Projection Optical System Separate Lens Curvature Optimization
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Solution Overview
Problem
Conventional projector optical systems experience chromatic aberration and transmittance drops due to Fresnel loss, especially with high heat generation from high output light sources, which is not effectively addressed by traditional achromatic lenses.
Innovation Solution
A projection optical system with separately arranged positive and negative lenses, where the negative lens has a refractive index of 1.7 or higher and an Abbe's number of 55 or less, and specific curvature-to-focal-length ratios are maintained to suppress Fresnel loss and enhance heat and light resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a cemented achromatic lens is used, then chromatic aberration is corrected, but heat resistance and light resistance deteriorate due to chemical changes from heat and light causing discoloration and separation
Solution Approach 1:
The cemented achromatic lens is divided into separate positive and negative lenses that are not in direct contact. This segmentation eliminates the cement layer that degrades under heat and light, while maintaining the chromatic aberration correction function through the combined optical power of the separate lenses.
2Reliability
If separate positive and negative lenses are used instead of cemented lens, then heat and light resistance is improved, but transmittance drops due to Fresnel loss at the air-glass interface
Solution Approach 1:
The radius of curvature of the positive lens facing the negative lens is specifically optimized to satisfy 0.005 < R/f < 0.02, where R is the radius of curvature and f is the focal length of the projection lens. This parameter optimization minimizes the incident angle of light at the interface, thereby reducing Fresnel reflection loss while maintaining the benefits of separate lens construction.
3Illumination intensity
If high output light sources are used to increase brightness, then illumination intensity is improved, but heat generation increases causing temperature rise in the projection optical system
Solution Approach 1:
By segmenting the achromatic lens into separate positive and negative lenses without cement, the system eliminates the cement layer that is vulnerable to thermal degradation. This allows the use of higher power light sources for increased brightness while maintaining structural integrity and optical performance at elevated temperatures.
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 prevents transmittance drops and maintains excellent heat and light resistance, achieving a bright projection image with reduced chromatic aberrations.
Implementation Method 1
an achromatic lens including a positive lens and a negative lens separately arranged in this order from the reduction side toward the magnification side
Implementation Method 2
since a Fresnel loss (a loss induced by Fresnel reflection) may be generated at a light incident surface of a lens arranged on the magnification side
Data Source
AI summary
In a projection optical system for projecting an optical image from a first image plane on a reduction side onto a second image plane on a magnification side, the system includes an achromatic lens including a positive lens and a negative lens separately arranged in this order from the reduction side toward the magnification side, and the negative lens having a refractive index of 1.7 or higher and an Abbe's number of 55 or less satisfies the following expression:3.5≤|R|/|f| (1),where the radius of curvature of a light incident surface is R and the focal length of an entire projection optical system is f.