Optical system and image pickup apparatus having the same

Abstract

The present disclosure relates to an optical system and an image pickup apparatus having the optical system. The optical system includes, in order from an object side to an image side, a first lens unit having positive refractive power, an aperture, a second lens unit having negative refractive power, and a third lens unit having positive refractive power. Distances between adjacent lens units change during focusing. The second lens unit moves toward the image side during focusing from an object at infinity to a short distance object. The first lens unit includes a positive lens closest to the object and two or more negative lenses. The second lens unit consists of a single negative lens. A predetermined condition is satisfied.

Description

Technical Field

[0001] This disclosure relates to an optical system suitable for digital video cameras, digital cameras, broadcast cameras, film-based cameras, surveillance cameras, and vehicle cameras, etc. Background Technology

[0002] Telescopic imaging optical systems (telescopic lenses) with long focal lengths are generally known. A long focal length is, for example, a focal length longer than the size of the effective imaging range. Generally speaking, telescopic lenses become larger and heavier as the focal length increases. Furthermore, in particular, longitudinal chromatic aberration and lateral chromatic aberration, among various aberrations, fluctuate during focusing.

[0003] Japanese Patent Publication No. 2016-151664 discloses a telescope lens comprising, from the object side to the image side, a first lens unit to a third lens unit having positive refractive power, negative refractive power, and positive refractive power, respectively. The second lens unit moves towards the image side during focusing from an object at infinity to a short-distance object (the closest or most proximate object). By appropriately setting the refractive power of the sub-units in the third lens unit, the telescope lens disclosed in JP 2016-151664 can be made lighter and satisfactorily corrects various aberrations.

[0004] In the telescope lens disclosed in JP 2016-151664, the second lens unit, serving as the focusing unit, includes a single positive lens and a single negative lens, or a single positive lens and two negative lenses. However, the focusing unit has a large number of lenses and becomes heavy. Furthermore, the drive system used for the focusing unit requires a heavy load and is difficult to achieve high-speed focusing. Summary of the Invention

[0005] This disclosure provides an optical system and an image pickup device having the optical system, each of which is capable of reducing the weight of the focusing unit.

[0006] An optical system according to one aspect of this disclosure comprises, from the object side to the image side, a first lens unit with positive refractive power, an aperture, a second lens unit with negative refractive power, and a third lens unit with positive refractive power. The distance between adjacent lens units changes during focusing. During focusing from an object at infinity to a short distance object, the second lens unit moves towards the image side. The first lens unit includes a positive lens closest to the object and two or more negative lenses. The second lens unit consists of a single negative lens. The following conditional expression is satisfied:

[0007] 0.2 <LD1 / LD<0.4

[0008] BF / f < 0.25

[0009] Where LD1 is the distance on the optical axis from the lens surface of the first lens unit closest to the object to the lens surface of the first lens unit closest to the image plane, LD is the distance on the optical axis from the lens surface of the first lens unit closest to the object to the image plane, f is the focal length of the optical system, and BF is the back focal length of the optical system when focused on an object at infinity.

[0010] According to another aspect of this disclosure, an image acquisition device includes the aforementioned optical system and an image sensor configured to receive an image formed by the optical system.

[0011] Other features of this disclosure will become clear from the following description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0012] Figure 1 It is a cross-sectional view of the imaging optical system according to Example 1 when it is in focus on an object at infinity.

[0013] Figure 2A and Figure 2B It is an aberration diagram based on Example 1 when objects at infinity and short distances are in focus.

[0014] Figure 3 It is a cross-sectional view of the imaging optical system according to Example 2 when it is in focus on an object at infinity.

[0015] Figure 4A and Figure 4B It is an aberration diagram based on Example 2 when objects at infinity and short distances are in focus.

[0016] Figure 5 It is a cross-sectional view of the imaging optical system according to Example 3 when it is in focus on an object at infinity.

[0017] Figure 6A and Figure 6B It is based on the aberration diagrams of objects at infinity and short distances in focus, as shown in Example 3.

