A large aperture lens

Abstract

The application discloses a large-aperture lens, which comprises, sequentially and spaced apart from an object side to an image side, a first fixed lens group, a first focusing lens group, a diaphragm, a second fixed lens group, a second focusing lens group and a third fixed lens group, wherein the first focusing lens group and the second focusing lens group are inner focusing groups; the technical scheme adopts a structure type of 'two focusing groups and three fixed groups', and reasonably matches and combines the optical power, shape and material of each optical lens; through simple inner focusing, clear focusing can be realized in a near distance range from infinity to 400 mm at a full aperture and a maximum F1.5, and the requirements of high resolution and achromatism are met.

Description

Technical Field

[0001] This invention relates to the field of optical lens technology, and in particular to a large aperture lens. Background Technology

[0002] With the development of culture and art, people's demands for lenses are increasing, and shooting styles are becoming more diverse. To enable lenses to meet the demands of more complex shooting environments, producing impactful videos even in relatively poor lighting conditions, while also offering high image quality and a compact, lightweight design, major established manufacturers have successively launched large-aperture lenses. However, some large-aperture lenses are designed for PL (Plexus) flange focal distance mounts, resulting in a larger overall length and diameter, making them less portable. Furthermore, to achieve high image quality at various object distances, most of these lenses employ a floating focus system, causing the front or rear of the lens to extend or retract during focusing, which is not only unsightly but also prone to dust accumulation inside the lens. In addition, the high prices of F1.8 series lenses from major international brands such as Nikon and Canon place a significant financial burden on ordinary consumers. Summary of the Invention

[0003] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a large-aperture lens that effectively solves problems such as long flange distance, dust falling into the lens interior during floating focus, and high cost.

[0004] According to an embodiment of the present invention, a large aperture lens includes, from the object side to the image side, the following elements are arranged at intervals: a first fixed lens group, a first focusing lens group, an aperture stop, a second fixed lens group, a second focusing lens group, and a third fixed lens group. The first focusing lens group and the second focusing lens group form an internal focusing group. The first fixed lens group includes, along the optical axis, a first lens, a second lens, a third lens, and a fourth lens. The first lens is a meniscus negative lens, the second lens and the third lens are cemented lenses or tightly connected combined positive and negative lenses, and the fourth lens is a biconvex positive lens. The first focusing lens group includes, along the optical axis, a fifth lens and a sixth lens. The fifth lens... The combined optical power of the sixth lens and the first lens is positive; the second fixed lens group includes the seventh lens, the eighth lens, and the ninth lens arranged sequentially along the optical axis, wherein the seventh lens and the eighth lens form a cemented doublet with positive optical power, and the ninth lens is a biconvex positive lens; the second focusing lens group includes the tenth lens, the eleventh lens, and the twelfth lens arranged sequentially along the optical axis, wherein the tenth lens is a positive lens, and the eleventh lens and the twelfth lens form a cemented doublet with negative optical power; the third fixed lens group includes the thirteenth lens and the fourteenth lens arranged at intervals along the optical axis, wherein the thirteenth lens is a biconvex positive lens, and the fourteenth lens is a meniscus negative lens with its concave surface facing the object side.

[0005] A large-aperture lens according to an embodiment of the present invention has at least the following beneficial effects:

[0006] This technical solution adopts a "two-group focusing, three-group fixing" structure, which rationally matches and combines the optical power, shape and material of each optical lens. Through a simple internal focusing method, it can still achieve clear focus from infinity to 400mm close object distance at the widest aperture, up to F1.5, meeting the requirements of high resolution and achromatic aberration.

[0007] According to some embodiments of the present invention, the large aperture lens satisfies the following relationship:

[0008] 2≤F1 / F≤4;

[0009] 80≤F2 / F≤90;

[0010] 3≤F3 / F≤5;

[0011] 6≤F4 / F≤7.5;

[0012] 10≤F5 / F≤11;

[0013] Wherein, F is the focal length of the large aperture lens, F1 is the focal length of the first fixed lens group, F2 is the focal length of the first focusing lens group, F3 is the focal length of the second fixed lens group, F4 is the focal length of the second focusing lens group, and F5 is the focal length of the third fixed lens group.

