Lens, camera device and optical system attached to the back

Abstract

The present application provides a rear attachment lens, an imaging device, and an optical system. The rear attachment lens according to the present application is configured to change the focal length of the entire system by being attached to the image side of a main lens. The rear attachment lens includes a positive lens arranged closest to the image side, wherein the lens face of the positive lens on the image side has a shape that is convex toward the image side. The focal length of the rear attachment lens, the magnification of the rear attachment lens when attached to the main lens, and the distance from the lens face of the positive lens on the image side to the position of the rear principal point of the rear attachment lens when attached to the main lens are appropriately set.

Description

[0001] (This application is a divisional application of the application filed on April 8, 2020, with application number 202010269383.8 and title "Rear-attached Lens, Imaging Device and Optical System".) Technical Field

[0002] The present invention relates to a rear-attached lens that is detachably attached between an imaging element and a main lens for imaging, and is configured such that the focal length of the entire system is longer than the original focal length of the main lens. Background Technology

[0003] The following are known rear-mounted lenses, which are attached between the imaging element and the main lens used for imaging, and are configured such that the focal length of the entire system is longer than the focal length of the main lens alone (Japanese Patent Application Laid-Open No. 63-106715 and 2011-123336, and International Publication No. WO2017 / 134928).

[0004] A rear-attached lens that makes the focal length of the entire system longer than the focal length of the primary lens alone typically has negative refractive power. By having this refractive power, the rear-attached lens magnifies the image to be formed, and according to the magnification, makes the focal length of the entire system longer than the focal length of the primary lens alone. In this operation, it has the characteristic of darkening with the F-number according to the magnification.

[0005] Since the aberrations of the primary lens are corrected by itself, the aberrations of the subsequent attachment lens, which is attached to the image side of the primary lens, also need to be well corrected by itself. Specifically, among the aberrations, for the subsequent attachment lens, field curvature and lateral chromatic aberration need to be adequately corrected. Japanese Patent Application Laid-Open No. 63-106715 discloses conditions for obtaining good image plane characteristics, while Japanese Patent Application Laid-Open No. 2011-123336 discloses a method for effectively correcting lateral chromatic aberration.

[0006] Since Japanese Patent Application Publication Nos. 63-106715 and 2011-123336 primarily disclose single-reflection systems (imaging devices), they ensure a considerably long back focus of the primary lens, allowing the secondary lens to be configured with relatively weak refractive power. Therefore, the secondary lens is characterized by its ability to easily achieve good aberrations. Furthermore, when a fast-return mirror is placed on the image side of the secondary lens, the primary lens needs to have a relatively long back focus.

[0007] On the other hand, in mirrorless cameras that do not employ a fast-return mirror, the primary lens can have a shorter back focus. Therefore, mirrorless cameras require a rear-mounted lens that can achieve good aberrations even with a short back focus.

[0008] International publication WO2017 / 134928 discloses a rear attachment lens for a mirrorless camera, which is suitable for a main lens with a short back focal length.

[0009] Typically, when the back focal length of the primary lens to be attached to a secondary lens is short, the focal length of the secondary lens is correspondingly short to achieve the same magnification. This is because the secondary lens with negative refractive power needs to be positioned on the image side. Generally, when the negative refractive power of the secondary lens is increased, Petzval increases in the negative direction, and image plane characteristics decrease. Therefore, proper correction of image plane characteristics is necessary.

[0010] Furthermore, when the back focal length of the primary lens is short, the length from the image plane to the exit pupil is also short. Therefore, in a primary lens with a short length between the image plane and the exit pupil, it is easier to increase the magnification of the subsequent attachment lens. However, in telephoto lenses that effectively utilize the subsequent attachment lens, a longer length from the image plane to the exit pupil is more advantageous from the viewpoint of obtaining high optical performance. Summary of the Invention

[0011] Therefore, the object of the present invention is to obtain a rear attachment lens that can achieve good optical performance even when the main lens has a relatively short back focal point and a relatively long length from the exit pupil.

[0012] The rear attachment lens according to the invention is configured to change the focal length of the entire system by being attached to the image side of the main lens. The rear attachment lens includes a positive lens arranged closest to the image side, wherein the lens surface of the positive lens on the image side has a shape convex toward the image side. The rear attachment lens satisfies the following conditional expression: |fe| / (fe×(1-βe)+np2)>9, where fe represents the focal length of the rear attachment lens, βe represents the magnification of the rear attachment lens when attached to the main lens, and np2 represents the distance from the lens surface of the positive lens on the image side to the rear principal point position of the rear attachment lens when attached to the main lens.

