JP2021032959A - Image-capturing optical system - Google Patents

Abstract

To achieve a bright interchangeable lens that gets stabilization of the lens with a fluctuation of various kinds of aberrations reduced in an entire focusing image-capturing area, and covers a sufficient optical performance in a standard lens area from a semi-wide angle area.SOLUTION: An image-capturing optical system comprises: a front lens group 101 that has a pair of negative lenses L1 and L4 arranged on both sides of two or three positive lenses L2..., and is configured to use a meniscus lens in which both surfaces face an air space S, and a convex surface is on an object OBJ side for the negative lens L4 on an aperture stop STO side; and a rear lens group 102 that has a pair of negative lenses L5 and L8 arranged on both sides of positive lenses L6 and L7 using two double-sided convex lenses, uses a double-sided concave lens for the negative lens L8 on an image IMG side, and is configured to arrange a final lens L9 arranged at the back of the negative lens L8 on the image IMG side, and by an aspherical lens in which both surfaces face the air space S and both curve surfaces are curved in the same direction of an optical axis Dc.SELECTED DRAWING: Figure 1

Description

The present invention relates to an imaging optical system suitable for use in an optical system of an interchangeable lens used in a digital camera or the like.

In general, interchangeable lenses used in digital cameras, etc. have less restrictions on back focus and rear lens diameter due to mirrorlessness and larger mount diameters, and the variety of lens types is expanding. Due to the increase in size and performance (high definition), bright interchangeable lenses in the wide to medium telescope range (shooting diagonal angle of view 70-40 °) have a F number of 2.2 or less, and brighter lenses have become more common. It has been demanded. Further, by downsizing the digital camera body, it is required to make the interchangeable lens compact, and further to stabilize the aberration in the entire focusing shooting region according to consumer needs.

In response to such a request, the front group (lens group) is arranged on the object side in the optical axis direction with respect to the aperture aperture, and the rear group (lens group) is arranged on the image side. An optical system having a symmetrical arrangement type lens configuration is also known in which the angle of incidence on the lens surface is reduced so that the occurrence of astigmatism and coma on each lens surface can be suppressed. In particular, in this type of symmetric arrangement type optical system, the closer the lens refractive power arrangement is to symmetry with respect to the aperture diaphragm, the more coma, distortion, chromatic aberration of magnification, etc. cancel each other out between the front group and the rear group. Therefore, good aberration correction can be realized for the entire optical system. However, this type of symmetrical arrangement type generally has a high imaging magnification, does not support infinity objects, and has significantly different specifications such as imaging size. Therefore, it is mainly used as a copying lens. It is limited to specific fields such as lenses for plate-making cameras. On the other hand, an imaging optical system has also been proposed that can be used as a lens for a camera such as a digital camera by modifying the lens configuration of this kind of general symmetrical arrangement type.

Conventionally, such an imaging optical system, particularly a symmetrical arrangement type photographing optical system in which an F number is 2.2 or less and 3 to 5 lenses are arranged before and after the aperture diaphragm, is known from Patent Document 1-5. Has been done. Patent Document 1 is applied to a lens for a lens shutter type camera, which is a quasi-wide-angle lens having an F number of 1.9 by being composed of five lenses, and Patent Document 2 has a quasi-angle of view of 32 °. This is applied to a camera objective lens that is a quasi-wide-angle lens with an F number of 1.4. Further, Patent Document 3-5 is applied to an imaging lens which is a camera lens having an F number of 2.8 in consideration of long-distance photography.

Japanese Unexamined Patent Publication No. 62-183419 Japanese Unexamined Patent Publication No. 5-80252 Japanese Unexamined Patent Publication No. 2013-250534 Japanese Unexamined Patent Publication No. 2014-594666 Japanese Unexamined Patent Publication No. 2016-218486

However, the conventional lens (imaging optical system) disclosed in Patent Document 1-5 described above has the following problems.

First, in the case of a symmetrically arranged type imaging optical system in which the F number is 2.2 or less and 3 to 5 lenses are arranged before and after the aperture diaphragm, the optical performance on the long distance side can be basically ensured. Even so, it tends to be difficult to secure sufficient optical performance on the short-distance side. In this way, it is not easy to realize a bright interchangeable lens that covers the short-range side, specifically, the wide-angle to medium-telephoto range (shooting diagonal angle of view 70-40 °) with sufficient optical performance. However, the reality is that it does not fully meet the needs of consumers who desire such interchangeable lenses.

Secondly, in the case of the symmetrical arrangement type imaging optical system, when the F number is made smaller or the shooting angle of view is changed, there is a problem that astigmatism and chromatic aberration increase as a basic tendency. Therefore, from the viewpoint of obtaining an interchangeable lens used for a digital camera or the like that is compatible with a large high-definition image sensor and is compact and compact, while reducing fluctuations in various aberrations in the entire focusing imaging region and stabilizing the aberration. However, it cannot be said that the problem has been sufficiently solved, and there is room for further improvement.
An object of the present invention is to provide an imaging optical system that solves the problems existing in such a background technique.

In order to solve the above-mentioned problems, the present invention is a symmetrical arrangement type in which the front lens group 101 is arranged on the object OBJ side in the optical axis Dc direction and the rear lens group 102 is arranged on the image IMG side with respect to the aperture aperture STO. In the imaging optical system C having the lens configuration of the above, the positive lens group Lf including two or three continuous positive lenses L2 ... And a pair of negative lenses L1 and L4 arranged on both sides of the positive lens group Lf are provided. A front lens group 101 composed of a negative lens L4 on the aperture aperture STO side, a meniscus lens having both sides facing the air space S and a convex surface on the object OBJ side, and a positive lens using two biconvex lenses. It has a positive lens group Lr in which L6 and L7 are continuous, and a pair of negative lenses L5 and L8 arranged on both sides of the positive lens group Lr. A rear lens group configured by arranging the final lens L9, which is an aspherical lens whose curved surfaces are curved in the same direction of the optical axis Dc, while being arranged behind the negative lens L8 on the side and both sides facing the air space S. It is characterized by having 102.

In this case, according to a preferred embodiment of the present invention, the front lens group 101 is configured by providing a negative lens L1 having a concave surface on the object OBJ side on the object OBJ side, and both curved surfaces are curved toward the object OBJ side on the optical axis Dc. It can be configured by including at least one aspherical lens. Further, the rear lens group 102 is provided with a negative lens L5 arranged on the aperture diaphragm STO side and having a concave surface on the aperture diaphragm STO side, and is arranged on the image IMG side and the image IMG side faces the air space S. A negative lens L8 can be provided. Further, when constructing the front lens group 101, a negative lens L1 which is arranged on the object OBJ side and uses a biconcave lens, both curved surfaces are curved toward the object OBJ side of the optical axis Dc, and an aspherical lens is used. A positive lens L2 located on the object OBJ side and a negative lens L4 having an aperture aperture STO side arranged on the object OBJ side and a negative lens L4 having a convex surface on the object OBJ side can be provided. It is composed of two bonded lenses J56 and J78, which are a combination of negative lenses L5 and L8 using a concave lens and positive lenses L6 and L7 using a biconvex lens, and the positive lenses L6 and L7 of the two bonded lenses J56 and J78 face each other. It is also possible to configure both concave lenses of one of the bonded lenses J56 as a negative lens L5 on the aperture aperture STO side.

In addition, according to a preferred embodiment of the present invention, the focal length of the negative lens L5 on the aperture aperture STO side of the rear lens group 102 to the negative lens L8 on the image IMG side is set to BFL, and the focal length of the entire lens system is set to EFL. Then, it is desirable to configure the lens so as to satisfy the condition of "0.7 <BFL / EFL <1.6", and the absolute value of the abnormal partial dispersibility ΔθgF in the glass material of the positive lens L2 ... In the front lens group 101. When the focal lengths of all the positive lenses having a value of 0.015 or more are EGFL and the maximum value of the focal lengths of all the positive lenses L2 ... In the front lens group 101 is AGMX, "0.6 <EGFL / AGMX". It is desirable to configure it so as to satisfy <1.2 ". On the other hand, one aspherical lens can be included in each of the front lens group 101 and the rear lens group 102, and each aspherical lens can be formed into the same shape and arranged symmetrically in the optical axis Dc direction. On the other hand, the partial lens group (designated lens group) Lp ... Before and after the air spacing that changes during focus adjustment in the front lens group 101 and the rear lens group 102 may be configured to be movable up to three designated lens groups Lp ... At this time, the air spacing that changes during focus adjustment is the air spacing including the aperture aperture STO, and the two positive lenses L2 of the front lens group 101. At least one of the air spacing between L3 and the air spacing between the two positive lenses L6 and L7 of the rear lens group 102 can be included. Further, when the focal length FFL of the front lens group 101 and the focal length RFL of the rear lens group 102 are both positive powers, the entire lens system is moved to the object OBJ side to change the air spacing on the image IMG side at the time of focus adjustment. A configuration can be provided.

According to the imaging optical system C according to the present invention having such a configuration, the following remarkable effects are obtained.

