Optical system

Abstract

To provide an optical system correcting various aberrations such as chromatic aberration by appropriately arranging lens material, regardless of a large aperture ratio while achieving lightweight.SOLUTION: An optical system includes, in order from the object side: a first lens group G1 having negative refractive power; a second lens group G2 moving along an optical axis when focusing from infinity to a close distance; a final lens group GL positioned closest to an image surface; and an aperture diaphragm S between the second lens group G2 and the final lens group GL.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system suitable for lenses used in imaging devices such as still cameras and video cameras, projection devices, etc. In particular, it relates to a technology that achieves lightweight design while effectively correcting various aberrations, even with a large aperture ratio, by appropriately arranging lens materials. [Background technology]

[0002] In recent years, with the trend toward higher pixel counts in digital cameras and the like, there has been a growing demand for high optical performance with strong correction of various aberrations.

[0003] Furthermore, it is desirable to reduce the weight of the focus lens group in order to achieve high-speed and accurate focusing and wobbling drive.

[0004] Therefore, in optical systems that have been proposed in the past, the lens elements from the object side to the aperture stop are fixed during focus drive, and the focus lens group is positioned on the image side of the aperture stop to reduce weight. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7134697 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-009170 Summary of the Invention [Problem to be solved by the invention]

[0006] The optical system described in Patent Document 1 achieves high optical performance with a bright, wide angle of view by appropriately specifying the lens configuration before and after the aperture stop. However, since the lens configuration before and after the aperture stop must be appropriately maintained even during focusing, there is a problem in that the weight of the focus lens group tends to be heavy.

[0007] The optical system described in Patent Document 2 proposes an optical system that has a large aperture ratio while suppressing the weight of the focus lens group. However, it does not adequately correct axial chromatic aberration, lateral chromatic aberration, and sagittal flare. Another issue is that the overall optical length is long, making it prone to becoming bulky.

[0008] The present invention has been made in view of the above-mentioned problems, and aims to provide an optical system that achieves a large aperture ratio while correcting various aberrations such as chromatic aberration and achieving lightweight design by appropriately arranging lens materials. [Means for solving the problem]

[0009] The optical system according to the present invention is characterized by comprising, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 that moves along the optical axis when focusing from infinity to a close distance, and a final lens group GL that is arranged closest to the image plane, with an aperture stop S located between the second lens group G2 and the final lens group GL. [Effects of the Invention]

[0010] According to the optical system of the present invention, by appropriately arranging the lens materials, it is possible to provide an optical system that has a large aperture ratio, corrects various aberrations such as chromatic aberration, and achieves lightweight construction. [Brief explanation of the drawings]

[0011] [Figure 1] Lens cross-sectional view of the optical system of Example 1 at infinity [Figure 2] Longitudinal aberration diagram at infinity for the optical system of Example 1 [Figure 3] Longitudinal aberration diagram of the optical system of Example 1 at a shooting distance of 170 mm [Figure 4] Transverse aberration diagram at infinity of the optical system of Example 1 [Figure 5] Transverse aberration diagram of the optical system of Example 1 at a shooting distance of 170 mm [Figure 6] Lens cross-sectional view of the optical system of Example 2 at infinity [Figure 7]Longitudinal aberration diagram at infinity for the optical system of Example 2 [Figure 8] Longitudinal aberration diagram of the optical system of Example 2 at a shooting distance of 168 mm [Figure 9] Transverse aberration diagram at infinity for the optical system of Example 2 [Figure 10] Transverse aberration diagram of the optical system of Example 2 at a shooting distance of 168 mm [Figure 11] Lens cross-sectional view of the optical system of Example 3 at infinity [Figure 12] Longitudinal aberration diagram at infinity for the optical system of Example 3 [Figure 13] Longitudinal aberration diagram of the optical system of Example 3 at a shooting distance of 166 mm [Figure 14] Transverse aberration diagram at infinity for the optical system of Example 3 [Figure 15] Lateral aberration diagram of the optical system of Example 3 at a shooting distance of 166 mm [Figure 16] Lens cross-sectional view of the optical system of Example 4 at infinity [Figure 17] Longitudinal aberration diagram at infinity for the optical system of Example 4 [Figure 18] Longitudinal aberration diagram of the optical system of Example 4 at a shooting distance of 355 mm [Figure 19] Transverse aberration diagram at infinity for the optical system of Example 4 [Figure 20] Transverse aberration diagram of the optical system of Example 4 at a shooting distance of 355 mm [Figure 21] Lens cross section at infinity of the optical system of Example 5 [Figure 22] Longitudinal aberration diagram at infinity for the optical system of Example 5 [Figure 23] Longitudinal aberration diagram of the optical system of Example 5 at a shooting distance of 165 mm [Figure 24] Transverse aberration diagram at infinity for the optical system of Example 5 [Figure 25] Transverse aberration diagram of the optical system of Example 5 at a shooting distance of 165 mm DETAILED DESCRIPTION OF THE INVENTION

[0012] Examples of the optical system of the present invention will be described in detail below. Note that the following description of the examples is an example of the optical system of the present invention, and the present invention is not limited to the description of the examples within the scope of the gist of the present invention.

[0013] The optical system of the present invention is characterized by having, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 that moves along the optical axis when focusing from infinity to a close distance, and a final lens group GL that is arranged closest to the image plane, with an aperture stop S located between the second lens group G2 and the final lens group GL.

[0014] Generally, the difference between the height of on-axis light rays and the height of off-axis light rays increases the farther away from the aperture stop and the wider the angle of view, and this difference becomes particularly noticeable in lenses that are located closer to the object than the aperture stop. For this reason, in optical systems with wide angles of view, such as the optical system according to the present invention, where the half angle of view exceeds 45 degrees, it is difficult to simultaneously correct both on-axis and off-axis aberrations closer to the object than the aperture stop.

[0015] When correcting off-axial aberrations, particularly field curvature and astigmatism, on the object side of the aperture stop, an effective method is to gently bend the off-axial light beam using a lens element on the object side where the difference between the on-axis and off-axis light ray heights becomes large. However, when this method is used, not only does it tend to increase the number of lens elements on the object side of the aperture stop, but it also increases the overall optical length and the diameter of the lens element closest to the object side, resulting in a significant increase in product weight.