[0018] Figure 7 It is a cross-sectional view of the imaging optical system according to Example 4 when it is in focus on an object at infinity.

[0019] Figure 8A and Figure 8B It is based on the aberration diagrams of objects at infinity and short distances in focus, as shown in Example 4.

[0020] Figure 9 This is a schematic diagram of an image pickup device. Detailed Implementation

[0021] A detailed description of embodiments according to the present disclosure will now be given with reference to the accompanying drawings. Corresponding elements in the corresponding figures will be denoted by the same reference numerals, and repeated descriptions thereof will be omitted.

[0022] Figure 1 , Figure 3 , Figure 5 and Figure 7 This is a cross-sectional view of the imaging optical system (optical system) according to Examples 1 to 4 in a focused state on an object at infinity. The imaging optical system according to the various examples is an optical system for image acquisition devices such as digital video cameras, digital cameras, broadcast cameras, film-based cameras, surveillance cameras, and vehicle-mounted cameras.

[0023] In the various cross-sectional views, the left side is the object side, and the right side is the image side. The optical systems according to the various examples include multiple lens units. In this specification, a lens unit is a group of lenses that moves or remains stationary as a whole during focusing. That is, in the imaging optical systems according to the various examples, the distance between adjacent lens units changes during focusing. A lens unit may include one or more lenses.

[0024] The imaging optical system according to the various examples includes, from the object side to the image side, a first lens unit L1 with positive refractive power, an aperture (aperture stop) SP, a second lens unit L2 with negative refractive power, and a third lens unit L3 with positive refractive power.

[0025] IP stands for Image Plane, and when the imaging optics system according to the various examples is used as an imaging optics system for a digital camera or digital camcorder, the imaging plane of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or a CMOS sensor is placed on the Image Plane IP. When the imaging optics system according to the various examples is used as an imaging optics system for a film-based camera, the photosensitive plane corresponding to the film plane is placed on the Image Plane IP. GB represents a filter deployed on the object side of the Image Plane IP.

[0026] The arrows shown in the various cross-sectional views indicate the direction of movement of the lens unit (focusing unit) during focusing from an object at infinity to a short-distance object. In the imaging optical systems according to the various examples, the second lens unit L2, which is the focusing unit, moves towards the image side during focusing from an object at infinity to a short-distance object.

[0027] Figure 2A , Figure 2B , Figure 4A , Figure 4B , Figure 6A , Figure 6B , Figure 8A and Figure 8B These are aberration diagrams based on the imaging optical systems of Examples 1 to 4. In each aberration diagram, Figure 2A , Figure 4A , Figure 6A and Figure 8A It is an aberration diagram when focused on an object at infinity, and Figure 2B , Figure 4B , Figure 6B and Figure 8B It is an aberration diagram when focusing on a short-distance object.

[0028] In the spherical aberration diagram, Fno represents the F-number and indicates the amount of spherical aberration for the d-line (wavelength 587.6 nm) and g-line (wavelength 435.8 nm). In the astigmatism diagram, S indicates the amount of astigmatism in the sagittal image plane, and M indicates the amount of astigmatism in the meridional image plane. The distortion diagram illustrates the distortion for the d-line. The chromatic aberration diagram illustrates the chromatic aberration for the g-line. ω is the half-angle of the image (degrees).

[0029] The following describes the characteristic configurations of the imaging optical systems for each example.

[0030] The lens closest to the object in the imaging optical system is a positive lens. That is, the first lens unit L1 includes a positive lens closest to the object. This enhances the converging effect of light on the lens closest to the object and reduces the diameter of the light beam incident on the image-side lens located on the lens closest to the object, allowing the optical system to have a small diameter and light weight.

[0031] The first lens unit L1 comprises two or more negative lenses. This configuration satisfactorily corrects chromatic aberration, especially longitudinal chromatic aberration.

[0032] The second lens unit L2 consists of a single negative lens. This configuration reduces the weight of the second lens unit L2, which serves as the focusing unit.