[0013] A camera device includes: a main lens; the aforementioned rear attachment lens; and an imaging element for receiving light from the rear attachment lens.

[0014] An optical system includes: a primary lens; and a rear attachment lens configured to change the focal length of the entire system by being attached to the image side of the primary lens, wherein the rear attachment lens includes a positive lens arranged closest to the image side, wherein the positive lens has a shape convex toward the image side on its lens surface, and wherein the following conditional expression is satisfied: |fe / BF|>9, where fe represents the focal length of the rear attachment lens, and BF represents the back focal point obtained when the rear attachment lens is attached to the primary lens.

[0015] A camera device includes: the optical system described above; and an imaging element for receiving light from the optical system, wherein the following condition expression is satisfied: 1.8 < φr / Yi < 2.2, where φr represents the effective diameter of the positive lens, and Yi represents the maximum image height obtained when the rear attachment lens is attached to the main lens.

[0016] Other features of the invention will become clear from the following description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0017] Figure 1 This is a cross-sectional view of the rear-mounted lens in Example 1;

[0018] Figure 2 This is an aberration diagram of the case where the rear attachment lens of Example 1 is attached to the main lens;

[0019] Figure 3 This is a cross-sectional view of the rear-mounted lens in Example 2;

[0020] Figure 4 This is an aberration diagram of the case where the rear attachment lens of Example 2 is attached to the main lens;

[0021] Figure 5 This is a cross-sectional view of the rear-mounted lens in Example 3;

[0022] Figure 6 This is an aberration diagram of the case where the rear attachment lens of Example 3 is attached to the main lens;

[0023] Figure 7 This is a cross-sectional view of the rear-mounted lens in Example 4;

[0024] Figure 8 This is an aberration diagram of the case where the rear attachment lens of Example 4 is attached to the main lens;

[0025] Figure 9 This is a cross-sectional view of the rear-mounted lens in Example 5;

[0026] Figure 10 This is an aberration diagram of the case where the rear attachment lens of Example 5 is attached to the main lens;

[0027] Figure 11 This is a cross-sectional view of the rear-mounted lens in Example 6;

[0028] Figure 12 This is an aberration diagram of the case where the rear attachment lens of Example 6 is attached to the main lens;

[0029] Figure 13 This is a cross-sectional view of the rear-mounted lens in Example 7;

[0030] Figure 14 This is an aberration diagram of the case where the rear attachment lens of Example 7 is attached to the main lens;

[0031] Figure 15 This is a cross-sectional view of the rear-mounted lens in Example 8;

[0032] Figure 16 This is an aberration diagram of the case where the rear attachment lens of Example 8 is attached to the main lens;

[0033] Figure 17 This is an illustration of the paraxial refractive power arrangement when the rear attachment lens is attached to the primary lens;

[0034] Figure 18 This is a cross-sectional view of the primary lens;

[0035] Figure 19 It is the aberration diagram of the primary lens;

[0036] Figure 20 This is a cross-sectional view of the case where the rear attachment lens of Example 1 is attached to the main lens;

[0037] Figure 21 This is an optical path diagram showing the relationship between the exit pupil of the primary lens and the subsequent attached lens; and

[0038] Figure 22 This is a schematic diagram showing the structure of a camera device (digital camera). Detailed Implementation

[0039] Preferred embodiments of the invention are described below with reference to the accompanying drawings.

[0040] The rear attachment lens of this invention is detachably attached to the image side of the primary lens (primary lens system). This results in a longer focal length for the entire system when the rear attachment lens is attached to the image side of the primary lens than the focal length of the primary lens.

[0041] Figure 1 , Figure 3 , Figure 5 , Figure 7 , Figure 9 , Figure 11 , Figure 13 and Figure 15 These are cross-sectional views of the rear-attached lenses in Examples 1 to 8, respectively. Figure 2 , Figure 4 , Figure 6 , Figure 8 , Figure 10 , Figure 12 , Figure 14 and Figure 16This is an aberration diagram showing the cases where the rear attachment lenses of Examples 1 to 8 are each attached to the main lens. In Examples 1, 2, and 7, the magnification of the focal length of the entire system relative to the focal length of the main lens (the magnification of the rear attachment lens) when the rear attachment lens is attached to the main lens is 1.4 times, and in Examples 3 to 6 and 8, the magnification is 2.0 times.

