JP7410556B2 - Large diameter semi-wide-angle imaging lens - Google Patents

Description

The present invention relates to a large-diameter semi-wide-angle imaging lens suitable for use as an interchangeable lens attached to various cameras such as digital cameras and video cameras.

In recent years, image sensors used in digital cameras and the like have become larger and have higher pixel counts, and as a result, imaging lenses have been required to have higher optical performance that allows them to better and sufficiently correct various aberrations. In addition, in order to increase the blurring of the foreground and background of a subject (blurring before and after the focal image), there is also a need for an imaging lens that has a small F number and enables a short photographing distance. In addition, with the advent of mirrorless cameras that do not have an internal return mirror, camera bodies have become smaller, and the lenses used (interchangeable lenses, etc.) are also required to be smaller and more compact.

Conventionally, the camera objective lens described in Patent Document 1 and the large diameter wide-angle lens described in Patent Document 2 are known as wide-angle lenses with an angle of view of 56 to 70 degrees and an F number smaller than F1.7. . The camera objective lens of Patent Document 1 is intended to improve image formation in the edge region of the image, and specifically, the aperture ratio is 1:1.4, the focal length is 35 mm, and The first component, the second component as a convex compound lens element on the subject side, the aperture lens, the third component as a single lens, and the fourth component as a concave compound lens element on the subject side and a fifth component, the first component being a concave compound lens element on the object side, the fifth component being a concave compound lens element on the image side, and the second component The main configuration is that the convex surface on the object side of the fifth component is aspherical, and in particular, two sets of cemented lenses are arranged on the object side from the aperture stop, and the aperture A convex meniscus single lens and two cemented lenses are arranged on the image side of the aperture diaphragm, and the convex surfaces of the cemented lens located in front of the aperture diaphragm and the cemented lens located in the last row are formed into aspherical surfaces. As a result, various aberrations are corrected for the brightness of F1.4.

Further, the large-diameter wide-angle lens disclosed in Patent Document 2 is a wide-angle lens already proposed by the applicant. This wide-angle lens aims to provide a large-diameter wide-angle lens with an angle of view of 60 degrees or more and F1.4 or less without increasing the lens diameter.Specifically, it includes two sets of negative lenses. The first lens group includes a cemented lens, and the second lens group includes a negative lens, a cemented lens, a positive lens, and a negative lens. At the same time, the negative lens and the positive lens are formed into aspherical surfaces, and the ratio of the focal length f of the wide-angle lens to the focal length f1 of the first lens group satisfies 0.4<f/f1<1.2. It is set as follows. In this case, the most object side and the image side of the diaphragm are aspherical negative lenses, which prevents the lens diameter from increasing and corrects various aberrations related to the brightness of an infinite object and F1.2.

Japanese Patent Application Publication No. 5-80252 Japanese Patent Application Publication No. 2004-101880

However, conventional wide-angle lenses that satisfy the above-mentioned angle of view and F-number conditions also have the following problems to be solved.

That is, when realizing an imaging lens having a semi-wide angle of view, that is, an imaging lens that is brighter than F1.7 and ensures sufficient optical performance up to close-range shooting, the above-mentioned conventional wide-angle lens requires: There is a drawback that various aberrations that worsen during close-range photography cannot be sufficiently suppressed. In particular, when obtaining an imaging lens that satisfies the F number of F1.1-F1.5 and also enables close-range photography with an imaging magnification of about 0.1x, good correction for various aberrations is required. Since this is not easy, there are issues that need to be further improved from the viewpoint of realizing a large-diameter semi-wide-angle imaging lens with sufficient optical performance.

An object of the present invention is to provide a large-diameter, semi-wide-angle imaging lens that solves the problems that exist in the background art.

In order to solve the above problems, the present invention provides lenses L1, L2, L3, and L4 that are arranged on the object OBJ side with respect to the aperture stop STO and have negative, positive, positive, and negative powers from the object OBJ side. The first lens group G1 is composed of five lenses, including a first partially symmetrical lens group G1s arranged in the front and rear sides of the first partially symmetrical lens group G1s, and one lens L5 added to one side of the front and rear sides of the first partially symmetrical lens group G1s, and an aperture diaphragm. A second partially symmetrical lens group G2s is arranged on the image IMG side with respect to the STO and has lenses L6, L7, L8, and L9 having negative, positive, positive, and negative powers from the object OBJ side, and this second partially symmetrical lens group G2s. A large-diameter semi-wide-angle imaging lens C having an imaging optical system GA including a second lens group G2 made up of five lenses including one lens L10 added to one side of the front and rear of the partially symmetrical lens group G2s is configured. In doing so, the power arrangement of the five lenses in the first lens group G1 and the power arrangement of the five lenses in the second lens group G2 are set to be the same, and the power arrangement of the five lenses in the first partially symmetrical lens group G1s is set to be the same. A first air space S1 between positive lenses L2 and L3, an intermediate air space Sm in which an aperture stop STO is arranged, a second air space S2 between two consecutive positive lenses L7 and L8 of the second partially symmetrical lens group G2s, functions as a variable interval for adjusting the focus when the shooting distance moves from infinity to a short distance, and when the F number satisfies F1.1 to F1.5 and the object distance is infinite, [Total system focal length/F number] is ED1, and the distance on the optical axis from the object OBJ side surface (i=1) of the lens closest to the object OBJ side to the image IMG surface is 2.0. <[TL/ED1]<5.1 (conditional expression 1) is satisfied, and the first lens group is configured by adding one positive lens to the image side of the first partially symmetrical lens group, and The second lens group is configured by adding one positive lens to the image side of the second partially symmetrical lens group, and the distance on the optical axis from the object side surface of the lens closest to the object side to the aperture stop is determined. When TL1 and the distance on the optical axis from the aperture stop to the image side surface of the lens closest to the image side are TL2, the condition (conditional expression 2) of 0.5<[TL1/TL2]<2.0 is satisfied. and satisfies the condition (conditional expression 3) of 0.35<[AFL/FL1]<1.20, where the focal length of the entire system is AFL and the focal length of the first lens group is FL1. shall be.

In this case, according to a preferred aspect of the invention, the variable interval for performing focus adjustment when the shooting distance moves from infinity to a short distance is set to any one of the first air space S1, the intermediate air space Sm, and the second air space S2. One air space S1, Sm or S2 can be selected. On the other hand, the first lens group G1 can be configured by disposing a biconcave lens L5c closest to the object OBJ. Note that the imaging optical system GA can be provided with at least one cemented lens Ej, which is formed by cementing a negative lens L2 located on the object OBJ side and a positive lens L3 located on the image IMG side.

According to a preferred aspect of the invention, the imaging optical system GA includes, from the object OBJ side, a biconcave lens L1c (L6c), a biconvex lens L2p (L7p), a biconvex lens L3p (L8p), and a biconcave lens L4c (L9c). A first partially symmetrical lens group G1s and/or a second partially symmetrical lens group G2s can be provided.

According to the large-diameter semi-wide-angle imaging lens C according to the present invention having such a configuration, the following remarkable effects can be achieved.

(1) The power arrangement of the five lenses in the first lens group G1 and the power arrangement of the five lenses in the second lens group G2 are set to be the same, and the two consecutive lenses in the first partially symmetrical lens group G1s are A first air space S1 between positive lenses L2 and L3, an intermediate air space Sm in which an aperture stop STO is arranged, a second air space S2 between two consecutive positive lenses L7 and L8 of the second partially symmetrical lens group G2s, functions as a variable interval for adjusting the focus when the shooting distance moves from infinity to a short distance, and when the F number satisfies F1.1 to F1.5 and the object distance is infinite, When [total system focal length/F number] is ED1, and the distance on the optical axis from the object OBJ side surface (i=1) of the lens closest to the object OBJ side to the image IMG surface is TL, conditional expression 1 is satisfied. Since the lens is configured to meet the above requirements, it is possible to secure the necessary image distance in a small F-number range, enable close-range photography, and enable appropriate and easy correction of various aberrations to obtain good aberration characteristics. . Thereby, it is possible to realize a large-diameter semi-wide-angle imaging lens that can secure sufficient optical performance and be made compact.

(2) When configuring the imaging optical system GA, one positive lens L5 is added to the image IMG side of the first partially symmetrical lens group G1s to configure the first lens group G1, and the second partially symmetrical lens group One positive lens L10 is added to the image IMG side of G2s to form the second lens group G2, and the configuration satisfies conditional expressions 2 and 3, so that the power of the first lens group G1 is appropriately secured. At the same time, it becomes possible to form an air lens by the positive lens L10 located closest to the image IMG side of the second lens group G2 and the negative lens L9 opposing this positive lens L10. Thereby, it is possible to easily increase the diameter of the lens while reducing the F number and ensuring good aberration (coma aberration). In addition, since the lens diameter of the second lens group G2 can be reduced and the overall length can be shortened, it can also contribute to miniaturization.

(3) According to a preferred embodiment, any one of the first air space S1, the intermediate air space Sm, and the second air space S2 is used as a variable interval for performing focus adjustment when the shooting distance moves from infinity to a short distance. If the air space S1, Sm or S2 is selected, the variable interval can be reduced to a minimum of one air space S1, Sm or S2, so the overall size and cost can be reduced by simplifying and simplifying the lens group movement mechanism. Can contribute to down.

(4) According to a preferred aspect, when configuring the first lens group G1, by arranging the biconcave lens L5c closest to the object OBJ, it is possible to appropriately correct off-axis aberrations due to an increase in the angle of view. It can be done easily.

(5) According to a preferred embodiment, the imaging optical system GA is provided with at least one cemented lens Ej, which is a negative lens L2 located on the object OBJ side and a positive lens L3 located on the image IMG side. , by making a difference in the Abbe number, it is possible to correct off-axial chromatic aberration, and by making a difference in the refractive index, it is possible to strengthen the correction of spherical aberration, so the amount of residual aberration of the first lens group G1 is reduced by the second lens group G2. Good correction and balance can be achieved. In particular, the effect becomes greater with the partially symmetrical lens groups G1s and G2s.

