Imaging Lens Group Segmentation for Autofocus Speed and Aberration Control
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Solution Overview
Problem
Existing imaging lens systems face challenges in achieving a small F number while maintaining high optical performance, reducing the weight of the focus group, and satisfactorily correcting aberrations, particularly sagittal coma aberration, which increases with increased angle of view.
Innovation Solution
The imaging lens system comprises a first lens group with a positive refractive power that remains stationary during focusing, a stop, and a second lens group with a positive refractive power that moves during focusing. The second lens group includes all lenses closer to the image side than the stop, and specific conditional expressions are satisfied to optimize the lens configuration, including the ratio of maximum to minimum paraxial ray heights in each lens group.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the F number is reduced to achieve higher light gathering capability, then the lens aperture increases, but the weight of the focus group increases and aberrations become harder to correct
Solution Approach 1:
The lens system is divided into multiple lens groups (first through fourth lens groups) with different functions. The first lens group handles initial light convergence, the second group corrects aberrations, the third group (containing the stop) controls light paths, and the fourth group provides final focusing. This segmentation allows each group to be optimized independently, enabling small F number achievement while keeping individual group weights manageable.
Solution Approach 2:
Different lens groups are assigned specific optical functions based on their local characteristics. The second lens group specifically targets aberration correction with its positive refractive power, while the fourth lens group focuses on fine-tuning focus. This localized functional assignment allows the focus group (fourth lens group) to remain lightweight while the overall system achieves high light gathering capability through the combined effect of all groups.
2Adaptability or versatility
If the angle of view is increased to achieve wider imaging coverage, then the field of view expands, but sagittal coma aberration increases
Solution Approach 1:
The second lens group is specifically designed with positive refractive power to address off-axis ray correction. By positioning this group strategically and assigning it the specific function of correcting sagittal coma aberration, the system can achieve wider angle of view while maintaining aberration correction performance. The stop in the third lens group also plays a role in controlling off-axis ray paths to reduce coma aberration.
3Speed
If the focus group weight is reduced to improve autofocus speed, then the focusing mechanism becomes faster, but achieving small F number and aberration correction becomes more difficult
Solution Approach 1:
The lens system separates aberration correction functions (primarily in the second lens group) from focusing functions (primarily in the fourth lens group). This segmentation allows the focus group to be minimized in weight for fast autofocus, while the second lens group handles the complex aberration correction task. The stop in the third lens group further assists in managing light paths to reduce the burden on the focus group.
4Illumination intensity
If a Gauss type lens system is used to achieve small F number, then the light gathering capability improves, but sagittal coma aberration increases with larger angle of view
Solution Approach 1:
While inspired by the Gauss type configuration, the system divides the optical path into distinct functional groups. The second lens group is specifically tasked with correcting sagittal coma aberration that arises from the wide angle of view, while the overall small F number is achieved through the combined effect of all four lens groups. This segmentation allows the system to overcome the limitations of traditional Gauss designs.
Solution Approach 2:
The second lens group is given the specific local function of correcting sagittal coma aberration with its positive refractive power. This localized correction approach allows the system to maintain the small F number characteristic of Gauss type systems while simultaneously addressing the coma aberration issue that plagues wide-angle implementations of such designs.
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 a small F number, reduces the weight of the focus group, and effectively corrects aberrations, including sagittal coma aberration, resulting in high optical performance and improved autofocus speed.
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 stop
Implementation Method 3
a second lens group that moves during focusing and has a positive refractive power
Data Source
AI summary
An imaging lens includes, successively in order from a position closest to an object side, a positive first lens group that does not move during focusing, a stop, and a positive second lens group that moves during focusing. The second lens group consists of all lenses that integrally move during focusing. The imaging lens satisfies predetermined conditional expressions.