high level, and improving the resolution. Securing brightness is required.

  Incidentally, zooming and focusing are known as methods for changing the imaging magnification in the photographic optical system. Zooming is a method of changing the imaging magnification by changing the focal length of the imaging optical system while fixing the distance between the object (test object) and the image (CCD surface or the like). Focusing refers to so-called zooming, and the distance between an object (test object) and an image (CCD surface, etc.) is changed while the focal length of the imaging optical system is almost fixed (changed somewhat) This is a method of changing the imaging magnification (see, for example, Patent Document 1 and Patent Document 2).

However, since the distance between the object and the image is fixed in the photographing optical system using the zooming method, in order to meet the above-mentioned high performance, the lens diameter is increased or the number of lens components is increased. It has to be dealt with by increasing the number, and there is a problem that the size of the apparatus is limited and the manufacturing cost is affected. In general, pattern inspection, image recognition devices, shape measurement devices, and the like rarely change the imaging magnification during reading. Therefore, it is not necessary to use an imaging optical system using a zooming method. It was. Thus, conventionally, it has been considered to use a photographing optical system using a focusing technique for the above-described apparatus.
JP-A-5-273465 JP 2000-275516 A

  However, when considering use in the above-described apparatus, the imaging optical system described in Patent Document 1 has a large variation in distortion due to a change in imaging magnification and a small amount of peripheral light. It was not suitable for a high-definition image pickup device. In addition, the imaging optical system disclosed in Patent Document 2 by the present inventor has a large distortion and is not suitable for achieving high resolution because of insufficient correction of chromatic aberration and coma.

  The present invention has been made in view of such problems, and an imaging optical system including a mechanism capable of zooming, having at least chromatic aberration and distortion corrected well, high resolution, and a wide image size. The purpose is to provide.

  In order to achieve such an object, the imaging optical system of the present invention includes, in order from the object side, a front group having a positive or negative refractive power, an aperture stop, and a rear group having a positive refractive power. An aberration variation compensation function that cancels out the generated aberration by widening the air space on the optical axis between the front group and the rear group when moving both the front group and the rear group to the object side to increase the imaging magnification. When the focal length of the front group is fF1, the focal length of the rear group is fF2, and the focal length of the entire optical system on the lowest magnification side is fAm, the following formula 40 <| fF1 | / fF2 <60, 25 <| fF1 | / fAm <45, and 0.5 <fF2 / fAm <1.1 are satisfied.

  As described above, according to the present invention, it is possible to provide an imaging optical system including a mechanism capable of zooming, having at least good correction of chromatic aberration and distortion, high resolution, and a wide image size.

  Hereinafter, preferred embodiments according to the present invention will be described. The imaging optical system according to the present invention includes a front group having a positive or negative refractive power, an aperture stop, and a rear group having a positive refractive power in order from the object side. When both the front group and the rear group are moved to the object side, and the imaging magnification is increased from the low magnification side to the high magnification side, the air gap on the optical axis between the front group and the rear group is widened to generate aberration ( It has an aberration fluctuation compensation function (also called floating) that cancels fluctuations in coma and curvature of field. The imaging optical system according to the present invention is not premised on use at infinity, but premised on use at a finite distance.

  In the imaging optical system according to the present invention having the above-described configuration, when the focal length of the front group is fF1, the focal length of the rear group is fF2, and the focal length of the entire optical system on the lowest magnification side is fAm, It is necessary to satisfy the expressions (1) to (3).

40 <| fF1 | / fF2 <60 (1)
25 <| fF1 | / fAm <45 (2)
0.5 <fF2 / fAm <1.1 (3)

  The conditional expression (1) defines an appropriate range for the ratio of the focal length fF1 of the front group and the focal length fF2 of the rear group. If the upper limit of conditional expression (1) is exceeded, the refractive power of the front group will be too weak, and it will be difficult to correct coma and field curvature fluctuations associated with changes in imaging magnification. On the other hand, if the lower limit of conditional expression (1) is not reached, it becomes difficult to correct various aberrations such as spherical aberration occurring in the front group in the rear group.