(6) According to a preferred embodiment, the imaging optical system GA includes, from the object OBJ side, a biconcave lens L1c (L6c), a biconvex lens L2p (L7p), a biconvex lens L3p (L8p), and a biconcave lens L4c (L9c). If the first partially symmetrical lens group G1s and/or the second partially symmetrical lens group G2s are provided, the first partially symmetrical lens group G1s and the second partially symmetrical lens arranged in the first lens group G1 and the second lens group G2, respectively. Since it is possible to make the groups G2s different from each other, residual aberrations of the first lens group G1 can be easily corrected in the second lens group G2, and mutual aberrations in the entire system can be well balanced. can. Moreover, since it becomes possible to construct highly symmetrical partially symmetrical lens groups G1s and G2s, it is possible to further enhance the effect of canceling aberrations inside the partially symmetrical lens groups G1s and G2s or between the partially symmetrical lens groups G1s and G2s. .

A configuration diagram of a large-diameter semi-wide-angle imaging lens according to Reference Example 1 related to a preferred embodiment of the present invention, A list of optical conditions in Reference Example 1-4 related to the preferred embodiment of the present invention and Example 1-3 related to the preferred embodiment, A longitudinal aberration diagram when the imaging magnification of the large-diameter semi-wide-angle imaging lens according to Reference Example 1 is taken as a parameter, A configuration diagram of a large-diameter semi-wide-angle imaging lens according to Reference Example 2, A longitudinal aberration diagram when the imaging magnification of the large-diameter semi-wide-angle imaging lens according to Reference Example 2 is taken as a parameter, A configuration diagram of a large-diameter semi-wide-angle imaging lens according to Reference Example 3, A longitudinal aberration diagram when the imaging magnification of the large-diameter semi-wide-angle imaging lens according to Reference Example 3 is taken as a parameter, A configuration diagram of a large-diameter semi-wide-angle imaging lens according to Reference Example 4, A longitudinal aberration diagram when the imaging magnification of the large-diameter semi-wide-angle imaging lens according to Reference Example 4 is taken as a parameter, Another longitudinal aberration diagram when the imaging magnification of the large-diameter semi-wide-angle imaging lens according to Reference Example 4 is used as a parameter, A configuration diagram of a large-diameter semi-wide-angle imaging lens according to Example 1 of the preferred embodiment, A longitudinal aberration diagram when the imaging magnification of the large-diameter semi-wide-angle imaging lens according to Example 1 is taken as a parameter, A configuration diagram of a large-diameter semi-wide-angle imaging lens according to Example 2 of the preferred embodiment, A longitudinal aberration diagram when the imaging magnification of the large-diameter semi-wide-angle imaging lens according to Example 2 is taken as a parameter, A configuration diagram of a large-diameter semi-wide-angle imaging lens according to Example 3 of the preferred embodiment, A longitudinal aberration diagram when the imaging magnification of the large-diameter semi-wide-angle imaging lens according to Example 3 is taken as a parameter,

Next, preferred embodiments of the present invention will be described in detail based on the drawings.

First, the basic configuration of the large-diameter semi-wide-angle imaging lens C will be described with reference to FIG. 1 (also used as Reference Example 1).

This large-diameter semi-wide-angle imaging lens C can be assumed to be applied to an interchangeable lens for a digital camera. In FIG. 1, OBJ indicates an object (subject), and IMG indicates an image (imaging device). Therefore, the object OBJ side is the front side in the optical axis Dc direction, and the image IMG side is the rear side in the optical axis Dc direction.

As shown in FIG. 1, the large-diameter semi-wide-angle imaging lens C includes a first lens group G1 disposed on the object OBJ side with respect to the aperture stop STO, and a first lens group G1 disposed on the image IMG side with respect to the aperture stop STO. It includes two lens groups G2.

The first lens group G1 includes lenses having powers of (negative) - (positive) - (positive) - (negative) from the object OBJ side, that is, negative lens L1, positive lens L2, positive lens L3, and negative lens L4. In addition, the first partially symmetrical lens group G1s is provided with a first partially symmetrical lens group G1s, and one lens L5 is added to one side of the front and rear sides of the first partially symmetrical lens group G1s, for a total of five lenses. The second lens group G2 includes lenses having (negative) - (positive) - (positive) - (negative) power from the object OBJ side, that is, negative lens L6, positive lens L7, positive lens L8, and negative lens. It includes a second partially symmetrical lens group G2s in which lens L9 is arranged, and one lens L10 is added to one side of the front and rear sides of the second partially symmetrical lens group G2s, for a total of five lenses. FIG. 1 shows an example in which a lens L5 is added to the front side of the first partially symmetrical lens group G1s, and also shows an example in which a lens L10 is added to the front side of the second partially symmetrical lens group G2s.

In this case, the power arrangement of the five lenses in the first lens group G1 and the power arrangement of the five lenses in the second lens group G2 are set to be the same. In other words, although the shapes of the lenses are different, the power arrangement is set to be the same, and the power arrangement of the fifth lens from the lens closest to the object OBJ in the first lens group G1 and the most aperture of the second lens group G2 are the same. The power distribution of the lenses from the lens on the STO side of the aperture to the fifth lens is the same. An imaging optical system GA is composed of an aperture stop STO and a first lens group G1 and a second lens group G2 arranged on both sides of the aperture stop STO, and the basic configuration of the large-diameter semi-wide-angle imaging lens C is this imaging optical system GA. Consisted of.

By the way, in the imaging optical system GA, when securing the angle of view in the semi-wide-angle region, it is desirable to arrange the negative lens L5 (or L1) closest to the object OBJ and to incorporate an aspherical lens. This widens the angle of view and is advantageous for correcting off-axis aberrations.

A so-called retrofocus type wide-angle lens usually uses a negative meniscus lens whose both surfaces are curved toward the object OBJ. Negative meniscus lenses can advantageously converge the off-axis light beam at a wide shooting angle at a position away from the optical axis onto the next lens, so they are used in various wide-angle systems to ensure a wide angle of view. Used in lenses.

However, when using a negative meniscus lens that curves toward the object OBJ side, the air space formed between it and the next lens following the image IMG side becomes wider, so the lens diameter on the object OBJ side becomes larger and the total length It also tends to be longer. Therefore, in a wide-angle lens with a relatively narrow photographing angle of view, a negative lens located closest to the object OBJ has a concave surface on the object OBJ side, or a biconcave lens is used. This allows a stronger negative power to be obtained than a negative meniscus lens, making it possible to reduce the overall length of the lens and the diameter of the front lens, making it possible to make the lens smaller and more compact. This method is particularly advantageous for semi-wide-angle lenses with large apertures because the axial light flux (entrance pupil diameter) becomes large. Normally, aberrations can be corrected advantageously by arranging a negative lens and a positive lens, or vice versa, but as mentioned above, if a lens with strong negative power is required, The positive lens also needs to have strong positive power and balance the power.

Furthermore, in the imaging optical system, the power of the entire system itself is made positive to form an image, so how to use a positive lens is also important. When the power of the positive lens is increased, the radius of curvature of the curved surface becomes smaller, which makes processing difficult, and the steepness of the angle of light entering and exiting the lens surface causes disadvantages such as increased error fluctuations. In particular, a biconvex lens can obtain strong positive power, but if the radius of curvature is small, the lens thickness must be increased to ensure the edge thickness.

Note that even if strong positive power is required, if it cannot be achieved with high refractive index glass alone, it is necessary to reduce the radius of curvature of the lens surface, but if the desired power cannot be obtained even then, two positive lenses may be used in succession. It can be used to share power. This makes it possible to reduce the angle of the light beam to the lens surface through which it passes, thereby suppressing the occurrence of aberrations and error sensitivity. At this time, if one lens is made to bear the power by using a high refractive index lens, the shape can be easily processed, and aberrations can be effectively corrected.

The large-diameter semi-wide-angle imaging lens C uses partially symmetrical lens groups, that is, the first partially symmetrical lens group G1s and the second partially symmetrical lens group G2s, so aberration generation and correction within the lens groups are balanced. This is advantageous when emitting light as a fixed luminous flux. In particular, since the first lens group G1 and the second lens group G2, which are arranged before and after the aperture stop STO, include a partially symmetrical lens group G1s and a partially symmetrical lens group G2s, mutual aberrations can be avoided when the optical system is fully closed. Able to maintain good balance. In the imaging optical system GA, the spatial distance to the object OBJ and the spatial distance to the image IMG are not symmetrical, and a perfectly symmetrical lens configuration cannot perform good aberration correction. The convergence effect is strengthened so that the light rays from OBJ can be converged.

Furthermore, with respect to the aperture stop STO, the symmetrical arrangement of the first lens group G1 and the second lens group G2, and the symmetrical arrangement within the partially symmetrical lens group G1s and the partially symmetrical lens group G2s have the effect of canceling aberrations within each group. can be increased, which is advantageous for correcting axial aberrations and off-axis aberrations, and it is possible to reduce fluctuations in aberrations due to changes in distance with respect to the object OBJ. In order to correct off-axis aberrations, aberrations can be easily corrected by using a lens configuration using a positive lens and a negative lens with different characteristics.

In addition, partially symmetrical lens groups G1s and G2s are arranged in front and behind the aperture diaphragm STO using four lenses and have a power distribution of (negative) - (positive) - (positive) - (negative) to ensure symmetry. At the same time, by adding one lens with negative or positive power to the front or rear side, the power of the partially symmetrical lens groups G1s and G2s is shared and balanced, thereby strengthening aberration correction. I'm trying.

On the other hand, the large-diameter semi-wide-angle imaging lens C includes a first air space S1 between the two successive positive lenses L2 and L3 of the first partially symmetrical lens group G1s, an intermediate air space Sm in which the aperture stop STO is arranged, and a second air space Sm. At least one air space, preferably any one air space S1, Sm or S2, of the second air space S2 between the two successive positive lenses L7 and L8 of the partially symmetrical lens group G2s is Function as a variable interval to adjust focus when moving from infinity to short distance. FIG. 1 shows a case where the intermediate air space Sm functions as a variable interval for focus adjustment, and arrows Fma and Fmb indicate that the first lens group G1 and/or the second lens group G2 can be moved with respect to the intermediate air space Sm. It shows that.

