CN110673313A

CN110673313A - Zoom fisheye lens system and design method

Info

Publication number: CN110673313A
Application number: CN201910924294.XA
Authority: CN
Inventors: 侯国柱
Original assignee: Shanghai Dianji University
Current assignee: Shanghai Dianji University
Priority date: 2019-09-27
Filing date: 2019-09-27
Publication date: 2020-01-10
Anticipated expiration: 2039-09-27
Also published as: CN110673313B

Abstract

The invention relates to a zoom fisheye lens system and a design method, wherein the lens system is provided with a front lens group and a rear lens group which respectively have negative and positive focal power correspondingly from an object end to an imaging end along an optical axis, and the design method comprises the following steps: step 1: determining relevant parameters of each negative meniscus lens aiming at the preliminary design of the front lens group; step 2: designing and selecting the structure and parameters of the rear lens group according to the image space field angle and the aberration distribution condition of the front lens group optical system, and forming an initial structure of the zooming fisheye lens system; and step 3: preliminarily designing a total optical path of the system; and 4, step 4: and (3) carrying out component division of a front group and a rear group on the initial structure of the fisheye lens, further carrying out optimization design on the initial structure by using related software, and finally obtaining the zoom fisheye lens system with the field angle varying in the range of 180-90 degrees and the corresponding system focal length varying in the range of 8-16 mm. Compared with the prior art, the invention has the advantages of wide focal length range, multiple application fields and the like.

Description

Zoom fisheye lens system and design method

Technical Field

The invention relates to the technical field of applied optics, in particular to a zoom fisheye lens system and a design method thereof.

Background

Under the condition that the staring visual angle of the optical system is not large, the optical axis is enabled to do two-dimensional rotary scanning according to a certain rule in a certain range through an electromechanical structure and servo control, so that the angular space domain of information perception is increased. This is also the method of engineering to maximize the extended viewing angle.

In order to ensure the real-time performance of information acquisition, the splicing of a plurality of lenses as the field angle is another practical technology for expanding an information perception angular space domain, and is also a commonly used method at present. The technology adopts a staring imaging sensor with large view field and high resolution, an advanced electronic component circuit and a signal processing technology, and has the outstanding advantage that the real-time property of information acquisition is ensured in a view angle coverage airspace.

The rotation/step-and-scan technique requires sufficient time to acquire information, and the main drawback of this technique is the loss of "real-time" nature of information acquisition. The technology is also limited by factors such as the rotational inertia of the system, the frame angle of a rotary scanning mechanism and the like, so that the quick response performance of the technology is reduced, and the technical device cannot cover a full airspace without a blind area and has the defects of information loss and alarm leakage.

The multi-lens splicing technique is only suitable for expanding plane angles, and it is not practical to splice into a solid angle covering the full airspace by using an engineering method. Another disadvantage of this technique is the difficulty in terms of volume, weight, power consumption, etc.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a zoom fish-eye lens system and a design method thereof.

Under the condition of keeping the image plane unchanged, the effect of changing the focal length of the whole system is achieved by changing the interval of two or more lens groups in the system, and the system can obtain continuous and clear images in the whole zooming process. Different from a fixed focal length lens, the zoom lens does not need to replace the lens, and the distance between the zoom groups can be changed by pushing, pulling or rotating the zoom ring, so that the increase or decrease of the focal length of the system is achieved. By zooming in or out the focal length of the lens, different parts of the object can be clearly observed without changing the position of the object. By changing the magnification of the lens, global observation and local accurate detection of an object can be realized, and the functions cannot be achieved by a single fixed-focus lens.

The purpose of the invention can be realized by the following technical scheme:

a zoom fisheye lens system is provided with a front lens group with negative focal power and a rear lens group with positive focal power in sequence from an object end to an imaging end along an optical axis direction, the front lens group consists of a first lens with negative focal power, a second lens with negative focal power, a third lens with negative focal power, a fourth lens with positive focal power and a fifth lens with negative focal power which are arranged in sequence from an object end to an imaging end along the direction of an optical axis, the rear lens group comprises a sixth lens with positive focal power, an aperture diaphragm, a seventh lens with negative focal power, an eighth lens with positive focal power, a ninth lens with positive focal power, a tenth lens with negative focal power, an eleventh lens with positive focal power, a twelfth lens with negative focal power, a thirteenth lens with positive focal power and a fourteenth lens with positive focal power, which are sequentially arranged from the object end to the imaging end along the optical axis direction.

Furthermore, the seventh lens and the eighth lens, the ninth lens and the tenth lens, and the twelfth lens and the thirteenth lens are combined into a double-cemented lens by means of cementing respectively.