[0014] According to some embodiments of the present invention, the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens, the ninth lens, the tenth lens, the eleventh lens, the twelfth lens, the thirteenth lens, and the fourteenth lens are all glass lenses.

[0015] According to some embodiments of the present invention, the fifth lens is a ZF material lens with high refractive index, the sixth lens is an ED material lens with ultra-low dispersion, the eighth lens is an ED material lens with ultra-low dispersion, and the eleventh lens is an ED material lens with ultra-low dispersion.

[0016] According to some embodiments of the present invention, the fifth lens and the sixth lens are cemented doublet lenses.

[0017] According to some embodiments of the present invention, the first focusing lens group further includes a fifteenth lens, the fifteenth lens being a meniscus positive lens, the fifth lens being a biconvex positive lens and maintaining a gap with the sixth lens, and the sixth lens being a biconcave negative lens with its image-side concave surface cemented to the fifteenth lens.

[0018] According to some embodiments of the present invention, the thickness of the twelfth lens is greater than or equal to 12 mm.

[0019] According to some embodiments of the present invention, a filter group and / or protective glass are disposed between the third fixed lens group and the image side.

[0020] According to some embodiments of the present invention, the optical back focal length of the large aperture lens is 20.5mm.

[0021] According to some embodiments of the present invention, the large aperture lens has a focal length F = 50mm, an aperture value FNO = 1.5, and an image size of 36mm × 24mm.

[0022] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0024] Figure 1 This is a schematic diagram of focusing a large aperture lens according to the first embodiment of the present invention;

[0025] Figure 2 Rayfan diagram of the large aperture lens of the first embodiment of the present invention at an object distance of 2M;

[0026] Figure 3 This is a transverse chromatic aberration diagram of a large-aperture lens according to the first embodiment of the present invention at an object distance of 2M;

[0027] Figure 4 This is a schematic diagram of focusing a large aperture lens according to the second embodiment of the present invention;

[0028] Figure 5 Rayfan diagram of the large aperture lens of the second embodiment of the present invention at an object distance of 2M;

[0029] Figure 6 This is a chromatic aberration diagram of a large-aperture lens according to the second embodiment of the present invention at an object distance of 2M.

[0030] Icon labels:

[0031] Aperture STO, first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5, sixth lens L6, seventh lens L7, eighth lens L8, ninth lens L9, tenth lens L10, eleventh lens L11, twelfth lens L12, thirteenth lens L13, fourteenth lens L14, fifteenth lens L15. Detailed Implementation

[0032] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0033] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, etc., are based on the orientation or positional relationship shown in the drawings and are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0034] In the description of this invention, "multiple" refers to two or more. The use of "first" and "second" is for distinguishing technical features only and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features or their sequential relationship.

[0035] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0036] Reference Figure 1 As shown, a large aperture lens according to an embodiment of the present invention includes the following components arranged sequentially from the object side to the image side: a first fixed lens group, a first focusing lens group, an aperture stop STO, a second fixed lens group, a second focusing lens group, and a third fixed lens group, forming a "two focusing groups and three fixed groups" structure. The aperture stop STO is located in the middle and is used to limit the beam diameter. The first focusing lens group and the second focusing lens group are internal focusing groups, which can overcome the problems of forward and backward extension and internal dust entry during floating focusing.

[0037] The first fixed lens group includes, in sequence along the optical axis, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4. The first lens L1 is a meniscus negative lens, the second lens L2 and the third lens L3 are cemented lenses or tightly connected combined positive and negative lenses, and the fourth lens L4 is a biconvex positive lens. After the light rays from the off-axis field of view pass through the negative optical power first lens L1, the field angle decreases, which slightly reduces the coma, field curvature, and distortion related to the field of view in the subsequent group. However, after the on-axis beams are diverged by the aforementioned negative optical power first lens L1, they have a high incident height on the second lens L2, which makes the spherical aberration very large. The third lens L3 and the fourth lens L4 are in the form of two biconvex lenses to minimize the spherical aberration to the greatest extent.

[0038] The first focusing lens group includes the fifth lens L5 and the sixth lens L6 arranged sequentially along the optical axis. The combined optical power of the fifth lens L5 and the sixth lens L6 is positive.