[0042] In the various cross-sectional views, ML represents the primary lens, and EL represents the secondary lens. In the primary lens ML, Bi represents the i-th lens unit. The arrows indicate the direction of movement of the lens unit during focusing from infinity to near. img represents the image plane. STO represents the aperture stop. Lr represents the positive lens on the image side closest to the secondary lens EL, and L1 represents the positive lens on the object side closest to the secondary lens.

[0043] The aberration diagrams of the primary lens ML and the secondary lens EL attached to the primary lens ML, from left to right on the paper, show spherical aberration, astigmatism, distortion, and lateral chromatic aberration, respectively.

[0044] In the spherical aberration diagram, the solid line represents the aberration of the d-line (wavelength 587.60 nm), the dotted line represents the aberration of the f-line (wavelength 486.10 nm), the dashed line represents the aberration of the C-line (wavelength 656.30 nm), and the double-dotted line represents the aberration of the g-line (wavelength 435.80 nm). The horizontal axis is marked with defocusing increments from -0.4 to +0.4 mm.

[0045] In the astigmatic diagram, the solid line S represents the field curvature of the sagittal image plane, and the dotted line M represents the field curvature of the meridional image plane. The horizontal axis is the same as the horizontal axis of the spherical aberration diagram.

[0046] In the distortion diagram, the horizontal axis is marked from -5 to +5 [%]. The lateral color difference diagram indicates the displacement relative to the d-line, and the horizontal axis is marked from -0.03 to +0.03 [mm].

[0047] Figure 17 The diagram above shows a schematic of a rear-attached lens EL with the primary lens (primary lens system) ML having a sufficiently long back focal length, and outward arrows indicate lenses with positive refractive power, while inward arrows indicate lenses with negative refractive power.

[0048] When the back focal length of the primary lens ML is long enough, the distance s from the imaging point MS of the primary lens ML to the secondary lens EL can be long enough. Therefore, a longer focal length of the secondary lens EL is required to achieve the same magnification β (because β = 1 / (1+s / fe)). If the refractive power can be reduced, Petzval and correction can be facilitated, thus achieving good field curvature.

[0049] On the other hand, when the back focal point of the primary lens ML is short, and the distance s from the imaging point of the primary lens ML to the rear attachment lens EL is short (e.g.) Figure 17 In the case shown in the figure below, the refractive power of the attached lens EL increases in the negative direction, contrary to the previous case. This causes Petzval to remain largely on the negative side, making it difficult to obtain good field curvature.

[0050] Because the refractive power of each lens can be used And the refractive index Nk of the material, through To simply express Petzval, Petzval is typically improved by using a high-refractive-index material for the negative lens and a low-refractive-index material for the positive lens. However, if the back focal length of the primary lens ML is short and the optical path length for arranging the lens is short, it is difficult to arrange the lens required for correction, thus the improvement may be insufficient, or chromatic aberration may be difficult to correct.

[0051] To address this issue, in the rear-attached lenses of each example, such as Figure 17 As shown in the figure below, the rear attachment lens EL is configured such that negative and positive refractive powers are arranged sequentially from the object side to the image side. Furthermore, the distance between the anterior and posterior principal points of the rear attachment lens EL is increased, and the posterior principal point is significantly shifted towards the object side, resulting in a weakening of the refractive power of the rear attachment lens EL (increased focal length). This allows for easy correction of Petzval and [other parameters] for rear attachment lenses with longer posterior focal lengths.

[0052] In order to achieve the ability to Figure 17 The figure below shows the structure of the rear-attached lens EL with refractive power arrangement, where the positive lens Lr is positioned as close as possible to the image side and as close as possible to the image position img.

[0053] The rear attachment lens EL includes a positive lens Lr positioned closest to the image side, and the positive lens Lr has a shape that convexes towards the image side. fe represents the focal length of the rear attachment lens EL, and βe represents the magnification of the rear attachment lens EL obtained when it is attached to the primary lens ML. Then, np2 represents the distance from the last lens surface to the rear principal point position in the rear attachment lens EL attached to the primary lens ML. Under the above conditions, the following conditional expression is satisfied:

[0054] |fe| / (fe×(1-βe)+np2)>9...(1)

[0055] The denominator component of conditional expression (1) corresponds to the sum of the paraxial aft focus and aft principal point positions, and indicates the approximate aft focus. When this value is below the lower limit in conditional expression (1), it is difficult to reduce Petzval.