[0033] The second lens unit L2 is adjacent to the image side of the aperture SP. This configuration reduces the weight of the second lens unit L2, which serves as the focusing unit, and suppresses fluctuations in lateral chromatic aberration during focusing.

[0034] The imaging optical systems of each example satisfy the following conditional expressions (1) and (2).

[0035] 0.2 <LD1 / LD<0.4 (1)

[0036] BF / f<0.25 (2)

[0037] Here, LD1 represents the distance along the optical axis from the lens surface of the first lens unit L1 closest to the object to the lens surface of the first lens unit L1 closest to the image plane. LD represents the distance along the optical axis from the lens surface of the first lens unit L1 closest to the object to the image plane (the total lens length below). f is the focal length of the imaging optical system. BF is the back focal length of the imaging optical system when it is in focus on an object at infinity (the distance along the optical axis from the lens surface of the imaging optical system closest to the image plane to the image plane, expressed in terms of air equivalent length).

[0038] Conditional expression (1) defines the ratio of the distance LD1 along the optical axis from the lens surface of the first lens unit L1 closest to the object to the lens surface of the first lens unit L1 closest to the image plane to the total lens length LD. If this value is below the lower limit of conditional expression (1), the weight of the imaging optical system can be easily reduced, but it is difficult to correct spherical aberration and longitudinal chromatic aberration. If this value is above the upper limit of conditional expression (1), it is advantageous from the point of view of aberration correction, but it becomes difficult to reduce the weight of the imaging optical system.

[0039] Conditional expression (2) defines the ratio between the back focal length BF and the focal length f of the imaging optics. If this value is higher than the upper limit of conditional expression (2), then the total lens length becomes longer.

[0040] Due to this configuration, the imaging optics systems according to the various examples can reduce the weight of the focusing unit. The driving system of the focusing unit can have a smaller load and the focusing speed can be improved. The imaging optics systems according to the various examples can reduce weight and satisfactorily correct various aberrations.

[0041] Even configurations comprising four or more lens units can provide a similar effect by satisfying the above expression.

[0042] The numerical ranges of conditional expressions (1) and (2) can be replaced with the numerical ranges of the following conditional expressions (1a) and (2a).

[0043] 0.23 <LD1 / LD<0.35 (1a)

[0044] BF / f < 0.2 (2a)

[0045] The numerical ranges of conditions (1) and (2) can be replaced by the numerical ranges of the following conditions (1b) and (2b).

[0046] 0.26 <LD1 / LD<0.35 (1b)

[0047] BF / f < 0.17 (2b)

[0048] The following describes the configurations that can be satisfied in the imaging optics systems according to the various examples.

[0049] The third lens unit L3 consists of a first subunit L3a with positive refractive power, a second subunit L3b with negative refractive power, and a third subunit L3c with positive refractive power, arranged sequentially from the object side to the image side. The second subunit L3b, which serves as an image stabilization unit, can move in a direction including a component orthogonal to the optical axis during image stabilization (to correct image position fluctuations caused by jitter in the imaging optical system, etc.).

[0050] The following describes the conditions that the imaging optical systems according to the various examples can satisfy. The imaging optical systems according to the various examples can satisfy one or more of the following conditional expressions (3) to (7).

[0051]

[0052] Here, f1 is the focal length of the first lens unit L1. f2 is the focal length of the second lens unit L2. f3 is the focal length of the third lens unit L3. νdG1 is the Abbe number of the lens (positive lens) closest to the object in the imaging optical system.

[0053] Conditional expression (3) defines the ratio between the total lens length LD and the focal length f of the imaging optical system. If conditional expression (3) is satisfied, the imaging optical system can be considered an imaging optical system with a long focal length. Depending on the examples, the imaging optical system can be a medium telephoto lens to a telephoto lens, and if this value is higher than the upper limit of conditional expression (3), then the imaging optical system is considered a lens with a short focal length.

