Zoom Lens Chromatic Aberration Correction via Segmented First Unit
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Solution Overview
Problem
High zoom ratio zoom lenses face challenges in maintaining high optical performance due to increased variations in aberrations, particularly axial and lateral chromatic aberrations, across the entire zoom range, making it difficult to achieve consistent imaging quality from wide angle to telephoto ends.
Innovation Solution
A zoom lens design with specific refractive power distributions and movements of lens units, including a first lens unit with fixed positive refractive power, a second lens unit with negative refractive power that moves, a third lens unit that moves for image plane correction, and a fourth lens unit with positive refractive power that does not move, while adhering to specific Abbe constant and partial dispersion ratio conditions to effectively correct chromatic aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a high zoom ratio is achieved using a positive lead telephoto type four-unit zoom lens, then the zoom ratio is improved, but the variation of chromatic aberration (axial and lateral) increases
Solution Approach 1:
The first lens unit is divided into three sub-lens units (front, middle, rear) with different refractive powers and movement characteristics. The front first lens unit has negative refractive power and does not move, the middle first lens unit has positive refractive power and moves for focusing, and the rear first lens unit has positive refractive power and does not move. This segmentation allows independent optimization of each sub-unit's contribution to chromatic aberration correction while maintaining the overall high zoom ratio function.
Solution Approach 2:
Different lens units are assigned different refractive power characteristics and movement behaviors tailored to their specific functions. The front first lens unit with negative refractive power is optimized for correcting lateral chromatic aberration at the wide angle end, while the middle and rear first lens units with positive refractive power contribute to focusing and telephoto end performance. This local optimization of quality characteristics resolves the contradiction between high zoom ratio and chromatic aberration correction.
2Adaptability or versatility
If the zoom ratio is increased from wide angle to telephoto end, then the adaptability is improved, but the lateral chromatic aberration variation increases
Solution Approach 1:
The middle first lens unit is designed to move along the optical axis during focusing from infinity to short distances, dynamically adjusting the optical path to correct chromatic aberration at different focal lengths. This dynamic movement allows the lens system to maintain consistent lateral chromatic aberration correction across the entire zoom range from wide angle to telephoto ends.
Solution Approach 2:
The lens design utilizes specific parameter relationships between the refractive powers and Abbe constants of different lens units. By controlling the ratio (θ11p−θ11n)/(ν11p−ν11n) and the focal length relationship −8.0≤(11cp/f11)≤−3.0, the system optimizes the balance between zoom ratio and lateral chromatic aberration correction at different zoom positions.
3Adaptability or versatility
If a three-unit inner focus type is used to achieve high zoom ratio, then the zoom ratio is improved, but the complexity of lens structure increases
Solution Approach 1:
The first lens unit is segmented into three functional sub-units with distinct refractive powers and movement characteristics. This segmentation, while increasing structural complexity, enables independent optimization of each sub-unit's function: the front unit for lateral chromatic aberration correction, the middle unit for focusing, and the rear unit for telephoto performance. The segmented structure resolves the contradiction by making the complex system modular and optimizable.
Solution Approach 2:
The first lens unit with its three sub-units serves multiple functions simultaneously: correcting lateral chromatic aberration at the wide angle end, enabling focusing from infinity to short distances, and maintaining performance at the telephoto end. This multi-functionality justifies the increased structural complexity by delivering multiple performance benefits from a single integrated lens unit.
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 allows for appropriate correction of lateral chromatic aberration and secondary spectrum variations across the entire zoom range, ensuring high optical performance and minimizing aberrations, thereby enhancing the imaging quality from wide angle to telephoto ends.
Implementation Method 1
a first lens unit having positive refractive power which does not move for varying magnification; a second lens unit having negative refractive power which moves during magnification-varying
Data Source
AI summary
A zoom lens includes, in order from object side: a positive first unit immovable for zooming; a negative second unit moving during zooming; a third unit moving during zooming; a stop; and a positive fourth unit immovable for zooming. The first unit includes, in order from object side, a fixed negative front first unit, a positive middle first unit moving for focusing, and a fixed positive rear first lens unit. Each of the front first and the second units includes at least one positive lens and two negative lenses. Average of Abbe constants and average of partial dispersion ratios of positive lenses in the front first unit, average of Abbe constants and average of partial dispersion ratios of negative lenses in the front first unit, combined focal length of the positive lenses in the front first unit and focal length of the front first unit are appropriately set.