In FIG. 1, in the first lens group G1, three lenses, the lens L5 located closest to the object OBJ, the second negative lens L1, and the third positive lens L2, are defined as a first front lens group G1f, If the two lenses, the positive lens L3 located fourth from the object OBJ side and the negative lens L4 located fifth from the object OBJ side, are the first rear lens group G1r, then the distance between the first front lens group G1f and the first rear lens group G1r is On the other hand, in the second lens group G2 in FIG. 1, the lens L10 located closest to the aperture stop STO side, the second negative lens L6, and the third The three positive lenses L7 located at the aperture stop STO side constitute the second front lens group G2f, and the two lenses, the positive lens L8 located fourth from the aperture stop STO side and the negative lens L9 located fifth from the aperture stop STO side, constitute the second rear lens group G2r. If so, a second air space S2 is created that functions as a variable interval for focus adjustment between the second front lens group G2f and the second rear lens group G2r.

In this case, if the power arrangement of the partially symmetrical lens groups G1s and G2s itself and the aperture stop STO are symmetrical in the entire system, when the shooting distance changes from the far point to the near point, the entire lens can be moved toward the object OBJ. By moving the two focus movement groups (in the case of Fig. 1, the first lens group G1 and the second lens group G2) at different intervals, the aberrations that occur when moving the lens to the center are canceled. can. For example, in the case of the first lens group G1 and the second lens group G2, if the amount of movement of the second lens group G2 is greater than the amount of movement of the first lens group G1, as the shooting distance becomes closer, the two lens groups The gap between G1 and G2 becomes narrower, and vice versa.

The imaging optical system GA performs imaging while changing the distance to the object OBJ, so the imaging performance is maintained while slightly deforming the symmetry of the optical system (changing the air space). At this time, in order to reduce aberration fluctuations due to changes in the distance to the object OBJ, when changing the air space Sm before and after the aperture stop STO, one or both of the first lens group G1 and the second lens group G2 should be moved. This reduces the imaging position (movement amount from infinity) of the first lens group G1 to maintain image performance. For this reason, by utilizing the fact that a symmetrical optical system has the effect of canceling out aberrations before and after the point of symmetry, in the example, the air space Sm of the aperture stop STO, the two biconvex lenses L2p in the first lens group G1, The first lens group G1 and the second lens group G2, which are separated by the air space S1 between L3p and the air space S2 between the two biconvex lenses L7p and L8p in the second lens group G2, are mainly moved.

That is, the object OBJ side with respect to the air space S1 is the first front lens group G1f, the space between the air space S1 and the aperture stop STO is the first rear lens group G1r, and the space between the aperture stop STO and the air space S2 is the second front lens group. The second rear lens group G2r is located on the image IMG side with respect to the air space S2, and the power distribution and aberration correction of each lens group are balanced. Then, at least one of the three air spaces S1, Sm, and S2 is configured to easily change as a variable interval during focusing, and when the object point (subject) moves from infinity to a short distance, this variable interval On the other hand, focus adjustment is made possible by moving the front lens group located on one side and the rear lens group located on the other side. Therefore, all three air spaces S1, Sm, and S2 may be used as the variable interval during focusing, or any one or any two may be used. good.

The air spaces S1, Sm, and S2, which are variable intervals during focusing, serve as points of symmetry for the first partially symmetrical lens group G1s, the lens groups G1 and G2 before and after the aperture stop STO, and the second partially symmetrical lens group G2s. Therefore, it is possible to utilize the advantage of canceling out aberrations by the front and rear lens groups in a symmetrical lens configuration, and it is possible to flexibly construct a focus adjustment mechanism.

Therefore, the lens groups that can be moved back and forth due to the air spaces S1, Sm, and S2 that change during focus adjustment are a combination of four lens groups G1f, G1r, G2f, and G2r at most. In this case, if any one of the air spaces S1, Sm, or S2 is selected, the variable interval can be reduced to a minimum of one air space S1, Sm, or S2, so that by simplifying and simplifying the lens group movement mechanism, It can contribute to overall miniaturization and cost reduction. On the other hand, if the number of air spaces S1, Sm, and S2 used for variable spacing is increased, the focus adjustment mechanism in the lens barrel will become more complicated, leading to increased cost and larger diameter in the radial direction. It is not possible to make the device smaller and more compact, and the weight also increases.

Therefore, at imaging magnifications up to approximately 0.1x, where fluctuations in aberrations are relatively small, one of the three variable focus intervals S1, Sm, and S2 is selected, and the two front and rear lens groups separated by this are selected. In the example, in other reference examples and examples other than reference example 4, the first lens group G1 and the second lens group G2 are moved on the optical axis Dc. On the other hand, at imaging magnifications of approximately 0.1x or higher, where fluctuations in aberrations become large, all three focus variable intervals S1, Sm, and S2, or any two or more of them, are selected and separated by these. Aberration fluctuations are reduced by moving the front and rear lens groups G1f, G1r, etc. to enhance the effect of correcting aberrations. In the fourth embodiment, one air space S2 is used as a variable interval during focus adjustment when the imaging magnification is up to about 0.1x, and when the imaging magnification is about 0.1x or more, the accompanying aberration fluctuation is reduced. , two air spaces S1 and S2 were used as variable intervals during focus adjustment.

On the other hand, on the condition that the F number satisfies the range of F1.1 to F1.5, at infinite object distance,
2.0<[TL/ED1]<5.1... (Conditional expression 1)
Set to meet the following conditions. In this case, TL is the distance on the optical axis from the object OBJ side surface (i=1) of the lens closest to the object OBJ side to the image IMG surface, and ED1 is (total system focal length/F number).

Conditional expression 1 is the range of the axial beam diameter and the total length determined by the F number of F1.1 to F1.5. Therefore, in conditional expression 1, if the magnitude of [TL/ED1] is less than "2.0", the ray angle of the large luminous flux with a large aperture becomes sharp even when it is converged by the first lens group G1, so that It becomes impossible to suppress the occurrence of aberrations, and it becomes impossible to secure the necessary image distance. On the other hand, if the magnitude of [TL/ED1] exceeds "5.1", the overall length of the lens becomes long, making it impossible to achieve miniaturization.

As described above, the large-diameter semi-wide-angle imaging lens C basically has a lens L1 arranged on the object OBJ side with respect to the aperture stop STO and having negative, positive, positive, and negative powers from the object OBJ side. , L2, L3, and L4, and a lens L5 added to one side of the front and rear sides of the first partially symmetrical lens group G1s. A second partially symmetrical lens including lens group G1 and lenses L6, L7, L8, and L9, which are arranged on the image IMG side with respect to the aperture stop STO and have negative, positive, positive, and negative powers from the object OBJ side. A large aperture lens having an imaging optical system GA comprising a group G2s, and a second lens group G2 made up of five lenses including one lens L10 added to one side of the front and rear sides of the second partially symmetrical lens group G2s. When configuring the semi-wide-angle imaging lens C, the power arrangement of the five lenses in the first lens group G1 and the power arrangement of the five lenses in the second lens group G2 are set to be the same, and the first partially symmetrical lens group A first air space S1 between two consecutive positive lenses L2 and L3 of G1s, an intermediate air space Sm where an aperture stop STO is arranged, and a space between two consecutive positive lenses L7 and L8 of the second partially symmetrical lens group G2s. At least one air space in the second air space S2 of the second air space S2 functions as a variable interval for adjusting the focus when the shooting distance moves from infinity to a short distance, and the F number satisfies F1.1 to F1.5. , and the configuration satisfies conditional expression 1 at infinite object distance, ensuring the necessary image distance in a small F-number range, enabling close-range photography, and making it possible to appropriately and easily correct various aberrations. Good aberration characteristics can be obtained. Thereby, it is possible to realize a large-diameter semi-wide-angle imaging lens that can secure sufficient optical performance and be made compact.

Next, Reference Example 1-4 related to this embodiment and Example 1-3 according to this embodiment will be described with reference to FIGS. 1 to 15.

Reference Example 1-4 shows a large-diameter semi-wide-angle imaging lens C that has a semi-wide angle of around F1.2, and Example 1-3 shows a large-diameter semi-wide-angle imaging lens C that has a semi-wide angle of around F1.4. shows.

In Reference Example 1-4, the first lens group G1 has a strong positive power, and the imaging position is close to the aperture stop STO. For this reason, in the first front lens group G1f, the function of converging the light beam with a wide angle of view is enhanced by the two negative lenses L5 and L1. At the same time, in order to make the maximum ray of the axial ray of the large-diameter lens the same as the outermost ray of the converged off-axis ray, balance is achieved by increasing the powers of the positive lenses L2 and L3. Note that it is desirable to set the power of the positive lens L3 of the first rear lens group G1r to be strong from the viewpoint of power distribution and balance. Further, the image point of the first lens group G1 is close to the aperture stop STO side, and this image point becomes the object point of the second lens group G2, so the two negative lenses L10, By L6, the image point after passing through the second front lens group G2f is moved away to set the imaging position of the second rear lens group G2r.

In Example 1-3, the positive power of the first lens group G1 is relatively low, and the imaging position of the first lens group G1 is far from the aperture stop STO side. That is, since the single negative lens L1 is responsible for converging the light beam having a wide angle of view by the first front lens group G1f, the image point of the positive lens L2 following this negative lens L1 is located at a far position. Therefore, after the light ray enters the first rear lens group G1r where this image point becomes the object point, a position closer to this becomes the image point of the first rear lens group G1r. In addition, since the image point of the first lens group G1 becomes the object point of the second lens group G2, the image point position of the second front lens group G2f is set closer to the image forming position of the second rear lens group 2Gr. are doing. Furthermore, the second partially symmetrical lens group G2s of the second lens group G2 has a four-lens configuration of (negative)-(positive)-(positive)-(negative), and in particular, (negative)-(positive), and (positive) - (negative) two sets of cemented lenses Ej, Ej were arranged in a symmetrical manner. As a result, it is possible to correct off-axis chromatic aberration by making a difference in the Abbe number, and to improve correction of spherical aberration by making a difference in the refractive index. A later lens group also produces a correction and balancing effect.

