Optical system and image pickup device

Abstract

The present disclosure relates to an optical system and an image pickup device. The optical system consists of a front unit and a rear unit. The front unit consists of a first lens having a positive refractive power, a second lens disposed on an image side of the first lens and having a positive refractive power, and a third lens. Each of the first lens and the second lens has a refractive index of 1.7 or higher for a d line. The rear unit consists of two or more and four or fewer lenses, and includes a fourth lens having a positive refractive power and a fifth lens adjacent to the fourth lens and having a negative refractive power. Each of the fourth lens and the fifth lens is made of an organic material. A predetermined condition is satisfied.

Description

Technical Field

[0001] This invention relates to optical systems and image acquisition devices. Background Technology

[0002] There is a recent need for a small and lightweight optical system with high performance (high imaging performance). Japanese Patent Publication No. (“JP”) 2019-35781 discloses an imaging lens (optical system) which consists of a positive lens, a negative lens, a negative lens, a negative lens and a positive lens arranged sequentially from the object side to the image side.

[0003] In the optical system disclosed in JP 2019-35781, each of the lenses is made of an organic material (resin) with a linear expansion coefficient greater than that of inorganic materials (glass), thus exhibiting a large change in thickness and curvature, i.e., a large change in aberrations. The R1 surface of the first lens corresponds to the aperture (aperture stop) surface, and the light beam entering the first lens is coarse. Moreover, when the temperature or humidity changes, the changes in spherical aberration and coma are significant due to the organic material and become factors that degrade the imaging performance of the entire image. Furthermore, the first lens has a low refractive index, thus its central or axial thickness increases, making it difficult to reduce the size of the optical system. Summary of the Invention

[0004] The present invention provides an optical system and an image acquisition device, each of which is small, lightweight, and high-performance.

[0005] An optical system according to one aspect of the invention comprises a front unit and a rear unit. The front unit comprises a first lens having positive refractive power, a second lens having positive refractive power disposed on the image side of the first lens, and a third lens. Each of the first and second lenses has a refractive index of 1.7 or higher for the d-line. The rear unit comprises two or more but less than four lenses, including a fourth lens having positive refractive power and a fifth lens adjacent to the fourth lens having negative refractive power. Each of the fourth and fifth lenses is made of an organic material. The following conditional expression is satisfied:

[0006] 0.75 < νdA / νdB < 1.30

[0007] 0.75 <- fA / fB < 1.30

[0008] Where νdA is the Abbe number of the fourth lens, νdB is the Abbe number of the fifth lens, fA is the focal length of the fourth lens, and fB is the focal length of the fifth lens.

[0009] An image acquisition device according to another aspect of the present invention includes the aforementioned optical system and an image sensor configured to image an optical image formed by the optical system.

[0010] Other features of the invention will become clear from the following description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0011] Figure 1 It is a cross-sectional view of the optical system based on Example 1.

[0012] Figure 2 It is an aberration diagram based on the optical system in Example 1.

[0013] Figure 3 It is a cross-sectional view of the optical system based on Example 2.

[0014] Figure 4 It is an aberration diagram based on the optical system in Example 2.

[0015] Figure 5 It is a cross-sectional view of the optical system based on Example 3.

[0016] Figure 6 It is an aberration diagram based on the optical system in Example 3.

[0017] Figure 7 It is a cross-sectional view of the optical system based on Example 4.

[0018] Figure 8 It is an aberration diagram based on the optical system in Example 4.

[0019] Figure 9 This is a schematic diagram of an image pickup device including an optical system according to various embodiments. Detailed Implementation

[0020] A description of embodiments of the present invention will now be given with reference to the accompanying drawings.

[0021] Figure 1 , Figure 3 , Figure 5 and Figure 7 These are cross-sectional views of the optical systems L0 according to Examples 1 to 4 in an infinity-focused state (focused state on an object at infinity). The optical systems according to each example are imaging optical systems used in image-capturing devices such as digital video cameras, digital cameras, broadcast cameras, film-based cameras, and surveillance cameras. In each cross-sectional view, the left side is the object side (front), and the right side is the image side (rear).

[0022] exist Figure 1In this diagram, LO represents the optical system (the entire imaging optical system), FG represents the front unit, and RG represents the rear unit. Within the rear unit RG, A represents a lens made of organic material (resin) with positive refractive power (the fourth lens), and B represents a lens made of organic material (resin), with negative refractive power, and adjacent to lens A (the fifth lens). SP represents the aperture (aperture stop), and IP represents the image plane. When the imaging optical system is used in a camera or digital camera, the imaging plane of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor is placed on the image plane IP. When the imaging optical system is used in a film-based camera, a photosensitive surface such as the film plane is deployed on the image plane IP.

[0023] Figure 2 , Figure 4 , Figure 6 and Figure 8 These are aberration diagrams for the optical systems LO at infinity focusing according to Examples 1 to 4. The spherical aberration diagram illustrates the spherical aberration amounts for the d-line (wavelength 587.6 nm) and g-line (wavelength 435.8 nm), where Fno is the F-number. In the astigmatism diagram, S represents the astigmatism amount in the sagittal image plane, and M represents the astigmatism amount in the meridional image plane. The distortion diagram illustrates the distortion amount for the d-line. The chromatic aberration diagram illustrates the chromatic aberration amount for the g-line. ω is the imaging half-angle (degrees).

