Projection Optical System Variable Diaphragm Contrast Brightness Trade-off
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Solution Overview
Problem
Projection image apparatuses using laser light sources face challenges in achieving high contrast while maintaining brightness, as conventional methods to increase contrast often result in reduced luminance and color changes due to the small etendue of laser light and interference between pixel-modulated light in the projection optical system.
Innovation Solution
A configuration that includes a light source with blue, green, and red laser units arranged in arrays, with afocal optical systems to equalize light source image heights and a relay optical system with a variable reflection diaphragm, combined with a projection optical system having a variable absorption diaphragm, to minimize light spread and maintain color balance while enhancing contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a diaphragm with large diaphragm ratio is introduced to increase contrast, then contrast is improved, but brightness is greatly impaired
Solution Approach 1:
The patent employs variable diaphragms in both the illumination optical system and projection optical system that can dynamically adjust their opening sizes. This dynamic adjustment capability allows the system to optimize the balance between contrast and brightness by coordinating the diaphragm ratios of both systems, rather than using a fixed large diaphragm ratio that would severely reduce brightness.
Solution Approach 2:
The patent changes the key parameter of diaphragm ratio from a fixed large value to a variable parameter that can be adjusted between the illumination and projection systems. By coordinating different diaphragm ratios in these two systems, the patent achieves high contrast while maintaining adequate brightness through parameter optimization.
2Illumination intensity
If laser light sources are used to achieve high brightness, then luminance is improved, but contrast is inferior to self-luminous devices
Solution Approach 1:
The patent introduces diaphragms as intermediary elements between the laser light source and the projection target. These diaphragms mediate the light path by controlling and filtering the laser light, effectively converting the high-luminance laser output into high-contrast illumination suitable for projection, thus bridging the gap between laser brightness and image contrast.
3Ease of manufacture
If illumination with small spread is introduced to increase contrast, then contrast is improved, but light with large spread is removed resulting in reduced brightness
Solution Approach 1:
The patent uses dynamically adjustable diaphragms in both illumination and projection systems to control light spread. By coordinating the adjustment of these diaphragms, the system can maintain illumination with sufficiently small spread for high contrast while preserving adequate brightness through optimized light path management.
Solution Approach 2:
The patent optimizes the spread parameter of illumination light by coordinating diaphragm ratios in the illumination and projection systems. This parameter optimization allows the system to achieve small enough spread for high contrast while maintaining sufficient brightness for practical use.
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 achieves high contrast with minimized luminance decrease and color changes, even with a high F-number, by optimizing the light distribution and diaphragm settings in both the illumination and projection optical systems, reducing stray light and maintaining color balance.
Implementation Method 1
a light source that emits laser light of a first color that is blue and laser light of a second color different from blue
Implementation Method 2
a first diaphragm of reflection type having a variable opening diameter, the first diaphragm disposed at a first pupil position where the illumination light is condensed
Implementation Method 3
a second diaphragm of absorption type having a variable opening diameter, the second diaphragm disposed at a second pupil position conjugate with the first pupil position
Data Source
AI summary
A projection image apparatus includes an illumination optical system generating illumination light by combining laser light of a first and a second color, a light modulator generating image light by modulating the illumination light, and a projection optical system enlarging and projecting the image light. The light source is configured to have a small difference between a height of a light source image of the laser light of the first color and a height of a light source image of the laser light of the second color. The illumination optical system includes a relay optical system including a first diaphragm of reflective type having a variable opening diameter, the first diaphragm disposed at a first pupil position. The projection optical system includes a second diaphragm of absorption type having a variable opening diameter, the second diaphragm disposed at a second pupil position conjugate with the first pupil position.