Therefore, the large-diameter semi-wide-angle imaging lens C can be roughly divided into four lens groups: the first front lens group Glf, which converges the large-diameter axial light beam and the wide-angle off-axis light beam, and the aperture stop STO. The first rear lens group Glr transmits the chief ray on the axis and provides an appropriate power balance to the first lens group G1, and corrects on-axis and off-axis aberrations that determine the power and image position of the entire system. It includes a second front lens group G2f, a second rear lens group G2r that focuses the off-axis light beam at an appropriate position and height, and performs final aberration correction.

Then, when focusing from the infinite object point to the short distance side, the power balance of each lens group Glf, Glr, G2f, G2r is set to an appropriate value, and the first front lens group Glf and the first rear lens An air space S1 between the group Glr, an air space Sm between the first rear lens group Glr and the second front lens group G2f, that is, an aperture stop STO, and an air space between the second front lens group G2f and the second rear lens group G2r. One of the three air spaces S1, Sm, and S2 of S2 is varied, and the front and rear thereof are made into two focus lens moving groups, that is, a front moving group and a rear moving group, and the image point range of the front moving group is As the object point of the rear moving group, the two moving groups are moved by different amounts of movement with respect to the image plane, which is the image forming surface, so that the amount of aberration can be kept constant.

From the above, partially symmetrical lens groups G1s and G2s are placed before and after the aperture stop STO, and while ensuring (negative)-(positive)-(positive)-(negative) symmetry due to the four lens configuration, One lens is added before and after each partially symmetrical lens group G1s, G2s. In other words, in Reference Example 1-4, by adding a lens with negative power on the object OBJ side, (negative) - (negative) - (positive ) - (positive) - (negative) power arrangement, and in Example 1-3, by adding a lens with positive power to the image IMG side, (negative) - (positive) - (positive ) - (negative) - (positive) power arrangement is illustrated.

Reference Example 1-4 and Example 1-3 will be specifically described below with reference to FIGS. 1 to 15 and Tables 1 to 7.

Reference example 1

First, a large-diameter semi-wide-angle imaging lens C according to Reference Example 1 will be described with reference to FIGS. 1 to 3 and Table 1.

FIG. 1 shows the configuration of a large-diameter semi-wide-angle imaging lens C according to Reference Example 1. Reference example 1 includes an imaging optical system GA, and this imaging optical system GA is configured by arranging, from the object OBJ side, a first lens group G1, an aperture stop STO, and a second lens group G2. The first lens group G1 on the object OBJ side with respect to the aperture diaphragm STO is a first partially symmetrical lens group consisting of one lens L5 located closest to the object OBJ side and four lenses arranged on the aperture diaphragm STO side. It includes a lens group G1s.

As the lens L5, a biconcave lens L5c made of a single lens is used. If the biconcave lens L5c is used as the lens closest to the object OBJ in the first lens group G1, it is possible to easily perform appropriate correction for off-axis aberrations caused by an increase in the angle of view. Further, the first partially symmetrical lens group G1s is composed of two sets of cemented lenses Ej and Ej located in the front and rear. The cemented lens Ej on the object OBJ side is composed of a negative lens L1 using a biconcave lens L1c located on the object OBJ side and a positive lens L2 using a biconvex lens L2p located on the image IMG side (aperture stop STO side). At the same time, the cemented lens Ej on the aperture stop STO side is constructed by cementing a positive lens L3 using a biconvex lens L3p located on the object OBJ side and a negative lens L4 using a biconcave lens L4c located on the aperture stop STO side. . As a result, the first lens group G1 has a lens configuration having a power of (negative)-(negative)-(positive)-(positive)-(negative).

In this way, if at least one set of cemented lenses Ej... is provided, in which the negative lens L2... located on the object OBJ side and the positive lens L3... located on the image IMG side are provided, the axis can be adjusted by differentiating the Abbe numbers. Since external chromatic aberration can be corrected and correction of spherical aberration can be strengthened by making a difference in refractive index, the second lens group G2 can achieve good correction and balance for the residual aberration amount of the first lens group G1. can. In particular, the effect becomes greater with the partially symmetrical lens groups G1s and G2s.

On the other hand, the second lens group G2 on the image IMG side with respect to the aperture diaphragm STO includes one lens L10 located closest to the object OBJ (aperture diaphragm STO side) and four lenses located on the image IMG side. A second partially symmetrical lens group G2s is provided.

A negative meniscus lens L10c having an aspherical surface is used as the lens L10. The second partially symmetrical lens group G2s uses a cemented lens Ej arranged on the aperture stop STO side, that is, a negative lens L6 using a biconcave lens L6c on the aperture stop STO side, and a biconvex lens L7p located on the image IMG side. A cemented lens Ej is formed by cementing the positive lens L7, and a positive lens L8 using a biconvex lens L8p made of a single lens is placed on the image IMG side for this positive lens L7. It is constituted by a negative lens L9 using a biconcave lens L9c which is a single lens having an aspherical surface disposed on the side. As a result, the second lens group G2 has a lens configuration having a power of (negative)-(negative)-(positive)-(positive)-(negative).

In this case, since a lens with an aspherical surface has a strong aberration-correcting power, it is advantageous from the viewpoint of ease of processing to use a lens with less uneven thickness (difference in thickness) between the center and periphery of the lens and a small diameter. Become. In particular, in the case of a large-diameter imaging lens with an F number of F1.2 class, the lens diameter of the first lens group G1 is large, but the lens diameter of the second lens group G2 is close to the diagonal size of the image sensor. So it doesn't change much. In the illustrated reference examples and examples, the lens diameter of the first lens group G1 is larger than that of the F1.4 lens when the F number is at the F1.2 level, but the lens diameter of the second lens group G2 is about the same. The lens diameter will be .

Therefore, in the imaging optical system GA of Reference Example 1, the power arrangement of the five lenses in the first lens group G1 is the same as the power arrangement of the five lenses in the second lens group G2. Further, in this case, the first partially symmetrical lens group G1s included in the first lens group G1 includes, from the object OBJ side, a biconcave lens L1c, a biconvex lens L2p, a biconvex lens L3p, a biconcave lens L4c, and a second lens group The second partially symmetrical lens group G2s provided for G2 includes, from the object OBJ side, a biconcave lens L6c, a biconvex lens L7p, a biconvex lens L8p, and a biconcave lens L9p.

In this way, when configuring the imaging optical system GA, the second lens is constructed of, from the object OBJ side, a biconcave lens L1c (L6c), a biconvex lens L2p (L7p), a biconvex lens L3p (L8p), and a biconcave lens L4c (L9c). If the first partially symmetrical lens group G1s and/or the second partially symmetrical lens group G2s are provided, the first partially symmetrical lens group G1s and the second partially symmetrical lens group arranged in the first lens group G1 and second lens group G2, respectively. Since it is possible to make G2s different from each other, residual aberrations of the first lens group G1 can be easily corrected in the second lens group G2, and mutual aberrations in the entire system can be well balanced. . Moreover, since it becomes possible to construct highly symmetrical partially symmetrical lens groups G1s and G2s, it is possible to further enhance the effect of canceling aberrations inside the partially symmetrical lens groups G1s and G2s or between the partially symmetrical lens groups G1s and G2s. .

Furthermore, when configuring the first lens group G1, the distance on the optical axis from the object OBJ side surface (i=1) of the lens L5 closest to the object OBJ to the aperture stop STO is TL1, and from the aperture stop STO When the distance on the optical axis from the lens L9 closest to the image IMG to the surface (i=18) on the image IMG side is TL2,
0.5<[TL1/TL2]<2.0... (Conditional expression 2)
Set to meet the following conditions.

In this case, the entire power of the first front lens group G1f is set to be negative. In the configuration of Reference Example 1, two wide-angle negative lenses are arranged on the object OBJ side of the first lens group G1, and the power of the positive lens that converges a large-diameter light beam is strengthened. The length of the group G1 is longer than the second lens group G2. Note that in Conditional Expression 2, if the magnitude of [TL1/TL2] is less than "0.5", aberrations will worsen, so the F number must be increased, making it difficult to increase the aperture. On the other hand, if the size of [TL1/TL2] exceeds 2.0, it is possible to advantageously correct aberrations for increasing the aperture, but the overall length of the lens becomes longer, making it difficult to achieve compactness. It becomes difficult.

Therefore, in such a configuration, one negative lens L5 is added to the object OBJ side of the first partially symmetrical lens group G1s to form the first lens group G1, and the object of the second partially symmetrical lens group G2s is If one negative lens L10 is added to the OBJ side to form the second lens group G2, and the entire power of the first lens group G1 is set to negative, and conditional expression 2 is satisfied, Two wide-angle negative lenses are placed on the object OBJ side of the first lens group G1, and the power of the positive lens that converges a large-diameter light beam can be strengthened, making it possible to make the entire lens compact and to reduce the F number. At the same time, it is possible to secure good aberrations and easily increase the diameter of the lens.

Further, in reference example 1, when the single lens is the first element Es and the cemented lens (Ej) is the second element Ej, it is composed of a total of seven elements Es..., Ej..., and the negative lens is connected from the object OBJ side. The first element Es used, the second element Ej using a cemented lens of a negative lens and a positive lens, the second element Ej using a cemented lens of a positive lens and a negative lens, the first element Es using an aspherical lens, It includes a second element Ej using a cemented lens of a negative lens and a positive lens, a first element Es using a positive lens, and a first element Es using a negative lens. Then, on the premise that it is composed of a total of seven elements Es..., Ej..., the condition that the refractive index of the positive lens in the cemented lens (Ej) is greater than 1.7 is satisfied, and the focal length of the entire system is When AFL and the focal length of the first lens group G1 are FL1,
0.35<[AFL/FL1]<1.20... (Conditional expression 3)
Set to meet the following conditions.