Further, the short focal length of the lens system is 8mm, the field angle corresponding to the short focal length is 180 °, the middle focal length of the lens system is 12mm, the field angle corresponding to the middle focal length is 120 °, the long focal length of the lens system is 16mm, and the field angle corresponding to the long focal length is 90 °.

Further, 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 made of materials which respectively correspond to: N-LASF44, N-LASF31A, N-PSK57, SF6, N-LASF31, N-LASF31A, N-LASF31A, K3, N-FK5, N-LASF31A, TIFN5, N-LASF40, N-PK52A, N-FK 5.

Further, 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 each have a refractive index of 1.8042, 1.8830, 1.5924, 1.8052, 1.8807, 1.8830, 1.8830, 1.5182, 1.4875, 1.8830, 1.5936, 1.8340, 1.4970, 1.4875.

The invention also provides a design method based on the zoom fisheye lens system, which comprises the following steps:

step 1: determining relevant parameters of each negative meniscus lens aiming at the preliminary design of the front lens group;

step 2: designing and selecting the structure and parameters of the rear lens group according to the image space field angle and the aberration distribution condition of the front lens group optical system, and forming an initial structure of the zooming fisheye lens system;

and step 3: preliminarily designing a total optical path of the system and further optimally designing an initial structure by using related software;

and 4, step 4: and (3) carrying out component division of a front group and a rear group on the initial structure of the fisheye lens, further carrying out optimization design on the initial structure by using related software, and finally obtaining the zoom fisheye lens system with the field angle varying in the range of 180-90 degrees and the corresponding system focal length varying in the range of 8-16 mm.

Further, the step 1 comprises the following sub-steps:

step 11: taking the curvature radius ratio and the refractive index of the front surface and the rear surface of a certain negative meniscus lens as independent variables and parameters, and preliminarily designing and selecting the curvature radius ratio and the refractive index according to various aberration distribution curves;

step 12: and finally obtaining parameters of the two negative meniscus lenses by utilizing the curvature radius ratio and the refractive index according to the maximum field light.

Furthermore, the related software in step 3 and step 4 adopts ZEMAX software.

Compared with the prior art, the invention has the following advantages:

(1) the zooming fisheye lens system is designed primarily by a front group, then a rear group system is designed primarily by the relationship between the angle of view emitted by the front group and the aberration balance of the front and rear groups, then the total optical path of the system is calculated, finally a zooming fisheye lens initial structure is formed, then the front group and the rear group of component division are carried out on the fisheye lens initial structure, the zooming fisheye lens system is further optimally designed by ZEMAX software, and finally the zooming fisheye lens system with the angle of view varying in the range of 180-90 degrees and the corresponding system focal length varying in the range of 8-16 mm is obtained. The zoom fisheye lens system consists of 14 spherical lenses and is beneficial to processing. According to the basic aberration analysis chart, the imaging quality of the zoom fisheye lens can meet the requirement of general imaging quality.

(2) The focal length of the zoom fisheye lens system can be adjusted within the range of 8 mm-16 mm, the field angle is adjusted within the range of 180-90 degrees, the whole hemispherical airspace can be monitored or photographed in real time, the MTF curve shows that the OTF value is not lower than 0.48 when the spatial frequency is 50lp/mm under all focal length states, the imaging quality of the lens system is good, and the monitoring or photographing requirements can be completely met.

(3) The zoom fisheye lens system can meet the requirement of imaging quality in a mode of mutual balance of anterior aberration and hindfoot aberration, can also be applied to the fields of national defense and military, and can also be widely applied to the fields of astronomy, photography, dome screen projection, pipeline detection, medical endoscopic inspection, meteorological monitoring, safety monitoring, engineering measurement, micro intelligent systems and the like.

Drawings

Fig. 1 is a component division diagram of a front group and a rear group of a zoom fisheye lens according to the invention;

fig. 2 is a layout diagram of each focal segment of the zoom fish-eye lens system of the present invention, wherein fig. 2(a) is a layout diagram of a short focal length (8mm), fig. 2(b) is a layout diagram of a middle focal length (12mm), and fig. 2(c) is a layout diagram of a long focal length (16 mm);

fig. 3 is a schematic diagram of MTF curves of each focal segment of the zoom fisheye lens system of the present invention, in which fig. 3(a) is a schematic diagram of an MTF curve of a short focal length (8mm), fig. 3(b) is a schematic diagram of an MTF curve of a middle focal length (12mm), and fig. 3(c) is a schematic diagram of an MTF curve of a long focal length (16 mm);

fig. 4 is a schematic view of field curvature and distortion curves of each focal segment of the zoom fish-eye lens system of the present invention, wherein fig. 4(a) is a schematic view of field curvature and distortion curves of a short focal length (8mm), fig. 4(b) is a schematic view of field curvature and distortion curves of a middle focal length (12mm), and fig. 4(c) is a schematic view of field curvature and distortion curves of a long focal length (16 mm);

