High-definition ultra-wide-angle flat-field objective lens
阅读说明：本技术 一种高清晰度超广角平场物镜 (High-definition ultra-wide-angle flat-field objective lens ) 是由 宋菲君 周鹏 何林 于 2019-09-20 设计创作，主要内容包括：本发明提供一种高清晰度超广角平场物镜,包括沿光轴从物体侧到像侧依次设置的第一透镜、第二透镜、第三透镜、第四透镜、第五透镜、第六透镜以及第七透镜,第二透镜与第三透镜之间设置一光阑,第一透镜、第二透镜和第七透镜为负光焦度透镜,第三透镜、第四透镜、第五透镜和第六透镜为正光焦度透镜,其中第六透镜与第七透镜组成具有正光焦度的胶合透镜。本物镜视角可达120°,具有足够高的分辨率和清晰度,且结构紧凑。(The invention provides a high-definition ultra-wide-angle field objective lens which comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens which are sequentially arranged from an object side to an image side along an optical axis, wherein a diaphragm is arranged between the second lens and the third lens, the first lens, the second lens and the seventh lens are negative focal power lenses, the third lens, the fourth lens, the fifth lens and the sixth lens are positive focal power lenses, and the sixth lens and the seventh lens form a cemented lens with positive focal power. The visual angle of the objective can reach 120 degrees, and the objective has high enough resolution and definition and compact structure.)
1. A high-definition ultra-wide-angle field objective lens is characterized by comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens which are sequentially arranged from an object side to an image side along an optical axis, wherein a diaphragm is arranged between the second lens and the third lens, the first lens, the second lens and the seventh lens are negative focal power lenses, the third lens, the fourth lens, the fifth lens and the sixth lens are positive focal power lenses, and the sixth lens and the seventh lens form a cemented lens with positive focal power.
2. The high definition ultra-wide field objective lens of claim 1, wherein the objective lens focal length f' is 3.40 ± 0.5 mm.
3. The high definition ultra-wide angle flat field objective lens of claim 1, wherein the horizontal field angle of the objective lens is at most 120 °.
4. The high definition ultra-wide angle flat field objective of claim 1, wherein the objective has a Petzval radius RPetzAnd focal length f': rPetz/f′＞20。
5. The high definition ultra-wide field objective lens of claim 1, wherein the first lens and the second lens are meniscus lenses and are curved toward the stop.
6. The high definition ultra-wide field objective of claim 1, wherein the first, second and seventh lenses are made of flint glass, and the third, fourth, fifth and sixth lenses are made of specialty crown glass, including type H-ZPK 5.
7. The high definition ultra-wide field objective of claim 1, wherein the full field ray diffuse spots each have an RMS radius of less than 1.4 μm.
8. The high definition ultra-wide field objective of claim 1, wherein the maximum spatial frequency is set to 200mm-1When the color light of each field of view and each wavelength is at a frequency of 100mm-1the MTF values at (a) are consistently above 0.60.
9. The high definition ultra-wide field objective of claim 1, wherein the detector is disposed on the image side, and the ratio of the distance TOTR from the center of the first objective to the detector surface to the focal length f' is: TOTR/f' < 7.
Technical Field
The invention relates to an imaging technology, in particular to a high-definition ultra-wide-angle flat-field objective lens.
Background
With the development of semiconductor technology, CCD or CMOS image sensors are smaller in size and have a larger number of pixels. In recent years, in application fields such as high-definition monitoring, intelligent transportation, video conference, robot vision, combat drilling, near-ground aerial-to-ground observation and the like, the following basic requirements are put on an imaging objective lens:
(1) The high definition, in the frequency domain, the objective lens has higher transmission characteristics for the spatial frequency of low frequency, intermediate frequency and high frequency; in the spatial domain, the resolution reaches or approaches the diffraction-limited (diffraction-limited);
(2) Miniaturization, high matching between the parameters of the imaging surface of the objective lens and the size of a CCD or CMOS image sensor, small enough overall dimension and light enough weight of the objective lens. For mass production, the objective lens structure cannot be too complex, and the technical requirements of the lens are in line with the requirements of mass production;
(3) flat field, with the center, edges and middle bands of the imaging plane (detector plane) having the same or nearly the same imaging quality or resolution;
(4) Wide angle (object field angle is more than or equal to 90 degrees) or super wide angle (object field angle is more than or equal to 110 degrees). .
