Aspherical Final Lens Layout for Compact Large-Aperture Imaging
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Solution Overview
Problem
Existing optical systems for image pickup apparatuses, such as digital cameras and surveillance cameras, face challenges in achieving a compact design with good optical performance from the center to the periphery of the angle of view while maintaining a large aperture and correcting aberrations like curvature of field and spherical aberration.
Innovation Solution
The optical system is designed with a lens unit comprising multiple lenses and a final lens having negative refractive power, featuring an aspherical shape with a concave area near the optical axis and an inflection point, and using glass materials with high refractive indices to correct aberrations, ensuring the inequality 1.780 < Nd < 2.500 for the average refractive index of the lenses, thereby allowing for miniaturization and improved optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the aperture diameter is increased to achieve a bright optical system with small F-number, then the light gathering ability is improved, but the optical system size increases and aberration correction becomes difficult
Solution Approach 1:
The patent applies aspherical surfaces to lens elements, specifically using at least one aspherical lens surface to correct spherical aberration and other off-axis aberrations. This allows the optical system to maintain a large aperture diameter while correcting aberrations that would normally require a smaller aperture or more complex lens arrangements. The aspherical shape enables better control of light rays across the entire aperture, resolving the contradiction between large aperture and aberration correction.
Solution Approach 2:
The patent employs high-refractive-index glass materials (with refractive index Nd ≥ 2.0) for specific lens elements to reduce the number of lenses required and minimize optical path length. By changing the material parameter (refractive index), the system achieves effective aberration correction and compact size while maintaining the large aperture design. This material parameter change allows fewer elements to achieve the same optical performance that would require more elements with standard materials.
2Manufacturing precision
If multiple lens elements are added to correct curvature of field and spherical aberration, then the optical performance is improved, but the overall length and complexity of the optical system increase
Solution Approach 1:
The patent uses composite lens designs combining different glass materials with distinct refractive indices and dispersion properties. Specifically, it employs high-refractive-index glass (Nd ≥ 2.0) in combination with other glass types to create cemented lens structures and multi-element configurations that correct both spherical aberration and curvature of field simultaneously. This composite approach allows effective aberration correction with fewer elements, reducing overall length while maintaining high optical performance.
Solution Approach 2:
The patent incorporates aspherical lens surfaces strategically positioned within the optical system to correct multiple types of aberrations including spherical aberration, coma, and astigmatism. The aspherical shape provides additional degrees of freedom for aberration control, allowing a compact number of elements to achieve correction that would otherwise require numerous spherical elements, thus reducing overall system length while improving optical performance.
3Length of stationary object
If the number of lenses is reduced to achieve miniaturization, then the optical system becomes compact, but the ability to correct aberrations deteriorates
Solution Approach 1:
The patent fundamentally changes the material parameters by using high-refractive-index glass (Nd ≥ 2.0) for key lens elements. This parameter change increases the bending power of each lens, allowing fewer elements to achieve the same optical effect that would require more elements with standard materials. The high refractive index enables stronger light control with reduced element count, maintaining aberration correction capability while achieving miniaturization.
Solution Approach 2:
The patent uses aspherical lens surfaces to provide enhanced aberration correction capability in a compact configuration. The aspherical shape offers additional control parameters for correcting spherical aberration, coma, and other off-axis aberrations, allowing a reduced number of lens elements to achieve performance that would normally require more elements. This geometric principle enables miniaturization without sacrificing aberration correction quality.
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 a compact optical system with a large aperture and excellent optical performance across the entire angle of view, effectively correcting aberrations and reducing the overall length while maintaining high resolution.
Implementation Method 1
a lens surface on the image side of the final lens has an aspherical shape that includes a concave area near an optical axis of the optical system and an inflection point
Implementation Method 2
A lens surface on the image side of the final lens has an aspherical shape that includes a concave area near an optical axis of the optical system and an inflection point
Implementation Method 3
1.780 < Nd < 2.500 where Nd is an average value of refractive indexes of all lenses included in the lens unit
Data Source
AI summary
An optical system consists of, in order from an object side to an image side, a lens unit including a plurality of lenses and a final lens having a negative refractive power. A lens surface on the image side of the final lens has an aspherical shape that includes a concave area near an optical axis and an inflection point. A predetermined condition is satisfied.