High performance low distortion close-up imaging optical system

Abstract

The present application relates to a kind of high-performance low-distortion close-range imaging optical systems, optical system is sequentially provided with focusing lens group, diaphragm, fixed lens group, imaging surface from object side to image side along optical axis direction, the focusing lens group can be moved along optical axis direction and fixed lens group is close or far away from fixed lens group and is focused, focusing lens group includes sequentially arranged from object side to image side along optical axis direction and the first lens with positive refractive power, the second lens with positive refractive power, the third lens with negative refractive power, the fourth lens with negative refractive power, the fifth lens with positive refractive power, the sixth lens with positive refractive power;The fixed lens group includes sequentially arranged from object side to image side along optical axis direction and the seventh lens with positive refractive power and the eighth lens with negative refractive power.The optical structure of the present application is compact, stable and reliable, each lens is reasonably arranged, and the structure is light, has the characteristics such as focusing fast and stable, suitable for 2 / 3 '' 10 million pixel CMOS adaptation.

Description

Technical fields:

[0002] This invention relates to a high-performance, low-distortion close-range imaging optical system. Background technology:

[0004] Industrial lenses are currently widely used in machine vision inspection, and many similar inspection lenses have been put into use. However, existing lenses commonly used in the market have shortcomings in close-range imaging, inconsistent image center and edge for lenses of the same focal length, insufficient resolution, and complex structures, which cannot meet more advanced inspection needs, thus limiting their widespread adoption. Summary of the Invention:

[0006] The present invention addresses the problems existing in the prior art, namely, the technical problem to be solved by the present invention is to provide a high-performance, low-distortion close-range imaging optical system.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a high-performance, low-distortion close-range imaging optical system. The optical system is provided with a focusing lens group, an aperture, a fixed lens group, and an imaging plane in sequence from the object side to the image side along the optical axis. The focusing lens group can move closer to or further away from the fixed lens group along the optical axis to perform focusing. The focusing lens group includes a first lens with positive optical power, a second lens with positive optical power, a third lens with negative optical power, a fourth lens with negative optical power, a fifth lens with positive optical power, and a sixth lens with positive optical power, arranged in sequence from the object side to the image side along the optical axis. The fixed lens group includes a seventh lens with positive optical power and an eighth lens with negative optical power, arranged in sequence from the object side to the image side along the optical axis.

[0008] Furthermore, the second lens and the third lens form a first cemented film with a negative total optical power; the fourth lens and the fifth lens form a second cemented film with a negative total optical power; and the seventh lens and the eighth lens form a third cemented film with a positive total optical power.

[0009] Furthermore, the air distance from the first lens to the first cemented sheet is 0.1 mm; the air distance from the first cemented sheet to the aperture is 2.99 mm; the air distance from the aperture to the second cemented sheet is 2.88 mm; the air distance from the second cemented sheet to the sixth lens is 0.1 mm; the air distance from the sixth lens to the third cemented sheet is 1.277–10.945 mm; and the distance from the third cemented sheet to the imaging plane D is 13.9 mm.

[0010] Furthermore, in the first cemented sheet, the materials of the second and third lenses are heavy phosphorus crown glass and heavy flint glass, respectively; in the second cemented sheet, the materials of the fourth and fifth lenses are heavy flint glass and heavy lanthanum flint glass, respectively; and in the third cemented sheet, the materials of the seventh and eighth lenses are heavy lanthanum flint glass and heavy flint glass, respectively.

[0011] Furthermore, the first lens is a crescent-shaped lens with a convex object-side surface and a concave image-side surface; the second lens is a crescent-shaped lens with a convex object-side surface and a concave image-side surface; the third lens is a crescent-shaped lens with a convex object-side surface and a concave image-side surface; the fourth lens is a crescent-shaped lens with a concave object-side surface and a convex image-side surface; the fifth lens is a crescent-shaped lens with a concave object-side surface and a convex image-side surface; the sixth lens is a biconvex lens with a convex object-side surface and a convex image-side surface; the seventh lens is a biconvex lens with a convex object-side surface and a convex image-side surface; and the eighth lens is a biconcave lens with a concave object-side surface and a concave image-side surface.

[0012] Furthermore, each lens in the focusing lens group and the fixed lens group is made of spherical glass.