[0024] Now for reference Figure 1 The following will describe the common configurations of the optical systems according to the various examples. The optical systems OL according to the various examples include five or more but no more than seven lenses. Five or more lenses can satisfactorily suppress various aberrations. Seven or fewer lenses can achieve a reduction in size and weight. Components without refractive power (such as flat glass) are not considered as components.

[0025] According to various examples, the optical system LO consists of a front unit FG and a rear unit RG. The front unit FG consists of three lenses: a lens with positive refractive power (first lens) Lp1, a lens with positive refractive power (second lens) Lp2, and a lens with negative refractive power (third lens) Ln3. The front unit FG may have at least two lenses, each with positive refractive power, and may include a lens with positive refractive power as the third lens. In this disclosure, the first, second, and third lenses do not necessarily have to be arranged in this order from the object side. The lens corresponding to the third lens may be closest to the object, or the lens corresponding to the third lens may be positioned between the lens corresponding to the first lens and the lens corresponding to the second lens. That is, unless otherwise stated, conditions that can be satisfied by the first lens as described below may be satisfied by one of the positive lenses in the front unit FG closest to the object, rather than another positive lens in the front unit FG closest to the image plane. Unless otherwise stated, conditions that can be satisfied by the second lens as described below may be satisfied by one of the positive lenses in the front unit FG closest to the image plane, rather than another positive lens in the front unit FG closest to the object.

[0026] At least two lenses (the first and second lenses) with positive refractive power in the front unit FG have a refractive index of 1.7 or higher for the d-line. Including at least two lenses with positive refractive power in the front unit FG guides the light beam to the rear unit RG while gently bending the marginal light of the on-axis rays towards the convergence direction, thereby achieving a telephoto structure (reduced size) and good imaging performance. Setting the refractive index of each of the at least two lenses to 1.7 or higher reduces the on-axis thickness of the lenses and the size of the imaging optics LO.

[0027] The rear unit RG consists of two or more but no more than four lenses, including lens A with positive refractive power and lens B adjacent to lens A with negative refractive power. Each of lenses A and B is made of organic material. Lenses A and B satisfy the following conditional expressions (1) and (2):

[0028] 0.75 < νdA / νdB < 1.30 ...(1)

[0029] 0.75 <- fA / fB < 1.30 ...(2)

[0030] In the conditional expressions (1) and (2), νdA is the Abbe number of lens A with positive refractive power, νdB is the Abbe number of lens B with negative refractive power, fA is the focal length of lens A with positive refractive power, and fB is the focal length of lens B with negative refractive power.

[0031] Specifically, for smaller wide-angle systems where the aperture SP is deployed in the front element FG, the rear element RG needs to be located close to the image plane IP. Therefore, the rear element RG is deployed at an off-axis beam height, and its diameter is increased relative to the front element FG. If the rear element RG is made of an inorganic material (glass), the weight increases. Optical systems according to various examples are made lightweight by using organic materials (resins). Here, organic materials (resins) refer to materials having a linear expansion coefficient ( / °C) in the range of 5.0 × 10⁻⁵ to 10.0 × 10⁻⁵.

[0032] The absolute values ​​of the ratio of the Abbe number of lens A (with positive refractive power) to the Abbe number of lens B (with negative refractive power), and the ratio of the focal lengths of lenses A and B, are set to include values ​​near 1, as in conditional expressions (1) and (2), respectively. This configuration can suppress fluctuations in longitudinal and lateral chromatic aberration when temperature or humidity changes. A detailed description is given below.

[0033] Now assume that h_i is the height of the on-axis ray of the i-th lens from the optical axis in paraxial tracking, and h_bar_i is the height of the off-axis principal ray of the i-th lens from the optical axis in paraxial tracking. Let ν_i be the refractive power of the i-th lens in paraxial tracking, and ν_i be the Abbe number of the i-th lens in paraxial tracking. Then, the longitudinal chromatic aberration coefficient L and the transverse chromatic aberration coefficient T of the optical system are represented by the following expressions (A) and (B).

[0034]

[0035]

[0036] From expressions (A) and (B), it can be understood that the longitudinal chromatic difference is proportional to the square of the height h_i, and the lateral chromatic difference is proportional to both the height h_i and the height h_bar_i. The longitudinal chromatic difference Δf and the lateral chromatic difference ΔY of the optical system are given by the following expressions (C) and (D).

[0037] Δf=-f×L ...(C)

[0038] ΔY=-Y×T ...(D)

[0039] In expressions (C) and (D), f is the focal length of the optical system (the entire system), and Y is the image height. That is, the longitudinal chromatic aberration coefficient L and the lateral chromatic aberration coefficient T of each lens are proportional to the refractive power and Abbe number of each lens.

