Zoom Lens Aberration Correction via Segmented Third Group
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Solution Overview
Problem
Existing zoom lens systems for digital SLR cameras face challenges in achieving sufficient correction of axial chromatic aberration and field curvature, which affects the optical quality due to high pixelization, especially at the long focal length extremity.
Innovation Solution
A zoom lens system comprising a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group, with specific configurations and conditions to optimize the power balance between lens groups, including the use of aspherical surfaces and low-dispersion lens elements to correct aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional four-lens-group zoom lens system is used, then the zoom ratio can be achieved, but the correction of axial chromatic aberration and field curvature is insufficient
Solution Approach 1:
The third lens group is divided into three sub-lens groups (positive first sub-lens group, positive second sub-lens group, and negative third sub-lens group) arranged in sequence. This segmentation allows independent optimization of each sub-group to correct specific aberrations, particularly axial chromatic aberration and field curvature, while maintaining the overall zoom functionality of the four-lens-group system.
2Measurement precision
If high pixelization is used in the image sensor, then the resolution sense is improved, but the requirement for image flatness and aberration correction becomes more stringent
Solution Approach 1:
Different regions of the optical system are assigned different functional characteristics. The third lens group, specifically its sub-lens groups, is designed with particular refractive powers and dispersion properties to address field curvature and chromatic aberrations locally, ensuring that the entire image plane achieves the required flatness and correction quality to match the high pixelization of modern sensors.
3Reliability
If the third lens group is configured with multiple sub-lens groups, then aberration correction is improved, but the device complexity increases
Solution Approach 1:
The third lens group is designed as a multi-functional unit that simultaneously corrects multiple types of aberrations (axial chromatic aberration, field curvature, spherical aberration) through its three sub-lens groups. This multi-functionality is achieved within the existing four-lens-group zoom system architecture, allowing the third group to handle multiple correction tasks without requiring additional independent lens groups, thus balancing complexity and 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 effectively corrects various aberrations such as chromatic aberration, spherical aberration, coma, and astigmatism across the entire focal length range, enhancing the optical quality and image flatness.
Implementation Method 1
The third lens group includes at least one positive lens element having at least one aspherical surface
Implementation Method 2
vd3gp−max>80 (5), wherein vd3gp−max designates the Abbe number with respect to the d-line of the positive lens element that has the maximum Abbe number with respect to the d-line out of the third lens group
Data Source
AI summary
A zoom lens system includes a positive first lens group, a negative second lens group, a positive third lens group and a positive fourth lens group, in that order from the object side, wherein distances between adjacent lens groups thereof change during zooming. The third lens group includes a positive first sub-lens group, a positive second sub-lens group and a negative third sub-lens group. The third sub-lens group consists of a single negative lens element. The following conditions (1) and (2) are satisfied:6.0<f1Gp/fw<9.0 (1), and1.3<f3Gp/f4Gp<2.0 (2),wherein fw designates the focal length of the entire zoom lens system at the short focal length extremity, f1Gp, f3Gp and f4Gp designate the focal lengths of the first, third and fourth lens groups, respectively.