[0013] Furthermore, the total focal length of the optical system is f, the focal length of the first lens and the first cemented sheet is f1, the focal length of the second cemented sheet and the sixth lens is f2, and the focal length of the third cemented sheet is f3. The ratio of f1 to f satisfies the following relationship: 1.0 < |f1 / f| < 2.5; the ratio of f2 to f satisfies the following relationship: 1.0 < |f2 / f| < 2.0; and the ratio of f3 to f satisfies the following relationship: 2.5 < |f3 / f| < 4.0.

[0014] Furthermore, the refractive indices of the first lens, second lens, third lens, fourth lens, fifth lens, sixth lens, seventh lens, and eighth lens are n1, n2, n3, n4, n5, n6, n7, and n8, respectively, satisfying the following relationships: 1.8 < n1 < 2.0; 1.55 < n2 < 1.62; 1.73 < n3 < 1.96; 1.65 < n4 < 1.92; 1.8 < n5 < 2.0; 1.8 < n6 < 2.0; 1.8 < n7 < 1.90; 1.73 < n8 < 1.96.

[0015] Compared with the prior art, the present invention has the following advantages: The present invention adopts five groups of eight spherical lenses, with a compact, stable and reliable optical structure, reasonable lens settings, lightweight structure, and features fast and stable focusing. It is suitable for 2 / 3” 10-megapixel CMOS adapters, with high image clarity, good uniformity, good contrast, and excellent relative illumination, making it suitable for industrial inspection. Attached image description:

[0017] Figure 1 This is a schematic diagram of the optical system according to an embodiment of the present invention. Figure 1 ;

[0018] Figure 2 This is a schematic diagram of the optical system according to an embodiment of the present invention. Figure 2 ;

[0019] Figure 3 This is an MTF curve diagram of a 200mm object distance in an embodiment of the present invention;

[0020] Figure 4 This is an MTF curve diagram of an 800mm object distance in an embodiment of the present invention;

[0021] Figure 5 This is an MTF curve diagram of the object distance at infinity in an embodiment of the present invention;

[0022] Figure 6 This is an optical distortion curve diagram from an embodiment of the present invention;

[0023] Figure 7 This is a relative illumination curve diagram in an embodiment of the present invention.

[0024] In the picture:

[0025] A - Focusing lens group; A1 - First lens; A2 - Second lens; A3 - Third lens; A4 - Fourth lens; A5 - Fifth lens; A6 - Sixth lens; B - Fixed lens group; B1 - Seventh lens; B2 - Eighth lens; C - Aperture stop; D - Imaging plane; H1 - First cemented sheet; H2 - Second cemented sheet; H3 - Third cemented sheet. Detailed implementation method:

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0028] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, 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.

[0029] like Figures 1-2As shown, the purpose of this invention is to solve the problem of inconsistent imaging center and edge in existing lenses with the same focal length, thereby providing a high-performance, low-distortion close-range imaging optical system that can achieve an ultra-short working distance of 200mm. Specifically, the optical system is provided with a focusing lens group A, an aperture stop C, a fixed lens group B, and an imaging plane D along the optical axis from the object side to the image side. The focusing lens group A can move closer to or further away from the fixed lens group B along the optical axis to achieve focusing at different object distances. The focusing lens group A includes a first lens A1 with positive optical power, a second lens A2 with positive optical power, a third lens A3 with negative optical power, a fourth lens A4 with negative optical power, a fifth lens A5 with positive optical power, and a sixth lens A6 with positive optical power, arranged sequentially from the object side to the image side along the optical axis. The fixed lens group B includes a seventh lens B1 with positive optical power and an eighth lens B2 with negative optical power, arranged sequentially from the object side to the image side along the optical axis.

[0030] In this embodiment, the first lens A1 is a positive power crescent-shaped lens, with its object-side surface being convex and its image-side surface being concave; the second lens A2 is a positive power crescent-shaped lens, with its object-side surface being convex and its image-side surface being concave; the third lens A3 is a negative power crescent-shaped lens, with its object-side surface being convex and its image-side surface being concave; and the fourth lens A4 is a negative power crescent-shaped lens, with its object-side surface being concave and its image-side surface being convex. The fifth lens A5 is a positive power crescent-shaped lens, with its object-side surface being concave and its image-side surface being convex; the sixth lens A6 is a positive power biconvex lens, with both its object-side and image-side surfaces being convex; the seventh lens B1 is a positive power biconvex lens, with both its object-side and image-side surfaces being convex; the eighth lens B2 is a negative power biconcave lens, with both its object-side and image-side surfaces being concave.