[0040] Generally, organic materials have a larger coefficient of linear expansion than inorganic materials during use, resulting in significant fluctuations in refractive power when temperature changes. That is, organic materials exhibit significant fluctuations in chromatic aberration. Therefore, to reduce weight and suppress chromatic aberration fluctuations with temperature changes, each of the adjacent lenses with positive and negative refractive powers is made of organic material, and the absolute ratio of the Abbe number to the optical power (refractive power) is set to a value close to 1. Due to the adjacent lenses, in paraxial tracking of the lenses with positive and negative refractive powers, the heights of the on-axis ray and the off-axis principal ray from the optical axis are relatively close to each other. By reversing the signs of the refractive power and Abbe number and making them approximately equal, the effect of eliminating chromatic aberration at room temperature takes effect. Furthermore, since organic materials have similar Abbe numbers between lenses with positive and negative refractive powers, their changes in refractive power at various wavelengths are approximately similar even with temperature changes, and the changes in refractive power are also approximately similar. Therefore, the effect of eliminating chromatic aberration is maintained. This configuration corrects astigmatism and field curvature through the aspherical effect of each lens, while also satisfactorily correcting chromatic aberration even with temperature variations, thus achieving high performance. This configuration enables a compact, lightweight, and high-performance optical system.

[0041] The numerical range of conditional expressions (1) and (2) can be set as follows.

[0042] 0.77 < νdA / νdB < 1.27 ... (1A)

[0043] 0.80 <- fA / fB < 1.25 ... (2A)

[0044] The numerical ranges of the conditional expressions (1A) and (2A) can also be set as follows.

[0045] 0.80 < νdA / νdB < 1.25 ...(1B)

[0046] 0.85 <- fA / fB < 1.20 ... (2B)

[0047] The front unit (FG) can include lenses with negative refractive power. This configuration can reduce longitudinal chromatic aberration and Petzval sum (field curvature), and achieve higher performance. The lens closest to the object in the front unit (FG) can have positive refractive power. This configuration allows for a telephoto structure, reducing the distance from the surface closest to the object to the imaging plane and miniaturizing the optical system.

[0048] The optical systems of each example can satisfy at least one of the following conditional expressions (3) to (20).

[0049] αp1<100×10^-7 ...(3)

[0050] 25<νdp1<60 ...(4)

[0051] αp2<100×10^-7 ...(5)

[0052] 25<νdp2<60 ...(6)

[0053] αn<100×10^-7 ...(7)

[0054] 1.60 <N<2.10 ...(8)

[0055] 15<νdn<35 ...(9)

[0056] 1.4 <fA / f<3.5 ...(10)

[0057] 1.00 <f / BF<3.00 ...(11)

[0058] 0.5<|Fu| / Fm<25.0 ...(12)

[0059] 0.10 <dA / BF<0.60 ...(13)

[0060] 0.05 <dB / BF<0.40 ...(14)

[0061] 0.50 <du / BF<1.50 ...(15)

[0062] 50<νdA<60 ...(16)

[0063] 1.45 <NA<1.60 ...(17)

[0064] 15<νdA<40 ...(18)

[0065] 1.55 <NA<1.75 ...(19)

[0066] 0.20<-fn / f<0.70 ...(20)

[0067] Here, αp1 is the linear expansion coefficient ( / ℃) of lens Lp1, which has positive refractive power and is closest to the object in the front unit FG. νdp1 is the Abbe number of lens Lp1. αp2 is the linear expansion coefficient ( / ℃) of lens Lp2, which has positive refractive power and is second closest to the object in the front unit FG. νdp2 is the Abbe number of lens Lp2. αn is the linear expansion coefficient ( / ℃) of lens Ln1, which has negative refractive power in the front unit FG. N is the refractive index of lens Ln1. νdn is the Abbe number of lens Ln1. fA is the focal length of lens A. f is the focal length of the optical system (the entire system) LO. BF is the back focal length of the optical system LO (the equivalent air length from the image-side surface of the last lens to the image plane IP in infinity focusing). Fu is the focal length (combined focal length) of the rear unit RG. Fm is the focal length (combined focal length) of the front unit FG. dA is the on-axis thickness of lens A. dB is the on-axis thickness of lens B. du is the on-axis distance from the vertex of the surface closest to the object in the rear unit RG to the vertex of the surface closest to the image plane in the rear unit RG. νdA is the Abbe number of lens A. NA is the refractive index of lens A. νdB is the Abbe number of lens B. NB is the refractive index of lens B. fn is the focal length of the lens with negative refractive power in the front unit FG.

[0068] A description of the technical meaning of each conditional expression will now be given.

[0069] Conditional expression (3) defines the linear expansion coefficient of the lens Lp1, which has positive refractive power and is closest to the object in the front unit FG. If this value is higher than the upper limit of conditional expression (3), the linear expansion coefficient becomes too large, and aberrations, especially spherical aberrations, are generated when the temperature changes, thus degrading the imaging performance. In particular, when the aperture SP is included in the front unit FG, the on-axis and off-axis beams become thicker near the lens Lp1, which has positive refractive power and is closest to the object in the front unit FG, thus degrading the overall image performance. The linear expansion coefficient here indicates the value at a temperature of 25 degrees Celsius.

[0070] Conditional expression (4) defines the Abbe number of lens Lp1, which has positive refractive power and is closest to the object in the front unit FG. If this value is higher than the upper limit of conditional expression (4), then the longitudinal chromatic aberration of the F line relative to the C line becomes overcorrected. On the other hand, if this value is lower than the lower limit of conditional expression (4), then the longitudinal chromatic aberration of the F line relative to the C line becomes undercorrected.