(1) The lens configuration is configured by a symmetrical arrangement type having symmetry with respect to the aperture aperture STO, which is advantageous for a small optical system, and the internal lens group (partially symmetric lens) in the front lens group 101 and the rear lens group 102. Since the power distribution of the group) also has symmetry, it is possible to balance the occurrence of aberration and the correction of the aberration in the lens groups 101 and 102 in an appropriate state. In particular, since both sides face the air space S and both curved surfaces include the final lens L9 made of an aspherical lens curved in the same direction of the optical axis Dc, the degree of separation between the on-axis ray and the off-axis ray increases. The correction effect on the residual aberration can be enhanced, and the effect of the symmetrical arrangement type can be enhanced. As a result, it is possible to reduce fluctuations in various aberrations in the entire focusing shooting region and improve its stability, and set the F number to 2.2 or less to cover sufficient optical performance in the quasi-wide-angle range to the standard lens range. It is possible to obtain a bright interchangeable lens, and thus it is possible to provide an optimal interchangeable lens used for a digital camera or the like that is compatible with a large high-definition image sensor and is compact and compact.

(2) According to a preferred embodiment, when the front lens group 101 is configured, a negative lens L1 having a concave surface on the object OBJ side is provided on the object OBJ side, and both curved surfaces are on the object OBJ side of the optical axis Dc. If at least one curved aspherical lens is included, a convex surface is often used on the lens surface, and the incident angle and the refraction angle can be made gentle. Therefore, in the case where the converging action of the incident light is enhanced in the front lens group 101. Even if there is, it is possible to suppress the occurrence of aberration and contribute to the overall compactness. Moreover, since the angle difference between the passing points of the light rays of each angle of view on each lens surface can be reduced, it is possible to advantageously correct the aberration of a large luminous flux.

(3) According to a preferred embodiment, the rear lens group 102 is provided with a negative lens L5 that is arranged on the aperture diaphragm STO side and has a concave surface on the aperture diaphragm STO side, and is arranged on the image IMG side and the image IMG side is air. If the negative lens L8 facing the space S is provided, the diameter of the lens to be used can be reduced (reduced in diameter), so that lens processing can be advantageously performed and a lens configuration having a symmetrical arrangement type can be constructed. Can be easily performed.

(4) According to a preferred embodiment, when the front lens group 101 is formed, the negative lens L1 arranged on the object OBJ side and using the biconcave lens, both curved surfaces are curved toward the object OBJ side of the optical axis Dc, and are not. If a positive lens L2 located on the object OBJ side using a spherical lens and a negative lens L4 having an aperture aperture STO side arranged on the object OBJ side and a negative lens L4 having a convex surface on the object OBJ side are provided, the front lens group 101 is on the object OBJ side. Since it is possible to include a negative biconcave lens and an aspherical lens that are strong against the sun, it is possible to enhance the effect of correcting the aberration of a wide incident angle in the field angle from the quasi-wide angle region to the standard region.

(5) According to a preferred embodiment, when the rear lens group 102 is configured, it is composed of two bonded lenses J56 and J78 in which negative lenses L5 and L8 using a biconcave lens and positive lenses L6 and L7 using a biconvex lens are joined. However, if the positive lenses L6 and L7 of the two bonded lenses J56 and J78 are arranged so as to face each other and the concave lenses of one of the bonded lenses J56 are configured as the negative lens L5 on the aperture aperture STO side, there is a difference in the number of abbreviations. It is possible to easily and effectively correct the off-axis chromatic aberration by providing the lens, and it is possible to further strengthen the correction of the spherical lens by providing a difference in the refractive index. As a result, the residual aberration of the front lens group 101 can be corrected in a well-balanced manner, and the aberration fluctuation can be reduced by setting the space between the junction lenses J56 and J78 as an adjustment space. Moreover, since the lens surface of the rear lens group 102 close to the aperture diaphragm STO can be made to face the aperture diaphragm STO, the effectiveness of the lens configuration using the symmetrical arrangement type can be further enhanced.

(6) According to a preferred embodiment, when the focal length of the negative lens L5 on the aperture aperture STO side of the rear lens group 102 to the negative lens L8 on the image IMG side is BFL and the focal length of the entire lens system is EFL, "0". If the condition of .7 <BFL / EFL <1.6 "is satisfied, an appropriate balance of refractive force in the rear lens group 102 can be ensured, so that an appropriate back focus, total length, and brightness can be obtained. At the same time, good image performance can be obtained without overloading the aberration correction of the front lens group 101 and the final lens L9.

(7) According to a preferred embodiment, the focal lengths of all the positive lenses in which the absolute value of the abnormal partial dispersibility ΔθgF in the glass material of the positive lens L2 ... In the front lens group 101 is 0.015 or more are set to EGFL, and the front lens group. When the maximum value of the focal lengths of all the positive lenses L2 ... In 101 is set to AGMX, if it is configured to satisfy "0.6 <EGFL / AGMX <1.2", the front lens group 101 has a wavelength dispersion. Since a glass material having a small amount of abnormal partial dispersibility is used and two or more low-dispersion lenses are continuously used, various aberrations such as spherical aberration, coma aberration, and non-point aberration can be satisfactorily corrected.

(8) According to a preferred embodiment, one aspherical lens is included in each of the front lens group 101 and the rear lens group 102, each aspherical lens is formed into the same shape, and the aspherical lenses are arranged symmetrically in the optical axis Dc direction. By doing so, it is sufficient to prepare the same lens, so that the types of lenses that require processing can be reduced, and in particular, it is possible to contribute to the cost reduction of the aspherical lens to be molded and manufactured. Moreover, if the lenses are arranged symmetrically, the aberration can be suppressed, and the aberration fluctuation can be reduced by changing the air spacing according to the object distance within the symmetrical lens arrangement.

(9) According to a preferred embodiment, a maximum of three designated lens groups Lp ... For a partial lens group (designated lens group) Lp ... Before and after the air spacing that changes during focus adjustment in the front lens group 101 and the rear lens group 102. If the lens is configured to be movable, the merit of canceling the aberration by the front lens group 101 and the rear lens group 102 in the symmetrical arrangement type lens configuration can be utilized. Therefore, it is possible to construct a flexible focus adjustment mechanism utilizing this merit. it can.

(10) According to a preferred embodiment, the air spacing that changes during focus adjustment includes the air spacing including the aperture stop STO, and the two positive lenses L2 of the front lens group 101. If at least one of the air spacing between L3 and the air spacing between the two positive lenses L6 and L7 of the rear lens group 102 is included, the optimum focus adjustment for the symmetrical arrangement type imaging optical system C according to the present embodiment is included. A mechanism can be constructed.

(11) According to a preferred embodiment, when the focal length FFL of the front lens group 101 and the focal length RFL of the rear lens group 102 are both positive powers, the entire lens system is moved to the object OBJ side at the time of focus adjustment to the image IMG side. By providing a configuration that changes the air spacing of the lens, it is possible to reduce the aberration fluctuation due to the change in the distance from the object OBJ while simplifying the overall structure of the focus adjustment mechanism.

Configuration diagram of the imaging optical system according to the first embodiment of the preferred embodiment of the present invention, The longitudinal aberration diagram of the imaging optical system according to the first embodiment at infinity and the focus method F11-F12 shown in FIG. The longitudinal aberration diagram of the focus methods F13 and F14 shown in FIG. 1 of the imaging optical system according to the first embodiment. List of optical conditions in each example according to the preferred embodiment of the present invention, Configuration diagram of the imaging optical system according to the second embodiment of the preferred embodiment, Configuration diagram of the imaging optical system according to the third embodiment, Configuration diagram of the imaging optical system according to the fourth embodiment, Configuration diagram of the imaging optical system according to the fifth embodiment, Configuration diagram of the imaging optical system according to the sixth embodiment, FIG. 6 is a longitudinal aberration diagram of the imaging optical system according to the sixth embodiment at infinity. Focus method F21-F2 shown in FIG. 9 of the imaging optical system according to the sixth embodiment. FIG. 9 is a longitudinal aberration diagram of the focus method F24-F26 shown in FIG. 9 of the imaging optical system according to the sixth embodiment. FIG. 9 is a longitudinal aberration diagram of the focus method F27 shown in FIG. 9 of the imaging optical system according to the sixth embodiment. Configuration diagram of the imaging optical system according to the seventh embodiment of the preferred embodiment, The longitudinal aberration diagram of the imaging optical system according to the seventh embodiment at infinity and the focus methods F31 and F32 shown in FIG. Configuration diagram of the imaging optical system according to the eighth embodiment of the preferred embodiment, The longitudinal aberration diagram of the image pickup optical system according to the eighth embodiment at infinity and the focus method F41 shown in FIG. Configuration diagram of the imaging optical system according to the ninth embodiment of the preferred embodiment, A longitudinal aberration diagram of the imaging optical system according to the ninth embodiment at infinity, FIG. 18 is a longitudinal aberration diagram of the focus method F51-F53 shown in FIG. 18 of the imaging optical system according to the ninth embodiment. FIG. 18 is a longitudinal aberration diagram of the focus method F54 shown in FIG. 18 of the imaging optical system according to the ninth embodiment. Configuration diagram of the imaging optical system according to the tenth embodiment of the preferred embodiment,

Next, Examples 1 to 10 which are preferable embodiments according to the present invention will be given and will be described in detail with reference to the drawings.