In this case, if the refractive index of each positive lens L2, L3, L7 used in the three sets of cemented lenses (second element Ej...) is smaller than 1.7, astigmatism and field curvature will worsen. Therefore, these corrections become difficult. In addition, in conditional expression 3, if [AFL/FL1] exceeds "1.20", the power of the first lens group G1 becomes stronger with respect to the entire system, so the lens diameter of the first lens group G1 becomes larger. , and it becomes difficult to correct the coma aberration that occurs along with this, and if [AFL/FL1] is less than 0.35, the power of the first lens group G1 becomes weaker, so the power of the second lens group G2 becomes smaller. The diameter of the lens increases, making it difficult to attach it to the camera body.

Therefore, if configured under such conditions, it is possible to avoid deterioration of astigmatism and field curvature, and also to easily correct these. Moreover, since the appropriate power of the first lens group G1 can be secured for the entire system, it is possible to reduce the lens diameter in the first lens group G1 and easily correct coma aberration, and also to realize the lens diameter in the second lens group G2. It is possible to realize miniaturization and easy installation to the camera body.

Furthermore, when configuring the imaging optical system GA, the overall power of the first lens group G1 is set to be positive, and the overall power of the lens on the object OBJ side from the first air space S1 of the first lens group G1 is set to be positive. At the same time, the overall power of the lenses from the first air space S1 to the intermediate air space Sm is set to positive, the focal length of the entire system is set to AFL, the focal length of the first lens group is set to FL1, and the power of the first air space is set to be negative. When the focal length of the lens from space to intermediate air space is FL1B,
0.8<[FL1/AFL]<1.8... (Conditional expression 4)
0.8<[FL1B/AFL]<1.6... (Conditional expression 5)
0.6<[FL1B/FL1]<1.5... (Conditional expression 6)
0.4<[|(FL1/AFL)-(FL1B/AFL)
-(FL1B/FL1)│]<1.5
... (conditional expression 7)
Set to satisfy all conditions.

In order to make the imaging optical system GA wide-angle and compact, the image point position of the first front lens group G1f is adjusted by two negative lenses L5 and L1 arranged on the object OBJ side in the first front lens group G1f. Although it is shortened by positioning it on the object OBJ side, it is desirable to ensure a certain length in order to appropriately balance the aberrations and power of the entire system. In addition, in order to advantageously correct aberrations for increasing the aperture and to ensure the compactness of the optical system, the power of the first rear lens group G1r and the power of the entire first lens group G should be set within an appropriate range. There is a need.

Therefore, the overall power of the first lens group G1 is set to be positive, and the overall power of the lens of the first lens group G1 from the first air space S1 to the object OBJ side is set to be negative, and each conditional expression It is necessary to ensure the balance of these three powers by setting the conditions to satisfy 4-7. Therefore, if these conditions are not met, problems such as insufficient correction of aberrations in the entire system and an increase in the total length will occur. Note that the image point position of the first front lens group G1f from the rearmost surface of the first front lens group G1f to the object OBJ side is within a range of 2 to 10 times the focal length AFL of the entire system x (F number of the entire system). It is desirable to set this.

As a result, the image point position of the lens on the object OBJ side from the first air space S1 can be set at an appropriate position on the object OBJ side, making it advantageous to correct aberrations for increasing the aperture and making the entire lens smaller and more compact. can be achieved. Moreover, the total power of the first lens group G1, the total power of the lens from the first air space S1 to the object OBJ side of the first lens group G1, and the total power of the lens from the first air space S1 to the intermediate air space Sm Since an appropriate power range can be secured and the balance of each power can be set within an appropriate range, it is possible to avoid the problem of insufficient aberration correction in the entire system, and it is also possible to shorten the overall length of the lens.

On the other hand, in the case of Reference Example 1, the intermediate air space Sm was set as a variable interval for performing focus adjustment when the photographing distance moves from infinity to a short distance. Therefore, the first lens group G1 including the first front lens group G1f and the first rear lens group G1r, and the second lens group G including the second front lens group G2f and the second rear lens group G2r are each integrally formed. It functions as a focus moving group that moves by moving.

In this way, as a variable interval for performing focus adjustment when the photographing distance moves from infinity to a short distance, any one of the air spaces S1, S1, Sm, and S2, the first air space S1, the intermediate air space Sm, and the second air space S2, If Sm or S2 is selected, a minimum of one air space S1, Sm or S2 is required for the variable interval, which contributes to the simplification and simplification of the lens group moving mechanism and further to the miniaturization of the entire lens group.

Table 1 shows lens data of the entire lens system of the large-diameter semi-wide-angle imaging lens C of Reference Example 1. The large-diameter semi-wide-angle imaging lens C at the infinite object point has a focal length of 36.00 mm, an F number of 1.24, and a half angle of view of 31.25 degrees. Also shown is data (focus variable interval) in which the imaging magnification is a parameter ("0.000", "0.105"). In this case, the photographing magnification of "0.000" indicates that the subject is at an infinite object point. Note that in optical lateral magnification, the image height is inverted with respect to the object height, so it is a negative value, but this imaging magnification is expressed as image height/(−object height).

In the "surface data" in Table 1, the surface number of the lens surface counted from the object OBJ side is indicated by i. This surface number i matches some of the symbols (some of the numbers) shown in FIG. Correspondingly, the radius of curvature R(i) of the lens surface, the axial distance D(i), the refractive index nd(i) of the glass material, and the Abbe number νd(i) of the glass material are shown, respectively. nd(i) and vd(i) are numerical values for the d-line (587.6 [nm]). The axial distance D(i) indicates the lens thickness or air space between opposing surfaces. Further, FL(i) indicates the focal length of a single lens (a cemented lens is treated as a plurality of lenses) placed in the air. The units of the radius of curvature R(i), the interplanar distance D(i), and the focal length FL(i) are [mm]. The surface number OBJ indicates the object, STO indicates the aperture stop, and IMG indicates the position of the image. Infinity of the radius of curvature R(i) is a plane, and a surface with A after the surface number i indicates that the surface shape is aspheric. Blank spaces in the refractive index nd(i) and Abbe number νd(i) indicate air.

The "aspheric coefficient" in Table 1 is expressed as follows: In the orthogonal coordinate system (X, Y, Z) with the center of the surface as the origin and the optical axis Dc direction as Z, when ASP is the surface number of the aspheric surface, Z is It is expressed by the number 1. In Equation 1, R is the central radius of curvature, K is the conic constant, A4, A6, A8, and A10 are the 4th, 6th, 8th, and 10th aspheric coefficients, respectively, and H is the radius of curvature from the origin on the optical axis. It is distance. In addition, in Table 4, "E" means "x10".

"Focus variable interval" in Table 1 indicates a variable interval at which focus adjustment is performed. It should be noted that if the "photographing magnification" has the same numerical value, it means that the lens groups before and after it move simultaneously on the optical axis Dc.

As shown in Table 1 and FIG. 2, TL in Conditional Expression 1 described above is 75.23 mm, and ED1 is 29.03 mm. Therefore, since TL/ED1=75.23/29.03=2.59, conditional expression 1 (2.0<[TL/ED1]<5.1) is satisfied. TL1 in conditional expression 2 is 33.86 mm, and TL2 is 21.51 mm. Therefore, TL1/TL2=33.86/21.51=1.57, so conditional expression 2 (1.0<[TL1/TL2]<2.0) is satisfied. AFL in conditional expression 3 is 36.00 mm, and FL1 is 40.00 mm. Therefore, since AFL/FL1=36.00/40.00=0.90, conditional expression 3 (0.35<[AFL/FL1]<1.20) is satisfied. AFL in conditional expression 4 is 36.00 mm, and FL1 is 40.00 mm. Therefore, since FL1/AFL=40.00/36.00=1.11, conditional expression 4 (0.8<[FL1/AFL]<1.8) is satisfied. FL1B in conditional expression 5 is 36.51 mm, and AFL is 36.00 mm. Therefore, since FL1B/AFL=36.51/36.00=1.01, conditional expression 5 (0.8<[FL1B/AFL]<1.6) is satisfied. FL1B in conditional expression 6 is 36.51 mm, and FL1 is 40.00 mm. Therefore, since FL1B/FL1=36.51/40.00=0.91, conditional expression 6 (0.6<[FL1B/FL1]<1.5) is satisfied. In conditional expression 7, FL1 is 40.00 mm, AFL is 36.00 mm, and FL1B is 36.51 mm. Therefore, |(FL1/AFL)-(FL1B/AFL)-(FL1B/FL1)|=|(40.00/36.00)-(36.51/36.00)-(36.51/40. 00)|=|1.11-1.01-0.91|=0.81, so conditional expression 7 (0.4<[|(FL1/AFL)-(FL1B/AFL)-(FL1B/ FL1) | < 1.5) is satisfied.

On the other hand, FIGS. 3(a) and 3(b) show longitudinal aberration diagrams using the imaging magnification as a parameter ("0.000", "0.105") in the large-diameter semi-wide-angle imaging lens C of Reference Example 1. . Each longitudinal aberration diagram shows, from the left side, spherical aberration (656.3 nm, 587.6 nm, 435.8 nm), astigmatism (587.6 nm), and distortion aberration (587.6 nm). Each scale is ±0.50 mm, ±0.50 mm, and ±3.0%. As shown in Figures 3(a) and (b), it was confirmed that good aberrations, that is, good imaging performance, were obtained regardless of the imaging magnification of 0.000 or 0.105. can. Note that the large-diameter semi-wide-angle imaging lens C of Reference Example 1 has an F number of F1.24 and satisfies the conditions of F1.1 to F1.5.

Reference example 2

Next, a large-diameter semi-wide-angle imaging lens C according to Reference Example 2 will be described with reference to FIGS. 4, 5, 2, and Table 2.

FIG. 4 shows the configuration of a large-diameter semi-wide-angle imaging lens C according to Reference Example 2. In Reference Example 2, the direction of the negative lens L10 added to the front side of the second partially symmetrical lens group G2s is reversed with respect to Reference Example 1. That is, in Reference Example 1, a negative meniscus lens L10c having an aspherical surface curved toward the object OBJ side was used as the negative lens L10, whereas in Reference Example 2, a negative meniscus lens L10c having an aspherical surface curved toward the image IMG side was used as the negative lens L10. A meniscus lens L10c is used.

