ND Filter Density Transition Region for Diffraction Reduction
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Solution Overview
Problem
Conventional ND filters, especially step ND filters, suffer from image quality deterioration due to diffraction and transmission wave front phase differences, making control complex and image quality worse compared to gradation ND filters, while gradation filters are difficult to control and require complex algorithms.
Innovation Solution
An ND filter with a first region of uniform density, a second region of different uniform density, and a density transition region where the density changes continuously between the two, reducing diffraction and phase differences, allowing for easier control and improved image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a step ND filter is used to simplify control, then control complexity is reduced, but image quality deteriorates due to diffraction and phase differences
Solution Approach 1:
The ND filter is divided into multiple regions with different densities (first region with density D1, second region with density D2), and the boundary between these regions features a continuous density transition. This local differentiation allows different parts of the filter to serve different functions: uniform density regions provide consistent light attenuation while the transition region minimizes diffraction effects, thus maintaining image quality while enabling simplified control.
Solution Approach 2:
A density transition region is introduced as an intermediary between the first and second uniform density regions. This transition region acts as a buffer that gradually changes the optical density, preventing abrupt phase differences and reducing diffraction effects. The transition region mediates between the two different density regions, allowing the filter to maintain both simplified control structure and high image quality.
2Reliability
If a gradation ND filter is used to improve image quality, then diffraction and phase differences are reduced, but control complexity increases
Solution Approach 1:
The ND filter is segmented into a finite number of discrete density regions (first region with density D1, second region with density D2) separated by transition regions. This segmentation approach combines the benefits of continuous density filters (reduced diffraction) with the simplicity of discrete control. The filter maintains a limited number of controllable states, avoiding the complexity of fully continuous gradation filters while still achieving smooth transitions that minimize optical artifacts.
3Illumination intensity
If the aperture diameter is small to change transmitted light quantity, then light quantity control is achieved, but the relationship between operation amount and transmitted light quantity becomes difficult to determine
Solution Approach 1:
Instead of changing the aperture diameter to control transmitted light quantity, the invention changes the optical density parameter of the ND filter. The filter switches between different density regions (D1 and D2) with well-defined optical properties. This parameter change approach provides a more predictable and easily measurable relationship between the filter's operation state and the transmitted light quantity, avoiding the complex non-linear relationships that arise when adjusting small aperture diameters.
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 ND filter with a continuous density transition region reduces image quality deterioration, allows for simpler control, and enables the use of a common control circuit similar to step ND filters, improving optical performance and reducing development efforts.
Implementation Method 1
as light is considered as a wave, a difference in the optical thickness of ND film in the regions of the filter that the light passes causes a phase difference, which affects the image quality
Implementation Method 2
a difference in the optical thickness of ND film in the regions of the filter that the light passes causes a phase difference, which affects the image quality
Data Source
AI summary
An ND filter that enables relatively easy control of light quantity when used in an iris device and realizes excellent optical performance. The ND filter has a first region having an ND film with a uniform density, a second region having an ND film with a uniform density different from the density of the first region, and a density transition region provided between the first region and the second region. The density transition region has an ND film whose density changes continuously from the density of the first region to the density of the second region.