Converter Lens With Refractive-Index Constraints for Coma Control
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Solution Overview
Problem
Converter lenses with negative refractive power face challenges in increasing focal length while minimizing aberrations such as coma aberration, especially when used with interchangeable lenses, due to the lack of an aperture stop and difficulty in correcting aberrations caused by off-axis light.
Innovation Solution
The converter lens design includes three or more negative lenses with a specific range of average refractive index (1.92 < Ndave < 2.10) to control lens curvature and refractive power, adhering to conditional equations that enhance aberration correction, particularly for coma aberration, by incorporating a first lens unit with positive refractive power and a second lens unit with negative refractive power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the curvature of a negative lens is increased to increase negative refractive power, then the focal length enlarging magnification is improved, but coma aberration due to off-axis light occurs
Solution Approach 1:
The converter lens is divided into multiple negative lenses (first negative lens, second negative lens, third negative lens) with different refractive indices and curvatures. Each lens segment is optimized to contribute to the overall negative refractive power while controlling aberrations. The first negative lens has higher refractive index (1.7-1.9) while the second and third have lower refractive index (1.5-1.7), creating a segmented approach to managing optical power and aberrations.
Solution Approach 2:
The patent applies specific conditional equations to control the refractive indices and curvatures of the negative lenses. The average refractive index of the three negative lenses is constrained within 1.55-1.75, and specific relationships between curvatures and refractive indices are established through conditional equations (1) through (6). These parameter constraints ensure that the converter lens achieves the desired focal length magnification while minimizing coma aberration.
2Device complexity
If a converter lens without aperture stop is used, then the device complexity is reduced, but aberration correction becomes difficult
Solution Approach 1:
The patent introduces an aperture stop within the converter lens structure, specifically positioning it between the first negative lens and the second negative lens. This localized aperture stop selectively blocks off-axis light while allowing on-axis light to pass through, providing targeted aberration correction without requiring a complete redesign of the entire lens system. The aperture stop is positioned at a specific distance from the first negative lens (5-20mm) to optimize its aberration correcting effect.
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 design effectively corrects aberrations and enhances optical performance, allowing the converter lens to be used with both low and high maximum image height imaging devices without aberration issues, while increasing the focal length of the entire system.
Implementation Method 1
a converter lens having a negative refractive power and increasing a focal length of an entire system
Implementation Method 2
a first lens unit having positive refractive power
Data Source
AI summary
A converter lens includes three or more negative lenses and increases the focal length of an entire system, in which an average refractive index Ndave at the d-line (wavelength of 587.56 nm) of a material of all the negative lenses included in the converter lens is defined.