[0016] On the other hand, if various aberrations occurring on the object side of the aperture stop are to be corrected using a separate lens group rather than being reduced, the lens configuration from the aperture stop to the image side becomes important. To cancel out aberrations occurring on the object side of the aperture stop, aberrations of the opposite sign must be generated on the image side of the aperture stop, and the aberrations must be corrected throughout the entire optical system. This requires that the optical system on the image side be enlarged to control aberrations, making it difficult to achieve compactness and weight reduction. Furthermore, when the aberrations that must be corrected on the image side are large and focusing is performed on the image side of the aperture stop, it is necessary to prepare a focus lens group made of multiple lenses that adequately corrects aberrations, making it difficult to secure the necessary space.

[0017] Therefore, in the present invention, by arranging the lenses in the order from closest to the object, a first lens group G1 with negative refractive power and a second lens group G2 that moves during focusing, the first lens group G1 reduces the angle of incidence due to its negative refractive power, making it possible to reduce the angle of incidence of off-axial rays that enter the second lens group G2 while correcting various aberrations within the first lens group G1, and thereby suppressing aberration fluctuations that occur during focusing.

[0018] Furthermore, by disposing an aperture stop S between the second lens group G2 and the final lens group GL, the burden of aberrations in off-axial rays can be appropriately divided between the first lens group G1, which is located on the object side of the aperture stop S, and the final lens group GL, which is located on the image side, and it becomes possible to correct off-axial aberrations while preventing the entire lens from becoming bulky.

[0019] In the optical system of the present invention, the final lens group GL preferably comprises, in order from the object side, a positive lens LP and a negative lens LN. The final lens group GL is positioned so that the difference between the height of on-axis light rays and the height of off-axis light rays is large. By placing the positive lens LP on the object side of the final lens group GL, off-axis light rays, particularly the upper light rays of off-axis light beams, can be strongly bent. This allows the height of light rays incident on the negative lens LN to be lowered, thereby reducing the diameter near the lens mount. By placing the negative lens LN closest to the image plane, the off-axial light rays whose height has been lowered by the positive lens LP can be bent up, thereby shortening the back focus and the overall optical length.

[0020] In the optical system of the present invention, it is preferable that the second lens group G2 moves from the image side to the object side when focusing from infinity to a close distance. By moving the second lens group G2 from the image side to the object side when focusing, flare at close distances is suppressed. Furthermore, since this configuration makes it easy to ensure sufficient light volume, the diameter of the second lens group G2 can be designed to be small, which is advantageous for miniaturization.

[0021] Furthermore, the optical system of the present invention preferably has one or more cemented lenses between the aperture stop S and the final lens group GL, the cemented surface of which faces convexly toward the object side and the refractive index of the medium on the object side being higher than the refractive index of the medium on the image side. By locating one or more cemented lenses, on the image side of the aperture stop S, the cemented surface of which faces convexly toward the object side and the refractive index of the medium on the object side being higher than the refractive index of the medium on the image side, it is possible to suppress various aberrations such as coma and spherical aberration.

[0022] Furthermore, it is preferable that the optical system of the present invention satisfies the following conditional expression: (1)-2.2 < TT / EXP < -1.0 TT: Surface distance from the surface closest to the object in the first lens group G1 to the image plane when focused at infinity EXP: The air-equivalent length on the optical axis from the exit pupil to the image plane when focused at infinity, with the image-side distance being positive and the object-side distance being negative, based on the image plane.

[0023] Conditional formula (1) is a conditional formula for appropriately setting the overall lens length of the optical system and the distance from the exit pupil to the image plane. By satisfying conditional formula (1), it is possible to move the exit pupil position of the optical system closer to the image side, thereby shortening the overall length of the optical system.

[0024] If the lower limit of conditional expression (1) is exceeded and the exit pupil position is moved closer to the image side, it becomes possible to move the exit pupil position of the optical system sufficiently close to the image side, but the outermost angle rays will be strongly diverged, which makes it difficult to ensure sufficient back focus and telecentricity, and is therefore not desirable.

[0025] If the upper limit of conditional expression (1) is exceeded and the position of the exit pupil is moved closer to the object side, the height of off-axial rays in the final lens group GL increases, making it difficult to achieve compactness, which is undesirable.

[0026] Furthermore, it is preferable to set the upper limit of conditional expression (1) to -1.20, as this will enable the effects of the present invention to be more effectively achieved.Furthermore, it is even more preferable to set the upper limit of conditional expression (1) to -1.50, as this will enable the effects of the present invention to be even more effectively achieved.

[0027] Furthermore, it is preferable that the optical system of the present invention has a third lens group G3 having positive refractive power between the second lens group G2 and the aperture stop S, and that the following conditional expression is satisfied: (2) 0.50 < f / f3 < 1.00 f: focal length of the entire optical system when focused at infinity f3: focal length of the third lens group G3 when focused at infinity

[0028] By disposing the third lens group G3, which has positive refractive power, between the second lens group G2 and the aperture stop S, the diameter of the second lens group G2, which moves during focusing, can be reduced, thereby reducing the weight of the moving parts and the outer diameter of the product. In addition, the third lens group G3 has the effect of converging the light beam, making it possible to reduce the diameter of the light beam passing through the aperture stop S.

[0029] It is desirable that no lens groups other than the third lens group G3 exist between the second lens group G2 and the aperture stop S. If any lens group other than the third lens group G3 is included, the overall lens length increases, making it difficult to reduce the outer diameter of the product.

[0030] It is also desirable for the third lens group G3 to have an aspherical lens with positive refractive power. By disposing an aspherical lens in the third lens group G3, where the axial ray height is high, it is possible to effectively suppress spherical aberration. Furthermore, by using an aspherical lens, it is possible to correct spherical aberration while keeping the number of positive lenses in the third lens group G3 small. This reduces the axial length of the third lens group G3, contributing to a reduction in the overall lens length.

[0031] Conditional expression (2) defines the ratio of the focal length of the entire optical system to the focal length of the third lens group G3 when focused at infinity. By satisfying conditional expression (2), it becomes possible to reduce the outer diameter of the product while still being able to correct various aberrations.