[0031] In this embodiment, the second lens A2 (positive optical power) and the third lens A3 (negative optical power) are made of heavy phosphor crown glass and heavy flint glass, respectively. They are combined with optical adhesive to form the first cemented sheet H1 in the focusing lens group A, and the total optical power of the first cemented sheet is negative. The fourth lens A4 (negative optical power) and the fifth lens A5 (positive optical power) are made of heavy flint glass and heavy lanthanum flint glass, respectively. They are combined with optical adhesive to form the second cemented sheet H2 in the focusing lens group A, and the total optical power of the second cemented sheet H2 is negative. The seventh lens B1 (positive optical power) and the eighth lens B2 (negative optical power) are made of heavy lanthanum flint glass and heavy flint glass, respectively. They are combined with optical adhesive to form the third cemented sheet H3 in the fixed lens group B, and the total optical power of the third cemented sheet H3 is positive. By rationally allocating optical power, the influence of primary aberrations and chromatic aberrations on image quality is effectively corrected, thereby improving the contrast and resolution of the entire optical system.

[0032] In this embodiment, the air distance from the first lens A1 to the first cemented sheet H1 is 0.1 mm; the air distance from the first cemented sheet H1 to the aperture C is 2.99 mm; the air distance from the aperture C to the second cemented sheet H2 is 2.88 mm; the air distance from the second cemented sheet H2 to the sixth lens A6 is 0.1 mm; the air distance from the sixth lens A6 to the third cemented sheet H3 is variable, varying between 1.277 and 10.945 mm; and the distance from the third cemented sheet H3 to the imaging plane D is 13.9 mm. When the lens needs to focus at different object distances, it is only necessary to change the air gap between the focusing lens group A and the fixed lens group B to achieve focusing clarity, clear imaging at different object distances, support for an ultra-short working object distance of 200 mm, high image clarity, good uniformity, good contrast, and excellent relative illumination, making it suitable for industrial inspection.

[0033] In this embodiment, each lens in the focusing lens group and the fixed lens group is made of spherical glass, employing a five-group, eight-element glass lens structure. The R-value of each lens is ingeniously designed, which not only reduces the difficulty of the manufacturing process but also controls production costs. The combination of three cemented lenses effectively eliminates chromatic aberration and improves resolution, thereby further enhancing the optical characteristics and imaging performance of the optical system. Furthermore, the lens coating process of each spherical lens employs a high-transmittance multilayer AR film, effectively suppressing stray light and ghosting, resulting in higher contrast and resolution in the lens image.

[0034] In this embodiment, the total focal length of the optical system is f, the focal length of the first lens and the first cemented sheet is f1, the focal length of the second cemented sheet and the sixth lens is f2, and the focal length of the third cemented sheet is f3. The ratio of f1 to f satisfies the following relationship: 1.0 < |f1 / f| < 2.5; the ratio of f2 to f satisfies the following relationship: 1.0 < |f2 / f| < 2.0; and the ratio of f3 to f satisfies the following relationship: 2.5 < |f3 / f| < 4.0.

[0035] In this embodiment, the refractive indices of the first lens, second lens, third lens, fourth lens, fifth lens, sixth lens, seventh lens, and eighth lens are n1, n2, n3, n4, n5, n6, n7, and n8, respectively, satisfying the following relationships: 1.8 < n1 < 2.0; 1.55 < n2 < 1.62; 1.73 < n3 < 1.96; 1.65 < n4 < 1.92; 1.8 < n5 < 2.0; 1.8 < n6 < 2.0; 1.8 < n7 < 1.90; 1.73 < n8 < 1.96.

[0036] In this embodiment, the parameters of each lens are shown in the table below:

[0037]

[0038] Using the above lens parameters, an optical system for an industrial lens with a focal length of 35mm was achieved through apochromatic design and reasonable allocation of optical power: optical distortion ≤ -0.17%, total optical length TTL ≤ 44.46mm, optical back focal length ≥ 10mm, relative illumination ≥ 94%, and a half-group focusing mechanism; furthermore, it maintains excellent optical performance from 200mm to infinity and can meet the application requirements of different environments; at the same time, its aperture can also be flexibly adjusted, with an adjustment range from F2.8 to F16.

[0039] The advantages of this invention are: compact optical structure, low distortion, target surface of 2 / 3", relative aperture of 2.8", optical system fully utilizes crown glass and flint glass combination, fully balances the optical power of the system, and has good image quality from 200mm to infinity.