[0039] The second fixed lens group includes the following lenses arranged sequentially along the optical axis: the seventh lens L7, the eighth lens L8, and the ninth lens L9. The seventh lens L7 and the eighth lens L8 form a positive doublet lens, which is beneficial for correcting on-axis and off-axis chromatic aberration. The ninth lens L9 is a biconvex positive lens, which further reduces spherical aberration.

[0040] The second focusing lens group comprises, sequentially arranged along the optical axis, three lenses: the tenth lens L10, the eleventh lens L11, and the twelfth lens L12. The tenth lens L10 is a positive lens. The eleventh and twelfth lenses L11 and L12 form a negative power cemented doublet, which is beneficial for correcting on-axis and off-axis chromatic aberration. Spherical aberration in large-aperture lenses becomes a major factor limiting MTF (Mean Transmission Factor) increases and must be eliminated promptly where it occurs. After the light passes through the second fixed lens group, the height of the first paraxial ray is already relatively large. Therefore, the tenth lens L10, with its positive power, helps to share the spherical aberration generated by the second fixed lens group.

[0041] The third fixed lens group includes the thirteenth lens L13 and the fourteenth lens L14, which are arranged at intervals along the optical axis. The thirteenth lens L13 is a biconvex positive lens, and the fourteenth lens L14 is a meniscus negative lens with its concave surface facing the object side. The fourteenth lens L14 is used to help the light reach the required image plane height, and the meniscus shape is also beneficial for field curvature correction.

[0042] As can be seen, this technical solution adopts a "two-group focusing, three-group fixing" structure, which reasonably matches and combines the optical power, shape and material of each optical lens. Through a simple internal focusing method, it can still achieve clear focus from infinity to 400mm close object distance at the widest aperture, up to F1.5, meeting the requirements of high resolution and achromatic aberration.

[0043] In some embodiments of the present invention, the first embodiment of the large aperture lens (Embodiment 1) satisfies the following relationship:

[0044] 2≤F1 / F≤4;

[0045] 80≤F2 / F≤90;

[0046] 3≤F3 / F≤5;

[0047] 6≤F4 / F≤7.5;

[0048] 10≤F5 / F≤11;

[0049] Wherein, F represents the focal length of the large aperture lens, F1 is the focal length of the first fixed lens group, F2 is the focal length of the first focusing lens group, F3 is the focal length of the second fixed lens group, F4 is the focal length of the second focusing lens group, and F5 is the focal length of the third fixed lens group. It should be noted that the focal lengths of the above five lens groups are not limited to a single value; as long as they fall within the aforementioned focal length range, they are all within the protection scope of this invention.

[0050] In some embodiments of the present invention, the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, the sixth lens L6, the seventh lens L7, the eighth lens L8, the ninth lens L9, the tenth lens L10, the eleventh lens L11, the twelfth lens L12, the thirteenth lens L13, and the fourteenth lens L14 are all glass lenses. This all-glass combination has excellent temperature stability.

[0051] Furthermore, in some embodiments of the present invention, the fifth lens L5 is a ZF material lens (heavy flint glass) with a high refractive index, the sixth lens L6 is an ED material lens with ultra-low dispersion, which can minimize the impact of chromatic aberration; the eighth lens L8 is an ED material lens with ultra-low dispersion, used to eliminate on-axis chromatic aberration; and the eleventh lens L11 is an ED material lens with ultra-low dispersion, which plays a key role in correcting on-axis and off-axis chromatic aberration.

[0052] like Figure 1 As shown, in some embodiments of the present invention, the fifth lens L5 and the sixth lens L6 are cemented doublet lenses, serving as the first focusing lens group lens type in Embodiment 1 of the present invention.

[0053] like Figure 4 As shown, in some embodiments of the present invention, the first focusing lens group further includes a fifteenth lens L15, which is a meniscus positive lens, a fifth lens L5 is a biconvex positive lens and maintains a gap with a sixth lens L6, and a sixth lens L6 is a biconcave negative lens and its image-side concave surface is cemented to the fifteenth lens L15, which is the lens type of the second focusing lens group in Embodiment 1 of the present invention.