Except for this point, the other configurations are the same as Reference Example 1. Therefore, in the configuration of Reference Example 2 (Figure 4), the same parts and the same functional parts as Reference Example 1 (Figure 1) are given the same reference numerals to clarify the configuration and provide detailed explanations. is omitted.

Table 2 shows lens data of the entire lens system of the large-diameter semi-wide-angle imaging lens C of Reference Example 2. The large-diameter semi-wide-angle imaging lens C at the infinite object point has a focal length of 36.00 mm, an F number of 1.24, and a half angle of view of 31.26 degrees. Also shown is data (focus variable interval) in which the imaging magnification is a parameter ("0.000", "0.104").

As shown in Table 2 and FIG. 2, TL in Conditional Expression 1 described above is 84.14 mm, and ED1 is 29.03 mm. Therefore, since TL/ED1=84.14/29.03=2.90, conditional expression 1 (2.0<[TL/ED1]<5.1) is satisfied. TL1 in conditional expression 2 is 37.43 mm, and TL2 is 27.32 mm. Therefore, TL1/TL2=37.43/27.32=1.37, so conditional expression 2 (0.5<[TL1/TL2]<2.0) is satisfied. AFL in conditional expression 3 is 36.00 mm, and FL1 is 40.00 mm. Therefore, since AFL/FL1=36.00/40.00=0.90, conditional expression 3 (0.35<[AFL/FL1]<1.20) is satisfied. AFL in conditional expression 4 is 36.00 mm, and FL1 is 40.00 mm. Therefore, since FL1/AFL=40.00/36.00=1.11, conditional expression 4 (0.8<[FL1/AFL]<1.8) is satisfied. FL1B in conditional expression 5 is 39.92 mm, and AFL is 36.00 mm. Therefore, since FL1B/AFL=39.92/36.00=1.11, conditional expression 5 (0.8<[FL1B/AFL]<1.6) is satisfied. FL1B in conditional expression 6 is 39.92 mm, and FL1 is 40.00 mm. Therefore, since FL1B/FL1=39.92/40.00=1.00, conditional expression 6 (0.6<[FL1B/FL1]<1.5) is satisfied. In conditional expression 7, FL1 is 40.00 mm, AFL is 36.00 mm, and FL1B is 39.92 mm. Therefore, |(FL1/AFL)-(FL1B/AFL)-(FL1B/FL1)|=|(40.00/36.00)-(39.92/36.00)-(39.92/40. 00)|=|1.11-1.11-1.00|=1.00, so conditional expression 7 (0.4<[|(FL1/AFL)-(FL1B/AFL)-(FL1B/ FL1) | < 1.5) is satisfied.

On the other hand, FIGS. 5(a) and 5(b) show longitudinal aberration diagrams using the imaging magnification as a parameter ("0.000", "0.104") in the large-diameter semi-wide-angle imaging lens C of Reference Example 2. . As shown in Figures 5(a) and (b), it was confirmed that good aberrations, that is, good imaging performance, were obtained regardless of the imaging magnification of "0.000" or "0.104". can. Note that the large-diameter semi-wide-angle imaging lens C of Reference Example 2 has an F number of F1.24 and satisfies the conditions of F1.1 to F1.5.

Reference example 3

Next, a large-diameter semi-wide-angle imaging lens C according to Reference Example 3 will be described with reference to FIGS. 6, 7, 2, and Table 3.

FIG. 6 shows the configuration of a large-diameter semi-wide-angle imaging lens C according to Reference Example 3. In Reference Example 3, the first air space S1 is selected as a variable interval for focus adjustment when the shooting distance moves from infinity to a short distance, and other than this point, the other basic configuration is the same as Reference Example 2. is the same as

That is, in the reference example 2 (reference example 1) described above, the intermediate air space Sm is selected as the variable interval for focus adjustment, and the front moving group is formed by integrating the first front lens group G1f + the first rear lens group G1r. , a rear movable group is set in which the second front lens group G2f+the second rear lens group G2r are integrated.

On the other hand, in Reference Example 3, the first air space S1 is selected as the variable interval for focus adjustment, and the first front lens group G1f, that is, the front moving group that integrates lenses L5, L1, and L2, , the first rear lens group G1r+the second front lens group G2f+the second rear lens group G2r, that is, a rear moving group in which lenses L3, L4, L10, L6, L7, L8, and L9 are integrated is set. In FIG. 6, arrows Fma and Fmb indicate that the front moving group and the rear moving group are movable with respect to the first air space S1. In addition, in the configuration of Reference Example 3 (Figure 6), the same parts and functional parts as Reference Example 1 (Figure 1) and Reference Example 2 (Figure 4) are given the same reference numerals to clearly identify the configuration. At the same time, detailed explanation thereof will be omitted.

Table 3 shows lens data for the entire lens system of the large-diameter semi-wide-angle imaging lens C of Reference Example 3. The large-diameter semi-wide-angle imaging lens C at an infinite object point has a focal length of 31.06 mm, an F number of 1.24, and a half angle of view of 39.94 degrees. Also shown is data (focus variable interval) in which the imaging magnification is a parameter ("0.000", "0.098").

As shown in Table 3 and FIG. 2, TL in Conditional Expression 1 described above is 85.00 mm, and ED1 is 25.05 mm. Therefore, since TL/ED1=85.00/25.05=3.39, conditional expression 1 (2.0<[TL/ED1]<5.1) is satisfied. TL1 in conditional expression 2 is 33.76 mm, and TL2 is 29.56 mm. Therefore, since TL1/TL2=33.76/29.56=1.14, conditional expression 2 (0.5<[TL1/TL2]<2.0) is satisfied. AFL in conditional expression 3 is 31.06 mm, and FL1 is 46.46 mm. Therefore, since AFL/FL1=31.06/46.46=0.67, conditional expression 3 (0.35<[AFL/FL1]<1.20) is satisfied. AFL in conditional expression 4 is 31.06 mm, and FL1 is 46.46 mm. Therefore, since FL1/AFL=46.46/31.06=1.50, conditional expression 4 (0.8<[FL1/AFL]<1.8) is satisfied. FL1B in conditional expression 5 is 39.65 mm, and AFL is 31.06 mm. Therefore, since FL1B/AFL=39.65/31.06=1.28, conditional expression 5 (0.8<[FL1B/AFL]<1.6) is satisfied. FL1B in conditional expression 6 is 39.65 mm, and FL1 is 46.46 mm. Therefore, FL1B/FL1=39.65/46.46=0.85, so conditional expression 6 (0.6<[FL1B/FL1]<1.5) is satisfied. In conditional expression 7, FL1 is 46.46 mm, AFL is 31.06 mm, and FL1B is 39.65 mm. Therefore, |(FL1/AFL)-(FL1B/AFL)-(FL1B/FL1)|=|(46.46/31.06)-(39.65/31.06)-(39.65/46. 46)|=|1.50-1.28-0.85|=0.63, so conditional expression 7 (0.4<[|(FL1/AFL)-(FL1B/AFL)-(FL1B/ FL1) | < 1.5) is satisfied.

On the other hand, FIGS. 7(a) and 7(b) show longitudinal aberration diagrams using the imaging magnification as a parameter ("0.000", "0.098") in the large-diameter semi-wide-angle imaging lens C of Reference Example 3. . As shown in Figures 7(a) and (b), it was confirmed that good aberrations, that is, good imaging performance, were obtained whether the imaging magnification was 0.000 or 0.098. can. Note that the large-diameter semi-wide-angle imaging lens C of Reference Example 3 has an F number of F1.24 and satisfies the conditions of F1.1 to F1.5.

Reference example 4

Next, a large-diameter semi-wide-angle imaging lens C according to Reference Example 4 will be described with reference to FIGS. 8 to 10, FIG. 2, and Table 4.

FIG. 8 shows the configuration of a large-diameter semi-wide-angle imaging lens C according to Reference Example 4. Reference example 4 uses two air spaces S1 (ZD5) and S2 (ZD14) as variable intervals for focus adjustment when the shooting distance moves from infinity to a short distance. be. Reference Example 4 illustrates two embodiments.

That is, for imaging magnifications up to approximately 0.1x, one air space S2 (ZD14) is selected as a variable interval for focus adjustment, and the lens groups to be moved are: first front lens group G1f + first rear lens group G1r + A second front lens group G2f, that is, a front moving group that integrates lenses L5, L1, L2, L3, L4, L10, L6, and L7, and a second rear lens group G2r, that is, lenses L8 and L9 that are integrated. A moving group was set up on the rear side.

On the other hand, at imaging magnifications of approximately 0.1x or higher, in order to reduce the aberration fluctuations associated with this, two air spaces S1 (ZD5) and S2 (ZD14) are selected as variable intervals for focus adjustment, and the lens group to be moved is As, a first front lens group G1f, that is, a front moving group that integrates lenses L5, L1, and L2, and a first rear lens group G1r+a second front lens group G2f, that is,
An intermediate moving group that integrates L3, L4, L10, L6, and L7, and a rear moving group that integrates the second rear lens group G2r, that is, lenses L8 and L9, are set.

Other than these points, the other basic configurations are the same as Reference Example 2. In this way, as the variable interval for performing focus adjustment, one of the three focus variable intervals S1, Sm, and S2 is selected for photographing magnifications up to about 0.1x, where fluctuations in aberrations are relatively small. The two front and rear lens groups separated by this, ie, the first lens group G1 and the second lens group G2, as in other reference examples except reference example 4, may be moved on the optical axis Dc. On the other hand, at imaging magnifications of approximately 0.1x or higher, where fluctuations in aberrations become large, all three focus variable intervals S1, Sm, and S2 are used, or any two or more are selected. What is necessary is to move the lens groups G1f, G1r, . . . before and after the separation. Thereby, aberration fluctuations can be reduced by increasing the effect of correcting aberrations.

In FIG. 8, arrows Fma, Fmb, and Fmc indicate that the movement group can be moved before and after the first air space S1 and the second air space S2. In addition, in the configuration of Reference Example 4 (Figure 8), the same parts and functional parts as Reference Example 1 (Figure 1) and Reference Example 2 (Figure 4) are given the same reference numerals to clearly identify the configuration. At the same time, detailed explanation thereof will be omitted.