  Conditional expression (2) defines an appropriate range for the ratio of the focal length fF1 of the front group to the focal length fAm of the entire optical system at the minimum magnification. If the upper limit of conditional expression (2) is exceeded, the refractive power of the front group will be too weak compared to the refractive power of the entire optical system. As a result, in order to obtain a certain refractive power of the entire imaging optical system, it is necessary to increase the refractive power of the rear group, and it becomes difficult to correct various aberrations particularly at a high magnification. Furthermore, it affects the radial size of the front group, which is not preferable. Conversely, if the lower limit of conditional expression (2) is not reached, a strong refractive power is applied to the front group, and in order to satisfy the above-described conditional expression (1), it is necessary to apply a strong refractive power to the rear group. As a result, when the front group and the rear group are both moved to the object side and the imaging magnification is increased from the low magnification side to the high magnification side, the fluctuations in the various aberrations that occur will increase.

  The conditional expression (3) defines an appropriate range for the ratio between the focal length fF2 of the rear group and the focal length fAm of the entire optical system on the lowest magnification side. If the upper limit of conditional expression (3) is exceeded, the amount of movement of the rear group accompanying a change in imaging magnification increases, which is not preferable. On the other hand, if the lower limit of conditional expression (3) is not reached, fluctuations in various aberrations accompanying changes in imaging magnification, mainly negative spherical aberration, cannot be corrected, which is not preferable.

  In the imaging optical system according to the present invention, when both the front group and the rear group are moved to the object side and the imaging magnification is increased from the low magnification side to the high magnification side, the movement amount on the optical axis of the front group is set to F1d. When the movement amount on the optical axis of the rear group is F2d, it is preferable that the following expression (4) is satisfied.

            1.0 <F1d / F2d <1.1 (4)

  Conditional expression (4) indicates that, in the imaging optical system according to the present invention, the optimum amount of movement between the front group and the rear group when the imaging magnification is increased by moving both the front group and the rear group to the object side. The ratio is specified. Exceeding the upper limit of conditional expression (4) is not preferable because the amount of movement of the front group increases, resulting in an optical system that is disadvantageous to brightness (in which the effective diameter increases). On the other hand, if the lower limit of conditional expression (4) is not reached, the amount of movement of the rear group having a strong refractive power increases, and fluctuations in various aberrations further increase, which is not preferable.

  In the imaging optical system according to the present invention, the rear group includes a rear group first lens group mainly having a function of correcting spherical aberration and axial chromatic aberration, and a rear group second lens group having a positive refractive power. The rear lens group third lens unit mainly has a function of correcting astigmatism and lateral chromatic aberration. The focal length of the rear lens group first lens unit is fF2-1, and the focal length of the rear lens group second lens unit. Is set to fF2-2 and the focal length of the rear third lens group is set to fF2-3, it is preferable that the following expression (5) is satisfied.

  In this embodiment, the rear group first lens group includes at least one lens having negative refractive power and at least one lens having positive refractive power, and has negative refractive power. It is desirable to be configured. The rear group second lens group preferably includes at least one lens having a positive refractive power and has a positive refractive power. The rear group third lens group preferably includes at least one lens having a positive refractive power and at least one lens having a negative refractive power, and has a negative refractive power. .

    0.5 <| {(1 / fF2-1) + (1 / fF2-3)} / (1 / fF2-2) | <1.0 (5)

  Since the imaging optical system according to the present invention can correct aberrations in the rear group and can obtain high resolution in the entire optical system, as described above, the rear group is negative in order from the object side. It is desirable to have positive and negative refractive power arrangement. Conditional expression (5) defines an optimum balance in such a rear group refractive power arrangement. If the upper limit of conditional expression (5) is exceeded, the negative refractive power becomes too strong with respect to the positive refractive power inside the rear group, and fluctuations in various aberrations accompanying changes in the imaging magnification become large. On the other hand, if the lower limit of conditional expression (5) is not reached, it will be overcorrected for various aberrations with a strong positive refractive power, making it difficult to obtain high resolution in the entire optical system, which is not preferable.

  Here, the rear group second lens group includes a rear group second lens group first lens having a positive refractive power and a rear group second lens group second lens having a positive refractive power. The rear lens group second lens group second lens has a focal length of the rear lens group second lens group second lens of fF2-22, and the object side curvature radius of the rear lens group second lens group second lens is r1F2. It is preferable that the following expressions (6) and (7) are satisfied, where −22 and the image-side radius of curvature of the second lens in the rear group second lens group is rF2-22.