FIG. 5 is a schematic view of a zoom fisheye lens system according to the invention;

in the figure, 1 is a first lens, 2 is a second lens, 3 is a third lens, 4 is a fourth lens, 5 is a fifth lens, 6 is a sixth lens, 7 is a seventh lens, 8 is an eighth lens, 9 is a ninth lens, 10 is a tenth lens, 11 is an eleventh lens, 12 is a twelfth lens, 13 is a thirteenth lens, 14 is a fourteenth lens, 15 is an aperture stop, and 100 is an image plane.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, shall fall within the scope of protection of the present invention.

The basic technical principle of the invention is as follows:

generally, a fisheye lens system consists of a front group of negative meniscus lenses with a compressed field angle and a rear group of objective lenses of a conventional optical system, and in order to realize imaging with a very large field angle and a very high relative aperture, the fisheye lens must transmit a very inclined light beam with a very large relative cross section. In the design process of the fixed-focus fisheye lens, the first lens is a component with large focal power, is generally called as a 'hat-shaped lens', is the most important component in a fisheye lens system, and mainly plays a role in compressing the angle of view to an angle acceptable by a conventional optical system. The structure of the negative meniscus lens of the front group is basically shaped, after the cap lens of the front group is designed, the structure and the parameters of the rear group objective lens are selected according to the image space field angle and the aberration distribution condition of the front group optical system, the initial structure of the fisheye lens is designed by utilizing the mutual restriction of the front group optical system and the rear group optical system, then the front group and the rear group of the zoom lens are divided, and the purpose of changing the focal length of the whole system is achieved by changing the distance between the zoom groups.

Design result

According to the design process, the front group consists of 5 lenses, the rear group consists of 9 lenses, all the lenses are spherical surfaces, and finally, the variable-focus fisheye lens system in the visible light range is designed. The F number of the zoom fisheye lens system in the image space is 3.5. The component division and the light path layout of the front group and the rear group of the zoom fisheye lens are schematically shown in fig. 1 and 5. The angle of view is 180 ° at the short focal length of 8mm, 120 ° at the middle focal length of 12mm, and 90 ° at the long focal length of 16mm, as shown in fig. 2(a) to 2 (c). The MTF curves in different focal length states are shown in fig. 3(a) to 3 (c). The field curvature and distortion curves in different focal length states are shown in fig. 4(a) to 4 (c). As can be seen from fig. 3 and 4, the maximum curvature of field of the full-field lens is less than 0.13mm, the MTF value of the full-field lens is not less than 0.48 at a spatial frequency of 50lp/mm, and the MTF index of the zoom fisheye lens system can meet the requirement of general practical imaging.

In the corresponding drawings, Front zoom group in fig. 1 represents the Front group of the zoom fisheye lens, Front zoom group represents the rear group of the zoom fisheye lens, Modules of the OTF in fig. 3(a) to 3(c) represent OTF mode values, Spatial Frequency in cycles per mm represents Spatial Frequency: period/mm, Field Curvature in FIGS. 4(a) -4 (c), Millimeters, Millimeters, F-Tan (theta) Distortion, Percent.

The finally obtained zooming optical system is provided with a front lens group with negative focal power and a rear lens group with positive focal power in sequence from the object end to the imaging end along the optical axis direction, the front lens group consists of a first lens 1 with negative focal power, a second lens 2 with negative focal power, a third lens 3 with negative focal power, a fourth lens 4 with positive focal power and a fifth lens 5 with negative focal power which are arranged in sequence from the object end to the imaging end along the optical axis direction, and the rear lens group consists of a lens group with negative focal power along the optical axis direction, the optical lens system comprises a sixth lens 6 with positive focal power, an aperture diaphragm 15, a seventh lens 7 with negative focal power, an eighth lens 8 with positive focal power, a ninth lens 9 with positive focal power, a tenth lens 10 with negative focal power, an eleventh lens 11 with positive focal power, a twelfth lens 12 with negative focal power, a thirteenth lens 13 with positive focal power and a fourteenth lens 14 with positive focal power which are arranged in sequence from an object end to an imaging end.