[0054] Conditional expression (4) defines the ratio between the focal length f1 of the first lens unit L1 and the focal length f of the imaging optical system. If this value is below the lower limit of conditional expression (4), the refractive power of the first lens unit L1 increases, which is beneficial for shortening the total lens length, but makes it difficult to correct spherical aberration and longitudinal chromatic aberration. When this value is above the upper limit of conditional expression (4), the refractive power of the first lens unit L1 decreases and the total lens length increases.

[0055] Conditional expression (5) defines the ratio between the focal length f2 of the second lens unit L2 and the focal length f of the imaging optical system. When this value is below the lower limit of conditional expression (5), the refractive power of the second lens unit L2 decreases, resulting in a smaller focusing sensitivity (the amount of focus movement relative to the amount of movement of the focusing unit) of the second lens unit L2. The total lens length increases. When this value is above the upper limit of conditional expression (5), the refractive power of the second lens unit L2 increases, resulting in a larger focusing sensitivity of the second lens unit L2, and it becomes difficult to meet the optical performance requirements during focusing.

[0056] Conditional expression (6) defines the ratio between the focal length f3 of the third lens unit L3 and the focal length f of the imaging optics system. If this value is below the lower limit of conditional expression (6), the refractive power of the third lens unit L3 increases, which is beneficial for shortening the overall lens length, but makes it difficult to correct lateral chromatic aberration. When this value is above the upper limit of conditional expression (6), the refractive power of the third lens unit L3 decreases and the overall lens length increases.

[0057] The conditional expression (7) defines the Abbe number νdG1 of the lens closest to the object in the imaging optics system. If this value is below the lower limit of the conditional expression (7), then chromatic aberration is excessively generated in the lens closest to the object in the imaging optics system. If this value is above the upper limit of the conditional expression (7), then chromatic aberration generated in the lens closest to the object in the imaging optics system becomes insufficient.

[0058] The numerical range of conditional expressions (3) to (7) can be replaced with the numerical range of the following conditional expressions (3a) to (7a).

[0059]

[0060] The numerical range of conditional expressions (3) to (7) can be replaced with the numerical range of the following conditional expressions (3b) to (7b).

[0061]

[0062] The following describes the numerical examples 1 to 4 corresponding to Examples 1 to 4, respectively.

[0063] In the surface data provided for each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial distance (distance along the optical axis) between the m-th surface and the (m+1)-th surface, where m is the surface number measured from the light incident side. nd represents the refractive index of the optical element about the d-line, and νd represents the Abbe number of the optical element. The Abbe number νd of a certain material is calculated as follows:

[0064] νd=(Nd-1) / (NF-NC)

[0065] Nd, NF, and NC are the refractive indices of the Fraunhofer lines for the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm).

[0066] In the various numerical examples, each of d, focal length (mm), F-number, and half angle of view (degrees) has a value when the imaging optics system according to the various examples is focused on an object at infinity. "Back focal length" is the distance along the optical axis from the last lens surface (the lens surface closest to the image plane) to the paraxial image plane, expressed in air equivalent length. "Total lens length" is the length obtained by adding the back focal length to the distance along the optical axis from the foremost surface (the lens surface closest to the object) of the imaging optics system to the last surface. A "lens unit" may include one or more lenses.

[0067] Numerical Example 1

[0068] Unit: mm

[0069] Surface data

[0070]

[0071]

[0072]

[0073]

[0074] Lens unit data

[0075] Numerical Example 2

[0076] Unit: mm

[0077] Surface data

[0078]

[0079]

[0080]

[0081] Lens unit data

[0082] Numerical Example 3

[0083] Unit: mm

[0084] Surface data

[0085]

[0086]

[0087] Lens unit data

[0088] Numerical Example 4

[0089] Unit: mm

[0090] Surface data

[0091]

[0092]

[0093]

[0094] Lens unit data

[0095]

[0096] Table 1 below summarizes the various values ​​in the numerical examples.

