CN107402446B

CN107402446B - Front objective lens of endoscope

Info

Publication number: CN107402446B
Application number: CN201710600301.1A
Authority: CN
Inventors: 李凯; 朱晓冬; 李慧
Original assignee: Anhui Aerospace Biotechnology Co Ltd
Current assignee: Anhui Aerospace Biotechnology Co Ltd
Priority date: 2017-07-21
Filing date: 2017-07-21
Publication date: 2023-07-21
Anticipated expiration: 2037-07-21
Also published as: CN107402446A

Abstract

The invention discloses a front objective lens of an endoscope, which comprises a front lens, an aperture diaphragm, a first rear lens and a second rear lens, wherein the front lens, the aperture diaphragm, the first rear lens and the second rear lens are sequentially arranged in a lens barrel from an object side, the front lens has negative focal power, and the first rear lens and the second rear lens have positive focal power; the radius of curvature of the front lens surface is 1.44mm and 0.455mm respectively, the radius of curvature of the first rear lens surface is-0.382 mm and-0.35 mm respectively, and the radius of curvature of the second rear lens surface is 0.716mm and infinity respectively; the thicknesses of the front lens, the first rear lens and the second rear lens are respectively 0.142mm, 0.404mm and 0.285mm; the distance between the front lens and the aperture diaphragm is 0.285mm, the distance between the aperture diaphragm and the first rear lens is 0.1mm, and the distance between the first rear lens and the second rear lens is 0.362mm; the front objective has an effective F number of 4, a magnification of-0.038, a half field angle of 45 degrees, an image height of 0.27mm, a back focus BF of 0mm, a total length of 1.53mm and a focal length F of 0.265mm; has the advantages of small size, large visual field and good image quality, and meets the medical use requirement.

Description

Front objective lens of endoscope

Technical Field

The invention relates to the technical field of medical instruments, in particular to a front objective lens of an endoscope.

Background

With the development of science and technology, a medical endoscope has been widely used in the medical field, which is one of important tools for human peeping and treating organs in the human body. And medical endoscopes are becoming more and more popular in clinical applications, and are evolving towards miniaturization, multifunction and high image quality.

According to the use requirement of the practical medical endoscope, the endoscope must meet the conditions of small size, large field of view, good image quality and the like, so the front objective lens coupling system which is an important component of the fiber transfusion endoscope image system must also have the characteristics of small size, large field of view, good image quality and the like.

Disclosure of Invention

The invention aims to provide a front objective lens of an endoscope, which has the advantages of small size, large view field and good image quality and meets the medical use requirement.

The technical scheme adopted for solving the technical problems is as follows:

a front objective lens of an endoscope comprises a front lens, an aperture diaphragm, a first rear lens and a second rear lens which are sequentially arranged in a lens barrel from an object side, wherein the front lens has negative focal power, and the first rear lens and the second rear lens have positive focal power;

the radius of curvature of the front lens surface is 1.44mm and 0.455mm respectively, the radius of curvature of the first rear lens surface is-0.382 mm and-0.35 mm respectively, and the radius of curvature of the second rear lens surface is 0.716mm and infinity respectively;

the thicknesses of the front lens, the first rear lens and the second rear lens are respectively 0.142mm, 0.404mm and 0.285mm;

the distance between the front lens and the aperture diaphragm is 0.285mm, the distance between the aperture diaphragm and the first rear lens is 0.1mm, and the distance between the first rear lens and the second rear lens is 0.362mm;

refractive indexes of the front lens, the first rear lens and the second rear lens at the wavelength of 588nm are 1.528554, 1.729160 and 1.548300 respectively; the abbe numbers of the front lens, the first rear lens and the second rear lens at the wavelength of 588nm are 76.975515, 54.499235 and 74.244488, respectively.

The beneficial effects of the invention are as follows: in order to meet the requirement of a large view field, the incidence angle of the marginal view field light on the subsequent optical element is smaller, and the front lens adopts a negative lens with larger curvature; in order to further reduce field curvature, the refractive index of the selected negative lens material is smaller; in order to correct astigmatism and vertical axis chromatic aberration of the whole system, the lens groups before and after the aperture diaphragm adopt a back form so as to offset the vertical axis amount of the aberration of the front and back lens groups; the optical coupling system formed by mutually matching the lenses has the advantages of small size, large view field and good image quality, and meets the medical use requirement.

Drawings

The invention is further illustrated by the following examples in conjunction with the accompanying drawings:

FIG. 1 is a schematic diagram of the structure of the present invention;

FIG. 2 is a schematic diagram of the present invention;

FIG. 3 is a graph of the modulation transfer function of the present invention;

FIG. 4 is a graph of field curvature versus distortion for the present invention;

fig. 5 is an energy concentration profile of the present invention.

