Endoscope Objective Optical System with Aspheric Retro-Focus Design
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Solution Overview
Problem
The objective optical system for endoscopes faces challenges in maintaining a wide angle of view while minimizing oblique incident light degradation and correcting significant negative distortion, which affects the accuracy of observations, especially in stereoscopic vision applications.
Innovation Solution
The optical system incorporates a retro-focus type arrangement with a first group having a negative meniscus lens with an aspheric surface and a second group comprising positive lenses, including cemented lenses, to manage refractive power and correct distortion, coma, and curvature of field, while ensuring a compact design suitable for endoscopic applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the angle of view is widened to observe a wide range, then the observation coverage is improved, but the amount of oblique incident light is degraded rapidly according to cosine fourth law
Solution Approach 1:
The patent applies aspheric surfaces to lens elements, particularly the negative meniscus lens in the first group and the positive meniscus lens in the second group. The aspheric surfaces have different curvatures at different radial distances from the optical axis, allowing the lens to maintain effective light gathering capability across a wide angular range while correcting oblique incident light degradation
Solution Approach 2:
The patent changes the refractive index parameter by selecting specific glass materials with defined refractive indices (nd) and Abbe numbers (vd) for each lens element. This parameter optimization allows the optical system to maintain wide angle of view while compensating for the cosine fourth law degradation of oblique light
2Illumination intensity
If the diameter of the optical system is increased to prevent degradation of oblique incident light, then the light amount is improved, but the size of the inserting portion becomes large
Solution Approach 1:
The aspheric surfaces enable the optical system to achieve wide angle of view and adequate oblique light transmission without increasing the overall diameter. The curved surfaces are optimized to guide oblique light rays effectively through the compact lens arrangement
Solution Approach 2:
The patent employs a retro-focus type configuration where the first group with negative refractive power is positioned before the aperture stop, and the second group with positive refractive power follows. This nested arrangement of lens groups with alternating refractive powers allows compact sizing while maintaining optical performance
3Illumination intensity
If an optical system of retro-focus type is used to prevent degradation of oblique incident light, then the light amount is improved, but significant negative distortion occurs
Solution Approach 1:
The aspheric surfaces on the negative meniscus lens and positive meniscus lens are specifically designed to correct the negative distortion inherent in retro-focus systems. The varying curvature profiles compensate for the barrel distortion by adjusting the ray paths across the field of view
Solution Approach 2:
Different regions of the lens surfaces have different optical properties. The aspheric surfaces provide locally optimized refraction angles at different radial positions, correcting distortion in the peripheral regions while maintaining image quality in the central region
4Manufacturing precision
If multiple aspheric surfaces are used to correct distortion, then the distortion correction is improved, but the manufacturing complexity increases
Solution Approach 1:
Instead of applying aspheric surfaces to all lens elements, the patent selectively applies aspheric surfaces only to the negative meniscus lens and the positive meniscus lens in the second group. This partial application provides sufficient distortion correction while reducing manufacturing complexity compared to making all surfaces aspheric
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively maintains a wide angle of view, reduces barrel distortion, and allows for accurate distance measurement in stereoscopic vision, enhancing the precision of treatments by correcting astigmatism, coma, and chromatic aberration, thus improving the overall performance of the endoscope's optical system.
Implementation Method 1
a negative meniscus lens having a convex surface directed toward the object side... the negative meniscus lens has an aspheric surface
Implementation Method 2
a positive cemented lens including an object-side lens and an image-side lens... the positive cemented lens includes an object-side lens positioned on the object side and an image-side lens positioned on the image side
Data Source
AI summary
An objective optical system for endoscope includes a first group having a negative refractive power, an aperture stop, and a second group having a positive refractive power. The first group includes a negative meniscus lens having a convex surface directed toward the object side, and a positive lens having a convex surface directed toward the object side. The second group includes a predetermined lens, a positive cemented lens, and a positive single lens, or includes the predetermined lens, the positive single lens, and a positive cemented lens. The predetermined lens is a meniscus lens having a convex surface directed toward an image side. and an image-side lens, and the following conditional expressions (1′), (2), and (4′) are satisfied:0.7<|R1/R2|<1.1 (1′),0.6<|R1/FL|<3 (2), and5≤|Fc/FL|≤7 (4′).