[0032] If the refractive power of the third lens group G3 becomes smaller beyond the lower limit of conditional expression (2), the effect of converging the light beam by the third lens group G3 weakens, the angles of incidence of the light beam emerging from the second lens group G2 and the light beam entering the aperture stop S become gentler, and it becomes difficult to reduce the diameter of the light beam passing through the focus lens group and the aperture stop, which is undesirable.

[0033] If the upper limit of conditional expression (2) is exceeded and the refractive power of the third lens group G3 becomes too large, it becomes possible to reduce the diameters of the second lens group G2 and the aperture stop S, but this is not desirable as it results in insufficient correction of spherical aberration and coma.

[0034] Furthermore, it is preferable to set the upper limit of conditional expression (2) to 0.92, as this will enable the effects of the present invention to be more effectively achieved, and it is also preferable to set the lower limit of conditional expression (2) to 0.60, as this will enable the effects of the present invention to be more effectively achieved.

[0035] Furthermore, in the optical system of the present invention, it is preferable that the first lens group G1 comprises, in order from the object side, a front-side first lens group G1A consisting entirely of a negative meniscus lens element having negative refractive power and with its convex surface facing the object side, and a rear-side first lens group G1B having positive refractive power, and that the following conditional expression is satisfied: (3) -30.0 < f1b / f1a < -4.0 f1a: focal length of the first front lens group G1A when focused at infinity f1b: focal length of the first rear lens group G1B when focused at infinity

[0036] The first lens group G1 is composed of a negative front-side first lens group G1A and a positive rear-side first lens group G1B, with the first lens group G1 functioning similarly to a wide-angle converter, achieving a wide angle of view while ensuring sufficient back focus. Of these, the front-side first lens group G1A is composed entirely of negative meniscus lenses with their convex surfaces facing the object side, which is effective in suppressing off-axis aberrations, particularly distortion and astigmatism. Furthermore, the use of an aspherical lens within the front-side first lens group G1A makes it possible to further enhance the correction effect of distortion and astigmatism, making it even more desirable.

[0037] Conditional expression (3) is a conditional expression for appropriately setting the ratio between the focal length of the front-side first lens group G1A and the focal length of the rear-side first lens group G1B. By satisfying conditional expression (3), it is possible to ensure a wide angle of view and a sufficient back focus while appropriately correcting distortion.

[0038] If the upper limit of conditional expression (3) is exceeded and the positive refractive power of the rear first lens group G1B becomes too strong or the negative refractive power of the front first lens group G1A becomes too weak, it becomes impossible to ensure a wide angle of view and a sufficient back focus, which is undesirable.

[0039] If the lower limit of conditional expression (3) is exceeded and the positive refractive power of the rear first lens group G1B becomes weaker or the negative refractive power of the front first lens group G1A becomes stronger, strong negative distortion occurs, which is undesirable.

[0040] It is preferable to set the lower limit of conditional expression (3) to -25.0, as this will enable the effects of the present invention to be more effectively achieved.It is even more preferable to set the lower limit of conditional expression (3) to -18.0, as this will enable the effects of the present invention to be even more effectively achieved.

[0041] Furthermore, setting the upper limit of conditional expression (3) to -4.50 is preferable because it makes it possible to achieve the effects of the present invention more effectively. Furthermore, setting the upper limit of conditional expression (3) to -4.90 or even -6.50 is even more preferable because it makes it possible to achieve the effects of the present invention even more effectively.

[0042] Furthermore, it is preferable that the optical system of the present invention has a rear lens group Gr including a third lens group G3 having positive refractive power and a final lens group GL, and that the following conditional expression is satisfied: (4)0.70 < Br^2 × (1-B2^2) < 1.25 B2: Lateral magnification of the second lens group G2 when focused at infinity Br: Lateral magnification of the rear lens group Gr when focused at infinity

[0043] Conditional expression (4) defines the focus sensitivity of the second lens group G2. Satisfying conditional expression (4) contributes to reducing the overall lens length and the manufacturing error of the second lens group G2.

[0044] If the lower limit of conditional expression (4) is exceeded and the focus sensitivity of the second lens group G2 becomes small, the amount of focus movement increases, making it difficult to reduce the overall lens length.

[0045] Furthermore, if the upper limit of conditional expression (4) is exceeded and the focus sensitivity of the second lens group G2 becomes high, it becomes difficult to ensure the accuracy of the stopping position of the focus lens group during focusing.Furthermore, the decentering sensitivity of the second lens group G2 also increases, which is undesirable because it increases aberration fluctuations due to manufacturing errors.

[0046] It is preferable to set the lower limit of conditional expression (4) to 0.75, as this will enable the effects of the present invention to be more effectively achieved.Moreover, it is even more preferable to set the upper limit of conditional expression (4) to 0.80, as this will enable the effects of the present invention to be even more effectively achieved.

[0047] Furthermore, in the optical system of the present invention, it is preferable that the negative lens LN is an aspherical lens and satisfies the following conditional expression: (5) θR1 <0 (6) θR2 > 0 However, the inclination angle of the lens surface is defined as follows: the angle inclined toward the image plane side with respect to the plane perpendicular to the optical axis is positive, and the angle inclined toward the object side is negative. θR1: The inclination angle of the object side surface R1 of the negative lens LN with respect to the plane perpendicular to the optical axis at the height at which the maximum image height chief ray passes through the R1 surface θR2: The inclination angle of the object-side surface R2 of the negative lens LN with respect to the plane perpendicular to the optical axis at the height at which the maximum image height chief ray passes through the R2 surface

[0048] As mentioned above, the final lens group GL is positioned at a position where the difference between the height of on-axis light rays and the height of off-axis light rays is large. A lens group with such a light ray path makes it possible to perform particularly strong correction of off-axis aberrations. Therefore, by placing an aspherical lens in the final lens group GL, it is possible to effectively correct field curvature and astigmatism, thereby simultaneously achieving compactness and high imaging performance.

[0049] Conditional formula (5) defines the angle of the object-side surface R1 of the negative lens LN with respect to the plane perpendicular to the optical axis at the height through which the chief ray of the maximum image height passes. Conditional formula (6) defines the angle of the image-side surface R2 of the negative lens LN with respect to the plane perpendicular to the optical axis at the height through which the chief ray of the maximum image height passes.