[0040] If this invention discloses or relates to mutually fixedly connected components or structural parts, then, unless otherwise stated, a fixed connection can be understood as: a detachable fixed connection (e.g., using bolts or screws), or a non-detachable fixed connection (e.g., riveting, welding). Of course, mutually fixed connections can also be replaced by an integral structure (e.g., manufactured in one piece using a casting process) (except where it is obviously impossible to use an integral molding process).

[0041] In addition, unless otherwise stated, the terms used in any of the technical solutions disclosed in this invention to indicate positional relationships or shapes include states or shapes that are similar to, close to, or approximate with those states or shapes.

[0042] Any component provided by this invention can be assembled from multiple individual components or can be a single component manufactured by a one-piece molding process.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A high-performance, low-distortion near-field imaging optical system, characterized in that: The optical system comprises, from the object side to the image side, a focusing lens group, an aperture stop, a fixed lens group, and an imaging plane, arranged sequentially along the optical axis. The focusing lens group can move closer to or further away from the fixed lens group along the optical axis for focusing. The focusing lens group includes, from the object side to the image side, a first lens with positive optical power, a second lens with positive optical power, a third lens with negative optical power, a fourth lens with negative optical power, a fifth lens with positive optical power, and a sixth lens with positive optical power. The fixed lens group includes, from the object side to the image side, a seventh lens with positive optical power and an eighth lens with negative optical power, arranged sequentially along the optical axis. The second lens and the third lens form a first cemented film with a negative total optical power; the fourth lens and the fifth lens form a second cemented film with a negative total optical power; and the seventh lens and the eighth lens form a third cemented film with a positive total optical power. The total focal length of the optical system is f. The focal lengths of the first lens and the first cemented sheet are f1, the focal lengths of the second cemented sheet and the sixth lens are f2, and the focal length of the third cemented sheet is f3. The ratio of f1 to f satisfies the following relationship: 1.0 < |f1 / f| < 2.5; the ratio of f2 to f satisfies the following relationship: 1.0 < |f2 / f| < 2.0; and the ratio of f3 to f satisfies the following relationship: 2.5 < |f3 / f| < 4.

0.

2. The high-performance, low-distortion near-field imaging optical system according to claim 1, characterized in that: The air distance from the first lens to the first cemented sheet is 0.1 mm; the air distance from the first cemented sheet to the aperture is 2.99 mm; the air distance from the aperture to the second cemented sheet is 2.88 mm; the air distance from the second cemented sheet to the sixth lens is 0.1 mm; the air distance from the sixth lens to the third cemented sheet is 1.277–10.945 mm; and the distance from the third cemented sheet to the imaging plane D is 13.9 mm.

3. The high-performance, low-distortion near-field imaging optical system according to claim 1, characterized in that: In the first cemented sheet, the materials of the second and third lenses are heavy phosphorus crown glass and heavy flint glass, respectively; in the second cemented sheet, the materials of the fourth and fifth lenses are heavy flint glass and heavy lanthanum flint glass, respectively; and in the third cemented sheet, the materials of the seventh and eighth lenses are heavy lanthanum flint glass and heavy flint glass, respectively.

4. The high-performance, low-distortion close-range imaging optical system according to claim 1, characterized in that: The first lens is a crescent-shaped lens with a convex object-side surface and a concave image-side surface; the second lens is a crescent-shaped lens with a convex object-side surface and a concave image-side surface; the third lens is a crescent-shaped lens with a convex object-side surface and a concave image-side surface; the fourth lens is a crescent-shaped lens with a concave object-side surface and a convex image-side surface; the fifth lens is a crescent-shaped lens with a concave object-side surface and a convex image-side surface; the sixth lens is a biconvex lens with a convex object-side surface and a convex image-side surface; the seventh lens is a biconvex lens with a convex object-side surface and a convex image-side surface; and the eighth lens is a biconcave lens with a concave object-side surface and a concave image-side surface.

5. The high-performance, low-distortion near-field imaging optical system according to claim 1, characterized in that: Each lens in the focusing lens group and the fixed lens group is made of spherical glass.

6. The high-performance, low-distortion near-field imaging optical system according to claim 1, characterized in that: The refractive indices of the first lens, second lens, third lens, fourth lens, fifth lens, sixth lens, seventh lens, and eighth lens are n1, n2, n3, n4, n5, n6, n7, and n8, respectively, and satisfy the following relationships: 1.8 < n1 < 2.0; 1.55 < n2 < 1.62; 1.73 < n3 < 1.96; 1.65 < n4 < 1.92; 1.8 < n5 < 2.0; 1.8 < n6 < 2.0; 1.8 < n7 < 1.90; 1.73 < n8 < 1.96.

Images