First, the imaging optical system C of the first embodiment according to the present embodiment will be specifically described with reference to FIGS. 1 to 4.

First, the configuration of the imaging optical system C according to the present embodiment (Example 1) will be described with reference to FIG. It can be assumed that this imaging optical system C is applied to an interchangeable lens for a digital camera. In FIG. 1, OBJ indicates an object (subject), and IMG indicates an image (image sensor). Therefore, the object OBJ side is in front of the optical axis Dc direction, and the image IMG side is in the rear of the optical axis Dc direction.

As a basic configuration, the imaging optical system C according to the present embodiment has a front lens group 101 arranged on the object OBJ side in the optical axis Dc direction and a rear lens group 102 arranged on the image IMG side with respect to the aperture diaphragm STO. It has a symmetrical arrangement type lens configuration.

The front lens group 101 includes a positive lens group Lf including two or three consecutive positive lenses L2 ..., A negative lens L1 arranged on the front side of the positive lens group Lf, and a negative lens L4 arranged on the rear side, for a total of four. It is composed of a single lens L1-L4. More specifically, a negative lens L using a biconcave lens, a positive lens L2 using a biconvex lens, and a positive lens L3 using a positive meniscus lens, both sides (plane numbers i = 7, 8) face the air space S. However, it is configured as a partially symmetric lens group including a negative lens L4 on the aperture aperture STO side using an aspherical lens of negative meniscus with a convex surface on the object OBJ side, and the power of each lens is sequentially (-) (+) ( +) (-).

In this way, when the front lens group 101 is configured, the negative lens L1 having a concave surface on the object OBJ side and the object OBJ side is arranged, and at least both curved surfaces are curved toward the object OBJ side of the optical axis Dc. If one aspherical lens is included, a convex surface is often used on the lens surface, and the incident angle and the refraction angle can be made gentle. Therefore, even when the converging action of the incident light is enhanced in the front lens group 101. In addition to being able to suppress the occurrence of aberrations, it can also contribute to overall compactness. Moreover, since the angle difference between the passing points of the light rays of each angle of view on each lens surface can be reduced, it is possible to advantageously correct the aberration of a large luminous flux.

Further, the rear lens group 102 includes a positive lens group Lr in which positive lenses L6 and L7 using two biconvex lenses are continuous, a negative lens L5 arranged on the front side of the positive lens group Lr, and a negative lens L5 arranged on the rear side. It is equipped with a total of four lenses L5-L8, which are lenses L8, and is arranged behind the negative lens L8, both sides (i = 18,19) face the air space S, and both curved surfaces (i = 18,19). ) Is curved in the same direction of the optical axis Dc (in the example, the image IMG side direction), and the final lens L9 is provided by an aspherical lens. In this case, the negative lens L8 on the image IMG side uses a biconcave lens whose image IMG side faces the air space S, and the negative lens L5 on the aperture diaphragm STO side uses a biconcave lens. The rear lens group 102 is composed of a total of five lenses L5-L9, and in particular, the four lenses L5-L8 form a partially symmetrical lens group, so that the power of each lens is sequentially (-) (+). ) (+) (-).

In this way, when the rear lens group 102 is configured, the negative lens L5 is provided on the aperture diaphragm STO side and the aperture diaphragm STO side is concave, and is arranged on the image IMG side and the image IMG side is the air space. If the negative lens L8 facing S is provided, the diameter of the lens to be used can be reduced (reduced in diameter), so that lens processing can be advantageously performed and a lens configuration having a symmetrical arrangement type can be constructed. It can be done easily.

Therefore, the imaging optical system C according to the present embodiment includes a basic embodiment in which an aperture diaphragm STO is sandwiched and partially symmetrical lens groups are arranged before and after the aperture diaphragm STO. Further, each of the nine lenses L1-L9 in the entire lens system is separated by an air gap S.

The final lens L9 has the same shape as the negative lens L4, and is an aspherical lens of a negative meniscus in which the object OBJ side inverted in the optical axis Dc direction is concave, and is arranged symmetrically in the optical axis Dc direction. In this way, one aspherical lens is included in each of the front lens group 101 and the rear lens group 102, and each aspherical lens is formed into the same shape and arranged symmetrically in the optical axis Dc direction. For example, since it is sufficient to prepare the same lens, it is possible to reduce the types of lenses that require processing, and in particular, it can contribute to cost reduction of aspherical lenses to be molded and manufactured. Moreover, if the lenses are arranged symmetrically, the aberration can be suppressed, and the aberration fluctuation can be reduced by changing the air spacing according to the object distance within the symmetrical lens arrangement.

Table 1 shows the lens data of the entire lens system in the imaging optical system C of Example 1. The imaging optical system C at an infinite object point has a focal length of 50.00 mm, an F number of 1.95, and a half angle of view of 23.4 °.

The “plane data” in Table 1 indicates the surface number of the lens surface counted from the object OBJ side by i, and this surface number i corresponds to the reference numeral (number) shown in FIG. Correspondingly, the radius of curvature R (i) of the lens surface, the axial top surface distance D (i), the refractive index nd (i) of the lens, the Abbe number νd (i) of the lens, and the abnormal partial dispersion value ΔPgF (i) The absolute values of are shown respectively. nd (i) and νd (i) are numerical values for the d line (586.56 [nm]). The shaft upper surface distance D (i) indicates the lens thickness or the air space between the facing surfaces. The unit of the radius of curvature R (i) and the surface spacing D (i) is [mm]. The surface number OBJ indicates an object, STO indicates an aperture stop, and IMG indicates the position of an image. The Infinity of the radius of curvature R (i) is a plane, and the surface with A after the surface number i indicates that the surface shape is aspherical. The blanks of the refractive index nd (i) and the Abbe number νd (i) indicate that it is air.

Further, the "aspherical coefficient" in Table 1 is obtained when ASP is an aspherical surface number in a Cartesian coordinate system (X, Y, Z) in which the center of the surface is the origin and the optical axis Dc direction is Z. Z is represented by the equation 1. In Equation 1, R is the radius of curvature of the center, K is the conical constant, A4, A6, A8, and A10 are the aspherical coefficients of the 4th, 6th, 8th, and 10th orders, respectively, and H is the aspherical coefficient from the origin on the optical axis. The distance. In Table 2, "E" means "x10".

Further, the “variable focus interval” in Table 1 corresponds to the focus method [F11]-[F14] shown in FIG. That is, in the case of the first embodiment, the focus adjustment when the distance of the object OBJ changes from infinity to a short distance can be performed by any of the four types of focus methods [F11]-[F14]. In [F11], each of the three designated lens groups Lp ... In which "L1-L4", "L5-L6", and "L7-L9" are integrated is moved to the object OBJ side by different amounts, and the aperture aperture STO A method of changing the including air spacing, the air spacing between the positive lenses L6 and L7 of the rear lens group 102, and the air spacing on the image IMG side, respectively, [F12] is "L1-L4" and "L5-L9", respectively. The method of moving the two integrated designated lens groups Lp ... To the object OBJ side by different amounts and changing the air spacing including the aperture aperture STO and the air spacing on the image IMG side, [F13] is ". The two designated lens groups Lp ... In which "L1-L6" and "L7-L9" are integrated are moved to the object OBJ side by different amounts, and the air spacing between the positive lenses L6 and L7 of the rear lens group 102 is determined. The method of changing the air spacing on the image IMG side, [F14], is a method of moving the entire lens group "L1-L9" to the object OBJ side as a unit to change the air spacing on the image IMG side.

2 to 3 show a longitudinal aberration diagram corresponding to the focus method [F11]-[F14] in the imaging optical system C of the first embodiment. [F1s] in FIG. 2 shows a longitudinal aberration diagram at infinity. From the left side, each longitudinal aberration diagram shows spherical aberration (656.27 nm, 586.56 nm, 435.83 nm), astigmatism (586.56 nm), and distortion (586.56 nm). Each scale is ± 0.50 mm, ± 0.50 mm, ± 3.0%.

In the case of the focus methods [F1s] and [F11]-[F13], it is possible to take a picture in which a plane subject perpendicular to the plane optical axis is not blurred. In particular, when changing either the air spacing of the aperture diaphragm STO, which is the position of the symmetric point of the lens configuration, or the air spacing between the two positive lenses L6 and L7 in the rear lens group 102, whichever focus method is used. It can be confirmed that good and equivalent imaging performance can be obtained. Further, since the adjustment interval at which the imaging performance is good for a short-distance subject is known, it can also be used when controlling the degree of curvature of field. On the other hand, in the case of the focus method [F14], since the focused surface of curvature of field (astigmatism) is curved negatively, the subject focused in the center of both sides becomes closer toward the periphery of both sides. It can be seen that the curve is focused on, and the image or video that is farther from the subject becomes more blurred.