3.0 <fF2-22 / fF2 <5.0 (6)
0.2 <r1F2-22 / r2F2-22 <0.5 (7)

  Conditional expression (6) defines an appropriate refractive power of the second lens in the rear group second lens group inside the rear group. If the upper limit of conditional expression (6) is exceeded, the refractive power of the third lens in the rear group must be made relatively strong, but this is not preferable because it becomes difficult to correct distortion. On the other hand, if the lower limit of conditional expression (6) is not reached, fluctuations in coma and spherical aberration due to changes in imaging magnification become large, which is not preferable.

  The conditional expression (7) defines the optimum shape of the second lens in the rear group second lens group. Exceeding the upper limit of conditional expression (7) is not preferable because the refractive power of the second lens in the second lens group in the rear group is weak and correction of desired aberrations (particularly distortion) becomes difficult. On the other hand, if the lower limit of conditional expression (7) is not reached, distortion will be overcorrected, and the negative refractive power of the rear third lens group will increase. As a result, when the imaging magnification changes, fluctuations in coma and the like are difficult to correct, which is not preferable.

  In the imaging optical system according to the present invention, when both the front group and the rear group are moved to the object side and the imaging magnification is increased from the low magnification side to the high magnification side, the movement ratio between the front group and the rear group is constant. It is desirable that Thus, by moving each lens group at a constant ratio, the lens barrel mechanism can be simplified, which leads to cost reduction.

  In the imaging optical system according to the present invention, a lens having positive refractive power is disposed on the most object side of the front group, and the image surface side of the rear group third lens group is a concave surface on the most image side. It is desirable to place a lens. This is because it is possible to satisfactorily correct distortion aberration that occurs largely on the negative side.

  Furthermore, in the imaging optical system according to the present invention, it is desirable that at least one of the bonded lenses has a positive lens whose Abbe number is smaller than that of the negative lens. With such a configuration, in the front group and the rear group, it is possible to return the chromatic aberration that has been excessively achromatized by other cemented lenses to an appropriate correction state, and to make the entire optical system an optimal achromatic state. Is possible.

  By satisfying the above configuration, in the present invention, although the configuration is small and simple, fluctuations in various aberrations accompanying the change in imaging magnification from the low magnification side to the high magnification side in the finite distance optical system are reduced. It is possible to provide an imaging optical system that suppresses and has excellent imaging performance.

  Embodiments according to the present invention will be described below with reference to the drawings.

(First embodiment)
The imaging optical system according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a lens cross-sectional view of an imaging optical system according to the first example. In the imaging optical system according to the first example, a front group F1, an aperture stop S, and a rear group F2 having a positive refractive power are arranged in order from the object side. In FIG. 1, an object point is indicated by a symbol O, and an image plane is indicated by a symbol I (the same applies to the following examples).

  The front group F1 is composed of a biconvex lens in order from the object side, and is a cemented lens of a front group first lens group F1-1 having a positive refractive power and a biconcave lens and a positive meniscus lens having a convex surface facing the object side. A first lens unit F1-2 having a negative refractive power, and a cemented lens of a positive meniscus lens having a convex surface facing the object side and a negative meniscus lens having a convex surface facing the object side. And a front third lens group having a refractive power of 5.

  The rear group F2 includes, in order from the object side, a cemented lens of a negative meniscus lens having a convex surface facing the image side and a positive meniscus lens having a convex surface facing the image side, and has a negative refractive power. A rear lens group second lens unit F2-2 having a positive refractive power, and a cemented lens of a biconvex lens and a biconcave lens, comprising a group F2-1, a biconvex lens and a positive meniscus lens having a convex surface facing the object side And a rear-group second lens unit F2-3 having negative refractive power.

  In the imaging optical system according to the first example having the above-described configuration, both the front group F1 and the rear group F2 are moved on the optical axis to the object side, and the low magnification side (1-POS) to the high magnification side (4-POS). When the imaging magnification is increased, the apex interval (air interval on the optical axis) of the front group F1 and the rear group F2 is widened to cancel the aberration variation that occurs. The aperture stop S moves on the optical axis together with the rear group F2.

  Table 1 shows the specification values of the lenses constituting the imaging optical system according to the first example. In the specification table shown in FIG. 1, the first column m is the number of each optical surface from the object side (hereinafter referred to as surface number), the second column r is the radius of curvature of each optical surface, and the third column d is The distance on the optical axis from each optical surface to the next optical surface (or image surface) (hereinafter referred to as the surface interval), the fourth column νd is the Abbe number, and the fifth column ne is the e-line (wavelength 546.07 nm) The sixth column ng represents the refractive index for g-line (wavelength 435.83 nm).