Table 4 shows lens data for the entire lens system of the large-diameter semi-wide-angle imaging lens C of Reference Example 4. The large-diameter semi-wide-angle imaging lens C at the infinite object point has a focal length of 36.00 mm, an F number of 1.24, and a half angle of view of 31.25 degrees. Also shown is data (focus variable interval) in which the imaging magnification is a parameter ("0.000", "0.104", "0.149", "0.197").

As shown in Table 4 and FIG. 2, TL in Conditional Expression 1 described above is 85.00 mm, and ED1 is 29.03 mm. Therefore, since TL/ED1=85.00/29.03=2.93, conditional expression 1 (2.0<[TL/ED1]<5.1) is satisfied. TL1 in conditional expression 2 is 36.41 mm, and TL2 is 26.62 mm. Therefore, since TL1/TL2=36.41/26.62=1.37, conditional expression 2 (0.5<[TL1/TL2]<2.0) is satisfied. AFL in conditional expression 3 is 36.00 mm, and FL1 is 39.62 mm. Therefore, since AFL/FL1=36.00/39.62=0.91, conditional expression 3 (0.35<[AFL/FL1]<1.20) is satisfied. AFL in conditional expression 4 is 36.00 mm, and FL1 is 39.62 mm. Therefore, FL1/AFL=39.62/36.00=1.10, so conditional expression 4 (0.8<[FL1/AFL]<1.8) is satisfied. FL1B in conditional expression 5 is 42.00 mm, and AFL is 36.00 mm. Therefore, since FL1B/AFL=42.00/36.00=1.17, conditional expression 5 (0.8<[FL1B/AFL]<1.6) is satisfied. FL1B in conditional expression 6 is 42.00 mm, and FL1 is 39.62 mm. Therefore, since FL1B/FL1=42.00/39.62=1.06, conditional expression 6 (0.6<[FL1B/FL1]<1.5) is satisfied. In conditional expression 7, FL1 is 39.62 mm, AFL is 36.00 mm, and FL1B is 42.00 mm. Therefore, |(FL1/AFL)-(FL1B/AFL)-(FL1B/FL1)|=|(39.62/36.00)-(39.92/36.00)-(39.92/40. 00)|=|1.10-1.17-1.06|=1.13, so conditional expression 7(0.4<[|(FL1/AFL)-(FL1B/AFL)-(FL1B/ FL1) | < 1.5) is satisfied.

On the other hand, FIGS. 9(a) and 10(b)-(d) show the imaging magnification of the large-diameter semi-wide-angle imaging lens C of Reference Example 4 with parameters ("0.000", "0.104", " 0.149", "0.197") is shown. As shown in FIG. 9(a) and FIG. 10(b)-(d), when the imaging magnification is "0.000", "0.104", "0.149", or "0.197" It can be confirmed that good aberrations, that is, good imaging performance can be obtained even with the above conditions. Note that the large-diameter semi-wide-angle imaging lens C of Reference Example 4 has an F number of F1.24 and satisfies the conditions of F1.1 to F1.5.

Next, the large-diameter semi-wide-angle imaging lens C according to Example 1 will be described with reference to FIGS. 11, 12, 2, and Table 5.

FIG. 10 shows the configuration of a large-diameter semi-wide-angle imaging lens C according to the first embodiment. In Example 1, when configuring the imaging optical system GA, the basic configuration of the first partially symmetrical lens group G1s and the second partially symmetrical lens group G2s is the same as that of Reference Example 1, but the first partially symmetrical lens group When adding one lens to each of the lens group G1s and the second partially symmetrical lens group G2s, one positive lens L5 is added to the image IMG side of the first partially symmetrical lens group G1s to form the first lens. In addition to forming the lens group G1, one positive lens L10 is added to the image IMG side of the second partially symmetrical lens group G2s to form the second lens group G2.

In this case, a positive meniscus lens L5p having an aspherical surface curved toward the object OBJ was used as the positive lens L5, and a biconvex lens L10p having an aspherical surface was used as the positive lens L10. Further, in Example 1, when constructing the second partially symmetrical lens group G2s, the positive lens L8 and the negative lens L9 are constructed by a cemented lens Ej that is a cemented lens.

Then, according to conditional expression 2 described above, the distance on the optical axis from the object OBJ side surface (i = 1) of lens L1 closest to the object OBJ side to the aperture stop STO is TL1, and the distance from the aperture stop STO to the closest image IMG When the distance on the optical axis from the image of the side lens to the IMG side surface (i=17) is TL2, 0.5<[TL1/TL2]<2.0 is satisfied, and the focal length of the entire system is AFL. , and when the focal length of the first lens group is FL1,

0.35<[AFL/FL1]<1.20... (Conditional expression 3)
The system was configured to meet the following conditions.

In conditional expression 3, if [AFL/FL1] is less than "0.35", it is necessary to increase the F number in order to avoid deterioration of aberrations, making it difficult to achieve a large aperture. On the other hand, if [AFL/FL1] exceeds "1.20", although aberration correction for increasing the aperture can be advantageously performed, the overall length of the lens becomes long, making it impossible to achieve miniaturization. Furthermore, when the power of the first lens group G1 exceeds "1.20" in conditional expression 3, the power of the first lens group G1 becomes stronger with respect to the entire system, so the lens diameter of the first lens group G1 is becomes larger, and it becomes difficult to correct the comatic aberration that occurs along with this. On the other hand, if it is less than "0.35", the power of the first lens group G1 becomes weak, and the lens diameter of the second lens group G2 becomes large, making it difficult to attach it to the camera body.

Therefore, if the configuration satisfies these conditions, the power of the first lens group G1 can be ensured appropriately, and the power of the positive lens L10 located closest to the image IMG side of the second lens group G2 and this positive lens L10 can be Since an air lens can be formed by the opposing negative lens L9, it is possible to easily increase the diameter of the lens while reducing the F number and ensuring good aberration (coma aberration). In addition, since the lens diameter of the second lens group G2 can be reduced and the overall length can be shortened, it can also contribute to miniaturization.

Except for the above points, other basic configurations are the same as those of Reference Example 1. Therefore, the first air space S1 between the positive lenses L2 and L3, the intermediate air space Sm where the aperture stop STO exists, and the second air space S2 between the positive lenses L7 and L8 serve as variable intervals for focus adjustment. The selection points are also the same as in Reference Example 1. Therefore, in the configuration of Example 1 (FIG. 11), the same parts and functional parts as those in Reference Example 1 (FIG. 1) are given the same reference numerals to clarify the configuration and provide detailed explanations thereof. is omitted.

Table 5 shows lens data of the entire lens system in the large-diameter semi-wide-angle imaging lens C of Example 1. The large-diameter semi-wide-angle imaging lens C at the infinite object point has a focal length of 40.00 mm, an F number of 1.45, and a half angle of view of 28.65 degrees. Also shown is data (focus variable interval) in which the imaging magnification is a parameter ("0.000", "0.100").

As shown in Table 5 and FIG. 2, TL in Conditional Expression 1 described above is 77.00 mm, and ED1 is 27.61 mm. Therefore, since TL/ED1=77.00/27.61=2.79, conditional expression 1 (2.0<[TL/ED1]<5.1) is satisfied. TL1 in conditional expression 2 is 23.13 mm, and TL2 is 29.46 mm. Therefore, since TL1/TL2=23.13/29.46=0.79, conditional expression 2 (0.5<[TL1/TL2]<2.0) is satisfied. AFL in conditional expression 3 is 40.00 mm, and FL1 is 82.55 mm. Therefore, since AFL/FL1=40.00/82.55=0.48, conditional expression 3 (0.35<[AFL/FL1]<1.20) is satisfied. Note that conditional expression 4-7 is not applied to Example 1-3.

On the other hand, FIGS. 12(a) and 12(b) show longitudinal aberration diagrams using the imaging magnification as a parameter ("0.000", "0.100") in the large-diameter semi-wide-angle imaging lens C of Example 1. . As shown in Figures 12(a) and (b), it was confirmed that good aberrations, that is, good imaging performance, were obtained regardless of the imaging magnification of 0.000 or 0.100. can. Note that the large-diameter semi-wide-angle imaging lens C of Example 1 has an F number of F1.45 and satisfies the conditions of F1.1 to F1.5.

Next, a large-diameter semi-wide-angle imaging lens C according to Example 2 will be described with reference to FIGS. 13, 14, 2, and Table 6.

FIG. 13 shows the configuration of a large-diameter semi-wide-angle imaging lens C according to the second embodiment. Embodiment 2 has the same basic configuration as Embodiment 1, but the difference is that in configuring the first lens group G1, in Embodiment 1, negative lens L1 and positive lens L2, and positive lens L3 and negative lens are used. L4 was constructed by cemented lenses Ej and Ej, respectively, but in Example 2, negative lens L1, positive lens L2, and positive lens L3 were constructed by single lenses Es, Es, and Es, respectively, and negative lens L4 and positive lens L5 The difference is that the negative lens L1 is composed of a cemented lens Ej, and the negative lens L1 is composed of a biconcave lens L1c having an aspherical surface. Note that the configuration of the second lens group G2 in the second embodiment is the same as that in the first embodiment.

Other than the above points, other basic configurations are the same as in the first embodiment. Therefore, in the configuration of Example 2 (FIG. 13), the same parts and the same functional parts as Example 1 (FIG. 11) are given the same reference numerals to clarify the configuration and provide detailed explanations thereof. is omitted.

Table 6 shows lens data of the entire lens system in the large-diameter semi-wide-angle imaging lens C of Example 2. The large-diameter semi-wide-angle imaging lens C at the infinite object point has a focal length of 37.69 mm, an F number of 1.44, and a half angle of view of 30.11 degrees. Also shown is data (focus variable interval) in which the imaging magnification is a parameter ("0.000", "0.100").

