Zoom Lens Abbe Number Control for Chromatic Aberration
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Solution Overview
Problem
Current zoom lens systems with high zoom ratios face challenges in effectively reducing axial and lateral chromatic aberrations across the entire zoom range, particularly at the wide-angle and telephoto ends, while maintaining high optical performance.
Innovation Solution
A four-unit zoom lens system is designed with specific refractive power arrangements and Abbe number conditions for its lens units, including a first positive refractive power lens unit, a second negative refractive power lens unit, a third negative refractive power lens unit, and a fourth positive refractive power lens unit with a front and rear subunit configuration, where the fourth lens unit includes a large air interval and the rear lens subunit has a positive lens with extraordinary dispersion, optimizing the Abbe numbers and refractive powers to minimize chromatic aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a high zoom ratio is achieved in a four-unit zoom lens system, then the zoom capability is improved, but axial chromatic aberration increases across the zoom range
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Abbe numbers of lens elements and the air intervals between lens units. Specifically, it sets the air interval between the third and fourth lens units within a defined range (0.05× focal length of fourth unit ≤ air interval ≤ 0.30× focal length) and optimizes the Abbe numbers of positive and negative lens elements to correct axial chromatic aberration while maintaining high zoom ratio capability
Solution Approach 2:
The patent employs composite optical materials with different dispersion characteristics (different Abbe numbers) in the fourth lens unit. By combining positive lens elements with higher Abbe numbers and negative lens elements with lower Abbe numbers, it creates a composite lens structure that corrects axial chromatic aberration across the entire zoom range while preserving the high zoom ratio performance
2Object-affected harmful factors
If optical performance is enhanced to reduce chromatic aberration, then image quality is improved, but lens structure complexity increases
Solution Approach 1:
The patent applies local quality by concentrating chromatic aberration correction efforts specifically in the fourth lens unit (the rearmost positive lens unit), rather than uniformly distributing complexity across all four lens units. By optimizing only the air interval and Abbe number combinations in this specific location, it achieves effective chromatic aberration correction with minimal additional structural complexity
Solution Approach 2:
The patent segments the chromatic aberration correction function by dividing it into two parts: lateral chromatic aberration is corrected by the overall four-unit configuration, while axial chromatic aberration is specifically addressed by the optimized fourth lens unit design. This segmentation allows each part to be optimized independently, reducing overall complexity
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 achieves significant reduction in lateral chromatic aberration over the entire zoom range, particularly at the wide-angle end, and effectively corrects axial chromatic aberration at the telephoto end, maintaining high optical performance with a relatively simple lens structure.
Implementation Method 1
a first positive refractive power lens unit (U1), a second negative refractive power lens unit (U2), a third negative refractive power lens unit (U3), and a fourth positive refractive power lens unit (U4)
Implementation Method 2
where vm denotes an Abbe number of a material of a positive lens (Lm) having a largest dispersion among positive lenses included in the rear lens subunit
Data Source
Figure 1
Figure 2A~2C
Figure 3
AI summary
A zoom lens system including, in order of from an object side to an image side: a first lens unit (U1) having a positive refractive power; a second lens unit (U2) having a negative refractive power; a third lens unit (U3) having a negative refractive power; an aperture stop; and a fourth lens unit (U4) having a positive refractive power and including a front lens subunit and a rear lens subunit in which Abbe numbers of lenses in the rear lens subunit are suitably specified, such that the following expression is satisfied, 0.400<νm/ (νrp-νrn) <0.630, where νm represents the Abbe number of the material of a first positive lens (Lm) having the largest dispersion of the positive lenses included in the rear lens subunit, νrp represents the average Abbe number of materials of positive lenses other than the first positive lens in the rear lens subunit, and νrn represents the average Abbe number of materials of negative lenses in the rear lens subunit.