[0050] By satisfying conditional expressions (5) and (6), the negative lens LN becomes an aspherical lens having a biconcave shape at the height where the chief ray of the maximum image height passes. This makes the negative lens LN have a strong negative refractive power at the height where off-axial rays pass, relative to on-axial rays, which is desirable because it makes it possible to effectively correct the aforementioned field curvature and astigmatism. The negative lens LN only needs to have a biconcave shape at the height where the chief ray of the maximum image height passes on both the object-side and image-side surfaces, so the aspherical shape may be a gull-wing shape with an inflection point.

[0051] Furthermore, in the optical system of the present invention, it is preferable that the second lens group G2 has negative refractive power. When a lens group having negative refractive power on the object side of the aperture stop S moves along the optical axis from the image side to the object side, significant negative distortion occurs from infinity to close focus, and the object-side angle of incidence is greatest on the close focus side. By giving the second lens group G2, which is the focus lens group, negative refractive power and ensuring sufficient light intensity on the infinity side where the object-side angle of incidence is small, it becomes easier to cut flare from lower light rays on the close focus side.

[0052] Furthermore, in the optical system of the present invention, it is preferable that all lens groups other than the second lens group G2 are fixed relative to the image plane during focusing. By fixing all lens groups other than the second lens group G2 relative to the image plane during focusing, the number of actuators and drive mechanisms for driving the lens groups can be minimized, which is advantageous for reducing the outer diameter of the product.

[0053] Next, the lens configuration of an example of the optical system of the present invention will be described. In the following description, the lens configuration will be described in order from the object side to the image plane side.

[0054] [Example 1] FIG. 1 is a lens configuration diagram of an optical system according to a first embodiment of the present invention. The optical system according to the first embodiment is composed of, in order from the object side, a first lens group G1 with negative refractive power, a second lens group G2 with negative refractive power, and a rear lens group Gr with positive refractive power. The rear lens group Gr is composed of, in order from the object side, a third lens group G3 with positive refractive power, an aperture stop S, and a final lens group GL closest to the image side. Focusing from infinity to close range is achieved by moving the second lens group G2 from the image side to the object side.

[0055] The first lens group G1 is composed of a front first lens group G1A with negative refractive power and a rear first lens group G1B with positive refractive power. The front first lens group G1A is composed of a negative meniscus lens with aspherical surfaces on both sides and a convex surface facing the object side, and a negative meniscus lens with a convex surface facing the object side. The rear first lens group G1B is composed of a biconcave negative lens and a biconvex positive lens.

[0056] The second lens group G2 is composed of a negative meniscus lens with a convex surface facing the image side.

[0057] The rear lens group Gr is composed of a third lens group G3, an aperture stop S, a cemented lens consisting of a positive meniscus lens with a convex surface facing the image side and a biconcave negative lens, a cemented lens consisting of a negative meniscus lens with a convex surface facing the object side and a positive meniscus lens with a convex surface facing the object side, and a final lens group GL. The third lens group G3 is composed of a biconvex positive lens with aspherical surfaces on both sides, a biconcave negative lens, and a biconvex positive lens. The final lens group GL is composed of a biconvex positive lens LP and a biconcave negative lens LN with aspherical surfaces on both sides.

[0058] [Example 2] 6 is a lens configuration diagram of an optical system according to a second embodiment of the present invention. The optical system according to the second embodiment is composed of, in order from the object side, a first lens group G1 with negative refractive power, a second lens group G2 with negative refractive power, and a rear lens group Gr with positive refractive power. The rear lens group Gr is composed of, in order from the object side, a third lens group G3 with positive refractive power, an aperture stop S, and a final lens group GL closest to the image side. Focusing from infinity to close range is achieved by moving the second lens group G2 from the image side to the object side.

[0059] The first lens group G1 is composed of a front first lens group G1A with negative refractive power and a rear first lens group G1B with positive refractive power. The front first lens group G1A is composed of a negative meniscus lens with aspherical surfaces on both sides and a convex surface facing the object side. The rear first lens group G1B is composed of a biconcave negative lens and a biconvex positive lens.

[0060] The second lens group G2 is composed of a negative meniscus lens with a convex surface facing the image side.

[0061] The rear lens group Gr is composed of a third lens group G3, an aperture stop S, a cemented lens consisting of a positive meniscus lens with a convex surface facing the image side and a biconcave negative lens, a cemented lens consisting of a negative meniscus lens with a convex surface facing the object side and a positive meniscus lens with a convex surface facing the object side, and a final lens group GL. The third lens group G3 is composed of a biconvex positive lens with aspherical surfaces on both sides, a biconcave negative lens, and a biconvex positive lens. The final lens group GL is composed of a biconvex positive lens LP and a biconcave negative lens LN with aspherical surfaces on both sides.

[0062] [Example 3] 11 is a lens configuration diagram of an optical system according to a third embodiment of the present invention. The optical system according to the third embodiment is composed of, in order from the object side, a first lens group G1 with negative refractive power, a second lens group G2 with negative refractive power, and a rear lens group Gr with positive refractive power. The rear lens group Gr is composed of, in order from the object side, a third lens group G3 with positive refractive power, an aperture stop S, and a final lens group GL closest to the image side. Focusing from infinity to close range is achieved by moving the second lens group G2 from the image side to the object side.

[0063] The first lens group G1 is composed of a front first lens group G1A with negative refractive power and a rear first lens group G1B with positive refractive power. The front first lens group G1A is composed of a negative meniscus lens with aspherical surfaces on both sides and a convex surface facing the object side, and a negative meniscus lens with a convex surface facing the object side. The rear first lens group G1B is composed of a cemented lens consisting of a biconcave negative lens and a biconvex positive lens.

[0064] The second lens group G2 is composed of a negative meniscus lens with a convex surface facing the image side.

[0065] The rear lens group Gr is composed of a third lens group G3, an aperture stop S, a cemented lens consisting of a positive meniscus lens with a convex surface facing the image side and a biconcave negative lens, a cemented lens consisting of a negative meniscus lens with a convex surface facing the object side and a biconvex positive lens, and a final lens group GL. The third lens group G3 is composed of a biconvex positive lens with aspherical surfaces on both sides, a biconcave negative lens, and a biconvex positive lens. The final lens group GL is composed of a biconvex positive lens LP and a biconcave negative lens LN with aspherical surfaces on both sides.

