Four-piece object space telecentric lens

Abstract

The utility model belongs to the technical field of optical imaging systems, and particularly relates to a four-piece object space telecentric lens. The optical system comprises a first lens, a second lens, a third lens, a diaphragm, a fourth lens and an imaging surface which are sequentially arranged from an object side to an image side. The first lens has positive focal power, an object side surface is a convex surface, and an image side surface is a plane; the second lens has negative focal power, and the object side surface and the image side surface are concave surfaces; the third lens has positive focal power, and the object side surface and the image side surface are convex surfaces; the fourth lens has positive focal power, the object side surface is a convex surface, and the image side surface is a concave surface. Wherein the second lens and the third lens are bonded to form a bonding lens, and the lenses are made of glass materials. The four-piece object space telecentric lens is realized by reasonably distributing materials, thicknesses, curvatures and gaps of the lenses, has the advantages of simple structure, low cost, small distortion and good imaging quality, can be matched with 2 / 3 CCD (Charge Coupled Device), and is widely applied to the field of industrial detection lenses.

Description

Technical Field

[0001] The utility model belongs to the technical field of optical imaging systems, and in particular relates to a four-piece object-space telecentric lens. Background Art

[0002] At the beginning of the 21st century, with the wide application of machine vision systems in the field of precision inspection, ordinary industrial lenses are difficult to meet the inspection requirements. To make up for the deficiencies of ordinary lens applications and meet the needs of precision inspection, telecentric lenses came into being. Due to their unique parallel optical path design, telecentric lenses have always been favored by machine vision applications with high requirements for lens distortion. At present, there are many telecentric lenses on the market, but their structures are relatively complex, with a large number of lens elements and complex assembly. Therefore, there is a need for a telecentric lens with a simple structure, fewer lenses, and good imaging quality. Content of the Utility Model

[0003] To solve the defects and deficiencies of the prior art, the purpose of the present utility model is to provide an object-space telecentric lens with a simple structure, low cost, small distortion, large target surface, high imaging quality, and high overall reliability.

[0004] To achieve the above purpose, the technical solution adopted by the present utility model is: it includes a first lens, a second lens, a third lens, a diaphragm, a fourth lens, and an imaging surface. The first lens has a positive optical power, the object side is convex, and the image side is flat; the second lens has a negative optical power, and both the object side and the image side are concave; the third lens has a positive optical power, and both the object side and the image side are convex; the fourth lens has a positive optical power, the object side is convex, and the image side is concave. Among them, the second lens and the third lens are bonded into a cemented lens, and all the lenses are made of glass materials.

[0005] Preferably, the first lens also satisfies: N1≥1.68, V1≤55.1, where N1 is the refractive index of the first lens and V1 is the Abbe number of the first lens;

[0006] The second lens also satisfies: N2≥1.65, V2≤33.9, where N2 is the refractive index of the second lens and V2 is the Abbe number of the second lens;

[0007] The third lens also satisfies: N3≥1.65, V3≤55.9, where N3 is the refractive index of the third lens and V3 is the Abbe number of the third lens;

[0008] The fourth lens also satisfies: N4≥1.80, V4≤44.3, where N4 is the refractive index of the fourth lens and V4 is the Abbe number of the fourth lens.

[0009] Preferably, the first lens, the second lens, the third lens, and the fourth lens are all spherical lenses made of glass materials.

[0010] Preferably, the focal lengths of the first lens, the second lens, the third lens, and the fourth lens are f1, f2, f3, and f4 respectively, and the focal length of the overall optical system is f, which satisfies the following ratios: 1.1 < f1 / f < 1.3, -0.4 < f2 / f < -0.2, 0.3 < f3 / f < 0.4, 1.1 < f4 / f < 1.3.

[0011] Preferably, the air gap between the first lens and the second lens is 40 - 50 mm, the air gap between the second and third lenses and the diaphragm is 40 - 50 mm, the air gap between the diaphragm and the fourth lens is 1 - 3 mm, and the air gap between the fourth lens and the imaging surface is 20 - 30 mm.

[0012] Preferably, the focal length EFL of the optical system, the total optical length TOTR of the optical system, and the working distance T of the optical system also satisfy: 0.4 ≤ EFL / TOTR ≤ 0.6, 0.8 < T / TOTR < 1.2.

