Projection Lens Layout for Weight Balance and Long Back Focal Length
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Solution Overview
Problem
Existing projection systems face issues with balance and weight distribution due to increased weight at the enlargement-side end portion, leading to potential imbalance and difficulty in incorporating lenses, especially when changing projection distances.
Innovation Solution
A projection system with a first lens group having negative power and a second lens group forming a telecentric system, where the first lens group is composed of a single lens with aspheric surfaces and the second lens group is divided into sub-groups that move along the optical axis for focusing and zooming, adhering to specific conditional expressions to maintain a sufficient back focal length and lens count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple lenses are used in the first-a lens group and first-b lens group to improve optical performance, then image quality is improved, but the weight of the enlargement-side end portion increases causing balance issues
Solution Approach 1:
The first lens group is divided into three sub-groups (first-a, first-b, first-c) with different functions. The first-a and first-b lens groups are positioned on the enlargement side and their lens counts are restricted to minimize weight, while the first-c lens group on the reduction side handles additional optical correction, achieving balance between weight distribution and image quality
Solution Approach 2:
Different regions of the projection system are assigned different optical correction functions. The first-a and first-b lens groups focus primarily on basic optical performance with minimal lens count, while the first-c lens group provides additional aberration correction, creating local optimization of both weight and image quality
2Weight of moving object
If the number of lenses in the first-a lens group and first-b lens group is reduced to decrease weight, then balance is improved, but optical performance and aberration correction deteriorate
Solution Approach 1:
Instead of concentrating all optical correction functions in the front lens groups (first-a and first-b), the invention inverts the approach by placing additional correction capability in the rear first-c lens group. This allows the front groups to remain lightweight while the system as a whole maintains high optical performance
Solution Approach 2:
The first-c lens group acts as an intermediary that receives light from the lightweight first-a and first-b lens groups and provides additional optical correction. This mediator structure allows the front groups to be simplified for weight reduction while maintaining overall optical performance through the collaborative action of all three sub-groups
3Manufacturing precision
If lenses are added to correct distortion and aberrations, then image quality is improved, but the back focal length decreases making it difficult to incorporate the projection system
Solution Approach 1:
The optical correction function is segmented across three lens groups. The first-a and first-b lens groups handle basic optical performance with minimal impact on back focal length, while the first-c lens group provides additional distortion and aberration correction. This segmentation allows effective correction while maintaining a sufficient back focal length (BF/F ≥ 5.0)
Solution Approach 2:
The invention uses specific parameter ranges for the lens groups, particularly the conditional expression 0.3F/F1ab ≤ |F1c/F1ab| < 1.0, to optimize the distribution of optical power. This parameter control enables effective aberration correction while maintaining appropriate back focal length for system incorporation
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 manages weight distribution, corrects distortion, and maintains image quality while ensuring a sufficient back focal length, reducing the impact of heat on lens performance and minimizing aberrations during zooming.
Implementation Method 1
A first lens located at a position closest to the enlargement side in the first-a lens group has aspheric surfaces at opposite sides
Implementation Method 2
The first-b lens group and the first-c lens group each move in a direction of an optical axis during focusing
Implementation Method 3
The reduction side of the second lens group forms a telecentric system
Data Source
AI summary
A projection system includes first lens group having negative power and second lens group having positive power sequentially arranged from enlargement side toward reduction side. first lens group includes first-a lens group having negative power, first-b lens group located at reduction side of first-a lens group and having negative power, and first-c lens group located at reduction side of first-b lens group and having positive power. Sum of number of lenses of first-a lens group and number of lenses of first-b lens group is smaller than or equal to three. Projection system satisfies each of Conditional Expressions (1) and (2) below,BF/F>5.0 (1)0.3<|F/F1ab|<1.0 (2)where F represents the focal length of the overall projection system, BF represents the back focal length in air, and F1ab represents the combined focal length of the first-a lens group and the first-b lens group.