Optical System Aberration Correction for Machine Vision
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Solution Overview
Problem
Conventional optical systems for industrial cameras, particularly those used in machine vision, fail to adequately correct various aberrations across the visible light range to the near-infrared range, despite implementing bright optical systems with large apertures.
Innovation Solution
An optical system configuration that includes a focus lens group with positive refractive power, comprising lens subgroups A and B, an aperture stop, and specific conditional expressions to ensure well-corrected aberrations, including partial dispersion ratios and Abbe numbers, to maintain high imaging performance across the entire wavelength range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional optical systems implement large apertures to achieve bright imaging, then illumination intensity is improved, but aberration correction across the visible to near-infrared range deteriorates
Solution Approach 1:
The optical system divides the lens into multiple lens groups (first lens group with positive refractive power, second lens group with negative refractive power, third lens group with positive refractive power) and further segments them into lens elements with specific functions. This segmentation allows each group to correct different types of aberrations while maintaining overall bright imaging performance.
Solution Approach 2:
Each lens group and lens element is designed with specific local optical properties (refractive power, dispersion characteristics, curvature) to address particular aberration issues. For example, the second lens group with negative refractive power specifically addresses chromatic aberration, while the third lens group corrects spherical aberration and field curvature.
Solution Approach 3:
The patent specifies precise parameter ranges for lens materials (refractive indices nd1=1.80-2.20, νd1=20-50, nd2=1.45-1.70, νd2=30-80, etc.) and geometric parameters (curvature radii, thicknesses, focal lengths) to optimize aberration correction across the wavelength range while maintaining bright imaging.
2Measurement precision
If the number of pixels of image sensors is increased to achieve high-resolution imaging, then measurement precision is improved, but the requirement for bright and well-corrected optical systems becomes more stringent, increasing device complexity
Solution Approach 1:
The optical system is designed to serve multiple functions simultaneously: it provides bright imaging (F value 1.8-2.5), corrects various aberrations (spherical, chromatic, coma, astigmatism, field curvature, distortion), and maintains high imaging performance across a wide wavelength range (visible to near-infrared). This multi-functionality is achieved through the specific three-group configuration with carefully selected lens materials and parameters.
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 proposed optical system achieves bright and high imaging performance with well-corrected aberrations from the visible light range to the near-infrared range, enabling industrial cameras to effectively inspect both external and internal object structures using a single imaging device.
Implementation Method 1
θct≥0.800 where θct is a partial dispersion ratio from a C line to a t line of the negative lens
Implementation Method 2
nd_paved is an average value of refractive indices on the d line of all positive lenses disposed in the lens subgroup B
Data Source
AI summary
There is provided: an optical system including a focus lens group having positive refractive power and configured to move along an optical axis when focusing from an infinite-distance object to a short-distance object, and satisfying predetermined conditional expressions; and an imaging device including the optical system. The focus lens group includes a lens subgroup A, an aperture stop, and a lens subgroup B in order from the object side. The lens subgroup A includes a negative lens, a positive lens, and a positive lens in order from the image side. The lens subgroup B includes a negative lens and a positive lens in order from the object side.