[0071] Conditional expression (5) defines the linear expansion coefficient of the lens Lp2, which has positive refractive power and is the second closest to the object in the front unit FG. If this value is higher than the upper limit of conditional expression (5), the linear expansion coefficient becomes too large, and spherical aberration is particularly generated when the temperature changes, thus degrading the imaging performance. Especially in a configuration where the front unit FG includes the aperture SP, near the lens Lp2, which has positive refractive power and is the second closest to the object in the front unit FG, the on-axis and off-axis beams become thicker, degrading the overall image performance. Here, the linear expansion coefficient indicates the value at a temperature of 25 degrees Celsius.

[0072] Conditional expression (6) defines the Abbe number of the lens Lp2, which has positive refractive power and is second closest to the object in the front unit FG. If this value is higher than the upper limit of conditional expression (6), then the longitudinal chromatic aberration of the F line relative to the C line becomes overcorrected. On the other hand, if this value is lower than the lower limit of conditional expression (6), then the longitudinal chromatic aberration of the F line relative to the C line becomes undercorrected.

[0073] Conditional expression (7) defines the linear expansion coefficient of the lens Ln1 with negative refractive power in the front unit FG. If this value is higher than the upper limit of conditional expression (7), the linear expansion coefficient becomes too large, and spherical aberration is particularly generated when the temperature changes, thus degrading the imaging performance. Especially in a configuration where the front unit FG includes the aperture SP, the on-axis and off-axis beams become thicker near the lens Ln1 with negative refractive power in the front unit FG, thus degrading the overall image performance. The linear expansion coefficient here indicates the value at a temperature of 25 degrees Celsius.

[0074] Conditional expression (8) defines the refractive index of the lens Ln1 with negative refractive power in the front unit FG with respect to the d-line. If this value is higher than the upper limit of conditional expression (8), then the refractive index is too large, the Pötzwasser (field curvature) becomes larger, and the imaging performance deteriorates. On the other hand, if this value is lower than the lower limit of conditional expression (8), then the refractive index becomes too small, the curvature of the lens with negative refractive power becomes larger, the thickness in the thrust direction increases, and the size increases.

[0075] Conditional expression (9) defines the Abbe number of lens Ln1 with negative refractive power in the front unit FG. If this value is higher than the upper limit of conditional expression (9), then the longitudinal chromatic aberration of the F line relative to the C line becomes undercorrected. On the other hand, if this value is lower than the lower limit of conditional expression (9), then the longitudinal chromatic aberration of the F line relative to the C line becomes overcorrected.

[0076] The conditional expression (10) defines the ratio of the focal length of the lens A with positive refractive power to the focal length of the optical system LO. If this value is higher than the upper limit of the conditional expression (10), then the refractive power of the lens A becomes too small to satisfactorily correct for field curvature and astigmatism. On the other hand, if this value is lower than the lower limit of the conditional expression (10), then the refractive power of the lens A becomes too large, and the change in refractive power with temperature changes becomes too large, and in particular, the fluctuations in field curvature and astigmatism become too large.

[0077] Conditional expression (11) defines the ratio of the focal length of the optical system LO to the back focal length of the optical system LO in infinity focusing state. If this value is higher than the upper limit of conditional expression (11), the back focal length becomes too short, which may result in ghosting and prevent high performance from being achieved. In addition, the angle of incidence on the image sensor becomes too large at the periphery of the image, resulting in color shading. On the other hand, if this value is lower than the lower limit of conditional expression (11), the back focal length becomes too long and the optical system LO becomes too large.

[0078] Conditional expression (12) defines the ratio of the absolute value of the combined focal length of the rear unit RG to the combined focal length of the front unit FG. If this value is higher than the upper limit of conditional expression (12), then the combined focal length of the front unit FG becomes too short, the refractive power becomes too strong, and in particular, spherical aberration and coma become too large. On the other hand, if this value is lower than the lower limit of conditional expression (12), then the combined focal length of the rear unit RG becomes too short, the refractive power becomes too strong, and in particular, astigmatism and field curvature become too large.

[0079] The conditional expression (13) defines the ratio of the on-axis thickness of lens A with positive refractive power to its back focal length. If this value is higher than the upper limit of the conditional expression (13), then the on-axis thickness of lens A becomes too large and the weight increases. On the other hand, if this value is lower than the lower limit of the conditional expression (13), then the back focal length becomes too long and the entire optical system LO becomes large.

[0080] Conditional expression (14) defines the ratio of the on-axis thickness of lens B with negative refractive power to its back focal length. If this value is higher than the upper limit of conditional expression (14), then the on-axis thickness of lens B becomes too large and the weight increases. On the other hand, if this value is lower than the lower limit of conditional expression (14), then the back focal length becomes too long and the entire optical system LO becomes large.

[0081] Conditional expression (15) defines the ratio of the on-axis distance of the back element RG from the vertex closest to the object to the vertex closest to the image plane to the back focal length. If this value is higher than the upper limit of conditional expression (15), then the back element RG becomes heavy. On the other hand, if this value is lower than the lower limit of conditional expression (15), then the back focal length becomes too long and the LO of the entire optical system becomes large.

