Variable-Focal Projection Lens Curvature Compensation
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Solution Overview
Problem
Existing projection systems with variable focal lengths face significant deterioration in optical performance due to variations in projection distance, leading to curvature of field issues, especially with modern high-definition image display devices, which are not adequately addressed by existing varifocal lens systems.
Innovation Solution
A variable-focal-length lens system that includes two or more focal-length-varying lens groups and a separate distance-compensation lens group, which moves along the optical axis to adjust group-to-group distances and correct curvature of field as the projection distance varies, ensuring optimal performance across different distances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the projection lens system is left intact without distance compensation, then the device complexity is reduced, but the curvature of field varies significantly (20 μm to 30 μm) as projection distance changes from 45 m to 15 m
Solution Approach 1:
The lens system is divided into multiple lens groups (first through fourth lens groups) with different functions. The first and fourth lens groups remain stationary during magnification varying, while the second and third lens groups move to vary focal length. This segmentation allows independent optimization of each group's function.
Solution Approach 2:
The patent introduces dynamic movement mechanisms for specific lens groups. During focusing, the entire projection lens system moves forward or backward. During magnification varying, the second and third lens groups move relative to each other while the first and fourth groups remain stationary. This dynamic adjustment enables the system to maintain optimal optical performance across different projection distances and magnifications.
2Measurement precision
If recent high-definition image display devices with more pixels are used, then the image quality is improved, but the curvature of field variation becomes more problematic and reduces projection performance
Solution Approach 1:
The patent systematically adjusts multiple optical parameters including focal length, image height, and projection distance through coordinated movement of lens groups. By changing these parameters dynamically, the system maintains consistent projection performance across varying conditions while supporting high-definition image display devices with increased pixel counts.
3Reliability
If the entire projection lens system moves forward for focusing, then satisfactory focus is achieved even with back focal length deviation, but a large and heavy focusing mechanism is required
Solution Approach 1:
The focusing mechanism is segmented to move the entire projection lens system forward or backward as a unit, rather than moving individual lens groups. This segmentation approach allows the heavy lens system to be moved collectively by a centralized focusing mechanism, achieving satisfactory focus even when the back focal length deviates from the design value.
Data Source
AI summary
A variable-focal-length lens system for projection which achieves focusing by movement of the entire system has a second to a fourth lens group as focal-length-varying lens groups and a first lens group as a distance-compensation lens group. The second to fourth lens groups individually move in the optical axis direction to vary the group-to-group distances so as to vary the focal length of the entire system. During focusing, the first lens group moves in the optical axis direction such that, as the projection distance varies from a remote distance to a close distance, curvature of field varies to the under side.