Projection Lens Absorption Layer for Stray Light Control
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Solution Overview
Problem
Existing projection-type display devices face challenges in achieving a small and lightweight design with a low slow ratio while maintaining high contrast, as they often suffer from reduced contrast due to stray light, especially at shorter projection distances.
Innovation Solution
The design incorporates a projection optical system with specific lens configurations, including a first lens with a convex enlargement-side surface and a meniscus lens with a negative refractive power, along with an absorption layer on non-optically effective surfaces to minimize stray light, and satisfies conditional expressions for focal length, local radius of curvature, and surface shapes to optimize image projection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the projection distance is shortened to achieve a low slow ratio and compact design, then the device size is reduced, but the contrast of the projection image deteriorates due to increased stray light
Solution Approach 1:
The patent extracts and removes stray light from the optical system by introducing a blackening layer on the non-optically effective surfaces of lenses. This layer selectively absorbs stray light without interfering with the main optical path, effectively taking out the harmful stray light component while preserving the beneficial imaging light.
Solution Approach 2:
The patent converts the harmful stray light into a beneficial effect by using the blackening layer to absorb it. The stray light that would normally degrade image contrast is instead captured and converted into heat by the blackening material, transforming a harmful factor into a solution that improves image quality.
2Device complexity
If a plano-concave lens with a flat enlargement-side surface is used in the first lens group, then the optical system can be simplified, but the device size and weight cannot be sufficiently reduced
Solution Approach 1:
The patent replaces flat surfaces with curved surfaces in the lens design. Specifically, the enlargement-side surface of the first lens and the reduction-side surface of the second lens are designed with specific curvatures rather than being flat, which allows for more compact lens geometry and reduced device size while maintaining optical performance.
Solution Approach 2:
The patent optimizes various optical parameters including the focal lengths of individual lenses, the radii of curvature of lens surfaces, and the spacing between lenses. By carefully adjusting these parameters, the optical system achieves compact dimensions while correcting aberrations and maintaining image quality.
3Object-affected harmful factors
If lenses with large radius of curvature are used to reduce stray light reflection, then the contrast is improved, but the device becomes larger and heavier
Solution Approach 1:
The patent extracts stray light before it can cause contrast degradation by placing blackening layers on the non-optically effective surfaces of lenses. This allows the use of lenses with smaller radii of curvature without suffering from excessive stray light reflection, thereby maintaining compact device dimensions.
Solution Approach 2:
The blackening layer acts as an intermediary between the lens surfaces and the stray light. It intercepts stray light on the non-optically effective surfaces, preventing it from reflecting into the optical path and degrading image contrast, while allowing the main optical function to proceed uninterrupted.
4Weight of moving object
If the projection optical system is miniaturized to reduce device weight, then portability is improved, but stray light control becomes more difficult
Solution Approach 1:
The patent extracts stray light from the compact optical system by applying blackening layers to the non-optically effective surfaces of each lens. This approach is particularly effective in miniaturized systems where stray light paths are more pronounced due to the compact arrangement, allowing weight reduction without sacrificing stray light control.
Solution Approach 2:
The patent applies different treatments to different parts of the lens surfaces. The optically effective surfaces are polished to high precision for light transmission, while the non-optically effective surfaces (margins and peripheral areas) are blackened to absorb stray light. This local differentiation allows compact design while maintaining stray light control.
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
This configuration results in a compact, lightweight projection-type display device that effectively suppresses stray light-induced contrast reduction, enabling high-quality image projection with a low slow ratio and high brightness.
Implementation Method 1
an absorption layer that absorbs light is provided in at least a portion of a non-optically effective surface of a lens which is disposed closer to the reduction side than the first lens and at least a part of a portion which is irradiated with light that has been emitted from the image and reflected by the enlargement-side surface of the first lens or a reduction-side surface of the first lens
Implementation Method 2
a projection optical system that includes a plurality of lenses and projects the image displayed by the display element to form a projection image
Data Source
AI summary
A projection-type display device includes: a display element including a rectangular displayable region in which an image is displayable; and a projection optical system. Assuming that a focal length of the projection optical system is f and a length of a long side of the displayable region is w, 0.15<|f|/w<0.45 is satisfied. An absorption layer that absorbs light is provided in at least a portion of a non-optically effective surface of a lens which is disposed closer to a reduction side than a first lens closest to an enlargement side in the projection optical system and at least a part of a portion which is irradiated with light that has been emitted from an image and reflected by an enlargement-side surface of the first lens or a reduction-side surface of the first lens.