Detailed Description

As shown in fig. 1, the present invention provides a front objective lens of an endoscope, comprising a front lens 2, an aperture stop 3, a first rear lens 4 and a second rear lens 5 which are sequentially arranged in a lens barrel 1 from an object side, wherein the front lens 2 has negative optical power, and the first rear lens 4 and the second rear lens 5 have positive optical power;

the radius of curvature of the front surface and the back surface of the front lens 2 are respectively 1.44mm and 0.455mm, the radius of curvature of the front surface and the back surface of the first back lens 4 are respectively-0.382 mm and-0.35 mm, and the radius of curvature of the front surface and the back surface of the second back lens 5 are respectively 0.716mm and infinity, namely the back surface is a plane;

the thickness a1 of the front lens 2 is 0.142mm, the thickness a4 of the first rear lens 4 is 0.404mm, and the thickness a6 of the second rear lens 5 is 0.285mm; the thickness of the aperture stop 3 is negligible;

the distance a2 between the front lens 2 and the aperture diaphragm 3 is 0.285mm, the distance a3 between the aperture diaphragm 3 and the first rear lens 4 is 0.1mm, and the distance a5 between the first rear lens 4 and the second rear lens 5 is 0.362mm;

refractive indexes of the front lens 2, the first rear lens 4 and the second rear lens 5 at a wavelength of 588nm are 1.528554, 1.729160 and 1.548300, respectively; the abbe numbers of the front lens 2, the first rear lens 4 and the second rear lens 5 at the wavelength of 588nm are 76.975515, 54.499235 and 74.244488, respectively.

The optical coupling system formed by the front objective lens has the following parameters: the effective F number is 4, the magnification is-0.038, the half field angle is 45 degrees, the image height is 0.27mm, the back focus BF is 0mm, the total length a7 is 1.53mm, and the focal length F is 0.265mm.

With reference to fig. 2, the invention analyzes design criteria under the condition of meeting the requirements of small size and large field of view of an endoscope, and adopts a negative-positive image space telecentric system.

When designing the image-transmitting beam objective lens, the total reflection condition of the optical fiber is satisfied first, so that the numerical aperture of the incident light is smaller than that of the optical fiber. Because the imaging light beams of the on-axis object points are symmetrical about the optical axis, all the imaging light beams can enter the image transmission beam; and the incident beam of the off-axis object point is symmetrical with respect to the principal ray; the angle of incidence of a portion of the upper or lower light rays will exceed the numerical aperture angle of the image-bearing beam, resulting in a portion of the light rays being obscured.

In order to ensure that all imaging beams of on-axis object points and off-axis object points can enter the image transmission beam to propagate, an imaging telecentric system is designed for the objective lens. But it is considered that if an image-wise telecentric system is used, the lateral dimensions of the optical system will be too large for application.

Therefore, the system aperture diaphragm is considered to be arranged in the lens group, and in a typical photographic objective lens structure, the anti-remote objective lens has the characteristics of wide field of view, short focal length, simple structure and the like, is easy to realize an image space telecentric light path, and can ensure that an optical system has smaller volume and quality. Therefore, the negative group and the positive group are separated, the negative group is in front, and the anti-remote photographic objective lens with the aperture diaphragm positioned on the front focal plane of the rear group is used as the initial structure of the objective lens.

Optical testing is carried out on the pre-objective lens of the invention, and as shown in the figure 3, the transfer function value of the objective lens at 77 lp/mm frequency is above 0.65 and is close to the diffraction limit; as shown in connection with fig. 4, the field curvature of the objective lens is not large, and the distortion reaches a maximum at the fringe field of view, about-20%, because the field of view of the objective lens is large, and the structure is asymmetric; referring to fig. 5, the horizontal axis represents the image spot radius, the vertical axis represents the energy concentration, and it can be seen that 90% of the energy is concentrated in a circle with a radius of 10 μm and more than 95% of the energy is concentrated in a circle with a radius of 15 μm under three fields.

The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention in any way; any person skilled in the art can make many possible variations and modifications to the technical solution of the present invention or modifications to equivalent embodiments using the methods and technical contents disclosed above, without departing from the scope of the technical solution of the present invention. Therefore, any simple modification, equivalent substitution, equivalent variation and modification of the above embodiments according to the technical substance of the present invention, which do not depart from the technical solution of the present invention, still fall within the scope of the technical solution of the present invention.

Claims

1. The front objective lens of the endoscope is characterized by comprising a front lens, an aperture diaphragm, a first rear lens and a second rear lens which are sequentially arranged in a lens barrel from an object side, wherein the front lens has negative focal power, and the first rear lens and the second rear lens have positive focal power;