At present, the visual angle of many wide-angle lenses is only about 100 degrees, the resolution is not high enough, and particularly the wide-angle lenses do not meet the image quality index of a flat field objective and cannot meet the requirements of many application fields.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a high-definition ultra-wide-angle flat-field objective lens, which has a visual angle of 120 degrees, sufficiently high resolution and definition and a compact structure.
The invention provides a high-definition ultra-wide-angle flat field objective lens, which sequentially comprises the following components from an object side to an image side along an optical axis:
A first lens having a negative optical power (optical power is defined as the inverse of the focal length); a second lens having a negative optical power; a diaphragm; a third lens having a positive optical power; a fourth lens having a positive optical power; a fifth lens having a positive optical power; a sixth lens having positive optical power, a seventh lens having negative optical power; wherein the sixth lens and the seventh lens form a cemented lens with positive optical power. The lens of the diaphragm is a front group, the lens behind the diaphragm is a rear group, and the focal length f' of the objective lens is 3.40 +/-0.5 mm.
The front group consists of two lenses, the focal power is negative, so that the field angle of the chief ray passing through the center of the diaphragm is amplified twice to obtain the performance of an ultra-large field. The design value of the horizontal field angle of the objective lens reaches 120 °.
The first and second negative power lenses are meniscus shaped and are curved toward the stop such that the angle of incidence of the large field rays at the lens surface is not large to reduce aberrations caused by the large angle of incidence.
The rear group consists of four groups of five lenses, wherein the lens closest to the sensor is a double cemented lens, the negative lens material is super-high refractive index, high dispersion heavy flint glass, the positive lens material is special crown glass (H-ZPK5), the chromatic aberration of magnification of a large field of view is basically corrected, and the rear group has the characteristics of a semi-apochromatic objective lens.
The objective lens is a 'flat field objective lens' with a Petzval radius RPetzAnd focal length f
RPetz/f′＞20。
Petzval radius RPetzIs a parameter characterizing field curvature, RPetzA larger/f' indicates a flatter image field, and better image quality uniformity from the center to the edge of the field of view.
The image quality of each point of the full field of view is uniform and consistent, the RMS radius of the light ray diffuse spot of the full field of view is less than 1.4 μm, and the detector can detect more independent resolution units on the image surface.
The objective lens has strong transmission capability for image information, and the spatial frequencies of low frequency, medium frequency and high frequency have higher values, when the highest spatial frequency is set to be 200mm-1When the color light of each field of view and each wavelength is at a frequency of 100mm-1the MTF values at are consistently above 0.60, ensuring that the objective lens has a very high etendue value (i.e., spatial bandwidth product).
The rear group of the objective lens is designed, the chief rays of each field of view on the image side are approximately parallel and approximately perpendicular to the detector, the chief ray incident Angle (AOC) of each pixel on the detector is small, a near-image-side telecentric system is formed, and the detection efficiency of each pixel on the light power is ensured to be uniform and consistent, and the illumination is ensured to be uniform and consistent.
Compact objective lens structure, total system length (distance from the center of the first objective lens to the detector surface) TOTR and focal length f′Ratio of (A to B)
TOTR/f′＜7。
Drawings
The above and/or other advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic diagram of an optical system of a high-resolution ultra-wide-angle objective lens according to an embodiment;
FIG. 2 is a dot-column diagram of the scattered spot size of the object plane central field ray of the high-resolution super-wide-angle objective lens of the embodiment;
FIG. 3 is a dot-column diagram of the scattered spot size of 50-degree field-of-view light of the object plane of the high-resolution super-wide-angle objective lens according to the embodiment;
FIG. 4 is a dot-column diagram of the object plane 60 degree field of view of the high-resolution super-wide-angle objective lens according to the embodiment with a diffuse speckle size
FIG. 5 shows the MTF of the modulation transfer function of a high-resolution ultra-wide-angle objective lens of an embodiment, with the maximum frequency set at 200mm-1；
Fig. 6 is a field curvature diagram of a high-resolution ultra-wide angle objective lens of an embodiment.
Detailed Description
Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout.
Referring to fig. 1, the high-resolution super-wide-angle objective lens of the present embodiment includes, sequentially disposed from an object side OBJ to an image side IMA along an optical axis: first lens L with negative focal power1(ii) a Second lens L with negative focal power2(ii) a Diaphragm SSTO(ii) a Third lens L having positive optical power3(ii) a A fourth lens L having a positive refractive power4(ii) a A fifth lens L having a positive refractive power5A sixth lens L having positive refractive power6A seventh lens L having negative power7(ii) a Wherein the sixth lens L6And a seventh lens L7A cemented lens with positive optical power is formed. Lens L in front of diaphragm1、L2For "front group", lens L behind diaphragm3、L4、L5、L6、L7for "back group", the objective focal length f' is 3.40 mm.
