Inner Focus Lens Grouping for High-Speed Aberration Correction
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Solution Overview
Problem
Existing inner focus type imaging lenses face challenges in achieving high-speed focusing while effectively correcting various aberrations, as they either require moving a large number of lenses, leading to slow focusing, or moving only one lens, which fails to adequately suppress aberrations.
Innovation Solution
An inner focus type imaging lens configuration 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, where only the second lens group moves during focusing, incorporating a meniscus lens and cemented lenses to optimize refractive indices and curvatures, satisfying specific conditional expressions to balance focusing speed and aberration correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large number of lenses are moved during focusing, then fluctuations in various aberrations can be satisfactorily corrected, but focusing speed becomes slow
Solution Approach 1:
The lens system is divided into three lens groups (G1, G2, G3) with different functions. During focusing, only the second lens group G2 is moved, while the first and third lens groups remain stationary. This segmentation allows aberration correction through the optical design of G2 without requiring movement of all lenses, thus maintaining focusing speed.
Solution Approach 2:
The second lens group G2 is specifically designed with a particular configuration (including conditional expressions for focal length ratio f/f2 and Abbe number ν2) to handle aberration correction locally. This localized optimization allows G2 to correct aberrations effectively without needing to move additional lenses from other groups.
2Speed
If only one lens is moved during focusing, then focusing speed is high, but fluctuations in various aberrations cannot be suppressed
Solution Approach 1:
Multiple lenses are merged into the second lens group G2, which has a negative overall refractive power but contains lenses with both positive and negative powers. This combination allows G2 to correct various aberrations through its internal lens configuration while still moving as a single unit, achieving both high focusing speed and effective aberration suppression.
Solution Approach 2:
The second lens group G2 employs a composite structure with lenses of different refractive powers and Abbe numbers. The specific conditional expression for Abbe number (ν2 > 25) ensures that the composite lens configuration can correct chromatic and spherical aberrations effectively while maintaining the group's negative refractive power for high-speed focusing.
3Reliability
If various aberrations are corrected at a higher level, then optical performance improves, but the complexity of lens configuration increases
Solution Approach 1:
The aberration correction function is extracted and concentrated in the second lens group G2, which is specifically designed with negative refractive power and particular lens configurations. This extraction allows the first and third lens groups to maintain simpler structures focused on their primary functions, reducing overall system complexity while achieving high-level aberration correction.
Solution Approach 2:
Specific parameter ranges are defined for the second lens group (focal length ratio 0.3 < f/f2 < 1.2, Abbe number 25 < ν2 < 70) to optimize aberration correction. By constraining these parameters, the design achieves effective aberration control without requiring excessive complexity in the lens configuration, as the parameters guide the optimization process.
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 enables high-speed focusing while satisfactorily correcting various aberrations, such as chromatic and spherical aberrations, thereby improving the overall optical performance and video quality.
Implementation Method 1
a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a positive refractive power
Data Source
AI summary
The imaging lens includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power. During focusing, only the second lens group moves in the direction of the optical axis. A lens closest to the object side in the first lens group has a positive refractive power. The second lens group includes two or three lenses, a lens closest to the object side is a meniscus lens which is concave toward the object side and has a positive refractive power, and a lens adjacent thereto on the image side has a negative refractive power. A lens closest to the image side in the third lens group is a single lens which is concave toward the object side and has a negative refractive power. Further, predetermined Conditional Expression (1) is satisfied.