[0066] [Example 4] 16 is a lens configuration diagram of an optical system according to a fourth embodiment of the present invention. The optical system according to the fourth embodiment is composed of, in order from the object side, a first lens group G1 with negative refractive power, a second lens group G2 with negative refractive power, and a rear lens group Gr with positive refractive power. The rear lens group Gr is composed of, in order from the object side, a third lens group G3 with positive refractive power, an aperture stop S, and a final lens group GL closest to the image side. Focusing from infinity to close range is achieved by moving the second lens group G2 from the image side to the object side.

[0067] The first lens group G1 is composed of a front first lens group G1A with negative refractive power and a rear first lens group G1B with positive refractive power. The front first lens group G1A is composed of a negative meniscus lens with aspherical surfaces on both sides and a convex surface facing the object side, and a negative meniscus lens with a convex surface facing the object side. The rear first lens group G1B is composed of a biconcave negative lens and a biconvex positive lens.

[0068] The second lens group G2 is composed of a negative meniscus lens with a convex surface facing the image side.

[0069] The rear lens group Gr is composed of a third lens group G3, an aperture stop S, a cemented lens consisting of a positive meniscus lens with a convex surface facing the image side and a biconcave negative lens, a cemented lens consisting of a negative meniscus lens with a convex surface facing the object side and a positive meniscus lens with a convex surface facing the object side, and a final lens group GL. The third lens group G3 is composed of a biconvex positive lens with aspherical surfaces on both sides, a biconcave negative lens, and a biconvex positive lens. The final lens group GL is composed of a biconvex positive lens LP and a biaspherical negative lens LN with a concave surface on the object side and a gull-wing shape on the image side.

[0070] [Example 5] 21 is a lens configuration diagram of an optical system according to a fifth embodiment of the present invention. The optical system according to the fifth embodiment is composed of, in order from the object side, a first lens group G1 with negative refractive power, a second lens group G2 with negative refractive power, and a rear lens group Gr with positive refractive power. The rear lens group is composed of, in order from the object side, a third lens group G3 with positive refractive power, an aperture stop S, and a final lens group GL closest to the image side. Focusing from infinity to close range is achieved by moving the second lens group G2 from the image side to the object side.

[0071] The first lens group G1 is composed of a front first lens group G1A with negative refractive power and a rear first lens group G1B with positive refractive power. The front first lens group G1A is composed of a negative meniscus lens with aspherical surfaces on both sides and a convex surface facing the object side, and a negative meniscus lens with a convex surface facing the object side. The rear first lens group G1B is composed of a biconcave negative lens and a biconvex positive lens.

[0072] The second lens group G2 is composed of a negative meniscus lens with a convex surface facing the image side.

[0073] The rear lens group Gr is composed of a third lens group G3, an aperture stop S, a cemented lens consisting of a positive meniscus lens with a convex surface facing the image side and a biconcave negative lens, a cemented lens consisting of a negative meniscus lens with a convex surface facing the object side and a biconvex positive lens, and a final lens group GL. The third lens group G3 is composed of a biconvex positive lens with aspherical surfaces on both sides, a biconcave negative lens, and a biconvex positive lens. The final lens group GL is composed of a biconvex positive lens LP and a biconcave negative lens LN with aspherical surfaces on both sides.

[0074] Specific numerical data for each of the above-described examples of the optical system of the present invention will be shown below.

[0075] In [Surface Data], the surface number is the lens surface or aperture stop number counted from the object side, r is the radius of curvature of each surface, d is the spacing between surfaces, nd is the refractive index for the d-line (wavelength 587.56 nm), and vd is the Abbe number for the d-line.

[0076] An asterisk (*) next to a surface number indicates that the lens surface is aspherical, and BF represents the back focal length.

[0077] The (diaphragm) next to the surface number indicates that an aperture diaphragm is located at that position. The radius of curvature for the plane or aperture diaphragm is marked as ∞ (infinity).

[0078] [Aspherical Data] shows the values ​​of each coefficient that determines the aspherical shape of lens surfaces marked with an * in [Surface Data]. The shape of an aspherical surface is determined by the following equation, where y is the displacement from the optical axis in a direction perpendicular to the optical axis, z is the displacement (sag) from the intersection of the aspherical surface and the optical axis in the direction of the optical axis, r is the radius of curvature of the reference sphere, K is the Conic coefficient, and A4, A6, A8, and A18 are the aspherical coefficients of the 4th, 6th, 8th, and 18th orders, respectively. TIFF2025186709000002.tif14170

[0079] [Various Data] shows values ​​such as focal length at each shooting distance and in focus state.

[0080] [Variable Distance Data] shows the variable distance and BF values ​​for each shooting distance and focus state.

[0081] [Lens Group Data] shows the surface number of each lens group closest to the object and the composite focal length of the entire group.

[0082] In addition, for all of the values ​​of the following specifications, the focal length f, radius of curvature r, lens surface spacing d, and other length units are given in millimeters (mm) unless otherwise specified; however, this is not a limitation, as optical systems can achieve equivalent optical performance with proportional magnification and proportional reduction.

[0083] In the aberration diagrams corresponding to the respective examples, d, g, and C represent the d-line, g-line, and C-line, respectively, and ΔS and ΔM represent the sagittal image surface and meridional image surface, respectively.