[0082] Conditional expressions (16) and (17) define the Abbe number and refractive index of lens A with positive refractive power, respectively. Maintaining a high refractive index and a large Abbe number within the range of satisfying both conditional expressions (16) and (17) can reduce lateral chromatic aberration, while also reducing Pötzvar and (field curvature).

[0083] Conditional expressions (18) and (19) define the Abbe number and refractive index of lens A with positive refractive power, respectively. When an organic material with a higher dispersion than that in conditional expressions (16) and (17) is used, conditional expressions (18) and (19) will be satisfied. In conditional expressions (18) and (19), the Abbe number is less than that in conditional expressions (16) and (17), the lateral chromatic aberration is not as good, but the refractive index can be larger, thus allowing for a smaller Pötzvar and (field curvature).

[0084] Conditional expression (20) defines the ratio of the focal length of the lens Ln1 with negative refractive power in the front unit FG to the focal length of the optical system LO. If this value is higher than the upper limit of conditional expression (20), then the absolute value of the focal length of lens Ln1 becomes too large, the spherical aberration correction is insufficient, and the Pötzwasser sum (field curvature) increases. On the other hand, if this value is lower than the lower limit of conditional expression (20), then the absolute value of the focal length of lens Ln1 becomes too small, the front principal point moves towards the image side, the overall length becomes longer, and the size increases.

[0085] The numerical range of conditional expressions (3) to (20) can be set as follows.

[0086] αp1 < 90 × 10^-7 ... (3A)

[0087] 27<νdp1<55 ...(4A)

[0088] αp² < 90 × 10⁻⁷ ... (5A)

[0089] 30 < νdp² < 55 ... (6A)

[0090] αn<95×10^-7 ...(7A)

[0091] 1.65 <N<2.05 ...(8A)

[0092] 16<νdn<32 ...(9A)

[0093] 1.5 <fA / f<3.0 ...(10A)

[0094] 1.50 <f / BF<2.90 ...(11A)

[0095] 0.7 < |Fu| / Fm < 21.0 ... (12A)

[0096] 0.12 <dA / BF<0.50 ...(13A)

[0097] 0.08 <dB / BF<0.35 ...(14A)

[0098] 0.55 <du / BF<1.30 ...(15A)

[0099] 52<νdA<58 ...(16A)

[0100] 1.48 <NA<1.58 ...(17A)

[0101] 17<νdA<30 ...(18A)

[0102] 1.60 <NA<1.72 ...(19A)

[0103] 0.25 <- fn / f < 0.68 ... (20A)

[0104] The numerical range of the conditional expressions (3A) to (20A) can also be set as follows: αp1 < 80 × 10^-7 ... (3B)

[0105] 30<νdp1<50 ...(4B)

[0106] αp² < 80 × 10⁻⁷ ... (5B)

[0107] 35 < νdp² < 50 ... (6B)

[0108] αn<85×10^-7 ...(7B)

[0109] 1.73 <N<2.00 ...(8B)

[0110] 17<νdn<28 ...(9B)

[0111] 1.6 <fA / f<2.8 ...(10B)

[0112] 1.80 <f / BF<2.85 ...(11B)

[0113] 0.9 < |Fu| / Fm < 17.0 ... (12B)

[0114] 0.15 <dA / BF<0.45 ...(13B)

[0115] 0.10 <dB / BF<0.30 ...(14B)

[0116] 0.60 <du / BF<1.20 ...(15B)

[0117] 54<νdA<57 ...(16B)

[0118] 1.52 <NA<1.56 ...(17B)

[0119] 19<νdA<25 ...(18B)

[0120] 1.62 <NA<1.70 ...(19B)

[0121] 0.30 <- fn / f < 0.65 ... (20B)

[0122] The above configuration enables a small, lightweight, and high-performance imaging optical system. Detailed descriptions of the optical systems LO according to Examples 1 through 4 will be given.

[0123] Example 1

[0124] Now for reference Figure 1 A description of the optical system LO according to Example 1 will be given. In the optical system LO according to this example, the front unit FG consists of three lenses: a lens Lp1 with positive refractive power, an aperture (aperture stop) SP, a lens Lp2 with positive refractive power, and a lens Ln1 with negative refractive power, arranged sequentially from the object side to the image side. This configuration allows the front principal point to be moved towards the object side, enabling telephoto structures and miniaturization. Furthermore, each lens is made of an inorganic material. In the front unit FG, the on-axis and off-axis beams are so coarse that spherical aberration and coma change significantly with changes in curvature and thickness, and therefore these beams affect the imaging performance of the entire image. The front unit FG made of inorganic materials can suppress changes in curvature, thickness, and refractive index with temperature variations, and improve the imaging performance of the entire image.

[0125] The rear unit RG consists of three lenses: a lens B with negative refractive power, a lens A with positive refractive power, and a lens with positive refractive power, arranged sequentially from the object side to the image side. The inverted arrangement of the front unit FG relative to the lenses with positive, positive, and negative refractive powers provides a symmetrical (concentric) shape and satisfactorily corrects off-axis aberrations. Although the diameter of the rear unit RG is the same as the diameter of the sensor, all lenses are made of organic materials, thus reducing weight. Moreover, since the adjacent lenses B with negative refractive power and A with positive refractive power satisfy conditional expressions (1) and (2), chromatic aberration fluctuations due to temperature changes can be satisfactorily corrected. Satisfying conditional expressions (3) to (20) provides a small, lightweight, and high-performance optical system.

