Imaging Lens Segmentation for Autofocus Speed and Aberration Control
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Solution Overview
Problem
Gauss type lens systems face challenges in achieving a small F number while minimizing sagittal coma aberration and reducing the weight of the focus group, which affects autofocus speed and optical performance.
Innovation Solution
The design incorporates a first lens group that remains stationary during focusing, a second lens group that moves integrally, and a third lens group with positive refractive power, optimizing the arrangement of lenses and their movements to satisfy specific conditional expressions that reduce aberrations and weight, including the use of cemented lenses and aplanatic shapes to balance chromatic aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the F number is reduced to increase light intake, then the aperture size increases, but the lens weight and complexity increase
Solution Approach 1:
The lens is divided into multiple lens groups (first through fourth lens groups) with different functions. The first lens group handles wide-angle imaging with positive power, the second group corrects aberrations with negative power, the third group provides positive power for focusing, and the fourth group corrects residual aberrations. This segmentation allows each group to be optimized independently, reducing overall weight while maintaining small F number performance.
Solution Approach 2:
Different lens groups are assigned different refractive powers and positions based on their specific functions. The first lens group has positive refractive power for wide-angle capture, the second has negative power for aberration correction, and so on. This local differentiation of optical properties allows the system to achieve small F number without requiring uniform increases in all lens elements.
2Adaptability or versatility
If the angle of view is increased, then the field of view expands, but sagittal coma aberration increases
Solution Approach 1:
The second lens group with negative refractive power is extracted and positioned between the first and third lens groups. This negative power group specifically addresses and removes the sagittal coma aberration generated by the wide-angle first lens group, allowing the system to maintain both wide angle of view and acceptable aberration levels.
Solution Approach 2:
The lens configuration uses asymmetric arrangement of positive and negative lens groups rather than symmetric design. The first lens group has positive power for wide-angle imaging, followed by a negative power second group for aberration correction, then positive power third and fourth groups. This asymmetric arrangement is optimized to control sagittal coma aberration while maintaining wide angle of view.
3Speed
If the focus group weight is reduced to improve autofocus speed, then the moving mass decreases, but aberration correction capability may be compromised
Solution Approach 1:
The lens is segmented into stationary and movable groups. The first lens group remains stationary during focusing, while the second, third, and fourth lens groups form the focus group that moves. This segmentation allows the heavy aberration correction function to be handled by the stationary first group, while the lighter movable groups handle focusing, achieving both fast autofocus and maintained aberration correction.
Solution Approach 2:
Instead of having the primary imaging group move during focusing, the invention keeps the first lens group (which handles the bulk of imaging) stationary and moves the subsequent lens groups. This inverted approach to focusing maintains image quality while reducing the weight and complexity of the moving focus group.
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 achieves high optical performance with a small F number, reduced focus group weight, and effective aberration correction, enhancing autofocus speed and image quality.
Implementation Method 1
a first lens group that remains stationary with respect to an image plane during focusing and has a positive refractive power
Implementation Method 2
a second lens group that moves during focusing... a third lens group that moves during focusing and has a positive refractive power
Data Source
AI summary
The imaging lens comprises, successively in order from the object side, a positive first lens group that does not move during focusing, a second lens group that moves during focusing, a stop, and a positive third lens group that consists of all lenses moving integrally with the second lens group during focusing. The composite focal length of the second lens group and the third lens group is positive. The first lens group includes four or more positive lenses and three or more negative lenses. The imaging lens satisfies predetermined conditional expressions.