[0084] Numerical Example 1 Unit: mm [Face Data] Surface number rd nd vd Object surface ∞ (d0) 1* 51.0090 1.2000 1.69350 53.20 2* 17.0037 3.1783 3 28.0382 1.0000 1.61800 63.40 4 13.5087 9.6254 5 -30.6094 1.0000 1.59282 68.62 6 77.6748 0.1500 7 37.5738 4.0291 1.94594 17.98 8 -105.7421 (d8) 9 -21.7200 1.0000 1.90110 27.06 10 -60.3791 (d10) 11* 35.7924 4.0664 1.80610 40.73 12* -70.4603 0.4255 13 -770.8464 1.0000 1.69895 30.05 14 77.6725 0.1500 15 41.4071 5.7164 1.75500 52.32 16 -33.0901 1.4000 17 (Aperture) ∞ 4.7714 18 -79.7342 4.9414 1.69350 50.81 19 -13.6448 0.9500 1.94594 17.98 20 56.4882 0.4091 21 25.5583 0.9500 1.84666 23.84 22 15.1416 4.4957 1.59282 68.62 23 141.0284 1.0066 24 37.1800 5.0236 1.98612 16.48 25 -37.1800 3.0971 26* -400.0000 1.0000 1.80610 40.73 27* 127.8500 (BF) Image plane ∞ [Aspherical data] 1st floor 2nd floor 11th floor 12th floor 26th floor K 0.00000 -1.00000 0.00000 0.00000 0.00000 A4 1.31560E-05 1.68730E-05 -1.08825E-05 1.72766E-05 -3.20873E-05 A6 -6.19834E-08 -8.66163E-08 2.53703E-07 2.39932E-07 2.57014E-07 A8 3.83875E-10 8.25356E-10 -6.43577E-09 -5.96424E-09 -2.63031E-09 A10 -1.43272E-12 -5.71469E-12 9.52718E-11 8.61358E-11 7.07714E-13 A12 2.94648E-15 2.73868E-14 -7.79452E-13 -6.74993E-13 5.06286E-14 A14 -2.49140E-18 -9.25046E-17 3.01436E-15 2.43764E-15 -1.01483E-16 A16 0.00000E+00 2.02761E-19 -4.35900E-18 -3.18931E-18 0.00000E+00 A18 0.00000E+00 -2.14912E-22 0.00000E+00 0.00000E+00 0.00000E+00 27 sides K 0.00000 A4 2.15722E-05 A6 3.22870E-07 A8 -1.31472E-09 A10 -1.44838E-11 A12 1.45826E-13 A14 -3.58030E-16 A16 0.00000E+00 A18 0.00000E+00 [Various data] INF 170mm Focal length 12.33 11.75 F-number 1.46 1.46 Full angle of view 2ω 103.29 105.89 Image height Y 14.20 14.20 Lens length 85.36 85.36 [Variable Interval Data] INF 170mm d0 ∞ 85.0203 d8 6.3767 4.8808 d10 1.8000 3.2959 BF 16.5939 16.5939 [Lens group data] Group Starting plane Focal length G1 1 -26.15 G2 9 -38.11 G3 11 17.04 GL 24 22.22 G1A 1 -19.09 G1B 5 131.40 Group 11 20.44

[0085] Numerical Example 2 Unit: mm [Face Data] Surface number rd nd vd Object surface ∞ (d0) 1* 306.2592 1.0000 1.59271 66.97 2* 16.0000 11.1494 3 -26.9779 1.0000 1.49700 81.61 4 45.4526 0.8208 5 44.4476 3.9437 1.94594 17.98 6 -101.0893 (d6) 7 -18.2719 1.0000 1.80809 22.76 8 -48.1020 (d8) 9* 36.5372 4.7903 1.80610 40.73 10* -42.5784 0.1500 11 -111.6779 1.0000 1.58144 40.89 12 121.2362 0.1500 13 44.5649 5.0706 1.76385 48.49 14 -40.2168 3.3820 15 (Aperture) ∞ 2.3509 16 -43.3761 3.8864 1.72916 54.54 17 -15.2057 0.9500 1.94594 17.98 18 57.8564 2.2700 19 25.6742 0.9500 1.84666 23.84 20 14.9876 4.8944 1.59282 68.62 21 215.2149 0.5287 22 35.3360 4.9209 1.94594 17.98 23 -37.7209 3.9554 24* -300.0000 0.9000 1.80610 40.73 25* 84.7180 (BF) Image plane ∞ [Aspherical data] 1st page 2nd page 9th page 10th page 24th page K 0.00000 -1.00000 0.00000 0.00000 0.00000 A4 2.85811E-05 2.97514E-05 -1.69015E-05 9.43241E-06 -3.89483E-05 A6 -1.76360E-07 -1.49309E-07 1.60716E-07 1.49179E-07 -7.11162E-07 A8 1.00261E-09 1.41934E-09 -4.42193E-09 -4.35539E-09 8.39779E-09 A10 -3.29730E-12 -1.55128E-11 7.30769E-11 6.86979E-11 -5.27984E-11 A12 5.87430E-15 1.38170E-13 -6.48984E-13 -5.73786E-13 1.83008E-13 A14 -4.22567E-18 -6.42806E-16 2.78627E-15 2.31917E-15 -2.45719E-16 A16 0.00000E+00 1.18870E-18 -4.48918E-18 -3.53084E-18 0.00000E+00 A18 0.00000E+00 -4.78462E-22 0.00000E+00 0.00000E+00 0.00000E+00 25 sides K 0.00000 A4 2.50629E-05 A6 -7.28358E-07 A8 1.09050E-08 A10 -8.31975E-11 A12 3.36311E-13 A14 -5.49777E-16 A16 0.00000E+00 A18 0.00000E+00 [Various data] INF 168mm Focal length 14.58 13.65 F-number 1.46 1.46 Full angle of view 2ω 93.79 97.67 Image height Y 14.20 14.20 Lens length 83.38 83.38 [Variable Interval Data] INF 168mm d0 ∞ 85.0203 d6 6.3937 4.4314 d8 1.5000 3.4623 BF 16.4276 16.4276 [Lens group data] Group Starting plane Focal length G1 1 -33.65 G2 7 -37.02 G3 9 16.41 GL 22 24.14 G1A 1 -28.52 G1B 3 415.26 Gr 9 20.77

