Imaging Lens Astigmatism Control via Moving First Group
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Solution Overview
Problem
Conventional imaging lenses for machine vision cameras suffer from large field curvature and significant astigmatism fluctuations during focusing, which affect their optical performance, especially when capturing images of variously shaped objects at different distances with increased pixel density.
Innovation Solution
The design incorporates a first lens group that moves during focusing, comprising a positive refractive power, and a stationary second lens group with specific refractive index and curvature configurations, including a first-B sub-lens group with an aperture stop, to suppress astigmatism and field curvature, adhering to specific conditional expressions for optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional lens systems are used for machine vision cameras, then basic imaging function is achieved, but field curvature is large and astigmatism fluctuates significantly during focusing
Solution Approach 1:
The lens system is divided into multiple lens groups with specific refractive powers. The first lens group has positive refractive power and the second lens group has negative refractive power, allowing independent optimization of each group to reduce overall field curvature while maintaining focusing capability.
Solution Approach 2:
Each lens group is designed with specific local optical properties - the first lens group focuses on reducing astigmatism during focusing, while the second lens group primarily addresses field curvature. This localized optimization of optical quality in different parts of the system resolves the contradiction between measurement precision and manufacturing precision.
2Measurement precision
If conventional lens systems are used, then imaging capability is provided, but astigmatism fluctuation during focusing is large
Solution Approach 1:
The lens system incorporates a focusing mechanism that dynamically adjusts the positions of lens groups during focusing from distant to close-range objects. The first lens group moves along the optical axis while the second lens group remains stationary, allowing dynamic compensation of astigmatism fluctuations throughout the focusing range.
Solution Approach 2:
The system changes optical parameters during focusing by moving the first lens group with positive refractive power. This parameter change allows the system to maintain stable astigmatism characteristics across different object distances while preserving the ability to focus on various shaped objects.
3Manufacturing precision
If lens groups are configured to reduce field curvature, then manufacturing precision improves, but device complexity increases
Solution Approach 1:
The function of reducing field curvature is extracted and assigned specifically to the second lens group with negative refractive power, while the first lens group focuses on astigmatism control. This separation of functions simplifies the overall design by clearly defining the role of each lens group, reducing device complexity while maintaining manufacturing precision.
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 results in an imaging lens with reduced field curvature and improved optical performance by effectively controlling astigmatism fluctuations, ensuring high-quality imaging across various object distances and pixel densities.
Implementation Method 1
a first lens group that moves toward the object side during focusing from a distant object to a close-range object and has a positive refractive power
Implementation Method 2
a first-B sub-lens group including an aperture stop in an inside thereof
Data Source
AI summary
The imaging lens consists of, in order from the object side, a positive first lens group that moves to the object side during focusing from a long distance to a short distance, and a second lens group that does not move during focusing. The first lens group has a first-B sub-lens group. The first-B sub-lens group consists of, in order from the object side, a positive b1 lens, a negative b2 lens concave toward the image side, an aperture stop, a negative b3 lens concave toward the object side, and a positive b4 lens. The second lens group consists of, in order from the object side, a negative lens, a positive lens, and a negative lens. Predetermined conditional expressions are satisfied.