[0056] This arrangement of refractive power makes it easy to change the refractive power of the rear-attached lens EL from its original negative value to a weaker positive value, so the focal length fe is an absolute value.

[0057] More preferably, the numerical range of the conditional expression (1) can be set as follows:

[0058] |fe| / (fe(1-βe)+np2)>18...(1a)

[0059] Preferably, each example can satisfy one or more of the following conditional expressions.

[0060] R1 represents the radius of curvature of the object-side lens surface of the positive lens Lr arranged on the image side, and R2 represents the radius of curvature of the image-side lens surface of the positive lens Lr. The effective diameter of the positive lens Lr is given. Under the above conditions, the focal length fe is fe (mm), and the distance np2 is np2 (mm). De represents the lens thickness of the rear attachment lens EL (the length from the first lens surface to the image plane). BF represents the back focal point obtained using a camera optical system comprising the main lens ML and the rear attachment lens EL detachably attached to the image side of the main lens ML.

[0061] When using a camera device that includes a camera optical system and a camera element that receives light forming an image by the camera optical system, Let Lr represent the effective diameter of the positive lens, and Yi represent the maximum image height obtained when the rear attachment lens EL is attached to the primary lens ML. Then, This represents the effective diameter of the positive lens on the object side closest to the rear-attached lens EL. Under the above conditions, it is preferable to satisfy one or more of the following conditional expressions:

[0062] -5.00<(R2+R1) / (R2-R1)<-0.85...(2);

[0063]

[0064] -5<1000(mm) / (fe+np2)<5...(4);

[0065] -4<1000(mm) / (fe×βe)<4...(5);

[0066] |fe / De|>2...(6);

[0067] |fe / BF|>9...(7);

[0068] as well as

[0069]

[0070] Next, we will describe the technical meaning of the above conditional expression.

[0071] When the lens shape of the positive lens Lr closest to the image side is set within the range of conditional expression (2), the principal point can be easily moved closer to the image side by the positive lens Lr itself, thus making it easier to achieve a proper refractive power arrangement. When this value exceeds the upper limit in conditional expression (2), the principal point may be located on the object side, and the positive lens Lr may be too thick, which is undesirable. When this value is below the lower limit in conditional expression (2), the curvature of the lens surface on the image side is too strong, and many coma aberrations may occur on the upper edge of the peripheral light, which is also undesirable.

[0072] In each example, because the positive lens Lr is positioned on the image side, the positive lens Lr has a larger effective diameter. To collect peripheral light. When this value is below the lower limit in conditional expression (3), it is difficult to ensure the specific amount of peripheral light required when combined with a primary lens ML that has a long distance from the image plane to the exit pupil. When this value exceeds the upper limit in conditional expression (3), the positive lens Lr is too thick, which is therefore undesirable. In addition, due to the effective diameter It also needs to be located within the mounting components that connect the lens unit and the camera, thus requiring a relatively large effective diameter. The structure of the present invention is preferred for achieving large-diameter installation.

[0073] The denominator of conditional expression (4) indicates the position of the rear focal point, and when the denominator is set within the numerical range that satisfies conditional expression (4), the refractive power of the rear-attached lens EL can be reduced, thus making it easier to decrease Petzval. When this value is below the lower limit in conditional expression (4), Petzval may remain on the negative side, while when this value exceeds the upper limit in conditional expression (4), excessive correction is performed, and Petzval may remain on the positive side, both of which are undesirable.

[0074] When increasing the magnification of the attached lens EL, the negative refractive power needs to be increased to increase the magnification; however, Petzval and EL can be well corrected by setting the value within the range of the conditional expression (5). When the value exceeds the upper limit in the conditional expression (5), Petzval and EL may be overcorrected, while when the value is below the lower limit in the conditional expression (5), the correction may be insufficient, so both situations are undesirable.

[0075] To attach the rear attachment lens EL to the main lens ML, which has a shorter back focal length, the optical path length needs to be shortened proportionally to this shorter back focal length. Therefore, the lens thickness De may be relatively small. In view of this, setting the focal length of the rear attachment lens EL within the numerical range of the conditional expression (6) facilitates the correction of Petzval and . When this value is below the lower limit in the conditional expression (6), it is difficult to ensure a back focal length of the required length, or the back focal length of the main lens ML needs to be increased, which is therefore undesirable.