[0126] Example 2

[0127] Now for reference Figure 3 A description of the optical system LO according to Example 2 will be given. In this embodiment and subsequent embodiments, the descriptions shared with Example 1 will be omitted. The rear unit RG consists of four lenses, namely, lenses with negative refractive power, positive refractive power, positive refractive power and negative refractive power arranged sequentially from the object side to the image side. The rear unit RG consisting of four lenses can satisfactorily correct, in particular, astigmatism and field curvature. Moreover, the two lenses on the object side of the rear unit RG (negative lens and positive lens) are paired, and the two lenses on the image side (lens A and lens B) are paired, and each pair satisfies conditional expressions (1) and (2). This configuration can satisfactorily correct chromatic aberration between lens pairs when the temperature changes, and suppresses chromatic aberration fluctuations in general. Satisfying conditional expressions (3) to (20) can provide a small, lightweight and high-performance optical system.

[0128] Example 3

[0129] Now for reference Figure 5 A description of the optical system LO according to Example 3 will be given. In the optical system LO according to this example, the refractive power of the front unit FG is made approximately equal to that of the rear unit RG to appropriately distribute the refractive power. This configuration can suppress the bending of light emitted from the front unit FG relative to the light incident on the front unit FG, and in particular reduces spherical aberration and coma. Moreover, satisfying the conditional expressions (1) to (20) can provide a compact, lightweight and high-performance imaging optical system.

[0130] Example 4

[0131] Now for reference Figure 7 A description of the optical system LO according to Example 4 will be given. The front unit FG consists of three lenses, namely, a lens Lp1 with positive refractive power, a lens Ln1 with negative refractive power, an aperture SP, and a lens Lp2 with positive refractive power, arranged sequentially from the object side to the image side. Deploying lens Ln1 closer to the object than in Example 1 can more satisfactorily correct longitudinal chromatic aberration and spherical aberration.

[0132] The rear unit RG consists of two lenses: a lens B with negative refractive power and a lens A with positive refractive power, arranged sequentially from the object side to the image side. This dual-lens configuration can be lighter than the configuration in Example 1. Moreover, satisfying the conditional expressions (1) to (20) can provide a small, lightweight, and high-performance imaging optical system.

[0133] Now for reference Figure 9 The following will provide a description of using an optical system LO as an image pickup device for an imaging optical system, according to various examples. Figure 9 This is a schematic diagram of an image acquisition device (digital camera) 10. Figure 9 In the figures, reference numeral 100 denotes the camera body (image acquisition device body), and reference numeral 101 denotes the imaging optical system corresponding to the optical system LO according to the various examples. Reference numeral 102 denotes the image sensor (photoelectric conversion element) for receiving (imaging) the object image (optical image) formed by the imaging optical system 101. The image acquisition device 10 includes a display unit (not shown), such as a liquid crystal panel, which displays the object image formed on the image sensor 102. Applying the optical system LO according to the various examples in this way can provide an image acquisition device with high optical performance.

[0134] The following are numerical examples 1 to 4, corresponding to Examples 1 to 4 respectively. In the surface data of 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 counted from the light incident side. nd represents the refractive index of each optical element with respect to the d-line, and νd represents the Abbe number of the optical element.

[0135] The Abbe number νd of a certain material is expressed as follows:

[0136] νd=(Nd-1) / (NF-NC)

[0137] Nd, NF, and NC are the refractive indices of the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) in the Fraunhofer lines.

[0138] In each numerical example, d, focal length (mm), F-number, and half angle of view (degrees) are given by the values ​​of the optical system in focus on an object at infinity, according to the respective example. BF (back focal length) is the distance on the optical axis from the last lens surface (closest to the image plane) to the paraxial image plane, expressed as an air equivalent length. The total lens length is obtained by adding the back focal length to the distance on the optical axis from the foremost lens surface (closest to the object) to the last lens surface. A lens unit may include one or more lenses.

[0139] If the optical surface is aspherical, then the symbol * is appended to the right of the surface number. The shape of an aspherical surface is expressed as follows:

[0140]

[0141] Where x is the displacement from the surface vertex along the optical axis, h is the height from the optical axis in the direction orthogonal to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, and A10 are aspheric coefficients of various orders. "e±XX" in each aspheric coefficient represents "×10" ±XX ".

[0142] Numerical Example 1

[0143] Unit: mm

[0144] Surface data

[0145]