The front group of the objective lens is composed of two lenses with negative focal power, so that the field angle of the chief ray passing through the center of the diaphragm is amplified twice to obtain the performance of an ultra-large field angle, and the design value of the horizontal field angle of the objective lens reaches 120 degrees.
first and second negative power lenses L1、L2Both are meniscus lenses and are curved towards the stop so that the angle of incidence of the large field rays on the lens surface is not large to reduce aberrations caused by large angles of incidence.
The rear group of the objective lens consists of four groups of five lenses, of which the closest to the sensor is a double cemented lens, in which a positive lens L6The material of the optical fiber is special crown glass and a negative lens L7The material is heavy flint glass with ultrahigh refractive index and high dispersion, basically corrects the chromatic aberration of magnification of a large field of view, and has the characteristics of a semi-apochromatic objective lens.
The objective lens is a flat field objective lens and satisfies the following relational expression:
RPetz/f′＞20
Wherein R isPetzIs the Petzval radius, is a parameter characterizing the field curvature, f' is the focal length of the objective lens, RPetzA larger/f' indicates a flatter image field, and better image quality uniformity from the center to the edge of the field of view. In addition, referring to fig. 6, the field curvature of the objective lens is less than 0.02mm, and the image field is close to a flat field.
The image quality of each point of the full field of view of the objective lens is uniform, and referring to fig. 2, fig. 3 and fig. 4, the RMS radius of the light diffuse spot of the full field of view is less than 1.4 μm, so that the detector can detect more independent resolution units on the image plane.
The objective lens has a strong ability to transmit image information and is characterized in that the spatial frequencies of low, intermediate and high frequencies have high values, see fig. 5, when the highest spatial frequency is set to 200mm-1When the color light of each field of view and each wavelength is at a frequency of 100mm-1The MTF values at are consistently above 0.60, ensuring that the objective lens has a very high etendue value (i.e., spatial bandwidth product).
The rear group of the objective lens is designed, the chief rays of each field of view on the image side are approximately parallel and approximately perpendicular to the detector, the chief ray incident Angle (AOC) of each pixel on the detector is small, a near-image-side telecentric system is formed, and the detection efficiency of each pixel on the light power is ensured to be uniform and consistent, and the illumination is ensured to be uniform and consistent.
The objective lens has a compact structure, and the total length TOTR and the focal length f' of the system satisfy the following relation:
TOTR/f′＜7
Wherein the total system length TOTR represents the distance from the center of the first objective lens to the detector surface.
In the present embodiment, the design data of the high-resolution ultra-wide-angle objective lens is shown in table 1 below:
TABLE 1 design data for high resolution ultra wide angle objective
Surface of
Type (B)
radius of curvature
Thickness of
Refractive index/Abbe number
Article surface
STANDARD
Infinite number of elements
Infinite number of elements
1
STANDARD
95.84
1.0
1.59/68.5
2
STANDARD
3.03
3.1
3
STANDARD
4.80
1.2
1.62/35.9
4
STANDARD
3.46
1.0
diaphragm
STANDARD
infinite number of elements
1.0
6
STANDARD
22.56
2.5
1.67/51.7
7
STANDARD
-7.81
0.4
8
STANDARD
171.23
2.0
1.59/68.5
9
STANDARD
-8.39
0.1
10
STANDARD
44.46
1.7
1.59/68.5
11
STANDARD
-12.11
0.1
12
STANDARD
70.93
2.6
1.59/68.5
13
STANDARD
-4.82
1.1
1.92/20.8
14
STANDARD
-20.00
4.9
Image plane
STANDARD
Infinite number of elements
In addition, the effective focal length f' of the high-resolution ultra-wide-angle objective lens is 3.40 mm; aperture F2.8; the total length TOTR of the system is 22.7 mm; designing a horizontal field angle 2 omega as 120 degrees; diffuse speckle SPT0The resolution reaches the use requirement when the resolution is 0.8 mu m.
the above embodiments are only intended to illustrate the technical solution of the present invention and not to limit the same, and a person skilled in the art can modify the technical solution of the present invention or substitute the same without departing from the spirit and scope of the present invention, and the scope of the present invention should be determined by the claims.