As shown in Table 6 and FIG. 2, TL in Conditional Expression 1 described above is 77.00 mm, and ED1 is 26.18 mm. Therefore, since TL/ED1=77.00/26.18=2.94, conditional expression 1 (2.0<[TL/ED1]<5.1) is satisfied. TL1 in conditional expression 2 is 23.55 mm, and TL2 is 29.58 mm. Therefore, since TL1/TL2=23.55/29.58=0.80, conditional expression 2 (0.5<[TL1/TL2]<2.0) is satisfied. AFL in conditional expression 3 is 37.69 mm, and FL1 is 79.53 mm. Therefore, since AFL/FL1=37.69/79.53=0.47, conditional expression 3 (0.35<[AFL/FL1]<1.20) is satisfied. Note that conditional expression 4-7 is not applied to Example 1-3.

On the other hand, FIGS. 14(a) and 14(b) show longitudinal aberration diagrams using the imaging magnification as a parameter ("0.000", "0.100") in the large-diameter semi-wide-angle imaging lens C of Example 2. . As shown in Figures 14(a) and (b), it was confirmed that good aberrations, that is, good imaging performance, were obtained regardless of the imaging magnification of "0.000" or "0.100". can. Note that the large-diameter semi-wide-angle imaging lens C of Example 2 has an F number of F1.44 and satisfies the conditions of F1.1 to F1.5.

Next, a large-diameter semi-wide-angle imaging lens C according to Example 3 will be described with reference to FIGS. 15, 16, 2, and Table 7.

FIG. 15 shows the configuration of a large-diameter semi-wide-angle imaging lens C according to Example 3. Embodiment 3 has the same basic configuration as Embodiment 2, but the difference is that in configuring the first lens group G1, in Embodiment 2, the negative lens L1 and the positive lens L2 are replaced by single lenses Es and Es. In addition, the negative lens L1 was composed of a biconcave lens L1c having an aspherical surface, but in Example 3, the negative lens L1 and the positive lens L2 were composed of a cemented lens Ej, and the positive lens L3 was composed of a double concave lens L1c having an aspherical surface. The difference is that the lens is configured by a biconvex lens L3p having the following characteristics. Note that the configuration of the second lens group G2 in the third embodiment is the same as that in the first embodiment.

Except for the above points, other basic configurations are the same as in the second embodiment. Therefore, in the configuration of Example 3 (FIG. 15), the same parts and the same functional parts as Example 2 (FIG. 13) are given the same reference numerals to clarify the configuration and provide detailed explanations thereof. is omitted.

Table 7 shows lens data of the entire lens system in the large-diameter semi-wide-angle imaging lens C of Example 3. The large-diameter semi-wide-angle imaging lens C at the infinite object point has a focal length of 38.00 mm, an F number of 1.45, and a half angle of view of 29.92 degrees. Also shown is data (focus variable interval) in which the imaging magnification is a parameter ("0.000", "0.100").

As shown in Table 7 and FIG. 2, TL in Conditional Expression 1 described above is 74.61 mm, and ED1 is 26.22 mm. Therefore, since TL/ED1=74.61/26.22=2.85, conditional expression 1 (2.0<[TL/ED1]<5.1) is satisfied. TL1 in conditional expression 2 is 19.97 mm, and TL2 is 31.53 mm. Therefore, TL1/TL2=19.97/31.53=0.63, which satisfies conditional expression 2B (0.5<[TL1/TL2]<2.0). AFL in conditional expression 3 is 38.00 mm, and FL1 is 79.48 mm. Therefore, since AFL/FL1=38.00/79.48=0.48, conditional expression 3 (0.35<[AFL/FL1]<1.20) is satisfied. Note that conditional expression 4-7 is not applied to Example 1-3.

On the other hand, FIGS. 16(a) and 16(b) show longitudinal aberration diagrams using the imaging magnification as a parameter ("0.000", "0.100") in the large-diameter semi-wide-angle imaging lens C of Example 3. . As shown in Figures 16(a) and (b), it was confirmed that good aberrations, that is, good imaging performance, could be obtained whether the imaging magnification was 0.000 or 0.100. can. Note that the large-diameter semi-wide-angle imaging lens C of Example 3 has an F number of F1.45 and satisfies the conditions of F1.1 to F1.5.

Although preferred embodiments including Examples 1 to 3 have been described in detail above, the present invention is not limited to such embodiments, and the detailed configuration, shape, material, quantity, numerical value, etc. Any changes, additions, or deletions may be made without departing from the gist of the present invention.

For example, it is desirable to provide the imaging optical system GA with at least one cemented lens Ej... which is a negative lens L2... located on the object OBJ side and a positive lens L3... located on the image IMG side. The number is arbitrary, and does not exclude cases where the number is not provided. Furthermore, in the imaging optical system GA, from the object OBJ side, a first partially symmetrical lens group constituted by a biconcave lens L1c (L6c), a biconvex lens L2p (L7p), a biconvex lens L3p (L8p), and a biconcave lens L4c (L9c). Although it is desirable to provide G1s and/or the second partially symmetrical lens group G2s, any form of lens may be used, such as a single-concave lens, a single-convex lens, a meniscus lens, an aspherical lens, etc. On the other hand, the imaging optical system GA is composed of a total of seven elements Es..., Ej..., and from the object OBJ side, a first element Es using a negative lens, a second element using a cemented lens of a negative lens and a positive lens. Ej, second element Ej using a cemented lens of a positive lens and a negative lens, first element Es using an aspherical lens, second element Ej using a cemented lens of a negative lens and a positive lens, using a positive lens. In the case where the first element Es and the first element Es using a negative lens are provided, the refractive index of the positive lens in the cemented lens (Ej) satisfies the condition of being larger than 1.7, and the conditional expression 3 is satisfied. is desirable, but is not limited to this configuration. Similarly, as the imaging optical system GA, the overall power of the first lens group G1 is set to positive, and the overall power of the lens of the first lens group G1 from the first air space S1 to the object OBJ side is set to negative. At the same time, an example of a configuration in which the overall power of the lens from the first air space S1 to the intermediate air space Sm is set to be positive and satisfies all conditions of Conditional Expression 4 to Conditional Expression 7 has been given; however, the present invention is limited to this configuration. This does not exclude configurations that satisfy any one conditional expression or two or more conditions.

The large-diameter semi-wide-angle imaging lens according to the present invention can be used as a dedicated lens or an interchangeable lens for various optical devices, including still image photographing devices such as digital cameras and silver halide cameras, and moving image projection devices such as video cameras and cinema cameras. Available.

1: Large-diameter semi-wide-angle imaging lens, STO: Aperture diaphragm, OBJ: Object, IMG: Image, L1: Lens, L1c (L6c): Biconcave lens, L2: Lens, L2p (L7p): Biconvex lens, L3: Lens, L3p (L8p): Biconvex lens, L4: Lens, L4c (L9c): Biconcave lens, L5: Lens, L5c: Biconcave lens, L6: Lens, L7: Lens, L8: Lens, L9: Lens, L10: Lens, GA : Imaging optical system, G1: First lens group, G1s: First partially symmetrical lens group, G2: Second lens group, G2s: Second partially symmetrical lens group, S1: First air space, S2: Second air space , Sm: Intermediate air space, TL: Distance on the optical axis from the object-side surface of the lens closest to the object to the image plane, TL1: Light from the object-side surface of the lens closest to the object to the aperture stop Distance on the axis, TL2: Distance on the optical axis from the aperture stop to the image side surface of the lens located closest to the image side, AFL: Total system focal length, ED1: Total system focal length/F number, FL1: 1st Focal length of the first lens group, FL1B: Focal length of the lens from the first air space to the intermediate air space, Ej: cemented lens (second element), Es: first element

Claims (5)

A first partially symmetrical lens group arranged on the object side with respect to the aperture stop and having lenses having negative, positive, positive, and negative powers from the object side, and one side in front and behind the first partially symmetrical lens group. a first lens group composed of five lenses including one lens added to the aperture stop, and a lens arranged on the image side with respect to the aperture stop and having negative, positive, positive, and negative powers from the object side. an imaging optical system comprising a second partially symmetrical lens group arranged with a large-diameter semi-wide-angle imaging lens, wherein the power arrangement of the five lenses of the first lens group and the power arrangement of the five lenses of the second lens group are set to be the same, and the first partially symmetrical lens group at least one of a first air space between two successive positive lenses of the above, an intermediate air space in which an aperture stop is arranged, and a second air space between two successive positive lenses of the second partially symmetrical lens group. The air space functions as a variable interval for focus adjustment when the shooting distance moves from infinite to short distance, and when the F number satisfies F1.1 to F1.5 and the object distance is infinite, distance/F number] is ED1, and the distance on the optical axis from the object side surface to the image plane of the lens closest to the object side is TL,
2.0<[TL/ED1]<5.1...(Conditional expression 1)
and one positive lens is added to the image side of the first partially symmetrical lens group to form the first lens group, and one positive lens is added to the image side of the second partially symmetrical lens group. A positive lens is added to constitute the second lens group, and the distance on the optical axis from the object side surface of the lens closest to the object to the aperture stop is TL1, and the image side of the lens closest to the image side from the aperture stop When the distance on the optical axis to the surface of is TL2,
0.5<[TL1/TL2]<2.0...(Conditional expression 2)
When the following conditions are satisfied, and the focal length of the entire system is AFL, and the focal length of the first lens group is FL1,
0.35<[AFL/FL1]<1.20...(Conditional expression 3)
A large-diameter semi-wide-angle imaging lens that satisfies the following conditions. It is characterized in that any one of the first air space, the intermediate air space, and the second air space functions as a variable interval for adjusting the focus when the shooting distance moves from infinity to a short distance. The large-diameter semi-wide-angle imaging lens according to claim 1. 3. The large-diameter semi-wide-angle imaging lens according to claim 1, wherein the first lens group includes a biconcave lens disposed closest to the object side. The large aperture according to any one of claims 1 to 3, wherein the imaging optical system includes at least one cemented lens consisting of a negative lens located on the object side and a positive lens located on the image side. Semi-wide-angle imaging lens. The imaging optical system is characterized in that the imaging optical system includes the first partially symmetrical lens group and/or the second partially symmetrical lens group configured from a biconcave lens, a biconvex lens, a biconvex lens, and a biconcave lens from the object side. The large-diameter semi-wide-angle imaging lens according to any one of Items 1-4.

Images