Projection Lens Miniaturization via Folded Optical Path
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Solution Overview
Problem
Conventional projection lenses for rear-projection display devices face challenges in miniaturization, wide-angle projection, and effective chromatic aberration correction, making it difficult to achieve a high-resolution, compact, and low-profile design.
Innovation Solution
A projection lens design that includes a first lens group with negative refractive power and a second lens group with positive refractive power, featuring lens components formed of three lens elements, a mirror for optical path deflection, and specific optical component relationships to satisfy conditions for miniaturization, wide-angle projection, and aberration correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the projection distance is shortened to make the television thinner, then the profile of the display device is reduced, but the projection field angle must be widened which complicates the lens design and reduces resolution
Solution Approach 1:
The projection lens is divided into multiple lens groups (first lens group with negative refractive power, second lens group with positive refractive power) that can be independently optimized. Each lens group contains multiple lens elements that can be individually designed to correct specific aberrations, allowing the system to achieve wide-angle projection while maintaining high resolution through coordinated optimization of each segment.
Solution Approach 2:
The patent uses lens elements with different refractive powers and aberration characteristics combined in specific configurations. By compositeing lens elements with positive and negative refractive powers, and using materials with different dispersion properties, the system achieves both wide projection field angle and high resolution simultaneously.
2Volume of moving object
If a deflector such as a mirror is installed to fold the optical path for miniaturization, then the projection lens system can be miniaturized, but there is insufficient space for the deflector in conventional lens designs
Solution Approach 1:
The patent introduces a folded optical path configuration that utilizes the third dimension (depth) by installing a deflector (mirror or prism) to bend the light path at approximately right angles. This allows the optical system to achieve compact dimensions in the horizontal and vertical directions while accommodating the necessary optical path length through the folded configuration, effectively miniaturizing the overall system volume.
3Adaptability or versatility
If the projection lens is designed for wide-angle projection, then the projection field angle is widened, but chromatic aberration correction becomes insufficient leading to resolution degradation
Solution Approach 1:
Different regions of the optical system are assigned different functions to optimize overall performance. The first lens group with negative refractive power is specifically designed to control field angle and reduce distortion, while the second lens group with positive refractive power focuses on chromatic aberration correction. This local optimization allows each part to specialize in correcting specific types of aberrations, achieving both wide-angle projection and high image quality.
Solution Approach 2:
The patent systematically varies key optical parameters including the refractive powers of different lens groups, the number and arrangement of lens elements, and the focal lengths of individual components. By optimizing these parameters within specific ranges (e.g., the ratio of focal lengths between lens groups, the Abbe numbers of lens materials), the system achieves simultaneous correction of chromatic aberration and maintenance of wide projection field angle.
4Manufacturing precision
If the lens element on the magnification side is made large to improve resolution, then resolution improves, but the projection lens system becomes difficult to miniaturize
Solution Approach 1:
The patent employs an optical path deflector (mirror or prism) that dynamically folds the light path to redirect magnified images formed by the projection lens toward the projection screen. This dynamic path folding allows the use of smaller lens elements while achieving the same effective magnification, as the folded optical path compensates for the reduced physical size of the lens components, thereby enabling system miniaturization without sacrificing resolution.
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 design enables miniaturization of the projection lens system, provides wide-angle projection, and effectively corrects chromatic aberrations, resulting in high-resolution images with a reduced profile and thickness of the projection display device.
Implementation Method 1
a projection lens for magnifying and projecting display information on light valves
Implementation Method 2
folding the optical path of the projection lens system by installing a deflector, such as a mirror or a prism, for deflecting the optical path
Data Source
AI summary
A projection lens includes two lens groups, arranged as follows from the magnification side: a first lens group of negative refractive power, a mask, an aperture stop, and a second lens group of positive refractive power. The projection lens is telecentric or nearly telecentric on the reduction side. Each of the first lens group and the second lens group includes a lens component formed of three lens elements with the middle lens element of each of these lens components having refractive power of opposite sign from the other two lens elements. The distance between the first lens group and the second lens group is large enough for placement of a mirror for folding the optical path of the projection lens. The projection lens satisfies specified conditions regarding focal lengths and spacings of lens surfaces. A projection display device uses the projection lens.