Projection Lens System with Negative Power Second Unit
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Solution Overview
Problem
Existing projection systems face challenges in increasing the angle of view without inducing field curvature, which often requires adding more lenses, thereby increasing costs and manufacturing complexity.
Innovation Solution
A projection system with a first lens unit of positive power and a second lens unit of negative power, where the second-lens-unit intermediate-image-side first lens has positive power, allowing for increased angle of view without additional lenses by shifting the intermediate image formation and using aspheric lenses for aberration correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the number of lenses is increased to suppress field curvature, then the field curvature is reduced, but the overall length of the lens and the lens diameter increase, and the cost increases
Solution Approach 1:
The patent applies parameter changes by optimizing the focal length ratio between the first lens unit (fU1) and second lens unit (fU2) to satisfy -0.3 < fU1/fU2 < 0.1, and by specifying that the second-lens-unit intermediate-image-side first lens has positive power with refractive index nd > 1.7 and Abbe number νd < 35. These parameter optimizations enable field curvature suppression with only two lens units, avoiding the need to increase the number of lenses while maintaining manufacturing precision.
2Adaptability or versatility
If the angle of view is increased to enable projection from positions close to the screen, then the projection capability is improved, but field curvature occurs in the projected image
Solution Approach 1:
The patent resolves this contradiction through parameter changes by optimizing the focal length ratio fU1/fU2 to satisfy -0.3 < fU1/fU2 < 0.1, and by specifying that the second-lens-unit intermediate-image-side first lens has positive power with refractive index nd > 1.7 and Abbe number νd < 35. These parameter optimizations enable the system to achieve a wide angle of view (120° or more) while suppressing field curvature, allowing projection from positions close to the screen without image degradation.
3Area of stationary object
If the focal length of the first lens unit is increased, then the lens diameter is reduced, but it becomes difficult to increase the angle of view
Solution Approach 1:
The patent applies parameter changes by optimizing the focal length ratio fU1/fU2 to satisfy -0.3 < fU1/fU2 < 0.1. This ratio optimization enables the system to maintain a compact lens diameter while achieving a wide angle of view (120° or more), resolving the contradiction between lens size and angular coverage.
4Stability of the object's composition
If the second lens unit has positive power, then the light rays become telecentric, but the burden on the first lens unit increases and more lenses are needed for aberration correction
Solution Approach 1:
The patent applies inversion by giving the second lens unit negative power (fU2 < 0) instead of positive power, which is unconventional. This inversion allows the second-lens-unit intermediate-image-side first lens to have positive power, forming the intermediate image at a position that enables distortion correction by the second lens unit while maintaining a compact structure with only two lens units.
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
Enables increased angle of view without field curvature and reduces lens diameter, maintaining manufacturing cost efficiency by avoiding the need for more lenses and allowing for effective aberration correction.
Implementation Method 1
a first lens unit that makes an enlargement-side image formation plane, which is located on an enlargement-side, conjugate with an intermediate image
Implementation Method 2
a second lens unit that makes the intermediate image conjugate with a reduction-side image formation plane, which is located on a reduction side
Implementation Method 3
A second-lens-unit intermediate-image-side first lens, which is provided in the second lens unit and closest to the intermediate image, has positive power
Data Source
AI summary
A projection system that can be incorporated in a projector includes a first lens unit that makes a screen (enlargement-side image formation plane), which is located on the enlargement-side, conjugate with an intermediate image and a second lens unit that makes the intermediate image conjugate with a reduction-side image formation plane, which is located on the reduction side. The first lens unit has positive power, and the second lens unit has negative power. A second-lens-unit intermediate-image-side first lens, which is provided in the second lens unit and closest to the intermediate image, has positive power. The following expression is satisfied:−0.3≤fU1/fU2<0where fU1 denotes the focal length of the first lens unit, and fU2 denotes the focal length of the second lens unit.