In this way, if a maximum of three designated lens groups Lp ... Are configured to be movable with respect to the designated lens groups Lp ... Before and after the air spacing that changes during focus adjustment in the front lens group 101 and the rear lens group 102, they are symmetrical. Since the merit of canceling the aberration by the front lens group 101 and the rear lens group 102 in the arrangement type lens configuration can be utilized, a flexible focus adjustment mechanism can be constructed by utilizing this merit.

In particular, as the air spacing that changes during focus adjustment, the air spacing including the aperture stop STO and the two positive lenses L2 of the front lens group 101. At least one of the air spacing between L3 and the air spacing between the two positive lenses L6 and L7 of the rear lens group 102 can be included, which is optimal for the symmetrical arrangement type imaging optical system C according to the present embodiment. A focus adjustment mechanism can be constructed.

That is, in the case of the imaging optical system, since the shooting is performed by changing the distance to the object OBJ (subject), the imaging performance is ensured while slightly deforming the symmetry of the optical system (changing the air spacing). Therefore, the imaging optical system C in the present embodiment having symmetry utilizes the fact that the action of canceling the aberration occurs before and after the position of the symmetry point, so that the air spacing (air space S) including the aperture stop STO or the front lens The designated lens group Lp ... On both sides of the air spacing (air space S) between the two biconvex lenses (positive lenses L2, L3 / L6, L7) in the group 101 and the rear lens group 102 was moved.

For example, when the entire optical system is moved with respect to a short distance and the curvature of field changes negatively on the image IMG plane, the focal plane curves toward the lens from the center of the screen to the periphery on the image IMG plane. Therefore, when focusing on the center of the screen, it tends to be blurred toward the periphery. When this phenomenon is replaced with the object OBJ side, by focusing on the subject in the center of the screen, a curve that focuses closer toward the periphery becomes a curve, and a curve farther than this becomes a more blurred image or video. Therefore, it is common to reduce the aberration by narrowing down the aperture pattern STO and widen the subject depth to make a flat subject a plane image plane. That is, the focus adjustment method for moving the lens group so as to reduce aberrations is a shooting method in which a subject on a short-range plane (a plane perpendicular to the optical axis) is set to a plane image plane so as not to be blurred.

On the other hand, as a shooting technique, by focusing on a part of the subject on the screen, the entire optical system is moved at a short distance in order to "create an image" that blurs the space before and after it to obtain a shooting effect. There is also a method or a method of moving a lens group to generate aberration. When the adjustment interval that can obtain good imaging performance for a short-distance subject is known as in the present embodiment, it can also be used to control the degree of curvature of field.

In a wide-angle lens in which aberration fluctuation is small even if the distance to the object OBJ is changed and the amount of movement of the lens group is small, only the air spacing on the image IMG side is changed by moving the entire imaging optical system. In some cases, as in the inner focus method and the front focus method, the focus may be adjusted by moving a single lens group without changing the air spacing on the image IMG side.

When the focal length FFL of the front lens group 101 and the focal length RFL of the rear lens group 102 are both positive powers, the entire lens system is moved to the object OBJ side to change the air spacing on the image IMG side during focus adjustment. Can be adopted. In this case, it is possible to reduce the aberration fluctuation due to the change in the distance from the object OBJ while simplifying the overall structure of the focus adjustment mechanism. FIG. 4C shows the values of the focal lengths FFL and RFL in the present embodiment (Example 1-10).

Since such a total feeding method can be configured by a compact and simple mechanism, it is adopted in many other imaging optical systems. In the various focus methods described above, when the movement distance of all the lens groups is small, the focus method [F14] that moves the entire lens system to the object OBJ side can be adopted. Performance can be ensured. That is, in the overall feeding method, when the distance to the object OBJ changes from infinity to a short distance, the image IMG position changes, so the entire lens is moved to the object OBJ side for focusing. In the imaging optical system C according to the present embodiment, a symmetrical arrangement type lens configuration having a symmetric lens group or a partially symmetric lens group with respect to the aperture diaphragm STO is used to reduce aberration fluctuation due to a change in distance from the object OBJ. In the case of a lens configuration from a wide angle where the amount of lens movement is small, the entire extension method can be used.

In addition, the imaging optical system C according to the present embodiment is set so as to satisfy a predetermined optical condition. The first optical condition (applicable to Examples 1-4, 6-7) is that the focal length of the negative lens L5 on the aperture diaphragm STO side of the rear lens group 102 to the negative lens L8 on the image IMG side is BFL, and the entire lens is set. When the focal length of the system is EFL,
0.7 <BFL / EFL <1.6 ... (Optical condition 1)
Set on the condition that the condition is satisfied.

In the case of an imaging optical system (imaging lens), the refractive power of the front lens group 101 can tolerate a wide value from "positive" to "negative", but the refractive power of the rear lens group 102 focuses the entire lens system at a predetermined focal length. It is necessary to set it to "positive" in order to form an image at the image IMG position at a distance. In the case of the front lens group 101 in which the number of lenses is 5 or less, the entire lens group can be configured as a partially symmetric lens group, but in the case of the rear lens group 102, both curved surfaces of the final lens L9 are curved in the same direction of the optical axis Dc. , The refractive power cannot be increased, and almost all the refractive power is borne by the front lens group 101.

Therefore, by setting so as to satisfy the optical condition 1, an appropriate refractive power balance in the rear lens group 102 can be ensured. As a result, an appropriate back focus, overall length, and brightness can be obtained, and good image performance can be obtained without overloading the aberration correction of the front lens group 101 and the final lens L9. Therefore, if the optical condition 1 is not satisfied, proper back focus, overall length, and brightness cannot be obtained, and the aberration correction of the front lens group 101 and the final lens L9 is overloaded, resulting in a good image. Performance cannot be obtained. In the case of Example 1, as shown in FIG. 4A, the EFL is 50.00 and the BFL is 40.40. Therefore, BFL / AFL is 0.81, which satisfies the optical condition 1.

The second optical condition (applicable to Examples 1-5 and 9-10) is that the absolute value of the abnormal partial dispersibility ΔθgF in the glass material of the positive lens L2 ... In the front lens group 101 is 0.015 or more. When the focal length of the positive lens is EGFL and the maximum value of the focal lengths of all the positive lenses L2 ... In the front lens group 101 is AGMX.
0.6 <EGFL / AGMX <1.2 ... (Optical condition 2)
Set on the condition that the condition is satisfied.

By setting in this way, a glass material having anomalous partial dispersibility with little wavelength dispersion is used for the front lens group 101, and two or more low-dispersion lenses are continuously used. Therefore, spherical aberration, coma aberration, and astigmatism are used. Various aberrations such as these can be satisfactorily corrected.

Generally, as the angle of view becomes narrower, more chromatic aberrations such as axial chromatic aberration and magnifying chromatic aberration tend to occur, which tends to deteriorate the optical performance. Therefore, the front lens group 101 has anomalous partial dispersibility with less wavelength dispersion. It is known that chromatic aberration can be corrected by using a glass material. If the setting is made so as to satisfy the above-mentioned optical condition 2 and the correction for reducing the chromatic aberration is performed on the object OBJ side of the front lens group 101, the aberration burden on the subsequent lens group, that is, the rear lens group 102 can be reduced. In addition, the power per lens can be weakened by using two or more low-dispersion lenses in succession. As a result, the number of refracting surfaces increases, and various aberrations such as spherical aberration, coma aberration, and astigmatism can be reduced by the correction effect.

Moreover, when the front lens group 101 is configured as a partially symmetric lens group, the individual refractive powers can be weakened, so that the incoming light angle with respect to the lens surface through which the incident light is transmitted can be suppressed to a low level, resulting in aberration generation and errors. Sensitivity can be suppressed. In a low refractive index lens having anomalous dispersibility, when the curvature is weakened, a desired refractive power cannot be obtained, so that the incident light angle on the lens surface tends to be large. Therefore, continuous use of low-dispersion lenses is effective, and if a high-refractive index lens is added to the front lens group 101 to bear the refractive power, chromatic aberration can be corrected as an abnormally dispersive low-refractive index lens. It can be used effectively.

In the case of Example 1, as shown in FIG. 4 (b), EGFL is 57.05 and AGMX is 58.54. Therefore, EGFL / AGMX is 0.97, which satisfies the optical condition 2.

In the first embodiment, the power distribution of each lens of the partially symmetric lens group of the front lens group 101 is (negative)-(positive)-(positive)-(negative), and the positive lenses L2 and L3 are formed by the negative lenses L1 and L4. The power distribution of each lens in the partially symmetric lens group of the rear lens group 102 is set to (negative)-(positive)-(positive)-(negative), as in the case of the front lens group 101. The negative lenses L5 and L8 have symmetry so as to sandwich the positive lenses L6 and L8, and the negative lenses L5 and L8 use biconcave lenses and the positive lenses L6 and L7 use biconvex lenses. Since the two positive lenses L6 and L7 are opposed to each other via an air gap, the occurrence and correction of aberration in each group are balanced. As a result, a good mutual aberration balance can be ensured as a whole.