[0054] In some embodiments of the present invention, the thickness of the twelfth lens L12 is greater than or equal to 12 mm. The relatively thick twelfth lens L12 increases the distance between the positive optical power surface and the negative optical power surface, which is beneficial for field curvature correction.

[0055] In some embodiments of the present invention, by minimizing or eliminating vignetting, as much peripheral field light as possible is allowed to pass through the lens to the chip surface, thereby enabling the lens to obtain higher relative illumination and ensuring the overall uniformity and transparency of the image surface brightness.

[0056] Furthermore, in some embodiments of the present invention, a filter group and / or protective glass are disposed between the third fixed lens group and the image side. The filter can attenuate a portion of long-wavelength and stray light, preventing the photosensitive chip from being interfered with by infrared rays, thereby resulting in clear image quality and bright colors; the protective glass can protect the chip from direct damage by external forces.

[0057] In some embodiments of the present invention, the focal length of the large aperture lens is F = 50mm, the aperture value is FNO = 1.5, and the imaging size is 36mm × 24mm.

[0058] The following two specific embodiments illustrate this large-aperture lens. The parameters of each embodiment that meets the above conditions are shown in the table below: the units for radius R and thickness are millimeters.

[0059] Lens group Example 1 Example 2 F1 165.74 -281.65 F2 4081.84 98.92 F3 185.62 242.31 F4 360.71 451.63 F5 517.34 -3538.13

[0060] Table 1 shows the parameters of each lens in Example 1:

[0061]

[0062]

[0063] Table 2

[0064] The focusing data for different object distances in Example 1 are shown in the table below:

[0065] Infinity 2M 0.4M D1 1.00 1.30 4.09 D2 9.45 9.15 6.36 D3 12.44 9.95 0.2 D4 4.29 6.78 16.52

[0066] Table 3

[0067] See Figure 1 Combining Tables 1 to 3, we can see that:

[0068] With an optical back focal length of 20.5mm, it meets the requirements of RF mount, Z mount and E mount, thus achieving the goal of lightweighting the entire device.

[0069] This example ensures image quality at different object distances by moving the first and second focusing groups. Throughout the focusing process, the position of the image plane does not change, and the total length of the lens does not change, which can prevent dust from falling inside the lens. At the same time, when changing to different lenses of the same series, all accessories do not need to be reinstalled, and the camera stabilizer does not require major balance adjustments.

[0070] Figure 2 The image shown is a Rayfan diagram of Example 1 at an object distance of 2M. Throughout the entire field of view, both full-aperture and local spherical aberration are controlled within a relatively ideal range, which is beneficial for overall, especially, the improvement of MTF in the central field of view.

[0071] Figure 3The image shown is the transverse chromatic aberration diagram of Example 1 at an object distance of 2M. Throughout the entire field of view, the chromatic focus shift for both short and long wavelengths does not exceed 20 micrometers, and purple fringing is not easily produced even in environments with relatively strong contrast between light and dark.

[0072] The parameters of each lens in Example 2 are shown in the table below:

[0073]

[0074]

[0075] Table 4

[0076] The focusing data for different object distances (different magnifications) in Example 2 are shown in Table 5 below:

[0077] Infinity 2M 0.4M D1 1.00 1.64 2.92 D2 11.88 11.24 9.96 D3 11.88 9.33 0.2 D4 3.79 6.34 15.47

[0078] See Figure 4 According to Tables 4 and 5, this embodiment ensures the imaging quality at different object distances by moving the first focusing group and the second focusing group. During the entire focusing process, the position of the image plane does not change, and the total length of the lens does not change, which can prevent dust from falling inside the lens. At the same time, when replacing different lenses of the same series, all accessories do not need to be reinstalled, and the camera stabilizer does not need to be adjusted for large balance.

[0079] like Figure 5 The image shown is a Rayfan diagram of Example 2 at an object distance of 2M. Throughout the entire field of view, both full-aperture and local spherical aberration are controlled within a relatively ideal range, which is beneficial for overall, especially, the improvement of MTF in the central field of view.

[0080] like Figure 6 As shown, the chromatic aberration diagram of this embodiment 2 at an object distance of 2M shows that the chromatic focus shift of short and long wavelengths does not exceed 20 micrometers throughout the entire field of view, and purple fringing is not easily produced even in environments with relatively strong contrast between light and dark.