[0076] By shortening the back focal point BF, the positive lens Lr, which is closest to the image side, is made significantly closer to the image side, facilitating an increase in the focal length fe. Therefore, good field curvature can be easily obtained by setting the value within the numerical range of the conditional expression (7). When this value is below the lower limit in the conditional expression (7), the correction of Petzval and is either insufficient or excessive, which is therefore undesirable.

[0077] When this value is below the lower limit in conditional expression (8), the subsequent attachment lens EL, which is attached to the primary lens ML with a longer distance from the image plane to the exit pupil, may cause vignetting of the peripheral light, which is undesirable. When this value exceeds the upper limit in conditional expression (8), the lens thickness increases excessively, which is also undesirable.

[0078] When the primary lens ML has a relatively long distance from the image plane to the exit pupil, such as Figure 21 As shown in the diagram above, when the positive lens L1, closest to the object side, does not have a sufficiently large effective diameter, it cannot collect peripheral light. Conversely, when the primary lens ML has a shorter distance from the image plane to the exit pupil, as... Figure 21 As shown in the figure below, the effective diameter of the positive lens L1, which is closest to the object side, can be made smaller. Therefore, when this value is below the lower limit in conditional expression (9), the peripheral light intensity decreases when a primary lens ML with a long distance from the image plane to the exit pupil is attached, which is undesirable. When this value exceeds the upper limit in conditional expression (9), the positive lens L1 is too thick, and it is difficult to obtain the required magnification.

[0079] More preferably, the numerical range of conditional expressions (2) to (9) can be set as follows:

[0080] -5.00<(R2+R1) / (R2-R1)<-0.87...(2a);

[0081]

[0082] -3<1000(mm) / (fe+np2)<3...(4a);

[0083] -2<1000(mm) / (fe×βe)<2...(5a);

[0084] |fe / De|>4.8...(6a);

[0085] |fe / BF|>18...(7a);

[0086] as well as

[0087]

[0088] Figure 22 This is a schematic diagram showing the structure of the imaging device (digital camera) 10. Figure 22 The image above is a 3D model, and Figure 22 The figure below is a side view. The imaging device 10 includes a camera body 13, a main lens ML, and a rear attachment lens EL identical to any of Examples 1 to 8 described above. In addition, the imaging device 10 includes a light receiving element (imaging element) 12 that performs photoelectric conversion on the image formed by the main lens ML and the rear attachment lens EL.

[0089] Imaging elements such as CCD sensors and CMOS sensors can be used as light receiving elements 12. The main lens ML and the rear attachment lens EL can be integrally formed with the camera body 13, or they can be individually formed to be detachable from the camera body 13. When the main lens ML and the rear attachment lens EL are integrally formed with the camera body 13, the rear attachment lens EL is formed to be insertable and detachable on the optical axis.

[0090] Although preferred examples of the invention have been described above, the invention is not limited to these examples and various modifications and alterations can be made without departing from the spirit of the invention.

[0091] Numerical examples of the rear attachment lens EL of Examples 1 to 8, and numerical examples of the main lens ML to which the rear attachment lens EL of the present invention is attached, are shown below.

[0092] 'i' indicates the counting order from the object side. In the various numerical examples, Bi represents the i-th lens unit, and Si represents the i-th surface. EAi represents the effective diameter of the i-th surface, Ri represents the radius of curvature of the i-th surface, and di represents the surface spacing between the i-th and (i+1)-th surfaces. ndi and νdi represent the refractive index (wavelength 587.60 nm) of the d-line of the medium between the i-th and (i+1)-th surfaces, and the Abbe number based on that d-line, respectively. Surface numbers marked with 's' on the left indicate the location of the aperture stop.

[0093] Lens surfaces marked with an asterisk (*) on the right indicate that the lens surface has an aspherical shape according to the following function, with the coefficients indicated in the numerical examples. y represents the radial coordinate relative to the vertex of the lens surface, and x represents the coordinate along the optical axis relative to the vertex of the lens surface. A, B, C, and D are the aspherical coefficients:

[0094] x=(y 2 / R) / [1+{1-(1+K)(y 2 / R 2 )} 1 / 2 ]+Ay 4 +By 6 +Cy 8 +Dy 10 .