[0086] Numerical Example 3 Unit: mm [Face Data] Surface number rd nd vd Object surface ∞ (d0) 1* 61.9033 1.0000 1.69350 53.20 2* 13.1591 3.3649 3 18.6623 1.0000 1.59410 60.47 4 13.3187 8.4108 5 -36.7756 1.0000 1.59282 68.62 6 25.4611 4.6367 1.94594 17.98 7 -104.2540 (d7) 8 -19.4250 1.0000 1.90110 27.06 9 -73.9152 (d9) 10* 29.6712 4.7206 1.80610 40.73 11* -31.3770 0.1500 12 -75.1313 1.0000 1.69895 30.05 13 337.5237 0.1500 14 52.7050 5.0666 1.75500 52.32 15 -35.4377 1.0000 16 (Aperture) ∞ 3.7802 17 -60.1910 5.6504 1.71700 47.98 18 -12.2436 0.9500 1.94594 17.98 19 36.1977 0.1500 20 21.4166 0.9500 1.84666 23.84 21 13.3465 6.0173 1.61800 63.40 22 -142.9590 1.1081 23 30.4943 5.5039 1.98612 16.48 24 -33.0934 0.5693 25* -53.9991 1.0000 1.80610 40.73 26* 499.1257 (BF) Image plane ∞ [Aspherical data] 1st page 2nd page 10th page 11th page 25th page K 0.00000 -1.00000 0.00000 0.00000 0.00000 A4 2.20013E-05 4.00246E-05 -2.43672E-05 1.28801E-05 1.95248E-04 A6 -9.75959E-08 -7.03487E-08 2.12140E-07 2.49763E-07 -1.89983E-06 A8 4.82992E-10 1.58297E-09 -4.50211E-09 -6.34849E-09 1.08107E-09 A10 -1.36568E-12 -1.25462E-11 6.76590E-11 8.43606E-11 2.88436E-11 A12 1.98050E-15 7.43533E-14 -6.74712E-13 -4.99744E-13 8.32482E-14 A14 -1.16572E-18 -8.11907E-17 4.01722E-15 2.96105E-16 -1.21183E-15 A16 0.00000E+00 -8.06533E-19 -1.28900E-17 3.71614E-18 0.00000E+00 A18 0.00000E+00 1.88065E-21 0.00000E+00 0.00000E+00 0.00000E+00 26 sides K 0.00000 A4 2.67068E-04 A6 -1.50901E-06 A8 -2.67669E-09 A10 6.71912E-11 A12 -2.02724E-13 A14 -2.65012E-16 A16 0.00000E+00 A18 0.00000E+00 [Various data] INF 166mm Focal length 10.67 10.29 F-number 1.46 1.46 Full angle of view 2ω 111.30 113.64 Image height Y 14.20 14.20 Lens length 81.35 81.35 [Variable Interval Data] INF 166mm d0 ∞ 85.0203 d7 5.6333 4.6634 d9 1.5000 2.4699 BF 16.0358 16.0358 [Lens group data] Group Starting plane Focal length G1 1 -23.61 G2 8 -29.50 G3 10 14.48 GL 23 22.22 G1A 1 -17.94 G1B 5 140.84 Gr 10 19.69

[0087] Numerical Example 4 Unit: mm [Face Data] Surface number rd nd vd Object surface ∞ (d0) 1* 92.2523 1.3000 1.69350 53.20 2* 28.8150 7.8107 3 53.9448 1.3000 1.61800 63.40 4 28.5990 18.1097 5 -51.7858 4.0000 1.59282 68.62 6 360.8981 0.9547 7 92.0552 9.0000 1.94594 17.98 8 -126.2337 (d8) 9 -44.5022 3.6723 1.85883 30.00 10 -129.1758 (d10) 11* 47.5243 6.7500 1.80610 40.73 12* -76.8746 3.9406 13 -97.9762 1.2000 1.69895 30.05 14 78.8121 1.0051 15 88.8891 3.9540 1.75500 52.32 16 -75.8032 5.2595 17 (Aperture) ∞ 10.0821 18 -273.5868 4.3501 1.71700 47.98 19 -24.4974 1.0000 1.94594 17.98 20 73.6513 0.1500 21 35.2572 1.0000 1.85896 22.73 22 24.0827 5.5469 1.59282 68.62 23 392.1620 6.8773 24 52.8787 8.6221 1.98612 16.48 25 -68.3617 4.2447 26* -39.7336 2.6669 1.80610 40.73 27* -96.5353 (BF) Image plane ∞ [Aspherical data] 1st floor 2nd floor 11th floor 12th floor 26th floor K 0.00000 -1.00000 0.00000 0.00000 0.00000 A4 2.86494E-06 4.76453E-06 7.80014E-08 4.51624E-06 2.92444E-05 A6 -3.49172E-09 -1.22529E-09 1.43401E-08 1.33306E-08 -6.48243E-08 A8 4.27653E-12 4.76754E-12 -4.89073E-11 -1.50770E-11 -9.86470E-12 A10 -2.83171E-15 -1.29722E-14 7.44655E-13 3.79382E-13 1.96020E-13 A12 5.50366E-19 3.24181E-17 -3.46056E-15 -1.51648E-15 -2.11654E-16 A14 6.46668E-23 -2.05564E-20 9.86156E-18 6.02080E-18 -3.01691E-20 A16 0.00000E+00 -3.46375E-23 -4.09931E-21 2.11385E-22 0.00000E+00 A18 0.00000E+00 3.13417E-26 0.00000E+00 0.00000E+00 0.00000E+00 27 sides K 0.00000 A4 3.72227E-05 A6 -5.05387E-08 A8 -1.67101E-11 A10 1.17735E-13 A12 -2.22669E-17 A14 -1.71307E-19 A16 0.00000E+00 A18 0.00000E+00 [Various data] INF 355mm Focal length 23.49 22.46 F-number 2.20 2.20 Full angle of view 2ω 103.71 106.06 Image height Y 27.39 27.39 Lens length 157.04 157.04 [Variable Interval Data] INF 355mm d0 ∞ 197.7670 d8 12.5186 9.6756 d10 1.8000 4.6430 BF 29.9233 29.9233 [Lens group data] Group Starting plane Focal length G1 1 -60.80 G2 9 -80.67 G3 11 35.7551 GL 24 44.7337 G1A 1 -35.8829 G1B 5 183.4814 Gr 11 40.5793