Further, the final lens L9 corrects the residual aberration by making an aspherical surface capable of partially changing the surface shape by utilizing the fact that the on-axis ray and the off-axis ray pass separately. Further, by setting the air spacing between the partially symmetric lens group of the rear lens group 102 and the final lens L9, the degree of separation between the on-axis ray and the off-axis ray is increased, the effect of the aspherical lens is enhanced, and the symmetrical arrangement is performed. In order to maintain the effect of the type, an aspherical lens with both sides facing in the same direction was used. In the imaging optical system C, since the distance between the space on the object OBJ side and the space on the image IMG side is not symmetrical, good aberration correction cannot be performed with a completely symmetrical lens configuration. Therefore, the front lens group 101 has a strong astringent action so as to converge the light rays from a large object.

Next, the imaging optical system C of the second embodiment according to the present embodiment will be described with reference to FIGS. 4 and 5.

In the imaging optical system C of the second embodiment, the negative lens L5 using the biconcave lens and the positive lens L6 using the biconvex lens in the rear lens group 102 of the first embodiment described above are configured as the junction lens J56, and the biconvex lens is formed. The positive lens L7 used and the negative lens L8 using the biconcave lens are configured by the junction lens J78, and the positive lenses L6 and L7 of the two junction lenses J56 and J78 are arranged so as to face each other, and one of them is joined. The biconcave lens of the lens J56 was configured as a negative lens L5 on the aperture aperture STO side. The configuration of the front lens group 101, that is, the lenses L1, L2, L3, L4 and the final lens L9 is the same as in the first embodiment.

Table 2 shows the lens data of the entire lens system of Example 2. The imaging optical system C at an infinite object point has a focal length of 49.80 mm, an F number of 1.95, and a half angle of view: 23.5 °.

As described above, when the rear lens group 102 is configured, it is composed of two bonded lenses J56 and J78 in which the negative lenses L5 and L8 using the biconcave lens and the positive lenses L6 and L7 using the biconvex lens are joined. If the positive lenses L6 and L7 of the bonded lenses J56 and J78 are arranged so as to face each other and the concave lenses of one of the bonded lenses J56 are configured as the negative lens L5 on the aperture aperture STO side, the number of abbets can be different. The correction of off-axis chromatic aberration can be easily and effectively performed, and the correction of spherical aberration can be further strengthened by providing a difference in refractive index. As a result, the residual aberration of the front lens group 101 can be corrected in a well-balanced manner, and the aberration fluctuation can be reduced by setting the space between the junction lenses J56 and J78 as an adjustment space. Moreover, since the lens surface of the rear lens group 102 close to the aperture diaphragm STO can be made to face the aperture diaphragm STO, the effectiveness of the lens configuration using the symmetrical arrangement type can be further enhanced.

Further, there are four types of focus adjustment for a short-distance object, which are the same as those in the first embodiment. In the case of the second embodiment, as shown in FIG. 4A, the EFL is 49.80 and the BFL is 39.40. Therefore, BFL / AFL is 0.79, which satisfies the above-mentioned optical condition 1. Further, as shown in FIG. 4 (b), the EGFL is 57.05 and the AGMX is 58.54. Therefore, EGFL / AGMX is 0.97, which satisfies the above-mentioned optical condition 2. In addition, as shown in FIG. 4C, FFL has a positive power of 108.49 and RFL has a positive power of 75.31.

As described above, with respect to the basic embodiment of the first embodiment, even when the lens configuration in the partially symmetrical lens group in the rear lens group 102 is configured as the bonded lenses J56 and J78, the configuration is made by combining single lenses. It is possible to secure the same imaging performance as the basic embodiment of the first embodiment.

Next, the imaging optical system C of the third embodiment according to the present embodiment will be described with reference to FIGS. 4 and 6.

In Example 3, as shown in FIG. 6, five lenses L1, LS, L2, L3, L4 are used in the front lens group 101, and five lenses L5, L6, L7, L8 are used in the rear lens group 102. , L9 is used. In this case, a biconcave lens is used for the negative lens L1 of the front lens group 101, a meniscus lens having a convex surface on the object OBJ side is used for the positive lens LS, and the negative lens L1 and the positive lens LS are configured as a junction lens. Further, the positive lenses L3 and L4 have the same type of shape, and are composed of positive meniscus lenses whose both sides are convex toward the object OBJ side. In this way, if a meniscus lens whose both sides are convex toward the object OBJ side is used as the positive lens of the front lens group 101, the entire length can be compressed, so that the refractive power can be made evenly close, and the front lens group 101 can be made more uniform. Since it can be made compact and the incident light angle of the light beam can be reduced, it is possible to suppress the occurrence of aberration and the error sensitivity.

Further, the glass materials of the positive lenses L3 and L4 have an abnormal partial dispersion value of 0.0375. Further, the negative lens L5 is a negative meniscus lens having both sides convex on the object OBJ side, and is composed of an aspherical lens. The front lens group 101 is configured as a partially symmetrical lens group, and the powers of the lenses L1-L4 are (−) (+) (+) (+) (−).

The rear lens group 102 includes a negative lens L5 using a biconcave lens and a positive lens L6 using a biconvex lens as a junction lens J56, and a positive lens L7 using a biconvex lens and a negative lens L8 using a biconcave lens. It is composed of a bonded lens J78, and the positive lenses L6 and L7 of the two bonded lenses J56 and J78 are arranged so as to face each other, and both concave lenses of one bonded lens J56 are used as a negative lens L5 on the aperture aperture STO side. Configured. As a result, the four lenses L5-L8 are configured as a partially symmetrical lens group having powers (-) (+) (+) (-). In the third embodiment as well, a partial lens group having symmetry is arranged before and after the aperture diaphragm STO. Further, the final lens L9 is an aspherical lens of a negative meniscus having the same shape as the lens L4 and having a concave surface on the object OBJ side inverted on the optical axis Dc.

Table 3 shows the lens data of the entire lens system of Example 3. The imaging optical system C at an infinite object point has a focal length of 48.25 mm, an F number of 1.74, and a half angle of view of 24.2 °.

There are four types of focus adjustment for short-distance objects, which are the same as those in the first embodiment. In the case of Example 3, as shown in FIG. 4A, the EFL is 48.25 and the BFL is 40.77. Therefore, BFL / AFL is 0.85, which satisfies the above-mentioned optical condition 1. Further, as shown in FIG. 4B, the lenses L2 and L3 both have an EGFL of 94.26 and an AGMX of 94.26. Therefore, EGFL / AGMX is 1.00, which satisfies the above-mentioned optical condition 2. In addition, as shown in FIG. 4C, FFL has a positive power of 131.90 and RFL has a positive power of 60.82.

As described above, even when the number of lens groups and the lens form are changed with respect to the basic form of the first embodiment, the same imaging performance as the basic form of the first embodiment can be ensured.

Next, the imaging optical system C of the fourth embodiment according to the present embodiment will be described with reference to FIGS. 4 and 7.

Example 4 is a type in which the angle of Example 2 is further widened, and as shown in FIG. 7, the lenses L1-L4 of the front lens group 101 and the lenses L5-L8 (junction lenses J56, J78) of the rear lens group 102 are used. Configured. In this case, it is configured as a partially symmetrical lens group in which the powers of the lens groups 101 and 102 are (−) (+) (+) (−), respectively. For the final lens L9, an aspherical lens having the same shape as the lens (negative lens) L4 of the front lens group 101 and having a concave surface on the OBJ side of the object inverted on the optical axis Dc is used.

Table 4 shows the lens data of the entire lens system of Example 4. The imaging optical system C at an infinite object point has a focal length of 37.00 mm and an F number of 1.95.

There are four types of focus adjustment for short-distance objects, which are the same as those in the first embodiment. In the case of Example 4, as shown in FIG. 4A, the EFL is 37.00 and the BFL is 31.85. Therefore, BFL / AFL is 0.86, which satisfies the above-mentioned optical condition 1. Further, as shown in FIG. 4B, the lens L3 has an EGFL of 41.12 and an AGMX of 45.23. Therefore, EGFL / AGMX is 0.91, which satisfies the above-mentioned optical condition 2. In addition, as shown in FIG. 4C, FFL has a positive power of 97.17 and RFL has a positive power of 51.20.

In this way, when four types of focus adjustments that are the same as those of the first embodiment (second embodiment) are adopted, the specific configurations of the details are different as long as the configuration maintains the basic form of the first embodiment. Even in this case, it is possible to secure the same imaging performance as the basic embodiment of the first embodiment.

Next, the imaging optical system C of the fifth embodiment according to the present embodiment will be described with reference to FIGS. 4 and 8.

In the fifth embodiment, the angle is widened as in the fourth embodiment, and the F number is increased to 1.26 in particular. As shown in FIG. 8, the number of lenses in the front lens group 101 is four. The number of lenses in the rear lens group 102 was set to 5. That is, the front lens group 101 is a negative lens L1 of a biconcave lens, a positive lens L2 of a biconvex lens, a positive meniscus lens (positive lens) L3 having a convex surface on the object OBJ side, and a negative meniscus lens (negative) having a convex surface on the object OBJ side. Lens) It is composed of L4, and is configured as a partially symmetric lens group in which the power of each lens is (-) (+) (+) (-).