[0095] In a rear-attached lens (EL), the focal length f and the F-value F are values ​​obtained when the object distance is infinite. The total lens length here indicates the distance from the first lens surface to the imaging position. BF represents the rear focal point and is the distance from the lens surface with the refractive power closest to the image side to the image plane. When a non-refractive element, such as a plate, exists in the middle of this distance, the distance is the air equivalent length calculated without excluding such an element.

[0096] In the various numerical examples of the rear-attached lens EL, the negative spacing is denoted as the first lens surface, which indicates the distance from the imaging position of the primary lens ML to the first lens surface of the rear-attached lens EL. When the rear-attached lens EL is attached to the primary lens ML, the value is then entered as in numerical example 1.

[0097] In the numerical example, the distance from the image plane to the exit pupil in the primary lens ML is designed to be -106mm, which is a relatively long value in the imaging optics system of a mirrorless camera with a relatively short back focus (BF). For the performance and versatility of the rear attachment lens EL, the back focus (BF) of the primary lens ML is set to 35mm.

[0098] Each of Examples 1 through 6 has a rear-mounted lens EL suitable for a full-size sensor and optimized for an ideal optical system with a distance of 100 mm from the image plane to the exit pupil. Optical performance can be confirmed by attaching to the aforementioned main lens ML, or by mounting it on an ideal optical system with a distance of 100 mm. Although the initial F-number of the main lens ML is F2, depending on the F-number supported by the rear-mounted lens EL, it is preferable to use a main lens ML whose aperture is reduced to the aperture diameter listed in the numerical examples.

[0099] Examples 1 through 6 of the rear-attached lens EL were made with variations in magnification, supported F-number, and minimum back focus of the main lens, while Examples 7 and 8 indicate values ​​for designs with smaller sensor sizes. In Examples 7 and 8, the rear-attached lens EL is optimized for an ideal optical system with a 50mm distance to fit the sensor size, but still achieves sufficient light output even when attached to the main lens ML.

[0100] In numerical example 1, surfaces s1 to s26 correspond to the primary lens ML, and surfaces s27 to s38 correspond to the rear-attached lens EL. Surface s11 corresponds to the aperture stop. Surface s27 corresponds to a virtual surface used only for design purposes.

[0101] In numerical example 1, the magnification is 1.4, and the F-number supported by the primary lens ML is 2.8 (the F-number when using the primary lens ML together is F4.0), and it is assumed that the effective diameter of surface number s is reduced to

[0102] Assume that the first lens surface of the rear-attached lens EL is positioned at a distance of -33mm from the imaging position of the main lens ML, and under these conditions, the gap (interval) between the lens and the main lens ML is 2mm.

[0103] Numerical Examples 2 through 8 each indicate only the rear attachment lens EL of the main lens ML, which is assumed to be attached to the face numbers s1 through s26 of Numerical Example 1. In Numerical Example 2, the magnification is 2.0, and the F-number supported by the main lens ML is 2.0 (the F-number is F2.8 when the main lenses ML are used together), and Numerical Example 2 is applied to the main lens ML with a larger aperture.

[0104] When numerical example 2 is applied to a larger aperture lens, the field curvature typically changes at the periphery even as Petzval decreases, making correction easier by using an aspherical lens. In numerical example 2, an aspherical lens is used in surface number 3.

[0105] Additionally, in numerical example 2, the refractive power is reversed to a weak positive refractive power. In this case, the sign of the distance np2 from the final lens surface to the posterior principal point is reversed to have a positive value. As with numerical example 2, this also applies to numerical examples 3 through 8.

[0106] (Numerical example of the primary lens)

[0107]

[0108]

[0109]

[0110]

[0111] (Numerical Example 1) (Primary Lens) + (Rear Attached Lens)

[0112]

[0113]

[0114]

[0115] (Numerical Example 2) (with attached lens)

[0116]

[0117]

[0118]

[0119] (Numerical Example 4) (with attached lens)

[0120]

[0121] (Numerical Example 5) (with attached lens)

[0122]

[0123] (Numerical Example 6) (with attached lens)

[0124]

[0125]

[0126] (Numerical Example 7) (with attached lens)

[0127]

[0128]

[0129] (Numerical Example 8) (with attached lens)

[0130]

[0131]

[0132] Table 1 lists the values ​​associated with the conditional expression in the example.