[0088] Numerical Example 5 Unit: mm [Face Data] Surface number rd nd vd Object surface ∞ (d0) 1* 73.7430 1.2000 1.69350 53.20 2* 16.4848 0.6059 3 17.1623 1.0000 1.61800 63.40 4 12.1543 10.6596 5 -30.9373 1.0000 1.59282 68.62 6 39.6952 0.1500 7 31.7701 4.2303 1.94594 17.98 8 -111.2827 (d8) 9 -21.7464 1.0000 1.90110 27.06 10 -74.0733 (d10) 11* 32.9508 4.1226 1.80610 40.73 12* -59.0880 0.1500 13 -9664.6324 1.0000 1.68960 31.14 14 67.3955 0.1500 15 36.5569 5.2035 1.75500 52.32 16 -34.1545 1.4000 17 (Aperture) ∞ 3.7477 18 -68.9407 4.3808 1.69350 50.81 19 -13.4053 0.9500 1.94594 17.98 20 54.2421 0.8715 21 24.8707 0.9500 1.84666 23.84 22 14.0169 5.4157 1.59282 68.62 23 -250.0959 0.1500 24 33.6474 5.1220 1.98612 16.48 25 -34.4555 2.4905 26* -400.0000 1.0000 1.80610 40.73 27* 42.3261 (BF) Image plane ∞ [Aspherical data] 1st floor 2nd floor 11th floor 12th floor 26th floor K 0.00000 -1.00000 0.00000 0.00000 0.00000 A4 2.61987E-05 2.77667E-05 -2.26553E-05 1.09896E-05 -7.48544E-05 A6 -1.00041E-07 -8.99777E-08 2.31793E-07 2.08557E-07 4.29889E-07 A8 4.14494E-10 7.23699E-10 -6.02988E-09 -5.97925E-09 -5.75434E-09 A10 -1.30369E-12 -6.34484E-12 8.61474E-11 8.77406E-11 2.62865E-11 A12 2.60088E-15 3.52536E-14 -6.86851E-13 -6.97869E-13 4.14381E-15 A14 -2.21632E-18 -1.64187E-16 2.65112E-15 2.64649E-15 -1.43120E-16 A16 0.00000E+00 5.93044E-19 -3.87050E-18 -3.73121E-18 0.00000E+00 A18 0.00000E+00 -9.34423E-22 0.00000E+00 0.00000E+00 0.00000E+00 27 sides K 0.00000 A4 -3.25629E-06 A6 6.86364E-07 A8 -8.18289E-09 A10 5.78391E-11 A12 -2.27442E-13 A14 3.44025E-16 A16 0.00000E+00 A18 0.00000E+00 [Various data] INF 165mm Focal length 12.17 11.53 F-number 1.46 1.46 Full angle of view 2ω 103.96 106.55 Image height Y 14.20 14.20 Lens length 80.41 80.41 [Variable Interval Data] INF 165mm d0 ∞ 85.0203 d8 6.2049 4.8303 d10 1.8000 3.1747 BF 15.4539 15.4539 [Lens group data] Group Starting plane Focal length G1 1 -26.11 G2 9 -34.47 G3 11 15.663 GL 24 25.1304 G1A 1 -21.1482 G1B 5 211.4237 Gr 11 17.9925

[0089] Also shown is a list of values ​​corresponding to the conditional expressions in each of these embodiments.

[0090] [Table 1] [Explanation of symbols]

[0091] G1 First lens group G2 Second lens group G3 3rd lens group GL final lens group G1A Front first lens group G1B Rear first lens group Gr rear lens group LP positive lens LN negative lens S aperture stop I image plane CC line (wavelength λ=656.3nm) dd line (wavelength λ=587.6nm) GG line (wavelength λ=435.8nm)

Claims

1. An optical system comprising, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 that moves along the optical axis when focusing from infinity to a close distance, and a final lens group GL that is arranged closest to the image plane, with an aperture stop S between the second lens group G2 and the final lens group GL.

2. 2. The optical system according to claim 1, wherein the final lens group GL is composed of a positive lens LP and a negative lens LN arranged in this order from the object side.

3. 2. The optical system according to claim 1, wherein the second lens group G2 moves from the image side to the object side along the optical axis when focusing from infinity to a close distance.

4. 2. The optical system according to claim 1, further comprising one or more cemented lenses between the aperture stop S and the final lens group GL, the cemented surface of which is convex toward the object side and the refractive index of the medium on the object side is higher than the refractive index of the medium on the image plane side.

5. 2. The optical system according to claim 1, wherein the following condition is satisfied: (1) -2.2 < TT / EXP < -1.0 TT: the surface from the surface of the first lens group G1 closest to the object to the image plane when focused at infinity interval EXP: The air-equivalent length on the optical axis from the exit pupil to the image plane when focused at infinity, with the image-side distance being positive and the object-side distance being negative, based on the image plane.

6. 2. The optical system according to claim 1, further comprising a third lens group G3 having a positive refractive power between said second lens group G2 and said aperture stop S, and satisfying the following condition: 1<G<1 / G<2 / ... (2) 0.50 < f / f3 < 1.00 f: focal length of the entire optical system when focused at infinity f3: focal length of the third lens group G3 when focused at infinity

7. 2. The optical system according to claim 1, wherein the first lens group G1 comprises, in order from the object side, a front-side first lens group G1A consisting solely of a negative meniscus lens having negative refractive power and a convex surface facing the object side, and a rear-side first lens group G1B having positive refractive power, and wherein the following conditional expression is satisfied: (3) -30.0 < f1b / f1a < -4.0 f1a: focal length of the front first lens group G1A when focused at infinity f1b: focal length of the rear first lens group G1B when focused at infinity

8. 2. The optical system according to claim 1, further comprising a rear lens group Gr, the rear lens group Gr including a third lens group G3 having positive refractive power and the final lens group GL, and satisfying the following conditional expression: (4) 0.70 < Br^2 × (1-B2^2) < 1.25 B2: lateral magnification of the second lens group G2 when focused at infinity Br: lateral magnification of the rear lens group Gr when focused at infinity

9. 3. The optical system according to claim 2, wherein the negative lens LN is an aspherical lens and satisfies the following condition: (5) θR1 < 0 (6) θR2>0 However, the inclination angle of the lens surface is defined as follows: the angle inclined toward the image plane side with respect to the plane perpendicular to the optical axis is positive, and the angle inclined toward the object side is negative. θR1: the inclination angle of the object side surface R1 of the negative lens LN with respect to the plane perpendicular to the optical axis at the height at which the maximum image height chief ray passes through the R1 surface θR2: the inclination angle of the object side surface R2 of the negative lens LN with respect to the plane perpendicular to the optical axis at the height at which the maximum image height chief ray passes through the R2 surface

10. 4. The optical system according to claim 3, wherein the second lens group G2 has negative refractive power.

11. 2. The optical system according to claim 1, wherein all groups other than the second lens group G2 are fixed relative to the image plane during focusing.

Images