The rear lens group 102 includes a negative lens L5 using a biconcave lens and a positive lens L6 using a biconvex lens as a junction lens J56, and a positive lens L7 using a biconvex lens and a negative lens L8 using a biconcave lens. It is composed of a bonded lens J78, and the positive lenses L6 and L7 of the two bonded lenses J56 and J78 are arranged so as to face each other, and both concave lenses of one bonded lens J56 are used as a negative lens L5 on the aperture aperture STO side. Configured. As a result, the four lenses L5-L8 are configured as a partially symmetrical lens group having powers (-) (+) (+) (-). Also in the fifth embodiment, the aperture diaphragm STO is sandwiched, and the partially symmetrical lenses are arranged before and after the aperture diaphragm STO. The final lens L9 is a negative meniscus aspherical lens having a concave surface on the OBJ side of the object.

Table 5 shows the lens data of the entire lens system of Example 5. The imaging optical system C at an infinite object point has a focal length of 51.14 mm, an F number of 1.26, and a half angle of view of 22.9 °.

There are four types of focus adjustment for short-distance objects, which are the same as those in the first embodiment. In the case of Example 5, as shown in FIG. 4A, the EFL is 51.14 and the BFL is 51.43. Therefore, BFL / AFL is 1.01, which satisfies the above-mentioned optical condition 1. Further, as shown in FIG. 4C, FFL has a positive power of 128.46 and RFL has a positive power of 65.65.

Therefore, even when the imaging optical system C has a wide angle and the F number has a large aperture of 1.26 as in the fifth embodiment, the basic embodiment of the first embodiment is the same as in the second to fourth embodiments. It is possible to secure the same imaging performance as.

Next, the imaging optical system C of the sixth embodiment according to the present embodiment will be described with reference to FIGS. 4 and 9-13.

In the sixth embodiment, the front lens group 101 is composed of five lenses and the rear lens group 102 is composed of five lenses as the number of lenses. That is, the front lens group 101 includes a negative lens L1 using a biconcave lens, a positive lens LS using an aspherical lens having a positive meniscus with both sides convex toward the object OBJ side, and a positive lens L2 using a biconvex lens. It is composed of L3 and a negative meniscus lens (negative lens) L4 whose convex surface is on the object OBJ side, and is configured as a partially symmetric lens group in which the power of each lens is (-) (+) (+) (+) (-). .. The lenses L2 and L3 have substantially the same refractive power, and the abnormal partial dispersion value of the glass material in the lens L2 is 0.037, and the abnormal partial dispersion value of the glass material in the lens L3 is 0.0194. When constructing the front lens group 101, the negative lens L1 which is arranged on the object OBJ side and uses a biconcave lens, both curved surfaces are curved toward the object OBJ side of the optical axis Dc, and the object OBJ side using an aspherical lens. If the front lens group 101 is provided with a positive lens L2 located in the front lens group 101 and a negative lens L4 having a convex surface on the object OBJ side in addition to being arranged on the aperture aperture STO side, a strong negative biconcave lens or aspherical lens on the object OBJ side is provided. Since the configuration can include a spherical lens, it is possible to enhance the effect of correcting the aberration of a wide incident angle in the angle of view from the quasi-wide angle region to the standard region.

The rear lens group 102 includes a negative lens L5 using a biconcave lens and a positive lens L6 using a biconvex lens as a junction lens J56, and a positive lens L7 using a biconvex lens and a negative lens L8 using a biconcave lens. It is composed of a bonded lens J78, and the positive lenses L6 and L7 of the two bonded lenses J56 and J78 are arranged so as to face each other, and both concave lenses of one bonded lens J56 are used as a negative lens L5 on the aperture aperture STO side. Configured. As a result, the four lenses L5-L8 are configured as a partially symmetrical lens group having powers (-) (+) (+) (-). The final lens L9 uses an aspherical lens with a negative meniscus whose concave surface is on the OBJ side of the object.

Further, as a focus method, that is, a focus adjustment method when the distance of the object OBJ changes from infinity to a short distance, seven types of focus methods [F21]-[F27] are applied as shown in FIG. That is, in [F21], the two designated lens groups Lp ... In which "L1-L2" and "L3-L9" are integrated are moved to the object OBJ side by different amounts, and the positive lens L2 of the front lens group 101 is moved. The method of changing the air spacing between the lens and L3 and the air spacing on the image IMG side, [F22] is an object OBJ with two designated lens groups Lp ... In which "L1-L5" and "L6-L9" are integrated. A method of changing the air spacing between the positive lenses L6 and L7 of the rear lens group 102 and the air spacing on the image IMG side by moving them to the side by different amounts, [F23] is "L1, LS", "L2-L4". , Each of the three designated lens groups Lp ... In which "L5-L9" is integrated is moved to the object OBJ side by a different amount, and the air spacing between the positive lens LS and L2 of the front lens group 101 and the air including the aperture aperture STO. The method of changing the distance and the air distance on the image IMG side, [F24] is that the object OBJ side has three designated lens groups Lp ... In which "L1-L2", "L3", and "L4-L9" are integrated. The method of changing the air spacing between the positive lens L2 and L3 of the front lens group 101, the air spacing between the positive lens L3 and the negative lens L4 of the front lens group 101, and the air spacing on the image IMG side. In [F25], each of the three designated lens groups Lp ... In which "L1-L3", "L4-L6", and "L7-L9" are integrated is moved to the object OBJ side by different amounts, and the front lens group 101 The air spacing between the positive lens L3 and the negative lens L4, the air spacing between the positive lenses L5 and L6 of the rear lens group 102, and the air spacing on the image IMG side are changed. The three designated lens groups Lp ... In which "L3-L4" and "L5-L9" are integrated are moved to the object OBJ side by different amounts, and the air between the positive lens L3 and the negative lens L4 of the front lens group 101 is moved. The method of changing the interval, the air interval including the aperture throttle STO, and the air interval on the image IMG side, [F27] is each of the three integrated "L1-L4", "L5-L6", and "L7-L9". This is a method in which the designated lens group Lp ... Is moved to the object OBJ side by different amounts to change the air spacing including the aperture aperture STO, the air spacing between the positive lenses L6 and L7 of the rear lens group 102, and the air spacing on the image IMG side. ..

Table 6 shows the lens data of the entire lens system of Example 6. The imaging optical system C at an infinite object point has a focal length of 49.17 mm, an F number of 1.94, and a half angle of view of 23.7 °.

10-13 show a longitudinal aberration diagram corresponding to the focus method [F21]-[F27] in the imaging optical system C of the sixth embodiment. [F2s] in FIG. 10 shows a longitudinal aberration diagram at infinity. From the left side, each longitudinal aberration diagram shows spherical aberration (656.27 nm, 586.56 nm, 435.83 nm), astigmatism (586.56 nm), and distortion (586.56 nm). Each scale is ± 0.50 mm, ± 0.50 mm, ± 3.0%.

In the case of Example 6, as shown in FIG. 4A, the EFL is 49.28 and the BFL is 75.15. Therefore, BFL / AFL is 1.52, which satisfies the above-mentioned optical condition 1. Further, as shown in FIG. 4B, the EGFL of the lens L2 is 60.00, the AGMX is 74.53, and the EGFL / AGMX is 0.81, which satisfy the above-mentioned optical condition 2 and the lens. The EGFL of L3 is 55.00, the AGMX is 74.53, and the EGFL / AGMX is 0.74, which satisfy the above-mentioned optical condition 2.

In this way, the designated lens group Lp ... Before and after the air spacing that changes during focus adjustment in the front lens group 101 and the rear lens group 102 is configured to be movable up to three designated lens groups Lp ..., and the designated lens group is movable. By changing the position of Lp ..., good imaging performance can be ensured even when seven types of focus methods [F21]-[F27] are selected, and the merit of the symmetrical arrangement type lens configuration is utilized. Various focus adjustment mechanisms can be constructed.

Next, the imaging optical system C of the seventh embodiment according to the present embodiment will be described with reference to FIGS. 4, 14 and 15.

The basic lens configuration in Example 7 is the same as in Example 6. That is, as the number of lenses, the front lens group 101 is composed of five lenses, and the rear lens group 102 is composed of five lenses. That is, the front lens group 101 includes a negative lens L1 using a biconcave lens, a positive lens LS using an aspherical lens having a positive meniscus with both sides convex toward the object OBJ side, and a positive lens L2 using a biconvex lens. It is composed of L3 and a negative meniscus lens (negative lens) L4 whose convex surface is on the object OBJ side, and is configured as a partially symmetric lens group in which the power of each lens is (-) (+) (+) (+) (-). .. The lenses L2 and L3 have substantially the same refractive power, and the abnormal partial dispersion value of the glass material in the lens L2 is 0.037, and the abnormal partial dispersion value of the glass material in the lens L3 is 0.0194.

The rear lens group 102 includes a negative lens L5 using a biconcave lens and a positive lens L6 using a biconvex lens as a junction lens J56, and a positive lens L7 using a biconvex lens and a negative lens L8 using a biconcave lens. It is composed of a bonded lens J78, and the positive lenses L6 and L7 of the two bonded lenses J56 and J78 are arranged so as to face each other, and both concave lenses of one bonded lens J56 are used as a negative lens L5 on the aperture aperture STO side. Configured. As a result, the four lenses L5-L8 are configured as a partially symmetrical lens group having powers (-) (+) (+) (-). The final lens L9 uses an aspherical lens with a negative meniscus whose concave surface is on the OBJ side of the object.

