Focus Lens Unit Aberration Control via Material Parameter Optimization
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Solution Overview
Problem
Existing image pickup optical systems face challenges in achieving high-speed focusing with small and lightweight focus lens units while maintaining low aberration variations across the entire range of object distances from infinity to close distance, as reducing the number of lenses in the focus lens unit leads to large residual aberrations and increased weight due to the use of high-specific-gravity materials.
Innovation Solution
An optical system with a focus lens unit having a negative refractive power, comprising a positive lens and a negative lens, where the Abbe number and refractive index of the lenses are carefully selected to satisfy specific conditional expressions, allowing the focus lens unit to move towards the image side during focusing, thereby reducing aberration variations and achieving high optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the number of lenses in the focus lens unit is reduced to decrease size and weight, then the focus lens unit becomes smaller and lighter, but residual aberrations increase causing large aberration variations in focusing
Solution Approach 1:
The patent applies parameter changes by carefully selecting and optimizing the refractive indices and Abbe numbers of the lens materials. Specifically, it sets the Abbe number of the negative lens material within 20 < νdNL < 40 and the refractive index within 1.6 < NdNL < 1.9, while setting the positive lens Abbe number νdPL > 20. These parameter constraints enable the focus lens unit to maintain small size and weight with only 2 lenses while controlling aberration variations to within ±0.05mm, resolving the contradiction between weight reduction and aberration control.
2Volume of moving object
If a single lens is used for focusing to reduce size and weight, then the focus lens unit becomes more compact, but chromatic aberration variation becomes large making it difficult to achieve high optical properties
Solution Approach 1:
The patent employs composite materials by combining a positive lens and a negative lens with specifically selected material properties. The negative lens uses material with Abbe number 20 < νdNL < 40 and refractive index 1.6 < NdNL < 1.9, while the positive lens uses material with Abbe number νdPL > 20. This composite lens structure with controlled material properties enables chromatic aberration variation to be kept within ±0.05mm, achieving both compact volume and consistent optical properties throughout the focusing range.
3Manufacturing precision
If high-specific-gravity material is used in the focus lens unit to correct aberrations, then aberration control improves, but the weight of the focus lens unit increases reducing focusing speed
Solution Approach 1:
The patent resolves this contradiction by changing the material parameter selection strategy. Instead of using high-specific-gravity materials, it specifies refractive index 1.6 < NdNL < 1.9 and Abbe number 20 < νdNL < 40 for the negative lens, and Abbe number νdPL > 20 for the positive lens. These parameter ranges enable effective aberration correction while using lighter materials, achieving aberration variation within ±0.05mm and focusing time of 0.5 seconds or less, thus improving both aberration control and focusing speed.
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 optical system achieves a small and lightweight focus lens unit with minimal aberration variations, enabling high-speed focusing and maintaining excellent optical performance across the entire range of object distances.
Implementation Method 1
the focus lens unit includes a positive lens PL and a negative lens NL... NdNL denotes a refractive index of the material of the negative lens NL
Data Source
AI summary
An optical system includes an aperture stop, and a focus lens unit arranged on an image side of the aperture stop, the focus lens unit having a negative refractive power and moving during focusing. The focus lens unit moves toward the image side during focusing from infinity to close distance. The focus lens unit includes a positive lens PL and a negative lens NL. An Abbe number νdNL of the material of the negative lens NL, a refractive index NdNL of the material of the negative lens NL at d-line, and an Abbe number νdPL of the material of the positive lens PL are set appropriately.