The fourteen lenses are made of the following materials: N-LASF44, N-LASF31A, N-PSK57, SF6, N-LASF31, N-LASF31A, N-LASF31A, K3, N-FK5, N-LASF31A, TIFN5, N-LASF40, N-PK52A, N-FK5, each corresponding to a refractive index of: 1.8042, 1.8830, 1.5924, 1.8052, 1.8807, 1.8830, 1.8830, 1.5182, 1.4875, 1.8830, 1.5936, 1.8340, 1.4970, 1.4875.

The seventh lens 7 and the eighth lens 8 are combined into a double cemented lens by means of cementing.

The ninth lens 9 and the tenth lens 10 are combined into a double cemented lens by means of cementing.

The twelfth lens 12 and the thirteenth lens 13 are combined into a double cemented lens by means of cementing.

The field angle of the lens of the system is 180 degrees in short focal length, the short focal length is 8mm, the F number is 3.5, the total length is 163.963mm, the detectable wavelength range is 486nm-656nm, and the dominant wavelength is 588 nm.

The field angle of the lens of the system is 120 degrees in the middle focal length, 12mm in the middle focal length, 3.5 in the F number, 163.963mm in the total length, 486-656 nm in the detectable wavelength range and 588nm in the dominant wavelength.

The angle of field of view of the lens of the system is 90 degrees when long focal length is 16mm, the F number is 3.5, the total length is 170.153mm, the detectable wavelength range is 486nm-656nm, and the dominant wavelength is 588 nm.

While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and various equivalent modifications and substitutions can be easily made by those skilled in the art within the technical scope of the invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. The zoom fish-eye lens system is characterized in that a front lens group with negative focal power and a rear lens group with positive focal power are sequentially arranged from an object end to an imaging end along an optical axis direction, the front lens group consists of a first lens (1) with negative focal power, a second lens (2) with negative focal power, a third lens (3) with negative focal power, a fourth lens (4) with positive focal power and a fifth lens (5) with negative focal power, which are sequentially arranged from the object end to the imaging end along the optical axis direction, and the rear lens group consists of a sixth lens (6) with positive focal power, an aperture diaphragm (15), a seventh lens (7) with negative focal power, an eighth lens (8) with positive focal power, a ninth lens (9) with positive focal power, a tenth lens (10) with negative focal power and an eleventh lens (11) with positive focal power, which are sequentially arranged from the object end to the imaging end along the optical axis direction, A twelfth lens (12) with negative focal power, a thirteenth lens (13) with positive focal power and a fourteenth lens (14) with positive focal power.

2. A zoom fish-eye lens system according to claim 1, wherein the seventh lens (7) and the eighth lens (8), the ninth lens (9) and the tenth lens (10), and the twelfth lens (12) and the thirteenth lens (13) are combined into a double cemented lens by means of respective glue.

3. A zoom fisheye lens system according to claim 1, characterised in that the short focal length of the lens system is 8mm and the corresponding field of view is 180 °, the middle focal length of the lens system is 12mm and the corresponding field of view is 120 °, the long focal length of the lens system is 16mm and the corresponding field of view is 90 °.

4. A zoom fish-eye lens system according to claim 1, characterized in that the materials used for the first lens (1), the second lens (2), the third lens (3), the fourth lens (4), the fifth lens (5), the sixth lens (6), the seventh lens (7), the eighth lens (8), the ninth lens (9), the tenth lens (10), the eleventh lens (11), the twelfth lens (12), the thirteenth lens (13) and the fourteenth lens (14) correspond to: N-LASF44, N-LASF31A, N-PSK57, SF6, N-LASF31, N-LASF31A, N-LASF31A, K3, N-FK5, N-LASF31A, TIFN5, N-LASF40, N-PK52A, N-FK 5.

5. A zoom fish-eye lens system according to claim 1, wherein the first lens (1), the second lens (2), the third lens (3), the fourth lens (4), the fifth lens (5), the sixth lens (6), the seventh lens (7), the eighth lens (8), the ninth lens (9), the tenth lens (10), the eleventh lens (11), the twelfth lens (12), the thirteenth lens (13) and the fourteenth lens (14) each have a refractive index 1.8042, 1.8830, 1.5924, 1.8052, 1.8807, 1.8830, 1.8830, 1.5182, 1.4875, 1.8830, 1.5936, 1.8340, 1.4970, 1.4875.

6. A design method for a zoom fisheye lens system as claimed in any one of claims 1 to 5, characterized in that the design method comprises the following steps:

7. The method as claimed in claim 6, wherein the step 1 comprises the following sub-steps:

8. The method as claimed in claim 6, wherein the related software in step 3 and step 4 is ZEMAX software.