[0097] Table 1

[0098] Example 1 Example 2 Example 3 Example 4 f 85.40 101.78 131.00 148.00 Fno 1.85 1.85 1.85 1.85 LD 109.49 123.44 146.99 159.49 LD1 29.03 33.24 45.27 55.68 BF 13.39 13.39 13.64 14.69 f1 63.27 76.54 85.68 101.56 f2 -49.44 -58.48 -63.01 -68.45 f3 70.23 82.26 111.55 110.87 Expression 1 LD1 / LD 0.265 0.269 0.308 0.349 Expression 2 BF / f 0.157 0.132 0.104 0.099 Expression 3 LD / f 1.28 1.21 1.12 1.08 Expression 4 f1 / f 0.741 0.752 0.654 0.686 Expression 5 f2 / f -0.579 -0.575 -0.481 -0.463 Expression 6 f3 / f 0.822 0.808 0.852 0.749 Expression 7 v dG1 20.9 23.8 20.9 23.8

[0099] Image pickup device

[0100] Now for reference Figure 9 Examples of digital cameras (image pickup devices) using imaging optical systems according to various examples will be described. Figure 9 In this designation, reference numeral 10 denotes the camera body, and reference numeral 11 denotes any imaging optical system described in Examples 1 to 4. Reference numeral 12 denotes a solid-state image sensor (photoelectric conversion element), such as a CCD sensor or a CMOS sensor, which is built into the camera body 10 and receives the optical image formed by the imaging optical system 11 and performs photoelectric conversion. The camera body 10 can be a so-called single-lens reflex camera with a quick-turn mirror, or a so-called mirrorless (non-reflective) camera without a quick-turn mirror.

[0101] Applying imaging optical systems, according to various examples, to image pickup devices such as digital cameras in this way can provide image pickup devices with small lenses.

[0102] The various examples can provide optical systems and image pickup devices with optical systems, each of which can reduce the weight of the focusing unit.

[0103] While this disclosure has been described with reference to exemplary embodiments, it should be understood that this disclosure is not limited to the disclosed exemplary embodiments. The scope of the appended claims should be given the broadest interpretation to cover all such modifications and equivalent structures and functions.

Claims

1. An optical system comprising, from the object side to the image side, a first lens unit having positive refractive power, an aperture, a second lens unit having negative refractive power, and a third lens unit having positive refractive power, wherein the distance between adjacent lens units changes during focusing. Its features are, During the focusing process from an object at infinity to a short distance, the second lens unit moves towards the image side. The first lens unit includes a positive lens closest to the object and two or more negative lenses. The third lens unit consists of, from the object side to the image side, a first sub-unit with positive refractive power, a second sub-unit with negative refractive power, and a third sub-unit with positive refractive power. During image stabilization, the second subunit moves in a direction that includes a component orthogonal to the optical axis. The second lens unit consists of a single negative lens, and The following conditional expressions are satisfied: 0.2 < LD1 / LD < 0.35 BF / f < 0.25 Where LD1 is the distance on the optical axis from the lens surface of the first lens unit closest to the object to the lens surface of the first lens unit closest to the image plane, LD is the distance on the optical axis from the lens surface of the first lens unit closest to the object to the image plane, f is the focal length of the optical system, and BF is the back focal length of the optical system when focused on an object at infinity.

2. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: LD / f < 1.

5.

3. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: 0.50 < f1 / f < 0.85 Where f1 is the focal length of the first lens unit.

4. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: -0.65 < f² / f < -0.35 Where f2 is the focal length of the second lens unit.

5. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: 0.65 < f3 / f < 0.95 Where f3 is the focal length of the third lens unit.

6. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: 15 < νdG1 < 30 Where νdG1 is the Abbe number of the positive lens.

7. The optical system according to claim 1, characterized in that, The first and third lens units are stationary during focusing.

8. An image acquisition device, comprising: The optical system according to any one of claims 1 to 7; as well as An image sensor is configured to receive an image formed by an optical system.

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