[0146] Aspherical data

[0147] Seventh Surface

[0148] K=0.00000e+000 A 4=-1.30571e-002 A 6=1.07357e-003 A 8=1.13910e-006

[0149] A10=-3.23336e-006 A12=-1.01049e-006

[0150] Eighth surface

[0151] K=0.00000e+000 A 4=-1.05055e-002 A 6=1.04691e-003 A 8=-3.89159e-005

[0152] A10=-5.44432e-007 A12=2.59956e-008

[0153] Ninth Surface

[0154] K=0.00000e+000 A 4=8.11468e-003 A 6=-6.75729e-004 A 8=3.07488e-005

[0155] A10=-1.29401e-007 A12=-2.06278e-008

[0156] Tenth Surface

[0157] K=0.00000e+000 A 4=3.89314e-003 A 6=1.26901e-004 A 8=-2.57098e-005

[0158] A10=1.67415e-006 A12=-3.50220e-008

[0159] Eleventh Surface

[0160] K=0.00000e+000 A 4=-6.73863e-003 A 6=2.57932e-004 A 8=-4.04258e-006

[0161] A10=-1.83896e-008 A12=1.37821e-009 A14=-1.37275e-011

[0162] Twelfth Surface

[0163] K=0.00000e+000 A 4=-6.31402e-003 A 6=2.43612e-004 A 8=-8.06405e-006

[0164] A10=1.82462e-007 A12=-2.06718e-009 A14=7.83470e-012

[0165] zoom ratio

[0166]

[0167] Single lens data

[0168]

[0169] Numerical Example 2

[0170] Unit: mm

[0171] Surface data

[0172]

[0173]

[0174] Aspherical data

[0175] Seventh Surface

[0176] K=0.00000e+000 A 4=-6.66583e-003 A 6=9.69171e-004 A 8=-4.03272e-004

[0177] A10=8.79337e-005 A12=-6.17014e-006

[0178] Eighth surface

[0179] K=0.00000e+000 A 4=-4.77623e-003 A 6=4.25204e-004 A 8=-1.64811e-004

[0180] A10=3.15736e-005 A12=-1.59846e-006

[0181] Ninth Surface

[0182] K=-1.41036e+001 A 4=8.94812e-003 A 6=-1.68586e-003 A 8=1.57237e-004

[0183] A10=-6.42994e-006 A12=8.59335e-008

[0184] Tenth Surface

[0185] K=-4.59613e+000 A 4=5.05734e-003 A 6=-7.80669e-004 A 8=6.43193e-005

[0186] A10=-2.10462e-006 A12=1.30611e-008

[0187] Eleventh Surface

[0188] K=0.00000e+000 A 4=-1.05053e-002 A 6=4.81059e-004 A 8=-1.61741e-005

[0189] A10=-3.75795e-007 A12=4.18961e-008 A14=-7.14086e-010

[0190] Twelfth Surface

[0191] K=0.00000e+000 A 4=-5.20687e-003 A 6=1.44080e-004 A 8=-1.64974e-006

[0192] A10=-2.80569e-007 A12=1.62436e-008 A14=-2.08518e-010

[0193] Thirteenth Surface

[0194] K=0.00000e+000 A 4=-6.27407e-003 A 6=9.12346e-005 A 8=8.33783e-006

[0195] A10=-2.48711e-007 A12=-1.08995e-009 A14=5.50477e-011

[0196] Fourteenth Surface

[0197] K=0.00000e+000 A 4=-8.64112e-003 A 6=3.52520e-004 A 8=-1.18418e-005

[0198] A10=2.99352e-007 A12=-4.50466e-009A14=2.14589e-011

[0199] zoom ratio

[0200]

[0201] Single lens data

[0202]

[0203] Numerical Example 3

[0204] Unit: mm

[0205] Surface data

[0206]

[0207]

[0208] Aspherical data

[0209] Eighth surface

[0210] K=0.00000e+000 A 4=-8.23905e-003 A 6=-1.85106e-004 A 8=-2.80429e-004

[0211] A10=1.33504e-004 A12=-1.72217e-005

[0212] Ninth Surface

[0213] K=0.00000e+000 A 4=-5.05212e-003 A 6=-3.36300e-004 A 8=6.08201e-005

[0214] A10=9.33005e-007 A12=-6.60549e-007

[0215] Tenth Surface

[0216] K=0.00000e+000 A 4=8.48361e-003 A 6=-2.49024e-004 A 8=-2.47053e-006

[0217] A10=8.63458e-007 A12=-2.45232e-008

[0218] Eleventh Surface

[0219] K=0.00000e+000 A 4=3.76269e-003 A 6=1.03039e-004 A 8=-2.36342e-006

[0220] A10=-3.45118e-008 A12=5.29686e-009

[0221] Twelfth Surface

[0222] K=0.00000e+000 A 4=-3.67350e-003 A 6=1.30651e-004 A 8=-1.97917e-006

[0223] A10=1.19013e-008 A12=8.59667e-010 A14=-1.37275e-011

[0224] Thirteenth Surface

[0225] K=0.00000e+000 A 4=-2.93441e-003 A 6=6.87192e-005 A 8=-7.91416e-007

[0226] A10=-3.13873e-008 A12=1.57545e-009 A14=7.83470e-012

[0227] zoom ratio

[0228]

[0229]

[0230] Single lens data

[0231]

[0232] Numerical Example 4

[0233] Unit: mm

[0234] Surface data

[0235]