[0013] Preferably, the diaphragm of the optical system is located between the third lens and the fourth lens.

[0014] After adopting the above structure, the beneficial effects of the present utility model are as follows:

[0015] 1. It adopts a spherical lens design with four pieces of all - glass materials. Its structure is simple, the sensitivity is low, which is conducive to assembly and batch production. The all - glass lens design can adapt to different environments, and the overall reliability is high.

[0016] 2. Through optimized design and reasonable distribution of the optical power, it realizes small distortion, large target surface, and high imaging quality.

[0017] 3. The target surface is large, and it can be maximally matched with a photosensitive chip with a 2 / 3” CCD large target surface for use. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model or the prior art, the present utility model will be described in detail by the following specific embodiments and the accompanying drawings.

[0019] Figure 1 is the structural schematic diagram of the present utility model;

[0020] Figure 2 is the modulation transfer function curve diagram of the present utility model.

[0021] Figure 3 is the field curvature and distortion diagram of the present utility model

[0022] Figure 4 is the spot diagram of the present utility model

[0023] Figure 5 Vertical chromatic aberration diagram of the present utility model

[0024] Explanation of reference numerals: L1 - first lens, L2 - second lens, L3 - third lens, L4 - fourth lens, S - aperture stop, IMA - imaging plane Detailed implementation manners

[0025] To make the objectives, technical solutions and advantages of the present utility model clearer and more understandable, the present utility model will be described below through specific embodiments shown in the drawings. However, it should be understood that these descriptions are only exemplary and do not limit the scope of the present utility model. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present utility model.

[0026] Here, it should also be noted that in order to avoid obscuring the present utility model due to unnecessary details, only the structures and / or processing steps closely related to the solution according to the present utility model are shown in the drawings, while other details less related to the present utility model are omitted.

[0027] Referring to as Figure 1 shown, the following technical solutions are adopted in this detailed implementation manner: The optical system includes a first lens, a second lens, a third lens, an aperture stop, a fourth lens, and an imaging plane arranged in sequence from the object side to the image side. The first lens has a positive optical power, the object side is a convex surface, and the image side is a flat surface; the second lens has a negative optical power, and both the object side and the image side are concave surfaces; the third lens has a positive optical power, and both the object side and the image side are convex surfaces; the fourth lens has a positive optical power, the object side is a convex surface, and the image side is a concave surface. Among them, the second lens and the third lens are bonded into a cemented lens, and all the lenses are made of glass materials.

[0028] In this embodiment, the first lens further satisfies: N1≥1.68, V1≤55.1, where N1 is the refractive index of the first lens and V1 is the Abbe number of the first lens;

[0029] The second lens further satisfies: N2≥1.65, V2≤33.9, where N2 is the refractive index of the second lens and V2 is the Abbe number of the second lens;

[0030] The third lens further satisfies: N3≥1.65, V3≤55.9, where N3 is the refractive index of the third lens and V3 is the Abbe number of the third lens;

[0031] The fourth lens further satisfies: N4≥1.80, V4≤44.3, where N4 is the refractive index of the fourth lens and V4 is the Abbe number of the fourth lens.

[0032] In this embodiment, the first lens, the second lens, the third lens, and the fourth lens are all spherical lenses made of glass.

[0033] In this embodiment, the focal lengths of the first lens, the second lens, the third lens, and the fourth lens are f1, f2, f3, and f4 respectively, and the focal length of the overall optical system is f, which satisfies the following ratio: 1.1 < f1 / f < 1.3, -0.4 < f2 / f < -0.2, 0.3 < f3 / f < 0.4, 1.1 < f4 / f < 1.3.

[0034] In this embodiment, the air gap between the first lens and the second lens is 40 - 50 mm, the air gap between the second and third lenses and the diaphragm is 40 - 50 mm, the air gap between the diaphragm and the fourth lens is 1 - 3 mm, and the air gap between the fourth lens and the imaging surface is 20 - 30 mm.

[0035] In this embodiment, the focal length EFL of the optical system, the total optical length TOTR of the optical system, and the working distance T of the optical system also satisfy: 0.4 ≤ EFL / TOTR ≤ 0.6, 0.8 < T / TOTR < 1.2.

[0036] In this embodiment, the diaphragm of the optical system is located between the third lens and the fourth lens.

