Gradient ND Filter Antireflection Layer Design
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Solution Overview
Problem
Existing neutral density (ND) filters do not adequately reduce reflectance to achieve high-quality images with reduced ghosts and flares, particularly in gradation type ND filters where transmittance varies by area.
Innovation Solution
An optical element with first and second antireflection layers and an absorption layer in between, where the refractive indices of adjacent films satisfy specific conditional expressions to maintain low reflectance across different transmittance areas, thereby reducing reflectance and improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a gradation type ND filter with different film thickness is used to vary transmittance by area, then the luminance control and sharpness improvement are enhanced, but the reflectance is not sufficiently reduced causing ghosts and flares
Solution Approach 1:
The optical element is divided into multiple layers including first and second antireflection layers, an absorption layer with different refractive index films, and light transmitting members. Each layer serves a specific function: the absorption layer varies transmittance by area through different film thickness, while the antireflection layers reduce reflectance. This segmentation allows independent optimization of transmittance variation and reflectance reduction without compromising either function.
Solution Approach 2:
The patent uses composite material structures with films having different refractive indices (nA and nB) arranged in specific configurations. The absorption layer contains films with different refractive indices that are optically coupled to antireflection layers. This composite structure enables the system to achieve both area-dependent transmittance variation and consistently low reflectance across all regions, eliminating ghosts and flares while maintaining luminance control.
2Object-generated harmful factors
If the reflectance is reduced using an antireflection structure, then the image quality with reduced ghosts and flares is improved, but the structure does not work effectively for gradation type ND filters with varying transmittance
Solution Approach 1:
The absorption layer is designed with local quality variations through films having different refractive indices (nA and nB) and different film thicknesses in different areas. This allows each region of the optical element to have its own transmittance characteristics while the overall structure maintains low reflectance through the antireflection layers. The local quality approach enables the structure to be adaptable to gradation type ND filters where different areas require different transmittance levels.
3Ease of manufacture
If a simple ND filter structure is used, then the manufacturing is easier, but the antireflection performance is insufficient for high-quality images
Solution Approach 1:
The optical element is segmented into distinct functional layers: light transmitting members, antireflection layers, and an absorption layer. This segmentation allows each layer to be optimized for its specific function while maintaining overall manufacturing feasibility. The absorption layer can be formed with varying thickness to create gradation effects, and the antireflection layers can be applied using standard coating techniques, balancing manufacturing ease with high antireflection performance.
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 maintains low reflectance across the entire area, reducing ghosts and flares, and enhancing image quality by ensuring consistent antireflection performance regardless of incident light direction or wavelength.
Implementation Method 1
an absorption layer disposed between the first and second antireflection layers
Implementation Method 2
The following conditional expressions are satisfied, |nA−n1|≤0.35, |nB−n2|≤0.35 where nA is a refractive index of a first film adjacent to the first antireflection layer, nB is a refractive index of a second film adjacent to the second antireflection layer
Data Source
AI summary
An optical element has an area in which a transmittance varies, includes first and second antireflection layers, and an absorption layer disposed between the first and second antireflection layers, and satisfies certain conditions.