  In the table, the surface number 9 indicates the aperture stop S. Further, the surface distance d0 between the object point and the surface number 1, the surface distance indicated by the surface number 8 (namely, the surface distance between the surface number 8 and the surface number 9) d8 and the surface distance indicated by the surface number 19 (namely, the surface number 19 and the image). Since the surface spacing (Bf with respect to the surface I) Bf changes due to movement accompanying zooming, the low magnification state (1-POS), the first intermediate magnification state (2-POS), and the second intermediate magnification state (3-POS) And these values in the high magnification state (4-POS). Further, in the table, Fno (effective) indicates an effective F number, Bf indicates a back focus, and β indicates an imaging magnification. The values corresponding to the conditional expressions (1) to (7), that is, the condition corresponding values are also shown below.

  The unit of length is “mm” unless otherwise specified. However, since the optical system can obtain the same optical performance even when proportionally enlarged or proportionally reduced, the unit is not limited to “mm”, and other appropriate units can be used. Also, the refractive index of air of 1.00000 is omitted. The description of the above table is the same in other embodiments.

  As can be seen from the table of specifications shown in Table 1, it can be seen that the imaging optical system according to the present example satisfies all the conditional expressions (1) to (7).

  2 to 5 are graphs showing various aberrations (spherical aberration, astigmatism, distortion aberration, lateral chromatic aberration, and coma aberration) of the imaging optical system according to the present example. FIG. 2 is a diagram showing various aberrations in a low magnification state (1-POS), FIG. 3 is a diagram showing various aberrations in a first intermediate magnification state (2-POS), and FIG. 4 is a second intermediate magnification state (3 FIG. 5 is a diagram illustrating various aberrations in a high magnification state (4-POS).

  In each aberration diagram, e represents an aberration curve of the e-line (wavelength 546.07 nm), and g represents an aberration curve of the g-line (wavelength 435.83 nm). In the astigmatism diagram, the solid line represents the sagittal image plane, and the dotted line represents the tangential image plane. In the spherical aberration diagram, NA indicates the numerical aperture, and in the astigmatism diagram, distortion diagram, and coma aberration, Y indicates the image height. The description of the aberration diagrams is the same in the other examples.

  As apparent from the respective aberration diagrams shown in FIGS. 2 to 5, in the imaging optical system according to the first example, each magnification state from the low magnification state (1-POS) to the high magnification state (4-POS). It can be seen that various aberrations are corrected well and excellent imaging performance is secured.

(Second embodiment)
The imaging optical system according to the second embodiment of the present invention will be described with reference to FIGS. FIG. 6 is a lens cross-sectional view of the imaging optical system according to the second example. In the imaging optical system according to the second example, a front group F1, an aperture stop S, and a rear group F2 having a positive refractive power are arranged in order from the object side.

  The front group F1 is composed of a biconvex lens in order from the object side, and is a cemented lens of a front group first lens group F1-1 having a positive refractive power and a biconcave lens and a positive meniscus lens having a convex surface facing the object side. A front lens group second lens unit F1-2 having a negative refractive power, a cemented lens of a biconvex lens and a biconcave lens, and a front lens group third lens unit having a positive refractive power. .

  The rear group F2 is composed of a cemented lens composed of a biconcave lens and a biconvex lens in order from the object side, and has a rear group first lens group F2-1 having negative refractive power and a convex surface facing the biconvex lens and the object side. Rear group second lens group F2 comprising a positive meniscus lens and having a positive refractive power, a rear group second lens group F2-2 having a positive refractive power, and a cemented lens of a biconvex lens and a biconcave lens, and having a negative refractive power -3.

  In the imaging optical system according to the second example having the above-described configuration, both the front group F1 and the rear group F2 are moved on the optical axis to the object side, and the low magnification side (1-POS) to the high magnification side (4-POS). When the imaging magnification is increased, the apex interval (air interval on the optical axis) of the front group F1 and the rear group F2 is widened to cancel the aberration variation that occurs. The aperture stop S moves on the optical axis together with the rear group F2.

  Table 2 shows the specification values of the lenses constituting the imaging optical system according to the second example. In the table, the surface number 9 indicates the aperture stop S. Further, the surface distance d0 between the object point and the surface number 1, the surface distance indicated by the surface number 8 (namely, the surface distance between the surface number 8 and the surface number 9) d8 and the surface distance indicated by the surface number 19 (namely, the surface number 19 and the image). Since the surface spacing (Bf with respect to the surface I) Bf changes due to movement accompanying zooming, the low magnification state (1-POS), the first intermediate magnification state (2-POS), and the second intermediate magnification state (3-POS) And these values in the high magnification state (4-POS).