[0037] In the embodiment of the present application, for convenience of description, the following expressions are made: the object surface is OBJ, the front surface of the first lens is S1, the rear surface of the first lens is S2, the front surface of the second lens is S3, the rear surface of the second lens and the front surface of the third lens are S4, the rear surface of the third lens is S5, the diaphragm is STO, the front surface of the fourth lens is S6, the rear surface of the fourth lens is S7, and the imaging surface is IMA. The parameters of each lens are as follows in the table:

[0038]

[0039] In this embodiment, the optical lens achieves the following technical indicators:

[0040] The working distance is 135 mm, the image size is 11.2 mm, the object field of view is 24.9 mm, the magnification is 0.45178, the total optical length is 138 mm, the focal length is 65.15 mm, the object space NA is 0.01467, and the object resolution is 22 um.

[0041] Figure 2This is the modulation transfer function curve graph of the telephoto lens in this embodiment. It can be seen from the graph that the MTF of the optical lens performs well in the visible light band. At a spatial frequency of 30 LP / MM in the central field of view, its MTF value is greater than 0.65; at a spatial frequency of 30 LP / MM in the marginal field of view, its MTF value is greater than 0.57. It can be seen that the curve is close to the diffraction limit, indicating that the performance of the optical lens is good.

[0042] Figure 3 This is the field curvature and distortion graph of the telephoto lens in this embodiment. It can be seen from the graph that the maximum optical distortion value of the optical lens in the full field of view is less than 0.0692%, ensuring the authenticity of the picture and reducing the distortion of the picture. The optical lens effectively controls the field curvature within ±0.4 mm for light of different wavelengths, that is, the image quality in the center is less different from that in the periphery during imaging.

[0043] Figure 4 This is the spot diagram of the telephoto lens in this embodiment. It can be seen from the graph the spot sizes of each band in different fields of view. The maximum RSM radius is 6.387 um, which is less than the Airy disk radius, indicating that the aberrations of this optical system are small and the imaging quality is good.

[0044] Figure 5 This is the lateral chromatic aberration graph of the telephoto lens in this embodiment. It can be seen from the graph that the chromatic aberrations of each wavelength are within the Airy disk range, indicating that the chromatic aberrations of each wavelength are corrected well, effectively improving the image quality.

[0045] For those skilled in the art, it is obvious that the present utility model is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present utility model. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present utility model is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present utility model.

[0046] In addition, it should be understood that although this specification is described according to embodiments, not each embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A four-piece object-space telecentric lens, characterized in that: It includes a first lens, a second lens, a third lens, a diaphragm, a fourth lens, and an imaging surface arranged in sequence from the object side to the image side. The first lens has a positive optical power, the object side is convex, and the image side is flat; the second lens has a negative optical power, and both the object side and the image side are concave; the third lens has a positive optical power, and both the object side and the image side are convex; the fourth lens has a positive optical power, the object side is convex, and the image side is concave, wherein the second lens and the third lens are bonded into a cemented lens.

2. The four-piece object-space telecentric lens according to claim 1, wherein: The first lens further satisfies: N1≥1.68, V1≤55.1, where N1 is the refractive index of the first lens and V1 is the Abbe number of the first lens; The second lens further satisfies: N2≥1.65, V2≤33.9, where N2 is the refractive index of the second lens and V2 is the Abbe number of the second lens; The third lens further satisfies: N3≥1.65, V3≤55.9, where N3 is the refractive index of the third lens and V3 is the Abbe number of the third lens; The fourth lens further satisfies: N4≥1.80, V4≤44.3, where N4 is the refractive index of the fourth lens and V4 is the Abbe number of the fourth lens.

3. A four-piece object-space telecentric lens according to claim 1, characterized in that: The first lens, the second lens, the third lens, and the fourth lens are all spherical lenses made of glass.

4. A four-piece object-space telecentric lens according to claim 1, characterized in that: The focal lengths of the first lens, the second lens, the third lens, and the fourth lens are f1, f2, f3, and f4 respectively, and the focal length of the overall optical system is f, which satisfies the following ratios: 1.1<f1 / f<1.3, -0.4<f2 / f<-0.2, 0.3<f3 / f<0.4, 1.1<f4 / f<1.

3.

5. A four-piece object-space telecentric lens according to claim 1, characterized in that: The diaphragm is located between the third lens and the fourth lens.

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