Wide-Angle Objective Lens Distortion Correction via Aspherical Front Group
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Solution Overview
Problem
Endoscope objective lenses face challenges in achieving a wide field angle of 140° or larger while maintaining a sufficient depth of view and correcting distortion, especially when using high-resolution image acquisition elements.
Innovation Solution
An objective optical system is designed with a front group, an aperture stop, and a positive rear group, including a negative first lens with an aspherical surface, where specific curvature and focal length ratios are maintained to achieve a wide-angle configuration, correct distortion, and enhance depth of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the focal length of the objective lens is increased to match the larger image acquisition element, then the resolution is improved, but the depth of view is reduced
Solution Approach 1:
The objective lens is divided into multiple lens groups (first lens group with negative power, second lens group with positive power, third lens group with negative power, and fourth lens group with positive power). This segmentation allows each group to contribute differently to the overall optical performance, enabling the system to achieve both long focal length and wide depth of view simultaneously.
Solution Approach 2:
Different lens groups are assigned specific functions: the first and third groups (negative power) control the overall focal length and field angle, while the second and fourth groups (positive power) help maintain image quality and depth of view. The aspherical surfaces are strategically placed in specific lens groups to correct distortion locally where it occurs most.
2Area of moving object
If the field angle is increased to 140° or larger to achieve wide-angle imaging, then the coverage is improved, but the depth of view cannot be sufficiently increased
Solution Approach 1:
The lens system is segmented into four groups with alternating negative and positive powers. This segmentation enables the system to achieve a field angle of 140° or larger while maintaining a long focal length, because each group contributes differently to the field angle and focal length parameters.
Solution Approach 2:
The patent employs aspherical surfaces in the first and third lens groups to correct distortion that increases with field angle. The aspherical parameters are specifically optimized to maintain image quality across the wide field angle while preserving the long focal length needed for depth of view.
3Measurement precision
If an aspherical lens is added to correct distortion, then the image quality is improved, but the device complexity increases
Solution Approach 1:
Aspherical surfaces are applied selectively only in the first and third lens groups where they are most needed for distortion correction, rather than in all lens elements. This localized application corrects distortion effectively while minimizing the increase in manufacturing complexity.
Solution Approach 2:
The patent uses aspherical surfaces with specific curvature profiles to correct distortion in the wide-angle imaging system. The aspherical parameters are optimized to provide the necessary distortion correction while maintaining compatibility with standard manufacturing processes.
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
The system effectively corrects distortion and increases depth of view, ensuring a high-resolution image acquisition with a wide field angle, balancing magnification across the image region and preventing issues like water drainage and lens protrusion.
Implementation Method 1
a front group having at least one aspherical surface and including a negative first lens
Implementation Method 2
a negative first lens that is disposed closest to the object side
Implementation Method 3
a positive rear group arranged in order from an object side
Data Source
AI summary
An objective optical system including an objective optical system having a field angle of 140° or larger and including a front group, an aperture stop, and a positive rear group arranged in that order from an object side. The front group has at least one aspherical surface and includes a negative first lens disposed closest to the object side and satisfying the following conditional expression: 0≦̸r2/r1<0.24, 0.1<|g2/g1|<2.2 and −1.8<f1/fl<−0.8, where r1 denotes the radius of curvature of the object side of the first lens, r2 denotes the radius of curvature of an image side of the first lens, g1 denotes the focal length of the front group, g2 denotes the focal length of the rear group, f1 denotes a focal length of the first lens, and fl denotes the focal length of the entire system.