  As can be seen from the table of specifications shown in Table 2, it can be seen that the imaging optical system according to the present example satisfies all the conditional expressions (1) to (7).

  7 to 10 are graphs showing various aberrations (spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration) of the imaging optical system according to the present example. 7 is a diagram showing various aberrations in the low magnification state (1-POS), FIG. 8 is a diagram showing various aberrations in the first intermediate magnification state (2-POS), and FIG. 9 is a diagram showing the second intermediate magnification state (3 FIG. 10 is a diagram showing various aberrations in (-POS), and FIG. 10 is a diagram showing various aberrations in a high magnification state (4-POS).

  As is apparent from the aberration diagrams shown in FIGS. 7 to 10, in the imaging optical system according to the second example, each magnification state from the low magnification state (1-POS) to the high magnification state (4-POS). It can be seen that various aberrations are corrected well and excellent imaging performance is secured.

(Third embodiment)
The imaging optical system according to the third embodiment of the present invention will be described with reference to FIGS. FIG. 11 is a lens cross-sectional view of the imaging optical system according to the third example. In the imaging optical system according to the third example, a front group F1, an aperture stop S, and a rear group F2 having a positive refractive power are arranged in order from the object side.

  The front group F1 is composed of a biconvex lens in order from the object side, and is a cemented lens of a front group first lens group F1-1 having a positive refractive power and a biconcave lens and a positive meniscus lens having a convex surface facing the object side. A front lens group second lens unit F1-2 having a negative refractive power, a cemented lens of a biconvex lens and a biconcave lens, and a front lens group third lens unit having a negative refractive power. .

  The rear group F2 is composed of a cemented lens composed of a biconcave lens and a biconvex lens in order from the object side, and has a rear group first lens group F2-1 having negative refractive power and a convex surface facing the biconvex lens and the object side. Rear group second lens group F2 comprising a positive meniscus lens and having a positive refractive power, a rear group second lens group F2-2 having a positive refractive power, and a cemented lens of a biconvex lens and a biconcave lens, and having a negative refractive power -3.

  In the imaging optical system according to the third example having the above-described configuration, both the front group F1 and the rear group F2 are moved on the optical axis to the object side, and the low magnification side (1-POS) to the high magnification side (4-POS). When the imaging magnification is increased, the apex interval (air interval on the optical axis) of the front group F1 and the rear group F2 is widened to cancel the aberration variation that occurs. The aperture stop S moves on the optical axis together with the rear group F2.

  Table 3 shows the specification values of the lenses constituting the imaging optical system according to the third example. In the table, the surface number 9 indicates the aperture stop S. Further, the surface distance d0 between the object point and the surface number 1, the surface distance indicated by the surface number 8 (namely, the surface distance between the surface number 8 and the surface number 9) d8, and the surface distance indicated by the surface number 19 (namely, the surface number 19 and the image). Since the surface spacing (Bf with respect to the surface I) Bf changes due to movement accompanying zooming, the low magnification state (1-POS), the first intermediate magnification state (2-POS), and the second intermediate magnification state (3-POS) And these values in the high magnification state (4-POS).

  As can be seen from the table of specifications shown in Table 3, it can be seen that the imaging optical system according to the present example satisfies all the conditional expressions (1) to (7).

  12 to 15 are graphs showing various aberrations (spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration) of the image pickup optical system according to the present example. 12 shows various aberrations in the low magnification state (1-POS), FIG. 13 shows various aberrations in the first intermediate magnification state (2-POS), and FIG. 14 shows the second intermediate magnification state (3). FIG. 15 is a diagram illustrating various aberrations in the high magnification state (4-POS).

  As is apparent from the aberration diagrams shown in FIGS. 12 to 15, in the imaging optical system according to the third example, each magnification state from the low magnification state (1-POS) to the high magnification state (4-POS). It can be seen that various aberrations are corrected well and excellent imaging performance is secured.

  The present invention as described above is not limited to the above-described embodiment, and can be appropriately improved as long as it does not depart from the gist of the present invention.

