Rear Converter Lens Aberration Control via Segmented Groups
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Solution Overview
Problem
Existing rear converter lenses for non-reflex digital cameras face challenges in achieving high optical performance, particularly in spherical aberration and field curvature when combined with recent high-performance imaging elements.
Innovation Solution
A rear converter lens with a negative refractive power, comprising a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group with positive refractive power, optimized by specific focal length and Abbe number conditions to suppress aberrations and curvature, is mounted on a master lens to enhance focal length and optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional rear converter lens structures are used, then the basic focal length extension function is achieved, but spherical aberration and field curvature deteriorate when combined with recent high-performance imaging elements
Solution Approach 1:
The rear converter lens is divided into three distinct lens groups (first with positive refractive power, second with negative refractive power, and third with positive refractive power), each optimized to address specific aberration types. This segmentation allows independent optimization of each group's parameters to control spherical aberration and field curvature while maintaining the overall focal length extension function.
Solution Approach 2:
Each lens group is assigned specific local optical properties: the first group uses a positive meniscus lens configuration to control spherical aberration, the second group uses a negative lens configuration to correct field curvature, and the third group uses a positive lens configuration to fine-tune both aberrations. The Abbe numbers and focal lengths of individual lenses within each group are specifically selected to optimize local correction of optical aberrations.
2Reliability
If the rear converter lens structure is optimized for high optical performance, then spherical aberration and field curvature are suppressed, but the device complexity increases
Solution Approach 1:
The complex optical correction requirements are divided into three manageable lens groups, each with a specific function. This segmentation makes the design process more systematic and allows for modular optimization, reducing the overall complexity compared to attempting to correct all aberrations in a single monolithic lens design.
Solution Approach 2:
The patent establishes specific parameter ranges for each lens group (focal lengths, Abbe numbers, curvature radii) that, when satisfied, automatically ensure optimal optical performance. These parameter specifications provide clear design guidelines that simplify the optimization process and reduce the complexity of achieving high optical performance.
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 solution provides improved optical performance by minimizing spherical aberration and field curvature, ensuring a suitable back focal length and facilitating attachment to digital cameras while maintaining high magnification and resolution.
Implementation Method 1
a first lens group that has a positive refractive power... The first lens group consists of a cemented lens in which a negative lens concave toward the image side and a positive lens convex toward the object side are cemented
Implementation Method 2
a second lens group that has a negative refractive power... The second lens group consists of a cemented lens in which a negative lens concave toward the image side, a positive lens convex toward both sides, and a negative lens concave toward the object side are cemented
Implementation Method 3
a third lens group that has a positive refractive power... The third lens group consists of a cemented lens in which a positive lens convex toward the object side and a negative lens are cemented
Data Source
AI summary
The rear converter lens consists of, in order from an object side: a first lens group that has a positive refractive power; a second lens group that has a negative refractive power; and a third lens group that has a positive refractive power. The first lens group consists of a cemented lens in which a negative lens concave toward the image side and a positive lens convex toward the object side are cemented. The second lens group consists of a cemented lens in which a negative lens concave toward the image side, a positive lens convex toward both sides, and a negative lens concave toward the object side are cemented. The third lens group consists of a cemented lens in which a positive lens convex toward the object side and a negative lens are cemented. The rear converter lens satisfies predetermined Conditional Expressions (1) and (2).