[0133] [Table 1]

[0134]

[0135]

[0136] Although the invention has been described with reference to exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary embodiments. The appended claims should be interpreted in the broadest possible sense to encompass all such modifications and equivalent structures and functions.

Claims

1. A rear-attached lens configured to change the focal length of the entire system by being attached to the image side of a primary lens, the rear-attached lens comprising six, eight, or nine lenses, the rear-attached lens including: A first positive lens is arranged closest to the object side of the rear-attached lens; A first negative lens is arranged adjacent to the first positive lens on the image side of the first positive lens; A second positive lens is arranged adjacent to the first negative lens on the image side of the first negative lens; A positive lens Lr is arranged closest to the image side of the rear-attached lens; as well as A positive lens, which is arranged adjacent to the positive lens Lr on the object side of the positive lens Lr. The positive lens Lr has a lens surface on the image side that convexes towards the image side. The following conditional expression is satisfied: |fe| / (fe×(1-βe)+np2)>9, and 2<|fe / De|≤27.5, Wherein, fe represents the focal length of the rear-attached lens, βe represents the magnification of the rear-attached lens when attached to the main lens, np2 represents the distance from the image-side lens surface of the positive lens Lr to the rear principal point position of the rear-attached lens when attached to the main lens, and De represents the distance from the lens surface of the rear-attached lens closest to the object side to the image plane.

2. The rear-attached lens according to claim 1, wherein, The following conditional expression is satisfied: -5.00<(R2+R1) / (R2-R1)<-0.85, Wherein, R1 represents the radius of curvature of the lens surface on the object side of the positive lens Lr, and R2 represents the radius of curvature of the lens surface on the image side of the positive lens Lr.

3. The rear-mounted lens according to claim 1, wherein, The following conditional expression is satisfied: in, This indicates the effective diameter of the positive lens Lr.

4. The rear-attached lens according to claim 1, wherein, When the focal length fe is fe[mm] and the distance np2 is np2[mm], the following conditional expression is satisfied: -5<1000[mm] / (fe+np2)<5.

5. The rear-attached lens according to claim 1, wherein, When the focal length fe is fe[mm] and the distance np2 is np2[mm], the following conditional expression is satisfied: -4<1000[mm] / (fe×βe)<4.

6. The rear-attached lens according to claim 1, wherein, The object-side lens surface of the first negative lens has a shape that convexes toward the object side.

7. A camera device, comprising: Main lens; Rear-attached lens according to any one of claims 1 to 6; as well as A camera element for receiving light from the rear-attached lens.

8. The camera device according to claim 7, wherein, The following conditional expression is satisfied: in, The effective diameter of the positive lens Lr is represented, and Yi represents the maximum image height obtained when the rear attachment lens is attached to the main lens.

9. An optical system, comprising: Main lens; as well as A rear-mounted lens is configured to make the focal length of the optical system longer than that of the primary lens by attaching it to the image side of the primary lens. The rear-attached lens consists of six, eight, or nine lenses, and includes: A first positive lens is arranged closest to the object side of the rear-attached lens; A first negative lens is arranged adjacent to the first positive lens on the image side of the first positive lens; A second positive lens is arranged adjacent to the first negative lens on the image side of the first negative lens; A positive lens Lr, which is arranged closest to the image side of the rear-attached lens; and A positive lens, which is arranged adjacent to the positive lens Lr on the object side of the positive lens Lr. The positive lens Lr has a lens surface on the image side that convexes towards the image side. The following conditional expression is satisfied: |fe / BF|>9, and 2<|fe / De|≤27.5, Where fe represents the focal length of the rear-attached lens, BF represents the back focal point obtained when the rear-attached lens is attached to the main lens, and De represents the distance from the lens surface closest to the object side of the rear-attached lens to the image plane.

10. The optical system according to claim 9, wherein, The object-side lens surface of the first negative lens has a shape that convexes toward the image side.

11. A camera device, comprising: The optical system according to claim 9 or 10; as well as An imaging element for receiving light from the optical system. The following conditional expression is satisfied: in, The effective diameter of the positive lens Lr is represented, and Yi represents the maximum image height obtained when the rear attachment lens is attached to the main lens.

12. The camera device according to claim 11, wherein, The following conditional expression is satisfied: in, βe represents the effective diameter of the first positive lens, and βe represents the magnification of the subsequent attachment lens when it is attached to the main lens.

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