Further, in the seventh embodiment, the focus method when the distance to the object OBJ changes from infinity to a short distance is changed. That is, while changing one air spacing between the two positive lenses (biconvex lenses) L2 and L3 and between L6 and L7 that make up the partially symmetrical lens group, the amount of movement of the air spacing on the image IMG side is minimized. This is a so-called front focus method for keeping the lenses L7-L9 at a constant distance from the image IMG surface, and as shown in FIG. 14, two types of focus methods [F31] and [F32] are applied. In [F31], "L7-L9" is fixed, and two designated lens groups Lp ... In which "L1-L2" and "L3-L6" are integrated are moved to the object OBJ side by different amounts, and the front is moved. In the method of changing the air spacing between the positive lenses L2 and L3 of the lens group 101 and the air spacing between the positive lenses L6 and L7 of the rear lens group 102, [F32] fixes "L7-L9" and "L1-L1-". This is a method in which one designated lens group Lp in which "L6" is integrated is moved to the object OBJ side by a different amount, and the air spacing between the positive lenses L6 and L7 of the rear lens group 102 is changed.

Table 7 shows the lens data of the entire lens system of Example 7. The imaging optical system C at an infinite object point has a focal length of 48.73 mm, an F number of 1.94, and a half angle of view of 23.9 °.

FIG. 15 shows a longitudinal aberration diagram corresponding to the focus method [F31]-[F32] in the imaging optical system C of the seventh embodiment. [F3s] in FIG. 15 shows a longitudinal aberration diagram at infinity. From the left side, each longitudinal aberration diagram shows spherical aberration (656.27 nm, 586.56 nm, 435.83 nm), astigmatism (586.56 nm), and distortion (586.56 nm). Each scale is ± 0.50 mm, ± 0.50 mm, ± 3.0%.

In the case of Example 7, as shown in FIG. 4A, the EFL is 48.73 and the BFL is 71.22. Therefore, BFL / AFL is 1.46, which satisfies the above-mentioned optical condition 1. Further, as shown in FIG. 4B, the EGFL of the lens L3 is 60.03, the AGMX is 62.49, and the EGFL / AGMX is 0.96, which satisfy the above-mentioned optical condition 2.

In this way, the focus method [F31] in which the two lens groups of "L1-L2" and "L3-L6" are used as the moving group, and the focus in which one lens group of "L1-L6" is used as the moving group are integrated. Regardless of the focus method of the method, as in the case of the second to sixth embodiments, it is possible to secure the same imaging performance as the basic form of the first embodiment, and various focus adjustment mechanisms utilizing the merits of the symmetrical arrangement type lens configuration. Can be built.

Next, the imaging optical system C of the eighth embodiment according to the present embodiment will be described with reference to FIGS. 4 and 16-17.

In Example 8, as the number of lenses, the front lens group 101 is composed of four lenses, and the rear lens group 102 is composed of five lenses. That is, the front lens group 101 is composed of a negative lens L1 using both concave lenses, a positive meniscus lens (positive lens) L2 and L3 having a convex surface on the object OBJ side, and a negative meniscus lens (negative lens) L4 having a convex surface on the object OBJ side. However, it is configured as a partially symmetric lens group in which the power of each lens is (-) (+) (+) (-).

The rear lens group 102 includes a negative lens L5 using a biconcave lens and a positive lens L6 using a biconvex lens as a junction lens J56, and a positive lens L7 using a biconvex lens and a negative lens L8 using a biconcave lens. It is composed of a bonded lens J78, and the positive lenses L6 and L7 of the two bonded lenses J56 and J78 are arranged so as to face each other, and both concave lenses of one bonded lens J56 are used as a negative lens L5 on the aperture aperture STO side. Configured. As a result, the four lenses L5-L8 are configured as a partially symmetrical lens group having powers (-) (+) (+) (-). The final lens L9 uses an aspherical lens with a negative meniscus whose convex surface is on the OBJ side of the object.

Further, in the eighth embodiment, the focus method when the distance to the object OBJ changes from infinity to a short distance is changed. That is, as shown in FIG. 16, the focus adjustment method differs on the object OBJ side from each of the two designated lens groups Lp ... In which the lenses L4-L6 and L7-L9 constituting the designated lens group Lp ... Are integrated. A focus method [F41] is adopted in which the air spacing between the lenses L3 and L4 and the air spacing between the lenses L6 and L7 are changed by moving the lenses by an amount, and the lenses L1-L3 are kept at a constant distance from the image IMG surface. The rear focus method was used.

Table 8 shows the lens data of the entire lens system of Example 8. The imaging optical system C at an infinite object point has a focal length of 49.80 mm, an F number of 1.94, and a half angle of view: 23.5 °.

FIG. 17 shows a longitudinal aberration diagram corresponding to the focus method [F41] in the imaging optical system C of the eighth embodiment. [F4s] in FIG. 17 shows a longitudinal aberration diagram at infinity. From the left side, each longitudinal aberration diagram shows spherical aberration (656.27 nm, 586.56 nm, 435.83 nm), astigmatism (586.56 nm), and distortion (586.56 nm). Each scale is ± 0.50 mm, ± 0.50 mm, ± 3.0%.

In the case of Example 8, as shown in FIG. 4A, the EFL is 49.80 and the BFL is 47.73. Therefore, BFL / AFL is 0.96, which satisfies the above-mentioned optical condition 1.

In this way, the two designated lens groups Lp ... In which the lenses L4-L6 and L7-L9 constituting the designated lens group Lp ... Are integrated are moved to the object OBJ side by different amounts, and between the lenses L3 and L4. Even when the air spacing and the air spacing between the lenses L6 and L7 are changed and the lenses L1-L3 are kept at a constant distance from the image IMG surface, the same as in Example 2-7. It is possible to secure the same imaging performance as the basic embodiment of the first embodiment, and to construct various focus adjustment mechanisms utilizing the merits of the symmetrical arrangement type lens configuration.

Next, the imaging optical system C of the ninth embodiment according to the present embodiment will be described with reference to FIGS. 4 and 18-21.

The configuration of the imaging optical system C of the ninth embodiment is the same as that of the basic embodiment of the first embodiment described above. That is, in the front lens group 101, the negative lens L1 using the biconcave lens 1, the aspherical lens (positive lens) L2 of the positive meniscus whose both sides are convex toward the object OBJ side, the positive lens L3 using the biconvex lens, and the object OBJ side are It is composed of a negative meniscus lens (negative lens) L4 having a convex surface, and the power of each lens is configured as a partially symmetric lens group having (-) (+) (+) (-).

The rear lens group 102 includes a negative lens L5 using a biconcave lens and a positive lens L6 using a biconvex lens as a junction lens J56, and a positive lens L7 using a biconvex lens and a negative lens L8 using a biconcave lens. It is composed of a junction lens J78. Then, the positive lenses L6 and L7 of the two junction lenses J56 and J78 are arranged so as to face each other, and the concave lenses of one of the junction lenses J56 are configured as the negative lens L5 on the aperture diaphragm STO side. As a result, the power of each lens is configured as a partially symmetrical lens group of (-) (+) (+) (-). The final lens L9 is configured as an aspherical lens with a negative meniscus whose convex surface is on the OBJ side of the object.

Table 9 shows the lens data of the entire lens system of Example 9. The imaging optical system C at an infinite object point has a focal length of 36.01 mm, an F number of 1.27, and a half angle of view of 31.4 °.

There are four types of focus methods, which are the same as those in the first embodiment. [F51]-[F54] shown in FIG. 18 correspond to [F11]-[F14] shown in FIG. 1, respectively. In the case of Example 9, as shown in FIG. 4A, the EFL is 36.01 and the BFL is 38.40. Therefore, BFL / AFL is 1.07, which satisfies the above-mentioned optical condition 1. Further, as shown in FIG. 4C, FFL has a positive power of 111.36 and RFL has a positive power of 40.58.

20-21 show a longitudinal aberration diagram corresponding to the focus method [F51]-[F54] in the imaging optical system C of the ninth embodiment. [F5s] in FIG. 19 shows a longitudinal aberration diagram at infinity. From the left side, each longitudinal aberration diagram shows spherical aberration (656.27 nm, 586.56 nm, 435.83 nm), astigmatism (586.56 nm), and distortion (586.56 nm). Each scale is ± 0.50 mm, ± 0.50 mm, ± 3.0%.

Example 9 is an example in which the angle is widened and the F number is increased to 1.265, but good imaging performance is ensured for each aberration as in the other examples. In the focusing method that moves the entire lens, the focal plane of curvature of field (astigmatism) curves to the plus side, so if the focus is in the center of the subject, the focus will be farther toward the periphery of the subject. There is a matching curve, and images and videos that are closer to the subject can be obtained. Further, since the adjustment interval for ensuring good imaging performance can be known for a short-distance subject, it can also be used to control the degree of curvature of field.

