Zoom Lens Negative-Positive Floating for Curvature of Field Correction
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Solution Overview
Problem
Conventional zoom lenses for projectors face challenges in maintaining image quality and minimizing curvature of field variations due to changes in projection distance, particularly with retrofocus type lenses, which are prone to asymmetry and increased field angle issues, and existing solutions do not adequately address these problems for miniaturization and telecentric requirements.
Innovation Solution
A zoom lens configuration with six lens units, including a first lens unit divided into sub-units with negative and positive refractive powers, where the first-A and first-B lens sub-units are moved for focusing, allowing for negative-positive floating, while maintaining a long back focus and well-balanced aberration correction, satisfying specific refractive power ratios and conditions to control curvature of field effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a retrofocus type lens configuration is used to achieve a long back focus, then the back focus is extended, but curvature of field variation due to projection distance change increases
Solution Approach 1:
The first lens unit is divided into two separate lens sub-units (first-A and first-B) with different refractive powers. This segmentation allows independent movement of each sub-unit during focusing, enabling precise correction of curvature of field variation while maintaining the retrofocus configuration for long back focus.
Solution Approach 2:
The lens sub-units are designed to move dynamically during focusing operation. Specifically, the first-A and first-B lens sub-units move in opposite directions with different movement amounts, creating a floating effect that actively corrects curvature of field variation as projection distance changes.
2Manufacturing precision
If the first lens unit is divided into two lens sub-units for floating to correct curvature of field, then curvature of field variation is reduced, but lens movement amount increases making miniaturization difficult
Solution Approach 1:
The invention optimizes specific parameter ranges including the refractive power ratio between first-B and first-A lens sub-units (0.3 to 1.5), the focal length ratio of the first lens unit to the entire zoom lens (0.2 to 0.5), and the back focus to focal length ratio (0.3 to 0.7). These parameter constraints enable effective curvature of field correction while limiting excessive lens movement for miniaturization.
3Manufacturing precision
If a negative-negative type floating configuration is used, then curvature of field is corrected, but the configuration is not suitable for miniaturization due to increased lens movement amount
Solution Approach 1:
The invention employs an asymmetric refractive power configuration where the first-A lens sub-unit has negative refractive power and the first-B lens sub-unit has positive refractive power. This negative-positive asymmetric configuration differs from the conventional negative-negative symmetric floating and enables more compact lens movement while maintaining correction effectiveness.
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 proposed zoom lens configuration effectively corrects curvature of field variations across a wide projection distance range, ensuring good optical performance and miniaturization, while maintaining a long back focus and telecentricity, thus addressing the limitations of prior art.
Implementation Method 1
a first lens unit having a negative refractive power and divided into a first-A lens sub-unit and a first-B lens sub-unit respectively having a negative refractive power and a positive refractive power
Data Source
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AI summary
The zoom lens includes a plurality of lens units (10-60). The first lens unit (10) is disposed closest to a magnification side in the plurality of lens units and has a negative optical power, and magnification-varying lens units (20-50) that are disposed closer to a reduction side than the first lens unit and moved for variation of magnification. The first lens unit includes, in order from the magnification side, a first-A lens sub-unit having a negative optical power and a first-B lens sub-unit having a positive optical power. For focusing from an infinite side to a close side, the first-A and first-B lens sub-units are moved as a distance therebetween is increased, and the first-B lens sub-unit is moved toward the reduction side. The zoom lens is capable of correcting well variation of curvature of field due to a projection distance change and has a good optical performance.