[0081] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A large aperture lens characterized by, The lens comprises, from the object side to the image side, a first fixed lens group, a first focusing lens group, a diaphragm, a second fixed lens group, a second focusing lens group, and a third fixed lens group, wherein the first focusing lens group and the second focusing lens group are inner focusing groups. The first fixed lens group comprises, along the optical axis, a first lens (L1), a second lens (L2), a third lens (L3), and a fourth lens (L4), wherein the first lens (L1) is a meniscus negative lens, the second lens (L2) and the third lens (L3) are cemented lenses or a combined positive-negative lens with close connection, and the fourth lens (L4) is a biconvex positive lens. The first focusing lens group comprises, along the optical axis, a fifth lens (L5) and a sixth lens (L6), wherein the combined optical power of the fifth lens (L5) and the sixth lens (L6) is positive. The second fixed lens group comprises, along the optical axis, a seventh lens (L7), an eighth lens (L8), and a ninth lens (L9), wherein the seventh lens (L7) and the eighth lens (L8) form a double cemented lens with positive optical power, and the ninth lens (L9) is a biconvex positive lens. The second focusing lens group comprises, along the optical axis, a tenth lens (L10), an eleventh lens (L11), and a twelfth lens (L12), wherein the tenth lens (L10) is a positive lens, and the eleventh lens (L11) and the twelfth lens (L12) form a double cemented lens with negative optical power. The third fixed lens group comprises, along the optical axis, a thirteenth lens (L13) and a fourteenth lens (L14), wherein the thirteenth lens (L13) is a biconvex positive lens, and the fourteenth lens (L14) is a meniscus negative lens with a concave surface facing the object side. In the above lens, the optical elements with optical power are only the above fourteen lenses.

2. The large aperture lens of claim 1, wherein: The large-aperture lens satisfies the following relationships: 2≤F1 / F≤4; 80≤F2 / F≤90; 3≤F3 / F≤5; 6≤F4 / F≤7.5; 10≤F5 / F≤11; wherein F is the focal length of the large-aperture lens, F1 is the focal length of the first fixed lens group, F2 is the focal length of the first focusing lens group, F3 is the focal length of the second fixed lens group, F4 is the focal length of the second focusing lens group, and F5 is the focal length of the third fixed lens group.

3. The large aperture lens of claim 1 or 2, wherein: The first lens (L1), the second lens (L2), the third lens (L3), the fourth lens (L4), the fifth lens (L5), the sixth lens (L6), the seventh lens (L7), the eighth lens (L8), the ninth lens (L9), the tenth lens (L10), the eleventh lens (L11), the twelfth lens (L12), the thirteenth lens (L13), and the fourteenth lens (L14) are all glass lenses.

4. The large aperture lens of claim 1 or 2, wherein: The fifth lens (L5) is a ZF material lens with high refractive index, the sixth lens (L6) is an ED material lens with ultra-low dispersion, the eighth lens (L8) is an ED material lens with ultra-low dispersion, and the eleventh lens (L11) is an ED material lens with ultra-low dispersion.

5. The large aperture lens of claim 1 or 2, wherein: The fifth lens (L5) and the sixth lens (L6) are double cemented lenses.

6. The large aperture lens of claim 1, wherein: The first focusing lens group further comprises a fifteenth lens (L15), the fifteenth lens (L15) is a meniscus positive lens, the fifth lens (L5) is a double convex positive lens and is kept apart from the sixth lens (L6), and the sixth lens (L6) is a double concave negative lens and the image side concave surface is cemented with the fifteenth lens (L15).

7. The large aperture lens of claim 1, wherein: The thickness of the twelfth lens (L12) is greater than or equal to 12 mm.

8. The large aperture lens of claim 1, wherein: A filter group and / or a protective glass are arranged between the third fixed lens group and the image side.

9. The large aperture lens of claim 1, wherein: The optical back focal length of the large aperture lens is 20.5 mm.

10. The large aperture lens of claim 1, wherein: The focal length of the large aperture lens is F=50 mm, the aperture value is FNO=1.5, and the imaging size is 36 mm×24 mm.

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