Next, the imaging optical system C of the tenth embodiment according to the present embodiment will be described with reference to FIGS. 4 and 22.

In Example 10, as shown in FIG. 22, the front lens group 101 includes a negative lens L1 using a biconcave lens, a positive lens L2 using a positive meniscus aspherical lens having both sides convex toward the object OBJ side, and an object. It is composed of a positive meniscus lens (positive lens) L3 with a convex surface on the OBJ side and a negative meniscus lens (negative lens) L4 with a convex surface on the object OBJ side, and the power of the lenses L1-L4 is (-) (+) (+) (-). ) Is configured as a partially symmetric lens group.

The rear lens group 102 includes a negative lens L5 using a biconcave lens and a positive lens L6 using a biconvex lens as a junction lens J56, and a positive lens L7 using a biconvex lens and a negative lens L8 using a biconcave lens. It is composed of a bonded lens J78, and the positive lenses L6 and L7 of the two bonded lenses J56 and J78 are arranged so as to face each other, and both concave lenses of one bonded lens J56 are used as a negative lens L5 on the aperture aperture STO side. Configured. As a result, the four lenses L5-L8 are configured as a partially symmetrical lens group having powers (-) (+) (+) (-). The final lens L9 is an aspherical lens with a negative meniscus whose convex surface is on the OBJ side of the object.

Table 10 shows the lens data of the entire lens system of Example 10. The imaging optical system C at an infinite object point has a focal length of 48.00 mm, an F number of 1.26, and a half angle of view: 24.4 °.

There are four types of focus methods that are the same as those of the first and ninth embodiments. In the case of Example 10, as shown in FIG. 4A, the EFL is 48.00 and the BFL is 45.40. Therefore, BFL / AFL is 0.95, which satisfies the above-mentioned optical condition 1. Further, as shown in FIG. 4C, FFL has a positive power of 126.00 and RFL has a positive power of 53.15.

The tenth embodiment is, in particular, a large-diameter imaging optical system C having an F number of 1.261, but good imaging performance is ensured as in the other examples.

Although preferred embodiments including Examples 1-10 have been described in detail above, the present invention is not limited to such embodiments, and the present invention is not limited to such embodiments, and the detailed configuration, shape, material, quantity, numerical value, etc. It may be arbitrarily changed, added or deleted without departing from the gist of the present invention.

For example, when the front lens group 101 is configured, it is arranged on the object OBJ side and is arranged on the negative lens L1 and the aperture diaphragm STO side in which the object OBJ side is concave, and both curved surfaces are curved toward the object OBJ side of the optical axis Dc. Although the case where the negative lens L4 made of the aspherical lens is provided is illustrated, the form of each lens used does not exclude other forms. Further, the rear lens group 102 is arranged on the aperture aperture STO side, and the positive lens group Lr using the negative lens L5 and two biconvex lenses whose aperture aperture STO side is concave, and the image IMG side are in the air space S. It is desirable to provide a negative lens L8 with both concave lenses facing each other, but the form of each lens used does not exclude other forms. Similarly, when constructing the front lens group 101, a negative lens L1 arranged on the object OBJ side and using a biconcave lens, both curved surfaces curved toward the object OBJ side of the optical axis Dc, and an aspherical lens was used. , The positive lens L2 located second from the object OBJ side and the aperture aperture STO side are arranged, and the object OBJ side is a convex surface and the curved surface on the image IMG side is set to a curvature of a predetermined size or less. An example is illustrated in which a negative lens L4 is provided and the surface shape in contact with the air space S from the aperture aperture STO to the third is opposed to the aperture aperture STO, but the form of each lens used is other. It does not exclude the form. At this time, the rear lens group 102 faces the positive lenses L6 and L7 of the two bonded lenses J56 and J78, which are obtained by bonding the negative lenses L5 and L8 using the biconcave lens and the positive lenses L6 and L7 using the biconvex lens. The two concave lenses of one of the bonded lenses J56 are configured as the negative lens L5 on the aperture aperture STO side, and the surface shape in contact with the air space S from the aperture aperture STO to the third is opposed to the aperture aperture STO. However, the morphology of the individual lenses used does not preclude other morphologies. On the other hand, when the focal distance from the negative lens L5 on the aperture aperture STO side of the rear lens group 102 to the negative lens L8 on the image side is BFL and the focal distance of the entire lens system is EFL, "0.7 <BFL / EFL < The front lens group 101 is configured to satisfy the condition of "1.6", and the front lens group 101 sets the focal distances of all lenses in which the absolute value of the abnormal partial dispersibility ΔθgF in the glass material of the positive lenses L2 and L3 is 0.015 or more. When EGFL is used and the maximum values of all the positive lenses in the front lens group 101 and the rear lens group 102 are AGMX, it is desirable to configure the lens so as to satisfy the condition of "0.6 <EGFL / AGMX <1.2". However, it does not exclude the case where only one of these conditions is satisfied or the case where both are not satisfied.

The imaging optical system according to the present invention can be used as a dedicated lens or an interchangeable lens in various optical devices such as digital cameras and video cameras.

C: Imaging optical system, 101: Front lens group, 102: Rear lens group, STO: Aperture aperture, OBJ: Object, IMG: Image, Dc: Optical axis, L1: Negative lens, L2 ...: Positive lens, L4: Negative Lens, L5: Negative lens, L6 ...: Positive lens, L7: Positive lens, L8: Negative lens, L9: Final lens, Lf: Positive lens group, Lr: Positive lens group, Lp ...: Designated lens group, J56: Junction Lens, J78: Junction lens, S: Air space

Claims (11)

In an imaging optical system having a symmetrical arrangement type lens configuration in which a front lens group is arranged on the object side in the optical axis direction and a rear lens group is arranged on the image side with respect to the aperture aperture, two or three consecutive positive lenses are used. A meniscus lens that has a positive lens group including a lens and a pair of negative lenses arranged on both sides of this positive lens group, and has a negative lens on the aperture aperture side, both sides facing the air space and an object side having a convex surface. It has a front lens group constructed by using the lens group, a positive lens group in which positive lenses using two biconvex lenses are continuous, and a pair of negative lenses arranged on both sides of the positive lens group, and is negative on the image side. A biconcave lens is used as the lens, and a final lens made of an aspherical lens whose curved surfaces are curved in the same direction of the optical axis is arranged while being arranged behind the negative lens on the image side and both sides facing the air space. An image-manipulating optical system characterized in that it includes a rear lens group. The front lens group includes the negative lens which is arranged on the object side and whose object side is concave, and includes at least one aspherical lens whose curved surfaces are curved toward the object side of the optical axis. The imaging optical system according to claim 1. The rear lens group includes the negative lens arranged on the aperture diaphragm side and having a concave surface on the aperture diaphragm side, and also includes the negative lens arranged on the image side and facing the air space on the image side. The imaging optical system according to claim 1 or 2, wherein the imaging optical system is characterized. The front lens group is the negative lens which is arranged on the object side and uses a biconcave lens, and the positive lens which has both curved surfaces curved toward the object side of the optical axis and is located on the object side using an aspherical lens. The imaging optical system according to claim 1, further comprising the negative lens arranged on the aperture aperture side and having a convex surface on the object side. The rear lens group is composed of two bonded lenses in which the negative lens using a biconcave lens and the positive lens using a biconvex lens are joined, and the positive lenses of the two bonded lenses are arranged so as to face each other. The image control optical system according to claim 1, wherein the biconcave lens of one of the junction lenses is configured as a negative lens on the aperture aperture side. When the focal length of the negative lens on the image side from the negative lens on the aperture diaphragm side of the rear lens group is BFL and the focal length of the entire lens system is EFL.
0.7 <BFL / EFL <1.6
The imaging optical system according to claim 1, wherein the image pickup optical system according to claim 1 is satisfied. The focal lengths of all the positive lenses in which the absolute value of the abnormal partial dispersibility ΔθgF in the glass material of the positive lens in the front lens group is 0.015 or more are defined as EGFL, and the focal lengths of all the positive lenses in the front lens group. When the maximum value of the distance is AGMX,
0.6 <EGFL / AGMX <1.2
The imaging optical system according to claim 1, wherein the image pickup optical system according to claim 1 is satisfied. Claim 1 is characterized in that one aspherical lens is included in each of the front lens group and the rear lens group, each aspherical lens is formed into the same shape, and the aspherical lenses are arranged symmetrically in the optical axis direction. The imaging optical system described. Claim 1 is characterized in that the front and rear partial lens groups (designated lens groups) before and after the air spacing that changes during focus adjustment in the front lens group and the rear lens group are configured to be movable up to three designated lens groups. The imaging optical system described. The air spacing that changes during the focus adjustment is at least one of the air spacing including the aperture diaphragm, the air spacing between the two positive lenses in the front lens group, and the air spacing between the two positive lenses in the rear lens group. The imaging optical system according to claim 9, wherein the image pickup optical system comprises one. When the focal length FFL of the front lens group and the focal length RFL of the rear lens group are both positive powers, the entire lens system is moved to the object side to change the air spacing on the image side at the time of focus adjustment. The imaging optical system according to claim 1, 9 or 10.

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