[0236] Aspherical data

[0237] Fifth Surface

[0238] K=0.00000e+000 A 4=2.81554e-005 A 6=1.84850e-004 A 8=-3.15509e-005

[0239] Sixth Surface

[0240] K=0.00000e+000 A 4=1.44367e-003 A 6=1.74832e-004 A 8=-7.82800e-006

[0241] Seventh Surface

[0242] K=0.00000e+000 A 4=7.70082e-003 A 6=-1.14006e-003 A 8=1.49727e-004

[0243] A10=-1.18323e-005 A12=4.67624e-007 A14=-3.71569e-010

[0244] Eighth surface

[0245] K=0.00000e+000 A 4=4.07615e-003 A 6=-5.26957e-004 A 8=7.96433e-005

[0246] A10=-6.17853e-006 A12=2.32990e-007 A14=-3.35783e-009

[0247] Ninth Surface

[0248] K=0.00000e+000 A 4=-5.14713e-00 3A 6=3.05044e-004 A 8=-1.15182e-005

[0249] A10=2.36679e-007 A12=-2.10950e-009

[0250] Tenth Surface

[0251] K=0.00000e+000 A 4=-3.90330e-003 A 6=1.84171e-004 A 8=-6.54476e-006

[0252] A10=1.46975e-007 A12=-1.40581e-009

[0253] zoom ratio

[0254]

[0255] Single lens data

[0256]

[0257] Table 1 illustrates the values ​​of each conditional expression in various numerical examples.

[0258] Table 1

[0259]

[0260] The examples provide optical systems and image pickup devices, each of which is small, lightweight, and high-performance.

[0261] While the invention has been described with reference to exemplary examples, it should be understood that the invention 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.

[0262] For example, the aperture SP can be deployed as close as possible to the object to form a front aperture configuration. Alternatively, the aperture SP can be deployed as close as possible to the image plane in the front unit FG. Moreover, when the optical system is combined with an image pickup device including an image sensor that converts the optical image formed on the light-receiving surface into an electrical signal, electrical corrections can be added based on the amount of distortion and lateral chromatic aberration. In addition, the F-number (aperture value) can be adjusted by the aperture SP.

Claims

1. An optical system comprising a front unit and a rear unit, Its features are, The front unit consists of the following: The first lens has positive refractive power and a meniscus shape containing a convex surface facing the object side; The second lens, positioned on the image side of the first lens and having positive refractive power, and having a convex surface facing the object side; and The third lens has negative refractive power and a concave surface facing the image side. Each of the first and second lenses has a refractive index of 1.7 or higher for the d-line. The rear unit consists of two or more but no more than four lenses, including a fourth lens with positive refractive power and a fifth lens adjacent to the fourth lens with negative refractive power. Each of the fourth and fifth lenses is made of organic material. The fourth lens deployed from the object side in the optical system has a meniscus shape with a concave surface facing the object side. The sixth lens deployed from the object side in the optical system has positive refractive power and a meniscus shape containing a convex surface facing the object side. as well as The following conditional expressions are satisfied: 0.75 < νdA / νdB < 1.30 0.75 < -fA / fB < 1.30 1.4 < fA / f < 3.5 0.20 <- fn / f < 0.70 Where νdA is the Abbe number of the fourth lens, νdB is the Abbe number of the fifth lens, fA is the focal length of the fourth lens, fB is the focal length of the fifth lens, f is the focal length of the optical system, and fn is the focal length of the third lens.

2. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: αp1 < 100×10^-7 Where αp1 is the linear expansion coefficient ( / °C) of the first lens.

3. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: 25 < νdp1 < 60 Where νdp1 is the Abbe number of the first lens.

4. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: αp2 < 100×10^-7 Where αp2 is the linear expansion coefficient ( / °C) of the second lens.

5. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: 25 < νdp2 < 60 Where νdp2 is the Abbe number of the second lens.

6. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: αn < 100×10^-7 Where αn is the linear expansion coefficient ( / °C) of the third lens.

7. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: 1.60 < N < 2.10 Where N is the refractive index of the third lens.

8. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: 15 < νdn < 35 Where νdn is the Abbe number of the third lens.

9. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: 1.00 <f / BF < 3.00 Where BF is the back focal length of the optical system.

10. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: 0.5 < |Fu| / Fm < 25.0 Where Fm is the focal length of the front element and Fu is the focal length of the rear element.

11. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: 0.10 < dA / BF < 0.60 Where dA is the on-axis thickness of the fourth lens, and BF is the back focal length of the optical system.

12. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: 0.05 < dB / BF < 0.40 Where dB is the on-axis thickness of the fifth lens, and BF is the back focal length of the optical system.

13. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: 0.50 < du / BF < 1.50 Where du is the on-axis distance of the back element from the vertex of the surface closest to the object to the vertex of the surface closest to the image plane, and BF is the back focal length of the optical system.

14. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: 50 < νdA < 60 1.45 < NA < 1.60 Where NA is the refractive index of the fourth lens.

15. The optical system according to claim 1, characterized in that, The following conditional expression is satisfied: 15 < νdA < 40 1.55 < NA < 1.75 Where NA is the refractive index of the fourth lens.

16. The optical system according to claim 1, characterized in that, The first lens is positioned as close as possible to the object.

17. The optical system according to claim 1, characterized in that, The front unit consists of a first lens, a third lens with negative refractive power, and a second lens, arranged sequentially from the object side to the image side.

18. The optical system according to claim 1, characterized in that, The fourth lens is positioned on the object side or image side of the fifth lens and is adjacent to the fifth lens.

19. An image acquisition device, comprising: The optical system according to any one of claims 1 to 18; as well as An image sensor is configured to image an optical image formed by an optical system.

Images