It is a figure which shows lens sectional drawing of the imaging optical system which concerns on 1st Example based on this invention. FIG. 6 is a diagram illustrating various aberrations (spherical aberration, astigmatism, distortion) of the imaging optical system in the low magnification state (1-POS) of the first example. FIG. 6 is a diagram illustrating various aberrations (spherical aberration, astigmatism, distortion) of the imaging optical system in the first intermediate magnification state (2-POS) of the first example. FIG. 6 is a diagram illustrating various aberrations (spherical aberration, astigmatism, distortion) of the imaging optical system in the second intermediate magnification state (3-POS) of the first example. FIG. 6 is a diagram illustrating various aberrations (spherical aberration, astigmatism, distortion) of the imaging optical system in the high magnification state (4-POS) of the first example. It is a figure which shows lens sectional drawing of the imaging optical system which concerns on 2nd Example based on this invention. FIG. 12 is a diagram illustrating various aberrations (spherical aberration, astigmatism, distortion) of the imaging optical system in the low magnification state (1-POS) of the second example. FIG. 12 is a diagram illustrating various aberrations (spherical aberration, astigmatism, distortion) of the imaging optical system in the first intermediate magnification state (2-POS) of the second example. FIG. 12 is a diagram illustrating various aberrations (spherical aberration, astigmatism, distortion) of the imaging optical system in the second intermediate magnification state (3-POS) of the second example. FIG. 12 is a diagram illustrating various aberrations (spherical aberration, astigmatism, distortion) of the imaging optical system in the high magnification state (4-POS) of the second example. It is a figure which shows lens sectional drawing of the imaging optical system which concerns on 3rd Example based on this invention. FIG. 12 is a diagram illustrating various aberrations (spherical aberration, astigmatism, distortion) of the imaging optical system in the low magnification state (1-POS) of the third example. FIG. 10 is a diagram illustrating various aberrations (spherical aberration, astigmatism, distortion) of the imaging optical system in the first intermediate magnification state (2-POS) of the third example. FIG. 12 is a diagram illustrating various aberrations (spherical aberration, astigmatism, distortion) of the imaging optical system in the second intermediate magnification state (3-POS) of the third example. FIG. 12 is a diagram illustrating various aberrations (spherical aberration, astigmatism, distortion) of the imaging optical system in the high magnification state (4-POS) of the third example.

Explanation of symbols

F1 front group S aperture stop F2 rear group
O Object point I Image plane

Claims (4)

In order from the object side, a front group having positive or negative refractive power, an aperture stop, and a rear group having positive refractive power are arranged,
When the front group and the rear group are both moved toward the object side to increase the imaging magnification, the air gap on the optical axis between the front group and the rear group is widened to cancel the aberration variation that occurs. Has function,
When the focal length of the front group is fF1, the focal length of the rear group is fF2, and the focal length of the entire optical system on the lowest magnification side is fAm,
40 <| fF1 | / fF2 <60
25 <| fF1 | / fAm <45
0.5 <fF2 / fAm <1.1
An imaging optical system characterized by satisfying When both the front group and the rear group are moved toward the object side to increase the imaging magnification, the movement amount on the optical axis of the front group is F1d, and the movement amount on the optical axis of the rear group is F2d. When
1.0 <F1d / F2d <1.1
The imaging optical system according to claim 1, wherein: The rear group mainly includes a rear group first lens group having a function of correcting spherical aberration and axial chromatic aberration, a rear group second lens group having a positive refractive power, and mainly astigmatism and lateral chromatic aberration. It is composed of a rear group third lens group having a function of correcting,
When the focal length of the rear group first lens group is fF2-1, the focal length of the rear group second lens group is fF2-2, and the focal length of the rear group third lens group is fF2-3, 0.5 <| {(1 / fF2-1) + (1 / fF2-3)} / (1 / fF2-2) | <1.0
The imaging optical system according to claim 1, wherein: The rear group second lens group includes a rear group second lens group first lens having positive refractive power, and a rear group second lens group second lens having positive refractive power,
The rear lens group second lens group second lens has a rear lens group second lens group second lens focal length of fF2-22, the rear group focal length of fF2, and the rear group second lens group second lens. When the object side radius of curvature of the lens is r1F2-22, and the image side radius of curvature of the second lens in the rear group second lens group is rF2-22,
3.0 <fF2-22 / fF2 <5.0
0.2 <r1F2-22 / r2F2-22 <0.5
The imaging optical system according to claim 3, wherein:

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